Characteristics of thermionic energy converter with photoelectric emission. Kando, M. (Shizuoka Univ., Hamamatsu (Japan). Dept. of Electrical Engineering); Furukawa, H.; Ichikawa, M.; Yokoi, S. pp. 1067-1072 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

In order to improve the output characteristics of the thermionic energy converter, an effect of the irradiation of Xenon lamp radiation on the emitter has been investigated. The thermionic energy converter used here is specially designed to equip with the collector movable by the electric motor. The typical gap length between both electrodes is 20 mm, which is remarkably longer than that of usual thermionic energy converter. However, the output characteristics of the converter have not dropped, since the space charge neutrality is kept higher than unity. The radiation from the lamp with the nominal output of 3 kW is illuminated from the angle of 45{degree} to the emitter. The magnetic field of 20 gauss at the maximum is applied in the axial direction to suppress the radial electron loss. The authors observed that the short circuit current increased a few times, by illuminating the emitter when the external magnetic field is not applied. However, the increment of the short circuit current caused by the irradiation largely decreased as the magnetic field increased. These facts suggest that a number of Cs{sup +} or Cs{sub 2}{sup +} and electron created by the photoionization contribute to the improvement of the output characteristics.

Efficient binary sources of working-body vapor for thermionic converters. Kalandarishvili, A.G.; Kashiya, V.G. Atomic Energy (English Translation) (United States); 75 (6): 922-926 (Jun 1994).

The objective of this investigation was an experimental determination of the parameters of a cylindrical thermionic converter (TC), with the binary system being cesium with bismuth, antimony, selenium, and germanium. In all devices, the emitter was a layer of tungsten, and the collector consisted of niobium or an alloy of molybdenum with ruthenium. The system characteristics of each binary system were studied, with the interaction kinetics of the cesium vapor with the active sorbent being examined by the gravimetric method. For each TC, the current-voltage characteristics were investigated as was the work function. For each case investigated, there was a 25-30% higher TC power output due to the presence of the active additive.

(SAND--94-2506C)
Surface structural dependence of cesium adsorption on the {alpha}-Al{sub 2}O{sub 3}(0001) surface. Zavadil, K.R. (Sandia National Labs., Albuquerque, NM (United States)); Ing, J.L. Sandia National Labs., Albuquerque, NM (United States). [1994]. 7p. Sponsored by USDOE, Washington, DC (United States);Department of Defense, Washington, DC (United States). DOE Contract AC04-94AL85000. (CONF-950110--13: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995). Order Number DE95002610. Source: OSTI; NTIS; GPO Dep.

The structural dependence of Cs adsorption on the {alpha}-Al{sub 2}O{sub 3}(0001) surface has been studied using a combination of surface analytical techniques. The unreconstructed or (1{times}1) surface shows a high initial Cs adsorption probability of 0.9 based on reflection mass spectrometry (RMS). This value decreases rapidly after a critical Cs coverage of 1.5{times}10{sup 14} atoms/cm{sup 2} is reached. Thermally-induced surface reconstruction to form an O deficient surface results in a decrease in the critical coverage, probability and capacity for Cs adsorption. Low energy electron diffraction (LEED) demonstrates that a predominantly (3{radical}3{times}3{radical}3)R30{degree} surface yields an initial adsorption probability of 0.5 while a predominantly ({radical}31{times}{radical}31)R{plus_minus}9{degree} yields a value of 0.3. Thermal desorption mass spectrometry (TDMS) shows that surface reconstruction suppresses the high binding energy states of Cs, consistent with the observed changes in adsorption probability. X-ray photoelectron spectroscopy (XPS) provides no direct evidence for formal oxidative/reductive chemistry taking place at the interface. We interpret the facile adsorption and strong binding of Cs on sapphire to result from Cs interacting with coordinatively unsaturated O.

(WAPD-T--3108)
High Efficiency Thermionics (HET-IV) and Converter Advancement (CAP) programs. Final reports. Geller, C.B. (Bettis Atomic Power Lab., West Mifflin, PA (United States)); Murray, C.S.; Riley, D.R.; Desplat, J.L.; Hansen, L.K.; Hatch, G.L.; McVey, J.B.; Rasor, N.S. Rasor Associates, Inc., Sunnyvale, CA (United States); Bettis Atomic Power Lab., West Mifflin, PA (United States). Apr 1996. 386p. Sponsored by USDOE, Washington, DC (United States). DOE Contract AC11-93PN38195. Order Number DE96010173. Source: OSTI; NTIS; GPO Dep.

This report contains the final report of the High Efficiency Thermionics (HET-IV) Program, Attachment A, performed at Rasor Associates, Inc. (RAI); and the final report of the Converter Advancement Program (CAP), performed at the Bettis Atomic Power Laboratory, Attachment B. The phenomenology of cesium-oxygen thermionic converters was elucidated in these programs, and the factors that had prevented the achievement of stable, enhanced cesium-oxygen converter performance for the previous thirty years were identified. Based on these discoveries, cesium-oxygen vapor sources were developed that achieved stable performance with factor-of-two improvements in power density and thermal efficiency, relative to conventional, cesium-only ignited mode thermionic converters. Key achievements of the HET-IV/CAP programs are as follows: a new technique for measuring minute traces of oxygen in cesium atmospheres; the determination of the proper range of oxygen partial pressures for optimum converter performance--10{sup {minus}7} to 10{sup {minus}9} torr; the discovery, and analysis of the cesium-oxygen liquid migration and compositional segregation phenomena; the successful use of capillary forces to contain the migration phenomenon; the use of differential heating to control compositional segregation, and induce vapor circulation; the development of mechanically and chemically stable, porous reservoir structures; the development of precise, in situ oxygen charging methods; stable improvements in emitter performance, up to effective emitter bare work functions of 5.4 eV; stable improvements in barrier index, to value below 1.8 Volts; the development of detailed microscopic models for cesium-oxygen reservoir dynamics and collector work function behavior; and the discovery of new relationships between electrode geometry and Schock Instability.

A topaz international program overview. Thome, F.V. (USAF Phillips Laboratory/VTPN, 901 University Blvd SE, Albuquerque, New Mexico 87106 (United States)); Wyant, F.J.; Mulder, D.; McCarson, T.D. Jr. AIP Conference Proceedings; 324 (1): 877-882 (20 Jan 1995). DOE Contract AC04-94AL85000. (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

Little did these visionaries know that the formation of the ``TOPAZ II Program,'' using former military space power technology of the Soviet Union, would become the preeminent example of technology cooperation between two former adversaries. A unique teaming arrangement formed in New Mexico, called the New Mexico Strategic Alliance and consisting of the Air Force Phillips Laboratory, Sandia National Laboratories, the University of New Mexico, and Los Alamos Nationalo Laboratory, was a key ingredient in making this program a success. A brief summary of some of the highlights of this technology partnership is given to explain how international patnerships of this type can enable commercialization and technology transfer.

Electron induced surface chemistry at the Cs/sapphire interface. Zavadil, K.R. (Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185-0333 (United States)); Ing, J.L. AIP Conference Proceedings; 361 (1): 1189-1194 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

Electron induced etching of sapphire in the presence of Cs has been studied using a variety of surface analytical techniques. We find that this process occurs on both the (0001) and (1{bar 1}02) orientations of sapphire. Monolayer amounts of Al and sub-oxides of Al are thermally desorbed from the surface at temperatures as low as 1000 K when the surface is irradiated with electrons in the presence of Cs. Etching is highly dependent on Cs coverage with the (0001) and (1{bar 1}02) surfaces requiring 2.0{times}10{sup 14} and 3.4{times}10{sup 14} atoms/cm{sup 2} to support etching, respectively. Adsorption profiles demonstrate that these coverages correspond to initial saturation of the surface with Cs. Electron damage of the surface in the absence of Cs also produces desorption of Al and sub-oxides of Al, indicating a possible mechanism for etching. The impact of etching on the surface is to increase the adsorption capacity on the (0001) surface while decreasing both initial adsorption probability and capacity on the (1{bar 1}02) surface. {copyright} {ital 1996 American Institute of Physics.}

High-efficient solar power systems based on thermionic converter with small gap. Nikolaev, Y.V. (Research Institute of Scientific Industrial Association ``Lutch'', 142100, Podolsk, Moscow Region (Russian Federation)); Eryomin, S.A.; Kalmykov, S.S.; Karpechenko, Y.D.; Kucherov, R.Y.; Lapochkin, N.V. AIP Conference Proceedings; 361 (1): 1299-1304 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

Various configurations of power systems based on thermionic converter with small interelectrode gap have been considered. The results of studies of systems energy characteristics are presented. The high efficiency and perspectivety of such systems for different applications have been shown. {copyright} {ital 1996 American Institute of Physics.}

Sonic cesium supply for bi-modal thermionic reactors. Anderson, W.G. (Thermacore, Inc., Lancaster, PA (United States)); Bland, J.J.; Horner-Richardson, K. pp. 510-516 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 1. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 628p. DOE Contract FG05-93ER81644. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Recently proposed bimodal thermionic nuclear space power systems are attractive due to the benefits of the dual mode of operation. One of the key technologies that needs to be developed is a reliable cesium source for the thermionic converters. Significant quantities of hydrogen will permeate into the interelectrode gap of the converters during the propulsion mode of operation.This hydrogen must be removed from the interelectrode gap to allow efficient operation of the converters. Hydrogen pressures in unvented thermionic systems could exceed one atmosphere or more in less than one hour of operation, while detrimental effects have been observed with pressures of only 0.001 atmosphere. A Sonic Cesium Source (SCS) was designed to continuously sweep large quantities of contaminate gases from the interelectrode gap. A proof-of-principal device was designed and fabricated, based on the SCS conceptual design. The proof-of-concept device used water as the working fluid, and purged hydrogen from the system. The device incorporated the major features of the SCS, including maintaining pressures and temperatures in three different regions; returning condensate against a large pressure gradient; and venting non-condensable gas. The next major step is to demonstrate venting of hydrogen from a SCS operating with cesium.

Wireless power transmission: The key to solar power satellites. Nansen, R.H. (Solar Space Industries, Ocean Shores, WA (United States)). pp. 601-606 of Proceedings of the 30. intersociety energy conversion engineering conference. Volume 1. Goswami, D.Y. (ed.); Kannberg, L.D.; Somasundaram, S. (eds.); Mancini, T.R. (ed.). American Society of Mechanical Engineers, New York, NY (United States) (1995). 798p. (CONF-950729--: 30. Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995).

In the years following the OPEC oil embargo of 1973--74, the US aggressively researched alternative energy options. Among those studied was the concept of Solar Power Satellites -- generating electricity in space from solar energy on giant satellites and sending the energy to the earth with wireless power transmission. Much has happened in the fifteen years since the studies were terminated. Maturing of the enabling technologies has provided much of the infrastructure to support the development of a commercial Solar Power Satellite program. All of this will reduce the cost by one to two orders of magnitude so development can now be undertaken by industry instead of relying on a massive government program. Solar Space Industries was formed to accomplish this goal. The basis of their development plan for Solar Power Satellites is to build a Ground Test Installation that will duplicate, in small scale on the earth, all aspects of the power generating and power transmission systems for the Solar Power Satellite concept except for the space environment and the range and size of the energy beam. Space operations issues will be separated from the power generation function and verified by testing using the NASA Space Station and Space Shuttle. Solar Space Industries' concept is to built a Ground Test Installation that couples an existing 100 kW terrestrial solar cell array, furnished by an interested utility, to a phased-array wireless power transmitter based on the subarray developed by William Brown and The Center for Space Power. Power will be transmitted over a 1 1/4 mile range to a receiving antenna (rectenna) and then fed into a commercial utility power grid. The objective is to demonstrate the complete function of the Solar Power Satellites, with the primary issue being the validation of practical wireless power transmission. The key features to demonstrate are; beam control, stability, steering, efficiency, reliability, cost, and safety.

(DOE/SF/19645--T12)
High temperature materials technology research for advanced thermionic systems. Final report. Zee, R.H.; Rose, M.F. Auburn Univ., AL (United States). [1998]. 126p. Sponsored by USDOE Assistant Secretary for Nuclear Energy, Washington, DC (United States). DOE Contract FG03-93SF19645. Order Number DE98007450. Source: OSTI; NTIS; INIS; GPO Dep.

Tungsten and tungsten alloys are candidate materials for the thermionic emitter in the space nuclear power convertor. In this work, the creep behavior of HfC strengthened tungsten alloys was studied. An ultrahigh vacuum, high precision creep test system was constructed for this purpose so that the samples could be heated up to 3,000 K for heat treatment and creep strain could be measured from the creep sample inside the UHV chamber. To explain the creep behavior observed in this dispersion strengthened alloy, a creep model was proposed which accounted for the presence of HfC particles in the form of a back stress generated by these particles. This model was verified by the creep test data of W-0.37 HfC alloys tested under both extruded and recrystallized microstructural conditions. According to this model, the steady state creep of this type of alloys was expected to increase with time due to coarsening of HfC particle and recrystallization of the alloys under high temperatures. In contrast, conventional simple power law creep model only predicts a constant steady state creep for these materials, which does not represent the microstructural evolution of the materials. The creep of solid solution alloys such as W-Re, W-Nb and W-Hf and Mo-Nb was also studied. These materials are expected to be more stable in creep properties due to the absence of coarsening particles. These solid solution alloys, in their single crystalline state, are reported possessing better corrosion resistance over their polycrystalline counterparts. Existing creep data of both solid solution tungsten and molybdenum alloys were re-analyzed. The data of these alloys showed two distinct different creep mechanisms: Class I and Class II. The dominating creep mechanism at low stresses could be explained by the Takuchi-Argon model (Class I). At higher stresses, the data could not be explained by any of the existing creep models. (Abstract truncated)

High temperature creep strength of second phase particle strengthened tungsten alloy. Park, J.J. (Los Alamos National Lab., NM (United States). Reactor Design and Analytic Group); Jacobson, D.L. pp. 491-504 of Electrode materials and processes for energy conversion and storage. Proceedings Volume 94-23. Srinivasan, S. (ed.); Macdonald, D.D. (ed.); Khandkar, A.C. (ed.). Electrochemical Society, Inc., Pennington, NJ (United States) (1994). 517p. (CONF-940529--: 185. Electrochemical Society meeting, San Francisco, CA (United States), 22-27 May 1994).

Space nuclear power systems that utilize thermionic energy conversion are currently being investigated. One of the primary life limiting factors for space nuclear thermionic power systems is emitter deformation resulting from fuel swelling. Improving the creep properties of the emitter can thus increase the performance and lifetime of thermionic power systems. Tungsten base alloys have great potential for improving thermionic emitter performance because of their high temperature creep strength. The high temperature creep behavior of tungsten-4w/o rhenium-0.32w/o hafnium carbide (W-4Re-0.32HfC) was evaluated at temperature ranges of 2,200 to 2,400 K and stress ranges of 40 to 70 MPa in a vacuum better than 1.33 {times} 10{sup {minus}6} MPa (1.0 {times} 10{sup {minus}8} torr). The stress exponent for creep was estimated to be 5.2, and the activation energy for creep was estimated to be 142 Kcal/mol. The temperature compensated creep rate of W-4Re-0.32HfC was approximately two orders of magnitude lower than that of W, and one order of magnitude lower than that of W-5Re. Transmission electron microscopy (TEM) study revealed that the high creep strength of this alloy was associated with (a) finely dispersed submicron-size HfC particles that retard dislocation movements and (b) with subgrains containing dislocation networks.

(SAND98-2231C)
Results from the Microminiature Thermionic Converter Demonstration Testing Program. King, D.B.; Luke, J.R.; Wyant, F.J. Sandia National Laboratories, Albuquerque, NM, and Livermore, CA. 5 Oct 1998. 5 Oct 1998. [Unavailablep.] Sponsored by USDOE. DOE Contract AC04-94aL85000. Order Number DE00000757. Source: OSTI; NTIS; GPO Dep.

Research is in progress to develop microminiature thermionic converters (MTCS) with high energy conversion efficiencies and variable operating temperatures using semiconductor integrated circuit (IC) fabrication methods. The use of IC techniques allows the fabrication of MTCS with cathode to anode spacing of several microns or less and with anode and cathode materials that will have work fimctions ranging from 1 eV to 3 eV. The small cathode to anode spacing and variable electrode work functions should allow the conversion of heat energy to relatively large current densities (up to tens of Amps/cmz) at relatively high conversion efficiencies ( 15-25%).

The method of creating a small interelectrode spacing in thermionic energy converters. Kalandarishvili, A.G. (Russian Research Center Kurchatov Inst., Moscow (Russian Federation)). pp. 928-932 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

The method is proposed for creating a small interelectrode spacing in thermionic energy converters (TEC) using graphite-based laminated structures placed inside the converter interelectrode gap. The paper discusses conceptual design and fabrication technology of this device. The proposed method is compared with the methods currently implemented in practice.

Merits of the refractory metals single crystals in application to the TFE. Gontar, A.S. (State Research Inst. of Scientific Industrial Association LUTCH, Podolsk (Russian Federation)); Kucherov, R.Ya.; Nikolaev, Yu.V.; Nelidov, M.V. pp. 951-956 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

Development of a TFE with a long-term service life and a high electric power requires a substantiated choice and, in some cases, production of modern structural materials having improved operating characteristics. A lot of investigations like that including material-scientific, technological and calculated-and-engineering developments have been performed in RI of SIA LUTCH. A number of modern structural materials on molybdenum, tungsten and niobium single-crystal base has been developed and introduced into the TFE designs in course of this work. This report covers the results of experimental and calculated investigations justifying the advantages of the above materials over the similar polycrystal ones.

TOPAZ-2 single-cell TFE electric insulation properties study. Vasilchenko, A.V. (INERTEK (TOPAZ-2 Project), 901 University Blvd. SE, Albuquerque, New Mexico 87106-4439 (United States)); Izhvanov, O.L. AIP Conference Proceedings; 361 (1): 1215-1220 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

TOPAZ-II single cell thermoinic fuel element (TFE) electric insulation parameters under testing with electric heating were measured. TFE electric design schematic, experimental procedure and measurements results are described. Collector resistance was measured in helium at 420{endash}890 K. Metal ceramic ceals insulation properties were measured in vacuum P=10{sup {minus}4} Pa and in cesium vapor P=10{sup {minus}1}{minus}260 Pa, at 420{endash}730 K. Results of separate TFE are compared with the data; that were measured during nuclear power system (NPS) Ya-21U test. Based upon this data NPS power losses were estimated. {copyright} {ital 1996 American Institute of Physics.}

(SAND98-2777C)
Characterization of Sputter Deposited Thin Film Scandate Cathodes for Miniaturized Thermionic Converter Applications. King, D.B.; Ruffner, J.H.; Zavadil, K.R. Sandia National Laboratories, Albuquerque, NM, and Livermore, CA (United States). 14 Dec 1998. 14 Dec 1998. [vpp.] Sponsored by USDOE. DOE Contract AC04-94AL85000. Order Number DE00002342. Source: OSTI; NTIS; GPO Dep.

We have successfully developed a method for fabricating scandate-based thermionic emitters in thin film form. The primary goal of our effort is to develop thin film emitters that exhibit low work fimction, high intrinsic electron emissivity, minimum thermal activation properties and that can be readily incorporated into a microgap converter. Our approach has been to incorporate BaSrO into a SqOq matrix using rf sputtering to produce thin films. Diode testing has shown the resulting films to be electron emissive at temperatures as low as 900 K with current densities of 0.1 mA.cm-2 at 1100 K and saturation voltages. We calculate an approximate maximum work function of 1.8 eV and an apparent emission constant (Richardson's constant, A*) of 36 mA.cm-2.K-2. Film compositional and structural analysis shows that a significant surface and subsurface alkaline earth hydroxide phase can form and probably explains the limited utilization and stability of Ba and its surface complexes. The flexibility inherent in sputter deposition suggests alternate strategies for eliminating undesirable phases and optimizing thin film emitter properties.

Results of the ISUS system definition study. Kennedy, F.G. (Phillips Lab., Kirtland AFB, NM (United States)); Jacox, M.G. pp. 417-433 of Solar engineering 1996. Davidson, J.H. (ed.); Chavez, J. (ed.). American Society of Mechanical Engineers, New York, NY (United States) (1996). 544p. (CONF-9603117--: 1996 American Society of Mechanical Engineers international solar energy conference, San Antonio, TX (United States), 31 Mar - 3 Apr 1996).

The Integrated Solar Upper Stage (ISUS) Program at the USAF Phillips will demonstrate a solar bimodal power and propulsion system for military applications. The proposed ISUS space demonstration system provides orbit transfer capability combined with on-orbit electrical power production; in this way, ISUS functions first as a launch vehicle's upper stage, and then remains with the proposed satellite, providing electrical power throughout the life of the spacecraft. The proposed satellite, a military communications platform, is launched with ISUS aboard a Titan IIG booster from the Western Test Range. ISUS moves the satellite from a circular low earth orbit (i = 63.4{degree}) to a highly-elliptical Molniya orbit in thirty days. A series of 200 or more perigee and apogee kicks are required to minimize transfer delta-V and thus propellant consumption; this is achievable in part due to ISUS' relatively high thrust (up to 100 N) and peak specific impulse (800 s). Keeping the stage with the spacecraft to provide electrical power further increases the amount of mass available to the payload. The development and test of critical components are the current focus of the ISUS Program; component validation and subsystem tests will culminate in an Engine Ground Demonstration (EGD) at NASA Lewis Research Center in 1997. This flight demonstration of ISUS could be performed as early as 1999 for an estimated $85M.

Engine ground demonstration test approach. Kudija, C.T. (Rockwell Aerospace, Canoga Park, CA (United States). Rocketdyne Div.). pp. 334-338 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 1: Aerospace power systems, aerospace technologies. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 681p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

The hardware portion of the current phase of the Integrated Solar Upper Stage (ISUS) program culminates in a system ground demonstration test. The potential application of ISUS technology to a wide array of future missions complicates the process of selecting from among demonstration system design options and test approaches. The approach to this system demonstration has been to maximize system technology readiness level for the entire array of potential missions within the constraints of the program. To this end, system design and test operations planning has been carried out with a premium on demonstrating those elements of the system common to all missions. In addition, test planning has been managed to allow margin for testing those portions of the system envelope needed to confirm acceptable operation for scenarios within the mission set that are specific to a given mission or mission type. Examples drawn from the specific Engine Ground Demonstration (EGD) design selections are used to illuminate this approach, with the result that the EGD system design is not only described, but the reasons for its particular characteristics are made evident.

(WAPD-T--3066)
Integral cesium reservoir: Design and transient operation. Smith, J.N. Jr. (General Atomics, San Diego, CA (United States)); Horner, M.H.; Begg, L.L.; Wrobleski, W.J. Westinghouse Electric Corp., West Mifflin, PA (United States). Bettis Atomic Power Lab. [1995]. 7p. Sponsored by USDOE, Washington, DC (United States). DOE Contract AC11-93PN38195. (CONF-950729--1: Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995). Order Number DE95010152. Source: OSTI; NTIS; INIS; GPO Dep.

An electrically heated thermionic converter has been designed built and successfully tested in air (Homer et.al., 1995). One of the unique features of this converter was an integral cesium reservoir thermally coupled to the emitter. The reservoir consisted of fifteen cesiated graphite pins located in pockets situated in the emitter lead with thermal coupling to the emitter, collector and the emitter terminal; there were no auxiliary electric heaters on the reservoir. Test results are described for conditions in which the input thermal power to the converter was ramped up and down between 50% and 100% of full power in times as short as 50 sec, with data acquisition occurring every 12 sec. During the ramps the emitter and collector temperature profiles. the reservoir temperature and the electric output into a fixed load resistor are reported. The converter responded promptly to the power ramps without excessive overshoot and with no tendency to develop instabilities. This is the rust demonstration of the performance of a cesium-graphite integral reservoir in a fast transient

Maximum thermionic energy conversion efficiency based on the thermodynamics of irreversible processes. Moyzhes, B.Ya. (Space Power, Inc., San Jose, CA (United States)); Fitzpatrick, G.O. pp. 957-961 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

An electron gas in a vacuum between two electrodes is treated as a thermoelectric material, with thermopower, electrical conductivity, and thermal conductivity. Figure of merit zT values obtained from the analysis are very high compared with solid thermoelectrics due to the absence of parasitic phonon thermal conductivity. Due to the large zT, thermionic conversion can work even in the ignited mode regime, which is very paradoxical as a thermodynamic cycle. In this mode the electron gas (the working fluid of the cycle) is first heated by electrical power to a temperature T{sub M} much higher than the evaporator temperature T{sub E}, in order to generate positive ions for electron space charge compensation. The electrons are then cooled from T{sub M} to T{sub C} (the condenser temperature), and enough electrical power is generated to compensate for losses inside the cycle and to provide power to the electrical load. The voltage drop required in order to maintain the ignited mode regime is evaluated.

Thermally induced evolution of morphology on ceramic surfaces in a thermionic converter. Zavadil, K.R. (Sandia National Laboratories P.O. Box 5800 Albuquerque, New Mexico87185-0342 (United States)); Olson, D.L.; Klinkov, A.E. AIP Conference Proceedings; 387 (1): 337-344 (Jan 1997). DOE Contract AC04-94AL85000. (CONF-970115--: Space technology and applications international forum (STAIF - 97), Albuquerque, NM (United States), 26-30 Jan 1997).

The morphology of alumina and scandia ceramics exposed to controlled vacuum and diffusion modes in a thermionic converter has been studied. Evidence for vaporization at a temperature of 1770 K is manifest in the resulting surface morphologies of both ceramics, consistent with reported sample mass loss. Alumina shows intergranular relief with the formation of terrace-step structure on the grain surfaces. Terrace formation is not directly observed on scandia, however the development of vertical structure and maintenance of voids indicates that vaporization is initiated by structure at the grain edges. Extensive Sc{sub 2}O{sub 3} re-deposition occurs on the scandia surface, possibly mediated by the presence of molybdenum and tungsten. Evidence exists for refractory metal secondary phase formation in this deposit in the form of Sc{sub 6}MO{sub 12} (M=W or Mo). Alumina also shows evidence for materials{close_quote} interactions in the form of tantalum assisted vaporization which significantly alters the terrace structure. {copyright} {ital 1997 American Institute of Physics.}

Mo-6%Nb single crystal alloy creep strength demonstration for long life thermionic power systems. Rhee, H.S. (Space Power, Inc., 621 River Oaks Parkway, San Jose, California 95134 (United States)); Zheng, C.; Kent Koester, J.; Yastrebkov, A.; Nikolaev, Y.; Gontar, A. AIP Conference Proceedings (American Institute of Physics) (United States); 324 (1): 389-394 (20 Jan 1995). DOE Contract AC03-92SF19441. (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

Experimental results of one- and two-dimensional creep testing for single crystal Mo-6%Nb alloy are presented. Three 1-D specimens were creep-tested for up to 3000 hours at 1873 to 1973 K and 5 to 15 MPa. One 2-D specimen tube was creep-tested for 2000 hours at 1873 K/15MPa. Results confirm the high creep strength of Mo-6%Nb for long life (10 to 15 year) TFE emitter application in thermionic space nuclear power systems. After the initial transition stage (about 1000 hours), quasi-steady state 1-D and 2-D creep rates were within 20% of each other suggesting little significant effect of anisotropy. More data points will be needed to define the Sherby-Dom parameters with statistical accuracy. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}

(SAND--96-2665C)
Thermally induced evolution of morphology on ceramic surfaces in a thermionic converter. Zavadil, K.R. (Sandia National Labs., Albuquerque, NM (United States)); Olson, D.L.; Klinkov, A.E. Sandia National Labs., Albuquerque, NM (United States). [1996]. 8p. Sponsored by Defense Nuclear Agency, Washington, DC (United States). DOE Contract AC04-94AL85000. (CONF-970115--1: Space technology and application international forum, Albuquerque, NM (United States), 26-30 Jan 1997). Order Number DE97001096. Source: OSTI; NTIS; GPO Dep.

The morphology of alumina and scandia ceramics exposed to controlled vacuum and diffusion modes in a thermionic converter has been studied. Evidence for vaporization at a temperature of 1,770 K is manifest in the resulting surface morphologies of both ceramics, consistent with reported sample mass loss. Alumina shows intergranular relief with the formation of terrace--step structure on the grain surfaces. Terrace formation is not directly observed on scandia, however the development of vertical structure and maintenance of voids indicates that vaporization is initiated by structure at the grain edges. Extensive Sc{sub 2}O{sub 3} re-deposition occurs on the scandia surface, possibly mediated by the presence of molybdenum and tungsten. Evidence exists for refractory metal secondary phase formation in this deposit in the form of Sc{sub 6}MO{sub 12} (M = W or Mo). Alumina also shows evidence for materials' interactions in the form of tantalum assisted vaporization which significantly alters the terrace structure.

The effect of photoionization as an auxiliary discharge on characteristics of thermionic energy converter. Furukawa, H. (Shizuoka Univ., Hamamatsu (Japan)); Kando, M.; Yamada, J. pp. 169-170 of XXII International conference on phenomena in ionized gases. Contributed papers 2. Becker, K.H.; Carr, W.E.; Kunhardt, E.E. (eds.). Stevens Institute of Technology, Hoboken, NJ (United States) (1995). 226p. (CONF-950749--: 22. international conference on phenomena in ionized gases, Hoboken, NJ (United States), 31 Jul - 4 Aug 1995).

The cesium filled thermionic energy converters (TEC) operated by the ignited mode have been expected as novel electric power generators, suitable for the space power systems and such terrestrial uses as cogeneration devices. They have the advantage free from the maintenance because of the device without any moving parts. However, the gaps of the electrodes are usually kept less than 1 mm to suppress the negative space potential in the space between the electrodes. Furthermore, for the ignited mode operation, the emitter should be heated up to the temperature higher than 1700 K. Such a restriction and the operating condition should be relaxed to make TEC spread by manufacturing at a moderate price. In the present work, the effect of an auxiliary discharge due to the photoionization has been examined by using TEC operated by the unignited mode with a longer electrode gap, compared with conventional one. It is clarified that the space charge neutrality in the space between both electrodes is drastically improved by the irradiation of Xenon lamp in the case of the emitter temperature lower than 1100 K and that the output current increases by a few times, compared with one without irradiation. This is caused by the photoionized plasma whose density is nearly 10{sup 9} cm{sup -3}.

Modeling the high temperature creep deformation in single crystalline tungsten alloys. Hong Peter Gao (Materials Engineering, Auburn University, Alabama 36849 (United States)); Zee, R.H. AIP Conference Proceedings; 324 (1): 283-288 (20 Jan 1995). DOE Contract FG03-93SF19645. (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

A semi-mechanistic phenomenological model was developed to predict the high temperature creep properties of single crystalline binary tungsten alloys for thermionic applications. This new model is based on the limited theoretical and experimental results presently available in the literature for both polycrystalline and single crystalline tungsten alloys. It provides a better understanding on the creep deformation of single crystalline tungsten alloys and helps guide the development of this type of material for long-term high-temperature applications. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}

(PB--94-901900/XAB)
Government research and development summaries: Nuclear project briefs. Irregular. CSR, Inc., Washington, DC (United States). Power Information Center. 1994. 1p. Source: NTIS Prices: Standing Order. Supersedes PB--93-901900.

Nuclear, Te, Ti Project Briefs describe the status of all R&D program submitted to the Power Information Center by the government sponsors in energy conversion from fission, fusion, and radioisotope power sources and other thermal systems that use thermionic systems. These briefs also follow related investigations of plasma dynamics. The document is not to be reproduced, in whole or in part, for dissemination outside your own organization nor may it be reproduced for advertising or sales promotion purposes.

Bulk electrical conductivity of plasma-sprayed insulators exposed to cesium vapor. Agnew, P. (AEA Technology, Topaz International Program, 901 University Blvd. SE, Albuquerque, New Mexico 87106-4439 (United States)); Ing, J.L.; Olson, D. AIP Conference Proceedings; 361 (1): 1195-1202 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

A thin layer of plasma-sprayed alumina is used in single cell thermionic fuel elements to provide electrical insulation of the outer surface of the collector from ground. Under normal operating conditions this material is not exposed to cesium vapor. However under abnormal conditions, such as the leaking of a TFE seal, the plasma-sprayed insulator surface may be expected to come into contact with cesium. The porous nature of these materials raises the concern that the metal vapor may penetrate beyond the surface and degrade the bulk electrical resistance properties. In this paper we describe experiments to determine the effect of cesium vapor on the bulk electrical conductivity of two different plasma-sprayed insulators: alumina and magnesium aluminate spinel. The results clearly demonstrate that cesium is easily able to penetrate beyond the surface and into the bulk of these materials and does indeed cause a dramatic increase in the bulk electrical conductivity. This effect may be a potential degradation mechanism for thermionic reactor systems operated over an extended period. {copyright} {ital 1996 American Institute of Physics.}

Bimodal solar system based on a ultra-high-temperature TEC. Ogloblin, B.G. (Central Design Bureau of Machine Building, Krasnogvardeyskaya Square 3, St. Petersburg, (Russia) 195272); Kirillov, E.Y.; Klimov, A.V.; Shalaev, A.I.; Shumov, D.P.; Ender, A.Y.; Kuznetsov, V.I.; Sitnov, V.I. AIP Conference Proceedings; 361 (1): 1459-1462 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

The paper considers an ecological, solar, bimodal system with ultra-high temperature thermionic energy converter (TEC). The solar bimodal Space Electric Propulsion System (SEPS) characteristics are presented. {copyright} {ital 1996 American Institute of Physics.}

(DOE/SF/19645--T4)
High temperature materials technology research for advanced thermionic systems: Quarterly progress report, October 1, 1993--December 31, 1993. Zee, R.H.; Rose, M.F. Auburn Univ., AL (United States). [1993]. 10p. Sponsored by USDOE, Washington, DC (United States). DOE Contract FG03-93SF19645. Order Number DE94008444. Source: OSTI; NTIS; GPO Dep.

The effort was concentrated on two aspects of modeling of deformation in refractory alloy single crystals: deformation map in a tube with a [111] axial orientation and creep retardation due to solution strengthening (both effects are important in bcc single crystalline refractory alloys for high temperature emitters). Lattice misfit parameters are given between tungsten and 3 solutes (Re, Nb, Hf). 3 figs, 10 refs, 1 tab.

Integrated Solar Upper Stage (ISUS) mission trades. Frye, P. (Rockwell Aerospace, Canoga Park, CA (United States). Rocketdyne Div.). pp. 328-333 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 1: Aerospace power systems, aerospace technologies. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 681p. DOE Contract AC03-92SF19138. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

Solar thermal propulsion and propulsion/power systems were recently identified as key technologies in the Operational Effectiveness and Cost Comparison Study (OECS) sponsored by Phillips Laboratory (PL). These technologies were found to be pervasively cost effective with short transfer times and very good performance across a wide range of missions. The on-going Integrated Solar Upper Stage (ISUS) Program sponsored by PL represents development of a solar thermal propulsion/power (bimodal) system. As part of this effort, mission trades are being conducted to further define the ISUS system for geosynchronous equatorial orbit (GEO), high Earth orbit (HEO-Molniya class), and mid Earth orbit (MEO-GPS class) missions. These trades will consider launch vehicles ranging in size from a LLV3 to an Atlas IIAS that insert the ISUS into low Earth orbit (LEO). These trades will be used to define the ISUS system for the planned Engine Ground Demonstration, a space demonstration mission, and as a future operational system.

Power generation considerations in a solar biomodal receiver. Rochow, R.F. (NovaTech, Lynchburg, VA (United States)); Miles, B.J. pp. 345-350 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 1: Aerospace power systems, aerospace technologies. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 681p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

The Integrated Solar Upper Stage (ISUS), or solar bimodal stage provides both propulsive thrust for efficient orbital transfer(s) and electrical power generation for the spacecraft. The combined propulsive and power systems allow the solar bimodal system to effectively compete for a variety of missions. Once on station, thermionic converters are used to supply continuous electrical power to the satellite, even during periods when the spacecraft is in the Earth's shadow. The key to continuous power supply is thermal energy storage. The ISUS propulsion system also benefits through the use of thermal storage. By utilizing a graphite receiver, large amounts of sensible heat can be stored for later power generation. Waste heat is radiated to space through the use of heat pipes. Clearly, the graphite mass must be minimized without sacrificing electrical power capability. Voltage and current characteristics are carefully designed to operate within acceptable ranges. The detailed design of the receiver/absorber/converter (RAC) power system must meet these requirements with as little impact to the remainder of the bimodal system as possible. This paper addresses the key design considerations of a solar bimodal receiver as a power plant. Factors including the thermal storage and heat transfer from the graphite receiver to the thermionic converters, the support structures, electrical insulation and converter string design will be discussed.

Thermionic behavior of ZnSe junction devices. Chiu, D.M. (Victoria Univ. of Technology, Melbourne (Australia). Dept. of Electrical and Electronic Engineering). pp. 1035-1040 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Both Schottky type and p-n junction diodes are made from bulk growth ZnSe single crystal doped with iodine during growth and subsequently diffused with indium under high-temperature condition. Both type of diodes exhibit strong temperature dependency of the I/V and C/V characteristics, and thermionic diffusion nature of the devices is thus suggested. For Schottky diodes, the junction barrier height is about 1.6eV with an ideality factor of 1.40. In the case of p-n junction diodes, the activation energy of the exhaustion region is found to be about 0.33eV which is three times larger than hydrogen model calculation, and the diode ideality factor is about 6.3 with a junction barrier height of about 2.0eV; such large values of ideality factor and barrier height are considered to be coming mainly from the inhomogeneity of the specimen caused by heavy doping and high-temperature quenching.

(AD-A--286705/9/XAB)
Comparison of long-duration secondary-power schemes for space vehicles. Kelley, A.P. AiResearch Mfg. Co., Phoenix, AZ (United States). 2 Feb 1959. 8p. Source: NTIS Prices: PC A02/MF A01.

The status and limitations of seven basic schemes for converting solar or nuclear radiation to electricity are reviewed. The closed-heat engine cycle employing a hermetically sealed turbo-alternator is selected as the scheme offering the earliest availability for space power applications requiring above a few kilowatts of electrical power. Development problems of the small turbomachinery cycle are emphasized. The conclusion is made that development of the long-duration space power supply may be lagging behind vehicle launch capability.

Thermal conductivity reductions in SiGe using nanophase particles. Scoville, A.N. (ThermoTrex Coporation, 74 West Street, Waltham, Massachusetts 02254 (United States)); Rolfe, J.; Bajgar, C.; Vandersande, J.; Fleurial, J. AIP Conference Proceedings; 324 (1): 791-796 (20 Jan 1995). (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

Transport models have predicted that the thermal conductivity of SiGe alloys could be appreciably reduced by incorporating discrete 40A particles within the SiGe grains. These particles would scatter the thermal phonons which transport most of the heat in these alloys. Such a thermal conductivity reduction would lead to substantial improvements in the figure-of-merit and efficiency of thermoelectric materials used in power generation applications. This paper reports on the results of adding 40A particles to SiGe by using a spark erosion process. Thermal conductivity reductions consistent with the transport models have been achieved, however, the improvement in figure-of-merit has not been as large as predicted. {copyright}American Institute of Physics 1995

Modeling of a cesium-graphite reservoir critical component experiment for S-prime. Witt, T. (ThermoTrex Corporation, 85 First Avenue, Waltham, Massachusetts 02254 (United States)); Miskolczy, G.; Lieb, D.; McVey, J.; Hatch, L. AIP Conference Proceedings; 324 (1): 797-802 (20 Jan 1995). DOE Contract AC03-92SF19138. (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

This computer model indicated that the single test device is capable of simulating both types of cesium reservoirs required in the S-PRIME system. The nominal operating conditions utilizing the low temperature (high cesium loading) reservior are simulated without auxiliary heat to the collector or reservoir by the use of 25%He/75%Ar cooling gas. Simulation of the system using the low cesium loading (high temperature) reservoir condition requires auxiliary heating and different cooling gas composition(s). The wide ranges of emitter, collector and reservoir temperatures required by the test plan were satisfied by variation of the cooling gas composition and power inputs to the various heaters. {copyright}American Institute of Physics 1995

A new cascade-type heat conversion system. Newman, E. (Twenty-First Century Power Co., Northridge, CA (United States)). pp. 936-940 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

Various heat conversion systems have different operating temperatures. This paper shows how, in a solar energy system some of the waste heat from a thermophotovoltaic arrangement can be made to operate a thermionic power generator. The waste heat of the thermionic power generator can then be made to operate an alkali-metal thermal electric converter, and the waste heat from the alkali-metal thermal electric converter as well as the rest of the waste heat of the thermophotovoltaic system can be made to operate a methane reformation system. Stored heat from the methane reformation system can be made to operate the system at night. The overall system efficiency of the example shown is 42.6%. As a prime source of heat a nuclear pile or burning hydrogen may be used.

TEC electronic power system. Malyshkov, G.M. (Research Inst. of Applied Mechanics and Electrodynamics, Moscow (Russian Federation)); Ossokin, P.L.; Smirnov, V.P.; Averin, S.V.; Meleta, Ye.A. pp. 1073-1077 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

This paper presents the design concepts and the performance analysis of the 5V DC/220V AC power electronic converter. Converters of that type may be used for feeding power to a great variety of standard domestic and commercial devices operated from autonomous power plants comprising thermionic generators. Modular electronic 5V DC/220V AC converter consists of two parts: 5V DC/300V DC converter and 300V DC/220V AC converter connected in series. The paper deals with the 5V DC/300V DC and 300V DC/220V AC converters basic performance data and control algorithms. The 5V DC/220V AC converter basic performance data are as follows: output power--550 W; efficiency--80%; harmonic factor--2,4%. 5V DC/220V Ac converter modules may operate in parallel.

Considerations for modeling heterojunction transport in solar cells. Durbin, S.M. (Florida A and M Univ.-Florida State Univ., Tallahassee, FL (United States). Dept. of Electrical Engineering); Gray, J.L. pp. 1746-1749 of 1994 IEEE first world conference on photovoltaic energy conversion: Conference record of the twenty-fourth IEEE photovoltaic specialists conference -- 1994. Volume 2. Inst. of Electrical and Electronics Engineers, Inc., Piscataway, NJ (United States) (1994). 1268p. (CONF-941203--: 1. world conference on photovoltaic energy conversion, Waikoloa, HI (United States), 5-9 Dec 1994).

Heterojunctions are frequently employed in modern solar cell device structures as both wide-gap window layers and in place of heavily doped back surface field layers. The common approach to numerical modeling of such structures is based on the drift-diffusion formulation, where the Poisson equation is solved self-consistently with the current continuity equations. A key assumption in such an approach is that the quasi-Fermi energies are continuous across the interface. However, thermionic emission and tunneling can ultimately be responsible for determining the transport across a heterointerface, especially in the presence of a band spike. This paper describes the incorporation of a combined thermionic emission/tunneling expression for current through heterojunction interfaces into a finite-difference drift-diffusion solar cell simulation code. The modified program can be used to provide a more accurate numerical analysis of a heterojunction solar cell design.

Space Technology & Applications: International Forum (STAIF{minus}97). Proceedings. AIP Conference Proceedings, No.387[APCPCS]. El-Genk, M.S. (Institute for Space and Nuclear Power Studies/Dept. Of Chemical and Nuclear Engineering School of Engineering, The University of New Mexico, Albuquerque, NM 87131 (United States)). 1724p. American Institutes of Physics, New York, NY (United States) (Feb 1997). (CONF-970115--: Space technology and applications international forum (STAIF - 97), Albuquerque, NM (United States), 26-30 Jan 1997).

These proceedings represent the papers presented at the Second Space Technology and Applications International Forum held in January, 1997 in Albuquerque, New Mexico. This forum was co{minus}sponsored by the United State Department of Energy. The forum covered a wide range of topics concerning the commercial development of space technology. Several conferences were hosted at the forum including the following: Future Space Science & Earth Science Missions; Synergistic Power & Propulsion Systems Technology; Applications of Thermophysics in Microgravity; Commercial Development of Space; Next Generation Launch Systems Technology; and Space Nuclear Power and Propulsion. These proceedings are published in three parts covering all the above mentioned topics. There were 238 papers presented at the forum and 155 are abstracted for the Energy Science and Technology database.(AIP)

Precision control of high temperature furnaces using an auxiliary power supply and charged particle current flow. Pollock, G.G. To Dept. of Energy, Washington, DC (United States). 28 Jan 1997. Filed date 3 Nov 1994. U.S. Patent Application 8-335,342.

Two power supplies are combined to control a furnace. A main power supply heats the furnace in the traditional manner, while the power from the auxiliary supply is introduced as a current flow through charged particles existing due to ionized gas or thermionic emission. The main power supply provides the bulk heating power and the auxiliary supply provides a precise and fast power source such that the precision of the total power delivered to the furnace is improved. 5 figs.

Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, Stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). 867p. Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996). Source: Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08855-1331 (United States) $376.00 for the 4 volume set.

The 148 papers contained in Volume 2 are arranged topically as follows -- (A) Conversion Technologies: Superconductivity applications; Advanced cycles; Heat engines; Heat pumps; Combustion and cogeneration; Advanced nuclear reactors; Fusion Power reactors; Magnetohydrodynamics; Alkali metal thermal to electric conversion; Thermoelectrics; Thermionic conversion; Thermophotovoltaics; Advances in electric machinery; and Sorption technologies; (B) Electrochemical Technologies: Terrestrial fuel cell technology; and Batteries for terrestrial power; (C) Stirling Engines: Stirling machine analysis; Stirling machine development and testing; and Stirling component analysis and testing; (D) Thermal Management: Cryogenic heat transfer; Electronic components and power systems; Environmental control systems; Heat pipes; Numeric analysis and code verification; and Two phase heat and mass transfer. Papers within the scope of the data base have been processed separately.

TEC as electric generator in an automobile catalytic converter. Svensson, R. (Chalmers Univ. of Technology, Goeteborg (Sweden)); Holmlid, L. pp. 941-944 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

Modern cars use more and more electric power due to more on-board electric systems, e.g., ABS brakes, active suspension systems, electric windows, chair adjustment systems and electronic engine control systems. One possible energy source for electricity generation is to use the waste heat from the car's engine, which generally is as much as 80% of the total energy from the combustion of the gasoline. Maybe the best location to tap the excess heat is the Catalytic Converter (Cat) in the exhaust system or perhaps at the exhaust pipes close to the engine. The Cat must be kept within a certain temperature interval. Large amounts of heat are dissipated through the wall of the Cat. A Thermionic Energy Converter (TEC) in coaxial form could conveniently be located around the ceramic cartridge of the Cat. Since the TEC is a rather good heat insulator before it reaches its working temperature the Cat will reach working temperature faster, and the final temperature of it can be controlled better when encapsulated in a concentric TEC arrangement. It is also possible to regulate the temperature of the Cat and the TEC by controlling the electrical load of the TEC. The possible working temperatures of present and future Cats appear very suitable for the new low work function collector TEC, which has been demonstrated to work down to 470 K.

Cs-Ba ultrahigh-temperature solar TEC commutation element optimization. Ender, A.J. (Ioffe Physico-Technical Institute, Polytekhnicheskaya St. 26, St. Petersburg, (Russia) 194021); Kuznetsov, V.I.; Babanin, B.I.; Ogloblin, B.G.; Klimov, A.V.; Kirillov, E.J. AIP Conference Proceedings; 361 (1): 1511-1516 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

Theoretically studied is a problem involving the optimization of high-temperature thermionic energy converters (TEC) taking into account electrical and thermal losses in a metal jumper connecting at series TEC commutation the emitter of one diode with the collector of the other. It is shown that for emitter temperature of 2600 K at optimal selection of jumper dimensions the difference between an ideal conversion efficiency and actual converter efficiency amounts to about 4{percent}. {copyright} {ital 1996 American Institute of Physics.}

(AD-A--333399/4/XAB)
Comparative of nuclear technology and direct energy conversion methods for space power systems. Master's thesis. Reason, J.P. Naval Postgraduate School, Monterey, CA (United States). Jun 1997. 104p. Source: NTIS Prices: PC A07/MF A02.

The objectives of this thesis are to investigate the theory of direct energy conversion, research the development of space nuclear power systems, evaluate the status of current systems, and draw conclusions about the feasibility and merit of using nuclear power for future space missions. Development of the earliest systems began in 1955 with the Systems for Nuclear Auxiliary Power (SNAP) Program and Project Rover. A detailed review of system design and performance is provided for the reactors and radioisotope thermoelectric generators (RTG's) of past and current programs. Thermoelectric and thermionic energy conversion techniques have been used predominantly in space nuclear power systems. The theory of these direct energy conversion methods is analyzed. Also, the safety review procedures and regulations governing the launch of nuclear sources into space are characterized. Conclusions compare accomplished levels of system performance to theoretically predicted limits and comment on the usefulness of space nuclear power for space applications.

S-PRIME/TI-SNPS program activities in FY94 critical components testing. Brown, C. (U.S. Department of Energy, Office of Nuclear Energy Space Reactor Power Systems Division, 19901 Germantown Road, Germantown, Maryland 20874 (United States)); Dale Rogers, R.; Determan, W.R.; Van Hagan, T. AIP Conference Proceedings; 324 (1): 803-808 (20 Jan 1995). DOE Contract AC03-92SF19138. (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

A conceptual design for a 40-kWe thermionic space nuclear power system (TI-SNPS) known as the S-PRIME system is being developed by Rockwell and its subcontractors for the U.S. Department of Energy (DOE), United States Air Force (USAF), and Ballistic Missile Defense Organization (BMDO) under the TI-SNPS Program. Phase 1 of this program includes developing a conceptual design of a 5- to 40-kWe range TI-SNPS and validating key technologies that support the design. All key technologies for the S-PRIME design have been identified along with six critical component demonstrations, which will be used to validate the S-PRIME design features. {copyright}American Institute of Physics 1995

Ta-46%Ir as a brazing filler with low vapor pressure for high temperature thermionic applications. Tsao, B.H. (UES, Inc., Dayton, OH (United States)); Ramalingam, M.L.; Donovan, B.D.; Lamp, T.R. pp. 1021-1026 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

The research activity addresses the development of Ta-46%Ir refractory brazing filler and evaluation of its properties for high temperature and low vapor pressure applications. Joining and bonding refractory metal parts while still maintaining their effectiveness is a major concern. Fabrication with refractory metals requires bonds made at temperatures below the melting points of the pieces being joined. The bonding strength between the brazing filler and the base material constitutes the fundamental goal of this research activity. The focal point was the selection and fabrication of Ta-46%Ir eutectic brazing fillers and generation of data on mechanical strength, microstructural degradation and interfacial phenomenon of the brazing filler and base materials. Ta-46%Ir eutectic brazing fillers were successfully fabricated by using powder metallurgical techniques. Metallographic investigations were performed and the porosities of the as-annealed samples were determined with various characterization techniques. The Ta-46wt.%Ir brazing filler was actually used to braze Ta. X-ray computed tomography on the Ta-Ir brazing filler revealed no voids or inclusions, thereby confirming the homogeneity of the material in this region. Electron microprobe analysis to verify eutectic compositions revealed that the compositions deviated very little from expected values. There was some diffusion of Ir into the Ta matrix as indicated in the microhardness profile across the joint. Appropriate heat treatment would enhance the ductility of the brazing fillers and minimize failure by brittle fracture of Ta/Ta-Ir/Ta region.

The minimum collector work function and the possibility of the existence of negative Cs ions on the collector surface. Moyzhes, B.Y. (Space Power, Inc., San Jose, CA (United States)). pp. 933-935 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

Negative alkali metal ions are observed in some condensed phases; for example, ammonia solutions, tungsten bronzes, etc. Therefore one cannot exclude them from the set of basis functions for alkali metals adsorbed on the electrode surfaces in thermionic converters. On inhomogeneous surfaces Cs{sup +} and Cs{sup {minus}} can be separate species. On homogeneous surface they can be treated as resonance configuration of Cs{sub ad}. Stabilization of the work function {phi}(N{sub Cs}) when n{sub Cs} > 10{sup 14} cm{sup {minus}2} can be explained by the coexistence of Cs{sup +} and Cs{sup {minus}} on the surface. Suppose, for example, that {phi} decreases. In such a case the concentration of Cs{sup {minus}} on the surface must increase and that of Cs{sup +} decrease. Such processes lead to a net decrease in {phi}. To obtain a lower value of {phi} it is necessary to have on or in the metal surface defects or impurity atoms which increase the adsorption energy of Cs{sup +} or decrease the adsorption energy of Cs{sup {minus}}.

Studies on transport mechanism in indium tin oxide (ITO)/p-indium phosphide (InP) solar cells prepared by reactive electron beam evaporation and spray pyrolysis techniques. Subrahmanyam, A. (Indian Inst. of Tech., Madras (India)); Vasu, V.; Manivannan, P. pp. 1922-1925 of 1994 IEEE first world conference on photovoltaic energy conversion: Conference record of the twenty-fourth IEEE photovoltaic specialists conference -- 1994. Volume 2. Inst. of Electrical and Electronics Engineers, Inc., Piscataway, NJ (United States) (1994). 1268p. (CONF-941203--: 1. world conference on photovoltaic energy conversion, Waikoloa, HI (United States), 5-9 Dec 1994).

The aim of the present work is to study the effect of process induced defects on the transport mechanism in ITO/InP solar cells. A detailed analyses of electrical properties along with XPS studies have been carried out on ITO/p-InP cells prepared by reactive electron beam evaporation and spray pyrolysis techniques. It is observed that thermionic field emission (TFE) in ITO/p-InP junctions prepared by e beam and tunneling (below 300 K) and recombination at depletion region (above 300 K) in sprayed junctions are the dominant transport mechanisms. The cells prepared by both the techniques conform to Semiconductor-Insulator-Semiconductor model and the interfacial layer comprises of In{sub 2}O{sub 3} and InPO{sub 4} as revealed by XPS data.

An integral solar power and propulsion system concept for commercial space applications. Choong, P.T.S. (California International Power Associates, Los Altos Hills, CA (United States)). pp. 743-748 of Proceedings of the 30. intersociety energy conversion engineering conference. Volume 1. Goswami, D.Y. (ed.); Kannberg, L.D.; Somasundaram, S. (eds.); Mancini, T.R. (ed.). American Society of Mechanical Engineers, New York, NY (United States) (1995). 798p. (CONF-950729--: 30. Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995).

An integral space power concept deriving both the electrical and propulsion power from a common high-temperature heat source module offers superior performance capabilities over conventional chemical upper-stage propulsion with separate solar photovoltaic power systems. This hybrid system concept is based on a high efficiency solar concentrator-heated propulsion and a high temperature thermionic technology derived from the proven Solar Energy Thermionics (SET) or the advanced Hydrogen Thermo-ElectroChemical Conversion (HYTEC) for electrical power generation. The thermal hydrogen propulsion technology is derived from the NERVA rocket program. The integral system is capable of long-life power operation at an efficiency of at least twice the conventional photovoltaic approach. Because of anticipated high conversion efficiency of the HYTEC, the electrical power output can be increased several folds using the similarly sized solar concentrator. The propulsion module is capable of high specific impulse during the orbital transfer thrusting. The same module is also usable for long-term orbit management applications. The resulting savings in propellant and power generator equipment enable the use of new generation of low-cost launchers for many commercial satellite applications.

Introduction to workshop on spectral control and converters. Wanlass, M.W.; Schwartz, R.J. AIP Conference Proceedings; 321 (1): 6-12 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

This workshop focused on the portion of the TPV system that involves the photovoltaic energy converter and the spectral control element that affects subband-gap photon energy recovery. The discussion was divided into three major topic areas: status of the technology, status of the infrastructure, and champions of the technology. (AIP) {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

(NREL/TP--412-6845)
Thermophotovoltaics bibliography. Broman, L. National Renewable Energy Lab., Golden, CO (United States). Sep 1994. 23p. Sponsored by USDOE, Washington, DC (United States). DOE Contract AC36-83CH10093. Order Number DE94011898. Source: OSTI; NTIS; GPO Dep.

A bibliography containing 180 entries on thermophotovoltaic conversion of energy between 1950 and 1994 has been compiled. The entries are categorized with respect to type and contents.

Solar power-propulsion plant using heat accumulators of solar energy. Popov, E.B. (Scientific Production Association ``Lutch'', Podolsk, Moscow Region (Russia)); Salnikov, V.A.; Fedik, I.I. AIP Conference Proceedings; 361 (1): 1505-1510 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

This work covers the concept of a power-propulsion plant (PPP) for spacecraft. The PPP is intended: (a) to transport a spacecraft from one orbit to another to perform the spacecraft tasks; (b) to provide the spacecraft with electric power. {copyright} {ital 1996 American Institute of Physics.}

Photovoltaic principles used in thermophotovoltaic generators. Iles, P.A. (Applied Solar Energy Corporation, City of Industry, California 91745 (United States)). AIP Conference Proceedings; 321 (1): 67-79 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

This is a tutorial paper, reviewing photovoltaic principles, and their application to thermophotovoltaic (TPV) power generators. The treatment is not rigorous, but is intended to give a working model for the workshop attendees. The options available to TPV converter designers are described to help in the optimization of all components of the TPV system. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Workshop 4 Converter cooling & recuperation. Iles, P.; Hindman, D. AIP Conference Proceedings; 321 (1): 17-22 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

Cooling the PV converter increases the overall TPV system efficiency, and more than offsets the losses incurred in providing cooling systems. Convective air flow methods may be sufficient, and several standard water cooling systems, including thermo-syphon radiators, capillary pumps or microchannel plates, are available. Recuperation is used to increase system efficiency, rather than to increase the emitter temperature. Recuperators operating at comparable high temperatures, such as in high temperature turbines have worked effectively. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

The design and modeling of photovoltaic cells for TPV systems. Schwartz, R.J. (School of Electrical Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)); Gray, J.L. AIP Conference Proceedings; 321 (1): 379-389 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

There are a number of issues which arise in the modeling and design of photovoltaic cells for use in thermophotovoltaic (TPV) systems which make the design of these cells significantly different from those of one sun terrestrial or space cells. Some of the issues are the same as those that must be addressed in high concentration applications and in fact some of the early TPV cell designs were used in high concentration cells. This paper discusses these issues and illustrates their impact on cell performance. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

An InGaAsSb/GaSb photovoltaic cell by liquid-phase epitaxy for thermophotovoltaic (TPV) application. McNeely, J.B. (AstroPower, Inc., Solar Park, Newark, Delaware 19716-2000 (United States)); Mauk, M.G.; DiNetta, L.C. AIP Conference Proceedings; 321 (1): 221-225 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

Results of a preliminary study of the liquid-phase epitaxy of the InGaAsSb/GaSb quaternary system for use in 0.55 eV thermophotovoltaic cells are presented. While this work is currently in a preliminary stage, the background and overall experience database available indicate strongly that the 0.55 eV InGaAsSb/GaSb photovoltaic cell by liquid phase epitaxy is a practical and attractive development project for thermophotovoltaic applications. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Heat sources and the emitting surfaces. Noreen, D.; Benner, J.P. AIP Conference Proceedings (American Institute of Physics) (United States); 321 (1): 3-5 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

Thermophotovoltaics utilizing broadband and selective emitters require of various materials for a wide range of temperatures and environments. Currently, materials are available that will operate successfully in both vacuum and oxidizing ambients at temperatures of up to 1500 C. The use of silicon carbide (SiC) of various dimensions in applications such as heat exchangers and molten metal transfer lends credence to the expectation that it can be adapted for use as the emitter of the TPV system. New materials, composites, emissive coatings and control of micro-structure can be used to achieve improved radiant efficiency. (AIP)

Part II radiative transfer efficiency of a flat plate TPV system: Analytical model and numerical results. Hottel, H.C. (Professor of Chemical Engineering, Emeritus Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)). AIP Conference Proceedings; 321 (1): 437-454 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

The transfer efficiency has been evaluated for a base case and six variations of it. The base case is Ytterbia oxide fiber emitter operating at 2000 K, with emitter and PV cells forming 5{times}5 coextensive squares separated by 1 and provided with 85%-reflecting mirrors on opposite sides of the gap between emitter and cells, and with the fibers occupying a projected area that is 60% of the plane of the rug on which they are mounted. (AIP) {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Emittance theory for thin film selective emitter. Chubb, D.L. (NASA Lewis Research Center, Cleveland, Ohio 44135 (United States)); Lowe, R.A.; Good, B.S. AIP Conference Proceedings; 321 (1): 229-244 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

Thin films of high temperature garnet materials such as yttrium aluminum garnet (YAG) doped with rare earths are currently being investigated as selective emitters. This paper presents a radiative transfer analysis of the thin film emitter. From this analysis the emitter efficiency and power density are calculated. Results based on measured extinction coefficients for erbium-YAG and holmium-YAG are presented. These results indicate that emitter efficiencies of 50% and power densities of several watts/cm{sup 2} are attainable at moderate temperatures ({lt}1750 K). {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Experimental investigation of a Cs-Ba diode using Langmuir probes. Luke, J.R. (Institute for Space and Nuclear Power Studies/Chemical and Nuclear Engineering Departement, University of New Mexico, Albuquerque, New Mexico 87131 (United States)); El-Genk, M.S. AIP Conference Proceedings (American Institute of Physics) (United States); 324 (1): 111-116 (20 Jan 1995). (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

Experimental measurements are performed in a Cs-Ba diode to investigate the validity of the Maxwell-Boltzman energy distribution for electrons and the homogeneity of the plasma parameters throughout the discharge volume. Results show that the energy distribution is Maxwellian at high discharge current, but deviates from a Maxwell distribution at lower currents. Also, the ion densities and electron temperatures near the emitter and the collector are significantly different. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}

Electric power production using new GaSb photovoltaic cells with extended infrared response. Fraas, L. (JX Crystals, Inc., Issaquah, Washington (United States)); Ballantyne, R.; Samaras, J.; Seal, M. AIP Conference Proceedings; 321 (1): 44-53 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

New GaSb photovoltaic cells with infrared response extended out to 1.8 microns are well matched to hydrocarbon combustion heated silicon carbide infrared emitters operating at 1600 C. Power densities of up to 10 Watts/cm{sup 2} promise to make thermophotovoltaic generation of electricity economical. These continuous combustion thermophotovoltaic units run quietly and cleanly. Applications include small scale distributed cogeneration of heat and electricity and power units for clean electric vehicles. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Modeling of low-bandgap solar cells for thermophotovoltaic applications. Jain, R.K. (NASA Lewis Research Center, Cleveland, Ohio 44135 (United States)); Wilt, D.M.; Landis, G.A.; Jain, R.; Weinberg, I.; Flood, D.J. AIP Conference Proceedings; 321 (1): 202-209 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

Low-bandgap solar cells can be used effectively and efficiently for thermophotovoltaic applications. A 0.75 eV bandgap InGaAs solar cell is an ideal device for the Er-YAG selective emitter with a emission peak around 1.5 {mu}m. Modeling results predict that the InGaAs cell efficiencies of nearly 30% are possible for the Er-YAG selective emitter source at 1500 K. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Issues in the design of high-performance contacts to GaInAs TPV converters. Ward, J.S. (National Renewable Energy Laboratory Golden Colorado (United States)); Wanlass, M.W.; Wu, X.; Coutts, T.J. AIP Conference Proceedings (American Institute of Physics) (United States); 321 (1): 404-411 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

GaInAs is being investigated for use in the fabrication of thermophotovoltaic power conversion devices. In this paper a front surface grid metallization system composed of evaporated layers of Ti/Pd/Ag is proposed for these devices. The contacts are characterized and computer modeling techniques are used to predict the impact that they will have on the performance of these devices. Issues related to measurement conventions and their impact on the optimum design of these contacts is discussed. The effects on the optimum grid design of a system's ability to re-use photons reflected off of the metallization is also investigated.

The first NREL conference on thermophotovoltaic generation of electricity. AIP Conference Proceedings, No. 321 [APCPCS]. Coutts, T.J. (National Renewable Energy Laboratory (United States)); Benner, J.P. (eds.). CONF-9407100--: 1. National AIP, New York, NY (United States) (1995). (CONF-9407100--: 1. National Renewable Energy Laboratory (NREL) conference on thermophotovoltaic generation of electricity, Copper Mountain, CO (United States), 24-27 Jul 1994).

The First NREL Conference on Thermophotovoltaic Generation of Electricity was organized to assess the technology of this renewable energy source. The conference was sponsored by DOE and the National Renewable Energy Laboratory Director's Development Fund. These proceedings represent the papers presented at the conference. The topics discussed covered many aspects of thermophotovoltaic conversion. There were forty five papers presented at the conference and forty have been abstracted for the Energy and Science Technology database. (AIP)

Low-cost solar selective absorbers from Indian galena. Chatterjee, S. (Metallurgical and Engineering Consultants, Ranchi (India). Research and Development Div.); Pal, U. Optical Engineering (United States); 32 (11): 2923-2929 (Nov 1993).

The main thrust of the research is to prepare a low-cost solar-selective absorber from an indigenous semiconducting mineral, galena (galena aggregate and galena concentrate), for a solar thermoelectric generator. The authors report the results of preparation and characterization of solar-selective coatings made from galena aggregate and galena concentrate collected from the Zawar mines in Rajasthan, India. The coatings of galena are prepared by a thermal evaporation technique and exhibit high absorptivity ({alpha} {approximately} 0.95 and 0.97) in the solar spectral range and low emissivity ({epsilon}375{approximately}0.21 and 0.27) in the thermal range. Finally, these coatings were compared with synthesized PbS coating prepared in the laboratory and found to be quite comparable. The structure and composition of the coatings were studied by x-ray diffraction and electron spectroscopy for chemical analysis. Reflectance and absorption studies were made in the 0.3- to 3.1-{mu}m spectral range.

Parameter extraction for TPV cell development. Borrego, J. (Center for Integrated Electronics, Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)); Zierak, M.; Charache, G. AIP Conference Proceedings (American Institute of Physics) (United States); 321 (1): 371-378 (5 Jan 1995). (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

The internal quantum efficiency is a very sensitive characteristic of the diffusion length and surface/interface recombination velocity in the neutral regions of a TPV cell. In this paper we show how we have modeled the absorption constant of In{sub {ital x}}Ga{sub 1{minus}{ital x}}As alloys as to be able to calculate the internal quantum efficiency using a closed form computer model of the cell. Comparison between the experimentally measured and the modeled quantum efficiency allows extraction of the diffusion length and surface/interface recombination velocity.

TPV power source development for an unmanned undersea vehicle. Holmquist, G.A. (Quantum Group, Inc., San Diego, California 92121 (United States)). AIP Conference Proceedings (American Institute of Physics) (United States); 321 (1): 308-314 (5 Jan 1995). DOE Contract FG02-93ER81615. (CONF-940101--: 11. symposium on space nuclear power systems, Albuquerque, NM (United States), 9-13 Jan 1994).

The thermophotovoltaic (TPV) generation of electrical power promises efficiencies that are exploitable for military and commercial applications. TPV offers a combination of unique characteristics as a power source for military Unmanned Undersea Vehicles. In civilian applications TPV technology offers the potential for lightweight, rugged, and reliable power systems that can be environmentally benign. These systems can use a variety of fuels and can be scaled up in size. TPV is truly a dual use technology in which the United States appears to have a technical lead. The focus of the current Quantum program is the maturation of the technology and the demonstration of a 10 kilowatt generator. Preliminary results of this project are presented.

(SAND--98-0240C)
Re-START: The second operational test of the String Thermionic Assembly Research Testbed. Wyant, F.J. (Sandia National Labs., Albuquerque, NM (United States)); Luchau, D.; McCarson, T.D. Sandia National Labs., Albuquerque, NM (United States). Jan 1998. 8p. Sponsored by USDOE Office of Financial Management and Controller, Washington, DC (United States). DOE Contract AC04-94AL85000. (CONF-980103--: Space technology and applications international forum, Albuquerque, NM (United States), 25-29 Jan 1998). Order Number DE98002590. Source: OSTI; NTIS; GPO Dep.

The second operational test of the String Thermionic Assembly Research Testbed -- Re-START -- was carried out from June 9 to June 14, 1997. This test series was designed to help qualify and validate the designs and test methods proposed for the Integrated Solar Upper Stage (ISUS) power converters for use during critical evaluations of the complete ISUS bimodal system during the Engine Ground Demonstration (EGD). The test article consisted of eight ISUS prototype thermionic converter diodes electrically connected in series.

Efficient ternary sources of working-body vapors for thermionic converters. Kalandarishvili, A.G.; Kashiya, V.G. Atomic Energy (New York); 76 (5): 363-368 (Nov 1994).

The results of experiments to determine the energy characteristics of a cylindrical thermionic converter (TC) are presented. The TC investigated had ternary working-body vapor sources based on multicomponent cesium systems with either bismuth oxide, vanadium oxide, or tungsten oxide additions. Sorption characteristics of the systems were first determined, and then the ternary source was operated as part of the TC. The kinetics of the interaction of cesium vapor with the oxides was studied gravimetrically at various collector temperatures. The cesium TC electrical power output was increased 40 to 60% with a Cs{sub 12}Bi{sub 2}O{sub 3} ternary source in the arc mode. A Cs{sub 3}V{sub 2}O{sub 5} system increased TC output power from 20 to 40%, depending on emitter temperature. For the two Cs{sub x}WO{sub 3} sources examined, power increased almost 50%. The ternary sources examined also extended the working temperature range of the TC. 18 refs., 5 figs.

Emission properties of cathodes and relaxation characteristics of Cs-N{sub 2} thermionic energy converters with pulsed ionization. Antonov, E.E.; Korchevoi, Yu.P.; Podolyukh, I.Ya. High Temperature (English Translation) (United States); 31 (2): 203-207 (Sep 1993).

The relaxation of nitrogen-cesium plasmas under conditions close to the operating regimes of thermionic energy converters with pulsed ionization of Cs atoms is examined. A number of factors are identified which prolong the duration of the working phase of these converters when molecular nitrogen is added. The spatial profiles of the parameters of the relaxing plasma in the gap of a thermionic energy converter and the cathode emission properties which determine the kinetics of the plasma decay are studied.

SPACE-R nuclear power system SC-320 thermionic fuel element performance tests. Luchau, D.W. (Team Specialty Services, Inc., Albuquerque, NM (United States)); Bruns, D.R.; Nikolaev, Y.V. pp. 962-967 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

In 1993 and 1994, the Russian Scientific Research Institute NII NPO ``LUCH'' and Space Power, Inc., (SPI), of San Jose, California, developed a prototype of the single-cell thermionic fuel element (TFE) for the SPACE-R space nuclear power system (NPS). The SPACE-R system was designed as a part of the US Department of Energy's (DOE) Space Reactor Development Program to develop a long life, space reactor system capable of supplying up to 40 kW(e) output power. The jointly developed SC-320 TFE is a prototype of the next generation thermionic converter for nuclear applications in space. This paper presents the results of the initial demonstration tests and subsequent parametric evaluations conducted on the SC-320 TFE as compared to the calculated performance characteristics. The demonstration tests were conducted jointly by Russian and American specialists at the Thermionic Evaluation Facility (TEF) at the New Mexico Engineering Research Institute (NMERI) of the University of New Mexico in Albuquerque.

Mathematical modeling for a thermionic-AMTEC cascade system. Lodhi, M.A. (Department of Physics, Texas Tech University, Lubbock, Texas 79409 (United States)); Schuller, M.; Hausgen, P. AIP Conference Proceedings; 361 (1): 1285-1290 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

A mathematical modeling of a system consisting of a cascade of a thermionic energy conversion (TIEC) device and an alkali metal thermal to electrical conversion (AMTEC) device has been performed. The TIEC is heated by electron bombardment which converts heat partially into electricity and rejects the remaining. The AMTEC utilizes this reject heat of the TIEC. A mathematical thermal model of the cascade converter has been developed to analyze effects of key parameters such as power level, heat fluxes, temperatures, cascade geometry, etc. In this effort, a 9-node system of nonlinear simultaneous equations has been constructed which is solved by MATHCAD predicting the temperatures of the principal components and the heat flow. Through this study, a better understanding of the thermal coupling of the two converters was gained which helps to produce a more efficient cascade. {copyright} {ital 1996 American Institute of Physics.}

(SAND98-2255C)
START-3: Operational Evaluations of the ISUS Engine Ground Demonstration Thermionic Power System. Luchau, D.W.; Luke, J.R.; Wyant, F.J. Sandia National Laboratories, Albuquerque, NM, and Livermore, CA. 8 Oct 1998. 8 Oct 1998. [Unavailablep.] Sponsored by USDOE. DOE Contract AC04-94AL85000. Order Number DE00000763. Source: OSTI; NTIS; INIS; GPO Dep.

START-3 was a test program conducted in order to demonstrate and characterize the operational performance of the prototype Integrated Solar Upper Stage (ISUS) thermionic power system. The test device consisted of a graphite thermal storage uni~ multilayer foil insulation, and sixteen thermionic converters electrically connected in a series array. Several thermal input conditions were achieved during the test, which resulted in measuring converter performance at average converter hot shoe temperatures in the range of 1600 K to 2000 K. Results indicate that the ;hermionic converter; did not perform as weil as expected in the array individual sixteen converters is currently being performed.

Design of a power management and distribution system for a thermionic-diode powered spacecraft. Kimnach, G.L. (National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center). pp. 529-533 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 1: Aerospace power systems, aerospace technologies. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 681p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

The Electrical Systems Development Branch of the Power Technology Division at the NASA Lewis Research Center in Cleveland, Ohio is designing a Power Management and Distribution (PMAD) System for the Air Force's integrated Solar Upper Stage (ISUS) Engine Ground Test Demonstration (EGD). The ISUS program uses solar-thermal propulsion to perform orbit transfers from Low Earth Orbit (LEO) to Geosynchronous Orbit (GEO) and from LEO to Molnya. The ISUS uses the same energy conversion receiver to perform the LEO to High Earth Orbit (HEO) transfer and to generate on-orbit electric power for the payloads. On-orbit power generation is accomplished via two solar concentrators heating a dual-cavity graphite-core which has Thermionic Diodes (TIDs) encircling each cavity. The graphite core and concentrators together are called the Receiver and Concentrator (RAC). The TID-emitters reach peak temperatures of approximately 2,200 K, and the TID-collectors are run at approximately 1,000 K. Because of the high Specific Impulse (I{sub sp}) of solar thermal propulsion relative to chemical propulsion, and because a common bus is used for communications, GN and C, power, etc., a substantial increase in payload mass is possible. This potentially allows for a step-down in the required launch vehicle size or class for similar payload mass using conventional chemical propulsion and a separate spacecraft bus. The ISUS power system is to provide 1,000 W{sub e} at 28 {+-} 6V{sub dc} to the payload/spacecraft from a maximum TID generation capability of 1,070 W{sub e} at 2,200 K, producing power with this quality, protecting the spacecraft from electrical faults and accommodating operational constraints of the TIDs is the responsibility of the PMAD system. The design strategy and system options examined along with the proposed designs for the Flight and EGD configurations are discussed.

Out-of-pile simulation of deformation behavior of a thermionic fuel element under thermocycling conditions. Nikolaev, Yu.V. (Research Inst. of SIA Lutch, Podolsk (Russian Federation)); Gontar, A.S.; Vedenyapin, G.A.; Nelidov, M.V.; Sotnikov, V.N. pp. 1027-1031 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

The results of out-of-pile model testing of thermionic fuel elements (TFE) on the uranium dioxide base at the standard thermocycling conditions for research reactor testing of full-scale fuel elements are presented. Material (Mo, W, MN3-alloy) and thickness (0.4--1.0 mm) of cladding influence was studied. It is shown that the maximum decrease of cladding diameter during fuel element cooling is about 1.0% and maximum rate of diameter expansion due to the thermocycling is up to 0.1% per cycle. The cladding made from hardened MN3-alloy with 1.0 mm thickness is not practically sensible to the fuel element thermocycling conditions.

Output power characteristics and performance of TOPAZ II Thermionic Fuel Element No. 24. Luchau, D.W. (Team Specialty Services, Inc., TOPAZ International Program, 901 University Blvd., SE, Albuquerque, New Mexico 87106 (United States)); Bruns, D.R.; Izhvanov, O.; Androsov, V. AIP Conference Proceedings; 361 (1): 1163-1168 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

A final report on the output power characteristics and capabilities of single cell TOPAZ II Thermionic Fuel Element (TFE) No. 24 is presented. Thermal power tests were conducted for over 3000 hours to investigate converter performance under normal and adverse operating conditions. Experiments conducted include low power testing, high power testing, air introduction to the interelectrode gap, collector temperature optimization, thermal modeling, and output power characteristic measurements. During testing, no unexpected degradation in converter performance was observed. The TFE has been removed from the test stand and returned to Scientific Industrial Association {open_quote}{open_quote}LUCH{close_quote}{close_quote} for materials analysis and report. This research was conducted at the Thermionic System Evaluation Test (TSET) Facility at the New Mexico Engineering Research Institute (NMERI) as a part of the Topaz International Program (TIP) by the Air Force Phillips Laboratory (PL). {copyright} {ital 1996 American Institute of Physics.}

Close-spaced thermionic converters with active spacing control and heat-pipe isothermal emitters. Fitzpatrick, G.O. (Space Power, Inc., San Jose, CA (United States)); Koester, J.K.; Chang, J.; Britt, E.J.; McVey, J.B. pp. 920-927 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. Sponsored by USDOE, Washington, DC (United States). DOE Contract FG03-94ER81864. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

Thermionic converters with interelectrode gaps smaller than 10 microns are capable of substantial performance improvements over conventional ignited mode diodes. Previous devices which have demonstrated operation at such small gaps have done so at low power densities and emitter temperatures. Higher power operation requires overcoming two primary design issues: thermal distortion of the emitter due to temperature gradients and degradation of the in-gap spacers at higher emitter temperatures. This work describes two innovations for solution of these issues. The issue of thermal distortion was addressed by an isothermal emitter incorporating a heat-pipe into its structure. Such a heat-pipe emitter, with a single-crystal emitting surface, was fabricated and characterized. Finite-element computational modeling was used to analyze its distortion with an applied heat flux. The calculations suggested that thermal distortion would be significantly reduced as compared with a solid emitter. Ongoing work and preliminary experimental results are described for a system of active interelectrode gap control. In the present design an integral transducer determines the interelectrode gap of the converter. Initial designs for spacing actuators and their required cesium vapor seals are discussed. A novel hot-shell converter design incorporating active spacing control and low-temperature seals is presented. A converter incorporating the above features would be capable of near ideal-converter performance at high power densities. In addition, active spacing control can potentially completely eliminate short-circuit failures in thermionic converter systems.

Thermionic system space radiator design. Anderson, W.G. (Thermacore, Inc., Lancaster, PA (United States)); Rosenfeld, J.H. pp. 517-522 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 1. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 628p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Thermionic space power systems require a radiator to reject the waste heat. In the radiator, an armored NaK loop is used to transfer waste heat from the thermionic power source into a set of redundant header heat pipes. Heat is then distributed to a series of fin heat pipes with attached fins, and radiated to space. The optimum radiator design minimizes mass, while also minimizing the total number of fin heat pipes required. A computer model of the SPACE-R radiator was developed to determine the heat pipe and fin design that would lead to the optimum radiator design. This model includes an approximate, closed-form solution of the heat rejected from the fins, allowing rapid and accurate calculation of total heat rejected. Fin heat pipes play several important roles in the radiator design. A trade study was conducted that compared the mass of radiators with different fin materials, including carbon-carbon, comp-glas, beryllia, and no fins. The no-fin design replaced the fins with a series of broad, flat heat pipes fabricated from a lightweight titanium/titanium diboride composite. The trade study indicated that the no-fin design had the same mass as the design with carbon-carbon fins. Elimination of the carbon-carbon fins has a number of advantages, including elimination of the costly, brittle carbon-carbon fins, and elimination of the thermal expansion mismatch between the fins and the fin heat pipe.

(AD-A--284826/5/XAB)
Three region analysis of a bounded plasma using particle in cell and fluid techniques. Doctoral thesis. Nichols, D.F. Air Force Inst. of Tech., Wright-Patterson AFB, OH (United States). Sep 1994. 218p. (AFIT/DS/ENP--94-03). Source: NTIS Prices: PC A10/MF A03.

A detailed collisionless sheath theory and a three-region collisional model of a bounded plasma are presented, and the suitability of the collisional model for analysis of ignited mode thermionic converters is investigated. The sheath theory extends previous analyses to regimes in which the sheath potential and electron temperatures are comparable in magnitude. In all operating regimes typical of a ignited mode thermionic converter, the predicted sheaths extend several mean-free paths. The apparent collisionality of the sheaths prompted development of a collisional, three-region model of the converter plasma. By interfacing Particle-in-Cell regions (for the sheaths) and fluid regions (for the bulk of the plasma), a time-dependent, wall-to-wall model of the plasma in the inter-electrode space is created. The components of the model are tested and validated against analytic solutions and against one another, then applied to the analysis of an ignited mode thermionic converter. Under ignited mode operating conditions, the electron velocity distribution at the plasma/sheath boundary is found to be inconsistent with that assumed in the model development, and the calculation diverges. The observed distribution is analyzed and a new basis set of distribution functions is suggested that should permit application of the hybrid model to ignited mode thermionic converters.

Design of a thermionic converter for a domestic heating system. Kemenade, E. van (Eindhoven Univ. of Technology (Netherlands)); Veltkamp, W.B. pp. 1055-1060 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Developing a thermionic cogeneration system for optimal performance involves optimizing the thermionic converter in relation with the other system components. The demands on a thermionic energy converter for application in a typical Dutch single family house, assessed in a previous study, are used to redesign the TEC. The choice between ignited mode and unignited mode operation was decided in favor of the ignited mode as unignited mode operation requires large system dimensions. Optimizing the geometry of the thermionic converter with respect to the system efficiency leads to thin walled constructions. Creep considerations show that the ceramic part of the multilayer Mo-TiN-SiC hot shell must be regarded as the structural part of the construction. The sensitivity of the efficiency to elastic deformation and creep for a flat, cylindrical and spherical shape of the converter is assessed using a numerical model. Cylindrical and spherical shapes are shown to perform comparable. The cooling system, comprising a sodium heat pipe, has been designed for optimum performance balancing the heat duty and the required pumping power. A provisional design, based on these considerations is presented.

High temperature energy conversion for the Integrated Solar Upper Stage (ISUS). Ramalingam, M.L. (UES, Inc., Dayton, OH (United States)); Lamp, T.R.; Jacox, M.; Kennedy, F. pp. 351-356 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 1: Aerospace power systems, aerospace technologies. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 681p. Sponsored by Department of the Air Force, Washington, DC (United States). (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

Preliminary studies were conducted to assess the benefits of the Integrated Solar Upper Stage (ISUS) concept and key components including high temperature thermionic converters, have been tested and evaluated. Advanced radiatively coupled heat pipe cooled thermionic converters with rhenium and tungsten emitters were characterized individually for integration in a modular power unit. The converter with the tungsten emitter was performance mapped in the temperature range of 1,750 K to 2,400 K in order to conform to the ISUS requirements. Higher off-design temperatures yielded power densities as high as 12 watts/sq. cm. in the cesium pressure range of 4 to 9 torr. The converter with the rhenium emitter was tested in the temperature range of 1,575 K to 1,950 K and produced 10.5 watts/sq. cm. at the highest temperature. Dynamic switching characteristics were also measured to evaluate the possibility of interfacing a pulse width modulated (PWM) power regulator directly to a thermionic source.

Design and preliminary testing of a thermionic AMTEC cascade. Miskolczy, G. (Thermo Trex Corp., 85 First Avenue, Waltham, Massachusetts 02254 (United States)); Sievers, B.; Svedberg, B.; Schuller, M.; VanHagen, T.; Smith, J.; Reiners, E. AIP Conference Proceedings; 361 (1): 1291-1298 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

This paper describes the design of an experiment to demonstrate the feasibly of operating a cascade of a Thermionic Energy Converter (TEC) with an Alkali Metal Thermo Electric Converter (AMTEC). Both of these devices convert heat to electricity without moving mechanical parts and lend themselves to be incorporated into a cascade. Typically, the TEC operates from a hot temperature of 2000 K to 1700 K, rejecting heat at 1100 K to 700 K, while the AMTEC operates from a hot temperature of 1100 K to 900 K and a cold temperature of about 400 K. These temperature ranges form almost ideal cascade. {copyright} {ital 1996 American Institute of Physics.}

Thermionic/AMTEC cascade converter concept for high-efficiency space power. Hagan, T.H. van (General Atomics, San Diego, CA (United States)); Smith, J.N. Jr.; Schuller, M. pp. 629-634 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 1: Aerospace power systems, aerospace technologies. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 681p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

This paper presents trade studies that address the use of the thermionic/AMTEC cell--a cascaded, high-efficiency, static power conversion concept that appears well-suited to space power applications. Both the thermionic and AMTEC power conversion approaches have been shown to be promising candidates for space power. Thermionics offers system compactness via modest efficiency at high heat rejection temperatures, and AMTEC offers high efficiency at modest heat rejection temperature. From a thermal viewpoint the two are ideally suited for cascaded power conversion: thermionic heat rejection and AMTEC heat source temperatures are essentially the same. In addition to realizing conversion efficiencies potentially as high as 35--40%, such a cascade offers the following perceived benefits: survivability; simplicity; technology readiness; and technology growth. Mechanical approaches and thermal/electric matching criteria for integrating thermionics and AMTEC into a single conversion device are described. Focusing primarily on solar thermal space power applications, parametric trends are presented to show the performance and cost potential that should be achievable with present-day technology in cascaded thermionic/AMTEC systems.

Fabrication and testing of full-length single-cell externally fueled converters for thermionic reactors. Schock, A. (Fairchild Space and Defense Corp., Germantown, MD (United States)). pp. 471-489 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 1. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 628p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

The preceding paper described designs and analyses of thermionic reactors employing full-core-length single-cell converters with their heated emitters located on the outside of their internally cooled collectors, and it presented results of detailed parametric analyses which illustrate the benefits of this unconventional design. The present paper describes the fabrication and testing of full-length prototypical converters, both unfueled and fueled, and presents parametric results of electrically heated tests. The unfueled converter tests demonstrated the practicality of operating such long converters without shorting across a 0.3-mm interelectrode gap. They produced a measured peak output of 751 watts(e) from a single diode and a peak efficiency of 15.4%. The fueled converter tests measured the parametric performance of prototypic UO{sub 2}-fueled converters designed for subsequent in-pile testing. They employed revolver-shaped tungsten elements with a central emitter hole surrounded by six fuel chambers. The full-length converters were heated by a water-cooled RF-induction coil inside an ion-pumped vacuum chamber. This required development of high-vacuum coaxial RF feedthroughs. In-pile test rules required multiple containment of the UO{sub 2}-fuel, which complicated the fabrication of the test article and required successful development of techniques for welding tungsten and other refractory components. The tests measured a peak power output of 530 watts(e) or 7.1 watts/cm{sup 2} at an efficiency of 11.5%.

Thermionic technology programs at Wright Laboratory. Donovan, B.D. (Wright Lab., Wright-Patterson AFB, OH (United States). Aerospace Power Div.); Lamp, T.R. pp. 1015-1020 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Wright Laboratory has had a long standing interest in energy conversion dating back to the early 1960s when a heat pipe cooled thermionic converter was demonstrated through work at the predecessor to Wright Laboratory (WL). With the exception of the short hiatus in the mid-70s, Air Force thermionics work at Wright Laboratory has continued to the present time with thermionic technology programs. This paper summarizes work done under the Advanced Thermionics Initiative (ATI) program, the advanced out-of-core thermionic technology program called Thermionics Critical Technology (TCT) Investigation. Converter design parameters, specifications, and performance testing data is summarized. Also summarized is the recent performance testing of a variable gap window diode fabricated by Loral EOS. Planned projects in the area of remote power are also discussed. Even given the extensive experience in energy conversion and thermionic technology, calendar year 1994 will be the last full year that Wright Laboratory's Aerospace Power Division will have a major interest in thermionic technology. Existing programs will be concluded in a logical manner and relevant data will be presented and discussed from these final programs and in-house efforts.

Multi-diode converter feasibility experiments. Miskolczy, G. (ThermoTrex Corp., Waltham, MA (United States)); Reagan, P.; Lieb, D.P.; Schuller, M. pp. 1049-1054 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Major handicaps to the use of thermionic diodes are their low voltage, high current output characteristics. The typical performance of a state-of-the-art thermionic diode is approximately 0.5 V at 15 A/cm{sup 2} regardless of size or geometry. If a compact series combination of thermionic diodes could be fabricated to produce a higher output voltage, the total weight could be reduced and system efficiency improved. In this program the feasibility of constructing a cylindrical thermionic device consisting of a series/parallel combination of small area diodes with a common plasma in a single envelope was demonstrated. Both emitter and collector cylinders were fabricated by outside diameter Chemical Vapor Deposition (CVD) of silicon carbide (SiC) and tungsten (W) on graphite mandrels. The collector was thermally cycled to 1,400 C in vacuum four times and remained intact. The resistivity of the SiC was measured from room temperature to 1,200 C and found to be sufficient to operate a series/parallel connection of diodes. No significant reaction was observed with the emitter or W at 1,200 C during a 1,200 hour life test in a Cs vapor pressure of 2 torr.

Tests of effectiveness of thermionic heat pipe modules. Evans, R.M. (ORION International Technologies, Inc., Albuquerque, NM (United States)); LeMire, R.; Hidinger, D.; Suriano, M. pp. 442-445 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 1. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 628p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

The Thermionic Heat Pipe Module (THPM) is a thermionic converter. The THPM is designed as a cylindrical device, with the emitter external to the collector. The emitter heat pipe subassembly (EHP) is an annular sleeve of one or more heat pipes, which are designed to produce an isothermal inner surface. This inner surface is the actual emitter of the thermionic converter. The collector is the exterior surface of a cylindrical heat pipe, which is nested inside the EHP. This collector heat pipe is used as the first stage of the heat transport and rejection subsystem. The EHP subassembly is radiatively coupled to the heat source. This paper will document work at the Phillips Laboratory (PL) to characterize the performance of the EHP. The first THPM designs used an annular, Li-filled, Mo heat pipe. The performance of this heat pipe was never verified. A series of THPMs with collectors removed will be used for these experiments. The performance of a filled Li-EHP will be compared to the performance of a solid wall Mo annulus of the same dimensions. Follow-on testing at PL will include thermal and converter performance of THPMs with varied EHP designs. These tests will build on the emitter thermal characterizations accomplished.

Closed spaced thermionic converter with isothermic electrodes. Kucherov, R.Ya. (Research Inst. SIA Lutch, Podolsk (Russian Federation)); Nikolaev, Yu.V. pp. 490-492 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 1. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 628p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Thermal deformations and electrode nonparallelism are the main causes, limiting the exploitation characteristics of the close spaced thermionic converters. In the present report a converter is described where emitter and collector electrodes are the systems of short heat pipes connected by the holes in the walls between the adjacent pipes and spacers are fastened to the emitter. The heat pipes provide the electrode isothermability, the spacers fixed on the emitter provide the parallelism of the electrodes in the process of heating the converter. This allows to increase the electrode area to a considerable extent and to decrease the acceptable width of the interelectrode gap. As a result of decreasing the gap, the electric power and efficiency of the converter considerably increase.

Thermal performance of a high temperature phase change thermionic fuel cell. Anghaie, S. (Univ. of Florida, Gainesville, FL (United States)); Ding, Z. pp. 306-311 of Heat transfer -- Portland 1995. El-Genk, M.S. (ed.). American Inst. of Chemical Engineers, New York, NY (United States) (1995). 378p. (CONF-950828--: 1995 National heat transfer conference, Portland, OR (United States), 5-9 Aug 1995).

This paper describes the numerical simulation of the thermal performance of a multiphase thermionic fuel element (TFE) operating under zero gravity condition. An internal energy formulation is used to describe the phase-change process occurring during the bulk evaporation and condensation subjected to the constraint of constant volume. The evolution of the bulk evaporation and condensation, the phase-change processes between liquid and vapor, is obtained. The variations of temperature distribution with time and the motion of the liquid/vapor interface under the influence of a non-uniform internal heat generation are investigated.

Evaluation of the thermionic work function of the mandrel side of chemically vapor deposited and vacuum plasma sprayed refractory metals. Hartenstine, J.R. (Thermacore, Inc., Lancaster, PA (United States)); Horner-Richardson, K.D.; Bosch, D.R.; Jacobson, D.L. pp. 463-470 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 1. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 628p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

A Thermionic Heat Pipe Module (THPM) is a thermionic energy converter configured with a cylindrical emitter on the outside, which surrounds a central collector on the inside. Due to its configuration, the emitting surface is the inside diameter of the emitter sleeve. The emitter is fabricated by vapor depositing tungsten onto a mandrel, which is subsequently removed, exposing the emitting surface. Conventional emitters of Thermionic Fuel Elements are fabricated in a similar process, except the emitting surface is the outside surface of the cylinder. This paper presents the measurement and evaluation of the thermionic work function of mandrel side tungsten and rhenium deposited by Chemical Vapor Deposition (CVD) and tungsten deposited by Vacuum Plasma Spray (VPS) techniques. The metals evaluated are: hexachloride vapor deposited tungsten, hexachloride and hexafluoride duplex vapor deposited tungsten, hexachloride vapor deposited rhenium and VPS tungsten.

Investigation of TFE collector insulation of thermionic NPP. Nikolaev, Y.V. (Research Institute of Scientific Industrial Association ``Lutch'', Podolsk, Moscow region, 142100 (Russian Federation)); Vasilchenko, A.V.; Lapochkin, N.V.; Tzetzhladze, D.L. AIP Conference Proceedings; 361 (1): 1221-1226 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

Various configurations of thermionic fuel element (TFE) collector insulation of thermionic nuclear power plant (NPP) have been considered. The results of the experimental studies of collector insulation samples are presented. Their serviceability and high insulating characteristics which meet the requirements of high-voltage thermionic NPP have been shown. {copyright} {ital 1996 American Institute of Physics.}

Close-spaced Knudsen's mode thermionic converter. Kucherov, R.Ya. (Research Inst. of SIA Lutch, Podolsk (Russian Federation)); Nikolaev, Y.V. pp. 141-144 of Proceedings of the 30. intersociety energy conversion engineering conference. Volume 3. Goswami, D.Y. (ed.); Kannberg, L.D.; Somasundaram, S. (eds.); Mancini, T.R. (ed.). American Society of Mechanical Engineers, New York, NY (United States) (1995). 493p. (CONF-950729--: 30. Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995).

It is demonstrated that the Knudsen's mode of the thermionic converter (TIC) operation can be realized in a TIC with the interelectrode spacing 15{divided_by}30 {mu} and the emitter work function 5{divided_by}5.5 eV at the emitter temperature above 1800 K and cesium vapor pressure 0.5{divided_by}1 tor. With the use of reflective coating applied to the collector, efficiency of such TIC can achieve the level in excess of 30%.

Negative resistivity behavior in a thermionic energy converter. Davidsson, J. (Univ. of Goeteborg (Sweden)); Svensson, R. pp. 1032-1034 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

The resistivity of the interelectrode gap (IG) in the 4th quadrant has been studied at various frequencies and currents, and it was discovered that the resistivity of the IG was dependent of the electrode sweep voltage frequency. The resistivity showed a strong dependence in the range DC to approximately 5Hz. When the voltage across the electrodes was varied in a small interval in the fourth quadrant with a very low frequency or was varied manually in DC mode the slope of the I-V characteristics was negative, i.e. the resistance was seemingly negative. The onset of the high back current was also studied, as well as the ''regaintime'' of the high back current. The regaintime is the time elapsed between the extinguishing of the back current and the long time it still was possible to regain the back current again.

Peculiarities of a method for ex-reactor heating of electrodes and obtaining voltage-current characteristics of multi-cell thermionic fuel elements. Kalandarishvili, A.G. (Sukhumi Institute of Physics and Engineering, Tbilisi 380008 Republic of (Georgia)); Drozdov, A.A.; Stepennov, B.S. AIP Conference Proceedings; 361 (1): 1279-1284 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

The paper discusses principle of operation and applications of a pulse method of heating multi-cell thermionic fuel elements. Some experimental results are given for a cylindrical single-cell thermionic energy converter that simulates conditions close to that of multi-cell TFE operation. Basic requirements for technical parameters are stated that should be observed when testing TFE on thermal facilities. The means to improve the method are described, including both a computer-aided experiment and modifications in individual components of the test facility. {copyright} {ital 1996 American Institute of Physics.}

WAPD-T--3062)
Design and operation of a thermionic converter in air. Horner, M.H. (General Atomics, San Diego, CA (United States)); Begg, L.L.; Smith, J.N. Jr.; Geller, C.B.; Kallnowski, J.E. Westinghouse Electric Corp., West Mifflin, PA (United States). Bettis Atomic Power Lab. [1995]. 7p. Sponsored by USDOE, Washington, DC (United States). DOE Contract AC11-93PN38195. (CONF-950729--2: Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995). Order Number DE95010151. Source: OSTI; NTIS; INIS; GPO Dep.

An electrically heated thermionic converter has been designed, built and successfully tested in air. Several unique features were incorporated in this converter: an integral cesium reservoir, innovative ceramic-to-metal seals, a heat rejection system coupling the collector to a low temperature heat sink and an innovative cylindrical heater filament. The converter was operated for extended periods of time with the emitter at about 1900 K. the collector at about 700 K, and a power density of over 2 w(e)/sq. cm. Input power transients were run between 50% and 100% thermal power, at up to 1% per second, without instabilities in performance.

Study of tungsten oxide material for thermionic energy converter collector. Fukuda, R. (Electrotechnical Lab., Ibaraki (Japan)); Kasuga, Y.; Hayashi, K.; Katoh, K.; Shimizu, S. pp. 1041-1048 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

In order to improve efficiency of a thermionic converter, it is most effective to develop collector electrode materials with low work function ({approximately}1.0eV) and high temperature endurance capability ({approximately}1,000K). The authors have studied characters of tungsten oxide materials for a high performance collector. An apparatus was developed to evaluate thermionic emission of collector materials in caesium vapor, based on a principle of plasma immersion technique. A shortcoming of the usual plasma immersion technique, that a temperature of a sample electrode cannot be measured accurately, has been conquered by the new apparatus, by adopting a small disk as a sample electrode, not a loop of small wire as usually used, and by using thermocouples to measure the temperature. A tungsten oxide electrode on a tungsten single crystal (110) disk was fabricated by vacuum deposition, and its work function values were measured by the apparatus. The values were 1.45eV, almost constant independent to caesium vapor pressure (Tr = 423 {approximately} 513K). It is supposed that caesium may form a chemical compound with tungsten oxide. The atomic constituent of the tungsten oxide was identified by X-ray photoelectron spectroscopy (XPS), resulting in 0/W = 2.56 {approximately} 3.0.

Merits of the refractory metals single crystals in application to the TFE. Gontar, A.S. (State Research Inst. of Scientific Industrial Association LUTCH, Podolsk (Russian Federation)); Kucherov, R.Ya.; Nikolaev, Yu.V.; Nelidov, M.V. pp. 951-956 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

Development of a TFE with a long-term service life and a high electric power requires a substantiated choice and, in some cases, production of modern structural materials having improved operating characteristics. A lot of investigations like that including material-scientific, technological and calculated-and-engineering developments have been performed in RI of SIA LUTCH. A number of modern structural materials on molybdenum, tungsten and niobium single-crystal base has been developed and introduced into the TFE designs in course of this work. This report covers the results of experimental and calculated investigations justifying the advantages of the above materials over the similar polycrystal ones.

TOPAZ-2 single-cell TFE electric insulation properties study. Vasilchenko, A.V. (INERTEK (TOPAZ-2 Project), 901 University Blvd. SE, Albuquerque, New Mexico 87106-4439 (United States)); Izhvanov, O.L. AIP Conference Proceedings; 361 (1): 1215-1220 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

TOPAZ-II single cell thermoinic fuel element (TFE) electric insulation parameters under testing with electric heating were measured. TFE electric design schematic, experimental procedure and measurements results are described. Collector resistance was measured in helium at 420{endash}890 K. Metal ceramic ceals insulation properties were measured in vacuum P=10{sup {minus}4} Pa and in cesium vapor P=10{sup {minus}1}{minus}260 Pa, at 420{endash}730 K. Results of separate TFE are compared with the data; that were measured during nuclear power system (NPS) Ya-21U test. Based upon this data NPS power losses were estimated. {copyright} {ital 1996 American Institute of Physics.}

Out-of-pile simulation of deformation behavior of a thermionic fuel element under thermocycling conditions. Nikolaev, Yu.V. (Research Inst. of SIA Lutch, Podolsk (Russian Federation)); Gontar, A.S.; Vedenyapin, G.A.; Nelidov, M.V.; Sotnikov, V.N. pp. 1027-1031 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

The results of out-of-pile model testing of thermionic fuel elements (TFE) on the uranium dioxide base at the standard thermocycling conditions for research reactor testing of full-scale fuel elements are presented. Material (Mo, W, MN3-alloy) and thickness (0.4--1.0 mm) of cladding influence was studied. It is shown that the maximum decrease of cladding diameter during fuel element cooling is about 1.0% and maximum rate of diameter expansion due to the thermocycling is up to 0.1% per cycle. The cladding made from hardened MN3-alloy with 1.0 mm thickness is not practically sensible to the fuel element thermocycling conditions.

Investigation of (110)Mo, (110)W monocrystals and Nb polycrystal implanted by oxygen ions and used as TEC electrodes. Tsakadze, L.M. pp. 121-124 of Proceedings of the 30. intersociety energy conversion engineering conference. Volume 3. Goswami, D.Y. (ed.); Kannberg, L.D.; Somasundaram, S. (eds.); Mancini, T.R. (ed.). American Society of Mechanical Engineers, New York, NY (United States) (1995). 493p. (CONF-950729--: 30. Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995).

In an effort to improve efficiency of a thermionic energy converter (TEC), converting thermal power into electric power, there were investigated collectors made of (110)Mo and (110)W monocrystals, and Nb polycrystal, all being implanted by oxygen ions with fluence of 1*10{sup 18} cm{sup {minus}2}. For emitters there were used (110)Mo and (110)W monocrystals, and Nb polycrystal implanted by oxygen ions, respectively. The performance of TEC with implanted electrode material is compared with this of TEC having electrodes of non-implanted materials. It is demonstrated that for emitter temperature range of 1,473 to 1,873 K employment of (110)Mo and (110)W monocrystals, implanted by oxygen ions, for TEC collector allows to increase the specific output power of a converter approximately by a factor of 1.6, and employment of implanted Nb for electrodes -- to increase this value approximately by a factor of 3, as compared with non-implanted electrode materials. The upgraded performance of TEC with implanted electrode materials is caused by the increase of minimum values of the collector working function by {approximately}0.15--0.2 eV as compared with non-implanted collectors, as well as by improvement of emitter emissive and adsorption properties due to oxygen supply from collectors at operating temperatures.

Dynamic simulation of the thermal and electrical behavior of a thermionic converter coupled to a solar concentrator. Perez, G. (CUAP-UAP, Puebla (Mexico). Centro de Investigaciones en Dispositivos Semiconductores); Estrada, C.A.; Cervantes, J.G. pp. 465-468 of Proceedings of the 30. intersociety energy conversion engineering conference. Volume 2. Goswami, D.Y. (ed.); Kannberg, L.D.; Somasundaram, S. (eds.); Mancini, T.R. (ed.). American Society of Mechanical Engineers, New York, NY (United States) (1995). 658p. (CONF-950729--: 30. Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995).

A mathematical simulation for the dynamic thermal and electrical behavior of a thermionic converter coupled to a solar concentrator, is presented. The thermionic device is a Cesium-filled thermionic diode operating in the ignited mode. The emitter of the device is made of polycrystalline Rhenium and the collector of the device of Molybdenum. The solar concentrator is a parabolic dish. The designed emitter and collector temperatures are 1,850 K and 928 K, respectively. However, due to changes in ambient conditions, the collector efficiency varies and so does the system efficiency. This fact makes it necessary to evaluate the design of the system not just for one hour with constant conditions but also for a whole operating day. The paper presents plots for the emitter and collector thermionic device temperatures and power and voltage for a constant resistance load as a function of time.

Design of a core-length thermionic fuel element for electrical heating. Miskolczy, G. (ThermoTrex Coporation, 85 First Avenue, P.O. Box 8995, Waltham, MA 02254-8995 (United States)); Horner, H.; Lamp, T. AIP Conference Proceedings (American Institute of Physics) (United States); 271 (3): 1483-1488 (20 Jan 1993). (CONF-930103--: 10. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 10-14 Jan 1993).

This paper describes the design of an electrically heated version of a core-length Thermionic Fuel Element (TFE) with advanced features, as is suggested by the designation Advanced Thermionic Inititative (ATI). The advanced features include a high-strength emitter structure to be fabricated by Space Power, Incorporated. This structure consists of a cylindrical emitter, 15 mm diameter and 254 mm long of Chemically Vapor Deposited (CVD) tungsten, reinforced with tungsten-hafnium carbide wire wound over a CVD tungsten core with additional CVD tungsten incorporating and bonding the wire into the emitter. The emitter surface is CVD tungsten, deposited from tungsten chloride resulting in the desirable crystal orientation of {l_angle}110{r_angle}. It is possible to design a reactor with core-length TFEs so that it can be electrically tested prior to fueling. The program is focussed on the design and fabrication of a single core-length TFE with current collection at both ends which will be tested in a reactor. In parallel with this effort is the design, fabrication, and testing of an unfueled, electrically heated prototype. The intent is to make the electrically heated converter as similar as possible to the fueled one, while providing for accurate emitter and collector temperature measurement.

Analysis of emitter material transport in thermionic converter. Paramonov, D.V. (Institute for Space and Nuclear Power Studies, Chemical and Nuclear Engineering Department, University of New Mexico, Albuquerque, New Mexico 87131 (United States)); El-Genk, M.S. AIP Conference Proceedings; 361 (1): 1137-1148 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

Output power and efficiency of a thermionic converter depend on temperatures, cesiated work functions, and emissivities of electrodes as well as the interelectrode gap size. Operation lifetime of a thermionic converter is directly related to the values as well as the stability of these parameters, which can be seriously altered by the transport of emitter material to the collector during operation. Loss rate of tungsten, a preferred emitter material, by sublimation at typical operating temperatures is small (about 3{times}10{sup 7} atom/cm{sup 2}sec at 2000 K). The loss rate, however, can be several orders of magnitude higher in the presence of gaseous contaminants. Accelerated transport of emitter material to collector surface changes the effective emissivity and work functions of the electrodes, resulting in performance degradation. A phenomenological model was developed to simulate emitter material transport to the collector in the presence of oxygen, water vapor, and carbon oxide contaminants. The model accounts for interaction of these contaminants with both emitter and collector. Model results were in agreement with experimental data and theoretical results of other investigators. An analysis was performed to determine steady-state chemical composition of deposited material onto the collector surface in the presence of H{sub 2}O, O{sub 2}, and H{sub 2} gaseous contaminants. {copyright} {ital 1996 American Institute of Physics.}

Thermionic converters for an Integrated Solar Upper Stage (ISUS). Anderson, W.G. (Thermacore, Inc., Lancaster, PA (United States)); Horner-Richardson, K. pp. 339-344 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 1: Aerospace power systems, aerospace technologies. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 681p. (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

The Integrated Solar Upper Stage (ISUS) is a solar bimodal system which combines thermal propulsion and electric power generation in a single integrated system. A thermionic converter was designed and fabricated for the ISUS system. The ISUS thermionic energy converters differ from previous designs, due to the significant changes in operating temperature prior to and during an eclipse, with the emitter temperature increasing from 1,900 K to 2,200 K, and then back again. A complete thermal and electrical model was developed for a planar diode to determine optimum operating dimensions and parameters. The model includes an overall energy balance for the diode, and changes the interelectrode gap spacing due to thermal expansion of the parts as the emitter and/or collector temperatures change. Cesium pressure can be chosen from an external liquid reservoir, an integral reservoir using cesium intercalated into graphite attached to the collector heat pipe, or optimum cesium pressure. With optimum cesium pressure, the maximum efficiency increases from 14% to 16% as the emitter temperature increases from 1,900 K to 2,200 K. The improvement in efficiency is only 2% as the emitter temperature is increased. Optimum efficiency requires an external, actively controlled liquid reservoir.

WAPD-T--3066)
Integral cesium reservoir: Design and transient operation. Smith, J.N. Jr. (General Atomics, San Diego, CA (United States)); Horner, M.H.; Begg, L.L.; Wrobleski, W.J. Westinghouse Electric Corp., West Mifflin, PA (United States). Bettis Atomic Power Lab. [1995]. 7p. Sponsored by USDOE, Washington, DC (United States). DOE Contract AC11-93PN38195. (CONF-950729--1: Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995). Order Number DE95010152. Source: OSTI; NTIS; INIS; GPO Dep.

An electrically heated thermionic converter has been designed built and successfully tested in air (Homer et.al., 1995). One of the unique features of this converter was an integral cesium reservoir thermally coupled to the emitter. The reservoir consisted of fifteen cesiated graphite pins located in pockets situated in the emitter lead with thermal coupling to the emitter, collector and the emitter terminal; there were no auxiliary electric heaters on the reservoir. Test results are described for conditions in which the input thermal power to the converter was ramped up and down between 50% and 100% of full power in times as short as 50 sec, with data acquisition occurring every 12 sec. During the ramps the emitter and collector temperature profiles. the reservoir temperature and the electric output into a fixed load resistor are reported. The converter responded promptly to the power ramps without excessive overshoot and with no tendency to develop instabilities. This is the rust demonstration of the performance of a cesium-graphite integral reservoir in a fast transient

Quantifying the heat switching capability of a thermionic diode. Snyder, A.M. (Lockheed Idaho Technologies Co., Idaho Falls, ID (United States). Idaho National Engineering Lab.); Verrill, D.A. pp. 763-768 of Proceedings of the 30. intersociety energy conversion engineering conference. Volume 1. Goswami, D.Y. (ed.); Kannberg, L.D.; Somasundaram, S. (eds.); Mancini, T.R. (ed.). American Society of Mechanical Engineers, New York, NY (United States) (1995). 798p. (CONF-950729--: 30. Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995).

The Integrated Solar Upper Stage (ISUS) Advanced Technology Demonstrator (ATD) program, recently initiated by the US Air Force Phillips Laboratory (USAF PL), will demonstrate the feasibility of a combined solar power and propulsion upper stage. The solar bimodal design approach will use thermal energy storage to reduce engine mass and concentrator area. However, in order to store enough energy over an orbit period there must be minimal heat lost with a system that is designed to remove heat for energy conversion. A unique feature of thermionics is their ability to reduce heat flow by reducing or eliminating the electron cooling. However, demonstration and quantification of this capability is needed. This paper presents the results to date of the Receiver Diode Integration Test, one of two critical experiments of the ISUS ATD program being performed by the Idaho National Engineering Laboratory (ML). Results of the demonstration testing of thermionic heat pipe modules (THPMS) to operate as heat switches in conjunction with the solar receiver cavity are presented as are the performance limits and operational constraints of a combined receiver/diode subsystem.

Thermionic fuel element for the S-prime reactor. Van Hagan, T.H. (General Atomics P.O. Box 85608 San Diego, CA 92186-9784 (United States)); Drees, E.A. AIP Conference Proceedings (American Institute of Physics) (United States); 271 (3): 1469-1474 (20 Jan 1993). (CONF-930103--: 10. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 10-14 Jan 1993).

Technical aspects of the thermionic fuel element (TFE) design proposed for the S-PRIME space nuclear power system are discussed. Topics covered include the rational for selecting a multicell TFE approach, a technical description of the S-PRIME TFE and its estimated performance, and the technology readiness of the design, which emphasizes techology maturity and low risk.

Test of a TEC-module. Yarygin, V.I. (ECS-Russia, Obninsk (Russian Federation)); Meleta, Ye.A.; Tulin, S.M.; Klepikov, V.V.; Ruzhnikov, V.A.; Wolff, L.R. pp. 1061-1066 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Combustion heated Thermionic Energy Converters (TECs) will find application in various cogeneration systems. As a first step towards the development of full fledged thermionic systems, a TEC-module was designed, built and tested. This TEC-Module consists of one TEC which is heated by natural gas fired recuperative burner. The TEC-module will be the basic component in thermionic cogeneration systems like the TECTEM, a thermionic boiler for domestic application or the TECBURNER, an industrial burner equipped with an array of TECs. Three types of tests will be performed: (1) using an electrically heated research diode, the optimum TEC parameters were determined; (2) using a calorimeter in the shape of a combustion heated TEC, the heat flow of the natural gas burner to the TEC was measured and the thermal balance of the TEC-module was determined; and (3) a standard ECS combustion heated TEC was tested in the TEC-module in order to determine the TEC-module electrical and thermal performance. The report deals with results of the tests mentioned above and the progress that was made in the development of thermionic cogeneration systems.

Thermionic converter. Fitzpatrick, G.O. To Rasor Associates, Inc., Sunnyvale, CA (United States). 19 May 1987. Filed date 26 Nov 1982. U.S. Patent Application 6-444,736.

A thermionic converter is set forth which includes an envelope having an electron collector structure attached adjacent to a wall. An electron emitter structure is positioned adjacent the collector structure and spaced apart from opposite wall. The emitter and collector structures are in a common chamber. The emitter structure is heated substantially only by thermal radiation. Very small interelectrode gaps can be maintained utilizing the thermionic converter whereby increased efficiency results. 10 figs.

(DOE/OR/00033--T701)
An overview of thermionic power conversion technology. White, M.C. Florida Univ., Gainesville, FL (United States). Dec 1996. 93p. Sponsored by USDOE Assistant Secretary for Nuclear Energy, Washington, DC (United States). DOE Contract AC05-76OR00033. Order Number DE97053351. Source: OSTI; NTIS; GPO Dep.

Thermionic energy conversion is one of the many concepts which make up the direct power conversion technologies. Specifically, thermionics is the process of changing heat directly into electricity via a material's ability to emit electrons when heated. This thesis presents a broad overview of the engineering and physics necessary to make thermionic energy conversion (TEC) a practical reality. It begins with an introduction to the technology and the history of its development. This is followed by a discussion of the physics and engineering necessary to develop practical power systems. Special emphasis is placed on the critical issues which are still being researched. Finally, there is a discussion of the missions which this technology may fulfill.

Modeling the high temperature creep deformation in single crystalline tungsten alloys. Hong Peter Gao (Materials Engineering, Auburn University, Alabama 36849 (United States)); Zee, R.H. AIP Conference Proceedings; 324 (1): 283-288 (20 Jan 1995). DOE Contract FG03-93SF19645. (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

A semi-mechanistic phenomenological model was developed to predict the high temperature creep properties of single crystalline binary tungsten alloys for thermionic applications. This new model is based on the limited theoretical and experimental results presently available in the literature for both polycrystalline and single crystalline tungsten alloys. It provides a better understanding on the creep deformation of single crystalline tungsten alloys and helps guide the development of this type of material for long-term high-temperature applications. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}

Universal one dimension model TOR of thermionic converter. Sidelnikov, V.N. (Inst. of Physics and Power Engineering, Obninsk (Russian Federation)). pp. 1078-1082 of 29th Intersociety energy conversion engineering conference: Technical papers. Part 2. American Inst. of Aeronautics and Astronautics, Washington, DC (United States) (1994). 528p. (CONF-940812--: 29. intersociety energy conversion engineering conference, Monterey, CA (United States), 7-12 Aug 1994).

Model TOR of uniform TEC is based on the solution of differential equations system of plasma hydrodynamic model. The main elementary effects in plasma and on electrode surface have been taken into account. Three effects are responsible for appearance of the region with negative differential resistance in voltampere characteristic. A simple formula for operating voltage losses value versus collector electron emission had been received. A self-coordinated non-collision models of sheath had been developed for investigation of the non-monotonous potential behavior in the near-electrode layer.

Spring structure for a thermionic converter emitter support arrangement. Allen, D.T. To Dept. of Energy, Washington, DC (United States). 17 Mar 1992. Filed date 5 Jun 1990. U.S. Patent Application 7-533,555.

A support is provided for use in a thermionic converter to support an end of an emitter to keep it out of contact with a surrounding collector while allowing the emitter end to move axially as its temperature changes. The emitter end is supported by a spring structure that includes a pair of Belleville springs, and the spring structure is supported by a support structure fixed to the housing that includes the collector. The support structure is in the form of a sandwich with a small metal spring-engaging element at the front end, a larger metal main support at the rear end that is attached to the housing, and with a ceramic layer between them that is bonded by hot isostatic pressing to the metal element and metal main support. The spring structure can include a loose wafer captured between the Belleville springs. 7 figs.

A spectroscopic study of flashes in an open thermionic cesium diode. Olsson, B.E.R. (Univ. of Goeteborg (Sweden). Dept. of Physical Chemistry); Svensson, R.; Davidsson, J. pp. 137-139 of Proceedings of the 30. intersociety energy conversion engineering conference. Volume 3. Goswami, D.Y. (ed.); Kannberg, L.D.; Somasundaram, S. (eds.); Mancini, T.R. (ed.). American Society of Mechanical Engineers, New York, NY (United States) (1995). 493p. (CONF-950729--: 30. Intersociety energy conversion conference, Orlando, FL (United States), 30 Jul - 5 Aug 1995).

Observations of flashes on metal surfaces in the vicinity of the cesium emitting electrode in an open plasma diode have lead to this investigation. Such flashes occur only when the diode is run in the so called Rydberg mode and they are trigged by a switch of the electrical field between the plasma electrodes. A similar phenomenon has recently been described in the literature (Aaman, 1992). The spectra show a significantly more complex structure compared with the spectra from the cesium plasma. Together with strong cesium lines the authors observe strong lines from molybdenum, sodium and chromium. Atomic lines from oxygen are also observed in the spectra. In this paper they discuss the conditions necessary for this light phenomenon to appear and its relation to the Rydberg mode.

Effect of oxygen on performance and mass transport in a single-cell thermionic fuel element. Paramonov, D.V. (Univ. of New Mexico, Albuquerque, NM (United States)); El-Genk, M.S. pp. 945-950 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. Sponsored by Department of the Air Force, Washington, DC (United States). (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

The introduction of tracer amounts of oxygen into the interelectrode gap of a thermionic converter has been shown to improve converter performance. Excess oxygen, however, increases the loss rate of emitter material, reducing the converter performance and shortening its lifetime, owing to the increase in the effective emissivity of the electrodes, the change in the collector work function, and the deposition of emitter material oxides on spacers and insulators. In this paper, a model was developed, which calculated the emitter material loss rate, composition of the emitter material deposits on the collector surface and investigated the effect on performance of a single-cell Thermionic Fuel Element (TFE) in the presence of oxygen and cesium oxides in the interelectrode gap. The amount of oxygen and the cesium pressure in the interelectrode gap were varied parametrically and the TFE volt-ampere characteristics, and axial distributions of current density and emitter material loss rate along the TFE were calculated.

(AD-A--289310/5/XAB)
Analysis of instability growth and collisionless relaxation in thermionic converters using 1-d PIC simulations. Master's thesis. Kreh, B.B. Air Force Inst. of Tech., Wright-Patterson AFB, OH (United States). School of Engineering. Dec 1994. 70p. (AFIT/GAP/ENP--94D-06). Source: NTIS Prices: PC A04/MF A01.

This work investigates the role that the beam-plasma instability may play in a thermionic converter. The traditional assumption of collisionally dominated relaxation is questioned, and the beam-plasma instability is proposed as a possible dominant relaxation mechanism. Theory is developed to describe the beam-plasma instability in the cold-plasma approximation, and the theory is tested with two common Particle-in-Cell (PIC) simulation codes. The theory is first confirmed using an unbounded plasma PIC simulation employing periodic boundary conditions, ES1. The theoretically predicted growth rates are on the order of the plasma frequencies, and ESl simulations verity these predictions within the order of 1%. For typical conditions encountered in thermionic converters, the resulting growth period is on the order of 7{times}10 to the {minus}11 seconds. The bounded plasma simulation PDP was used to evaluate the influence of finite geometry and the electrode boundaries. For this bounded plasma, a two-stream interaction was supported and resulted in nearly complete thermalization in approximately 5{times}10 to the {minus}10 seconds. Since the electron-electron cornsion rate of 10{sup 9} Hz and the electron atom collision rate of 10{sup 7} Hz are significantly slower than the rate of development of these instabilities, the instabilities appear to be an important relaxation mechanism.

A review of cesium thermionic converters with developed emitter surfaces. Paramonov, D.V. (Institute for Space and Nuclear Power Studies, Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico 87131 (United States)); El-Genk, M.S. AIP Conference Proceedings; 361 (1): 1305-1314 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

Studies from US and Russian literature on experimental and theoretical investigations of thermionic converters with developed emitter surfaces are reviewed and analyzed. Experimental data for these converters is compared with that for close-spaced and traditional Cs arc converters. The former is most advantageous at low temperatures from 1300 to 1700 K, with the power gain increasing as the emitter temperature decreases and/or its emission properties deteriorate. This power gain is attainable at a larger load voltage and at a significantly larger optimum interelectrode gap size than traditional converters. Additional experiments and mathematical modeling are needed to understand the physical processes taking place and assess the performance of thermionic converters with developed emitter surfaces, compared to traditional ones operating under identical conditions. {copyright} {ital 1996 American Institute of Physics.}

Thermal conductivity reductions in SiGe using nanophase particles. Scoville, A.N. (ThermoTrex Coporation, 74 West Street, Waltham, Massachusetts 02254 (United States)); Rolfe, J.; Bajgar, C.; Vandersande, J.; Fleurial, J. AIP Conference Proceedings; 324 (1): 791-796 (20 Jan 1995). (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

Transport models have predicted that the thermal conductivity of SiGe alloys could be appreciably reduced by incorporating discrete 40A particles within the SiGe grains. These particles would scatter the thermal phonons which transport most of the heat in these alloys. Such a thermal conductivity reduction would lead to substantial improvements in the figure-of-merit and efficiency of thermoelectric materials used in power generation applications. This paper reports on the results of adding 40A particles to SiGe by using a spark erosion process. Thermal conductivity reductions consistent with the transport models have been achieved, however, the improvement in figure-of-merit has not been as large as predicted. {copyright}American Institute of Physics 1995

Modeling of a cesium-graphite reservoir critical component experiment for S-prime. Witt, T. (ThermoTrex Corporation, 85 First Avenue, Waltham, Massachusetts 02254 (United States)); Miskolczy, G.; Lieb, D.; McVey, J.; Hatch, L. AIP Conference Proceedings; 324 (1): 797-802 (20 Jan 1995). DOE Contract AC03-92SF19138. (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

This computer model indicated that the single test device is capable of simulating both types of cesium reservoirs required in the S-PRIME system. The nominal operating conditions utilizing the low temperature (high cesium loading) reservior are simulated without auxiliary heat to the collector or reservoir by the use of 25%He/75%Ar cooling gas. Simulation of the system using the low cesium loading (high temperature) reservoir condition requires auxiliary heating and different cooling gas composition(s). The wide ranges of emitter, collector and reservoir temperatures required by the test plan were satisfied by variation of the cooling gas composition and power inputs to the various heaters. {copyright}American Institute of Physics 1995

Development of a solar receiver for a high-efficiency thermionic/thermoelectric conversion system. Naito, H. (Tohoku Univ., Aramaki (Japan)); Kohsaka, Y.; Cooke, D.; Arashi, H. Solar Energy; 58 (4-6): 191-195 (Oct-Dec 1996). (CONF-950901--: International Solar Energy Society (ISES) solar world congress: in search of the sun, Harare (Zimbabwe), 9-16 Sep 1995).

Solar energy is one of the most promising energy resources on Earth and in space, because it is clean and inexhaustible. Therefore, we have been developing a solar-powered high-efficiency thermionic-thermoelectric conversion system which combines a thermionic converter (TIC) with a thermoelectric converter (TEC) to use thermal energy efficiently and to achieve high efficiency conversion. The TIC emitter must uniformly heat up to 1800 K. The TIC emitter can be heated using thermal radiation from a solar receiver maintained at a high temperature by concentrated solar irradiation. A cylindrical cavity-type solar receiver constructed from graphite was designed and heated in a vacuum by using the solar concentrator at Tohoku University. The maximum temperature of the solar receiver enclosed by a molybdenum cup reached 1965 K, which was sufficiently high to heat a TIC emitter using thermal radiation from the receiver. 4 refs., 6 figs., 1 tab.

Conceptual design of a multicell thermionic fuel element for a 40{minus}KWE space nuclear power system. Zrodnikov, A.V. (Institute of Physics and Power Engineering, Obninsk, Kaluga Region (Russian Federation)); Poupko, V.Y.; Ryzhkov, A.N.; Belov, A.P.; Bologov, P.M.; Vizgalov, A.V.; Kouptsov, G.A.; Van Hagan, T.H.; Rogers, R.D.; Determan, W.R. AIP Conference Proceedings (American Institute of Physics) (United States); 324 (1): 785-791 (20 Jan 1995). (CONF-950110--: 12. symposium on space nuclear power and propulsion, Albuquerque, NM (United States), 8-12 Jan 1995).

This paper addresses the conceptual design of a Russian thermionic fuel element (TFE) in support of the S-PRIME 40 kWe in-core thermionic space power reactor studies sponsored by the U.S. Department of Energy TI-SNPS program. The design responds to requirements specified by the U.S. component of the S-PRIME team and is based on the multicell ``flashlight'' TFE approach. Following a general description of the TFE design, the considerations leading to several key design decisions are discussed. These include nuclear and thermionic performance, cesium management, fission product management, materials selection, fuel system, and lifetime. {copyright}American Institute of Physics 1995