EFFECTS OF INERT GAS OVERPRESSURE ON ARC CHARACTERISTICS

摘要

To determine the effect of the presence of an inert gas on the properties of the non-equilibrium cesium plasma which exists in the interelectrode space of an arc-mode thermionic converter, detailed electrostatic probe measurements have been made of electron temperature, electron number density, and the plasma potential over a wide range of inert gas pressures. By employing electrostatic probe techniques to measure the properties of the non-equilibrium cesium plasma, direct assessment has been made of the effects of an overpressure of inert gas on the plasma properties without having to include extraneous effects such as changes in the work functions of the emitter and col¬lector produced by the interaction of the inert gas with these surfaces. In addition, spectroscopic measurements have been made to determine the behavior of the atomic and molecular excited state populations with changes in inert gas pressure, converter output and maximum electron density in the neutralization plasma. The range of inert gas pressure over which volume ionization processes can be sustained in the non-equilibrium neutralization plasma in the converter with argon used as the inert gas has been deter¬mined from these measurements. Correlation of the results obtained from the electro¬static probe measurements with spectroscopic measurements of the plasma properties for various argon background pressure levels indicates that multistage ionization processes, which depend on the formation of doubly excited cesium molecules to produce molecular ions, are not the dominant ionization mechanism responsible for producing the enhancement in the degree of ionization observed in the arc-mode operation.