INVESTIGATION OF THE CURRENT DENSITY LIMITATIONS IN A THERMIONIC CONVERTER.
Technical summary rept., 1 Mar-31 Oct 63,
MARQUARDT CORP VAN NUYS CALIF
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A pulsed-discharge measurement technique was used to obtain current-voltage characteristics for a cesium thermionic converter. This experimental technique consists of steady-state or pulsed operation at a high-current level, followed by rapid switching to a lower output current, where the measurement is made. Ions formed during the high-current operation provide space-charge neutralization at the lower output current, so that space-charge limitation of the output is not present during the measurement. Comparison of the pulsed-discharge data with the stead-state current-voltage characteristic and with the Boltzmann line allows measurement of the electron transport losses due to space-charge and plasma resistance normally present during steady-state operation. In addition, the collector work function can be measured under realistic diode operating conditions- i.e., large output current density and high collector temperature. Information pertaining to the variation of the emitter work function is also obtained. Work functions ranging from 1.80 to 1.95 eV were measured for the stainless-steel collector. These values are higher than expected for the operating conditions used. Several possible reasons for the discrepancy are discussed. Author