Effect of Interelectrode Spacing on Cesium Thermionic Converter Performance

Abstract

In the cesium thermionic conventer, energy dissipating interactions occur between emitted electrons and the plasma, thus reducing the net electrical output. These interactions can be suppressed by reducing either the cesium pressure or the interelectrode distance. At very high emitter temperatures cesium primarily neutralizes space charges and its effects on the emitter work function are small. For operation at moderate temperatures (1400 to 2000 deg C), cesium may modify the emitter work function as well as reduce space charge. In this mode of operation, the cesium pressure is fixed, and departure from this optimum pressure results in drastic reductions in converter output. The interelectrode spacing then becomes a variable of great importance. The results of experiments conducted with a variable spacing converter at 1400 to 2000 deg C affirm the importance of spacing. These results are presented graphically for: spacing as a function of specific power at temperatures of 1650, l700, 1750, and 1800 deg C; current as a function of voltage for interelectrode spacings of 3, l5, and 60 mils; and specific power as a function of voltage at spacings of 3, 15, and 60 mils. (B.O.G.)