Close-Spaced High Temperature Knudsen Flow.
Annual rept. 16 May 84-15 May 85,
RASOR ASSOCIATES INC SUNNYVALE CA
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This work continued to investigate thermionic energy conversion in the Knudsen collisionless operating mode. A SAVTEC-type converter with an interelectrode spacing of 18-22 microns was tested over a range of emitter temperatures up to about 1700 K. Maximum performance followed the predictions of vacuum-mode analysis for emitter temperatures below 1580 K. Above that temperature the converter operated in the unignited mode, with partial space-charge neutralization by surface ionization of cesium. It was found that collisionless and diffusion mode theories could be extended into the regime of maximum output power for the unignited mode spacing and electron mean-free path about equal to give good agreement with the experimental data. The Knudsen-mode thermionic converter with a structured emitter was also investigated. Analysis has shown that associative ionization between barium and cesium is unlikely to be the cause of the current enhancement observed in previously published work. An analysis which considered the trapping of positive ions in the emitter slots has given good qualitative agreement with published data. Work is continuing on this analysis. Parts for a structured emitter variable spacing converter have been constructed and are being assembled. Keywords Thermionic energy conversion Knudsen operating mode Structured emitter SAVTEC diodes.
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