Thermionics Quo Vadis? An Assessment of the DTRA's Advanced Thermionics Research and Development Program (2001) / Chapter Skim
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7 Assessment of Progress
7 Assessment of Progress
Pages 52-60
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From page 52... ...
However, even given the fairly large number of projects for the modest yearly funding available, the program does not sustain thermionic science and basic research related to electrode materials, plasma physics, and surface physics. The committee believes that the overall DTRA effort would be more successful if it were to emphasize a basic research program in electrode and materials processes relevant to thermionic energy conversion.
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From page 53... ...
Finding: The collaboration between the Defense Threat Reduction Agency thermionics program and Russian research facilities is ongoing and has been successful. Auburn University Materials Work The DTRA has sponsored research at Auburn University through General Atomics that concentrates on the fabrication methods and underlying science in the fabrication, processing, and characterization of refractory alloy single-crystals.
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From page 54... ...
High tem- In biaxial creep testing, a closed-end tube made of perature creep strength is enhanced, grain boundary the material to be tested is internally pressurized using diffusion is eliminated, end the highest bare workfunc- a static, inert gas. The test assembly is heated to the desired temperature in a diffusion pump vacuum cham ber using a 5 kilowatt heat source.
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From page 55... ...
There are several ultimate tradeoffs that must be evaluated between the geometrically simple, dem onstrated planar converters on the one hand and the the other. Oxygenation Previous work established that oxygenation of emitter and collector surfaces in a thermionic converter can be a useful technique for improving thermionic performance (Figure 7.3~.
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From page 56... ...
Hence, the barrier potential is nearly zero, and energy conversion efficiency is primarily limited by conduction and radiative losses. However, once the gap size increases beyond a few microns, the electron barrier potential can no longer be ignored, and it is necessary to provide charge neutralization with a plasma such as cesium.
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From page 57... ...
However, given the limited amount of funding for the thermionics program as a whole, the committee recommends that all theory and theory validation activities be discontinued. MICROMINIATURE THERMIONIC CONVERTER The DTRA-sponsored MTC program is another one of the major program elements in the overall DTRA effort and is slated to receive a significant percentage
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From page 58... ...
The current program consists of several efforts, including the following (Rightley 1998a,b) : · Development of electrode coatings to improve the emitter and collector properties, since the structural materials suitable for integrated circuit manufacturing methods are not those normally used for thermionic converters, · Analysis of MTC device configurations, and · Testing of MTC cells.
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From page 59... ...
With respect to model validation by experiment, while inexpensive manufacture using fully developed integrated circuit methodologies might be feasible, fabrication and testing of small numbers of experimental converters would be expensive. Given likely funding limits, the prospects are poor for obtaining adequate data with which to validate the MTC analysis from feasible experiments, even if this effort were to be the major funded effort of the entire DTRA thermionics program.
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From page 60... ...
The search for such materials has been thoughtfully and extensively pursued in a number of laboratories over the years without the constraint of compatibility with integrated circuit fabrication methods and materials. Even if low work function electrode materials can be fabricated inexpensively and made compatible with the integrated circuit industry fabrication methods used to form the main structure of the MTCs, the same electrode materials should also be helpful in forming more conventional Thermionic fuel elements.
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