INVESTIGATION OF THE CURRENT DENSITY LIMITATIONS IN A THERMIONIC CONVERTER.
Final rept., 1 Jan-15 Jul 65,
MARQUARDT CORP VAN NUYS CALIF
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Transient measurements were made in a thermionic converter to investigate the ion loss mechanism at various operating conditions. A small pulsed increase in current was applied to the converter just after the pulse an increase in output voltage was observed. The increased voltage then decayed back to the steady-state level. The time constant of the exponential voltage decay is a measure of the average lifetime of ions in the interelectrode space. The report contains an extension of the previous pulsed-discharge measurements to larger spacings and higher xenon pressures. At large electrode spacings the primary ion loss mechanism is volume recombination at small spacings 20 mils or less the ions are lost by diffusion to the electrodes, where surface recombination occurs. The volume-recombination lifetime decreases with increasing cesium andor xenon pressure. The output voltage was measured for a range of spacings extending to over 200 mils, at each value of the current, cesium pressure, and xenon pressure used. It was observed that, at constant current, the output voltage is a linearly-decreasing function of the spacing, for spacings of the order of 100 mils or larger. The decrease in the output voltage with increasing spacing is apparently due to a corresponding increase in the emitter sheath potential. This linear characteristic could prove useful in an analysis of converter theory. Author
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