Electron density and temperature measurements of the ignited mode plasma in a thermionic converter

Spectroscopic measurements of the electron density and temperature have been made on a planar thermionic converter operated in the quasi-saturation region of the ignited mode. The effects of several independent converter variables on the electron density were investigated quantitatively. From this investigation it was found that the emitter temperature and current density were the most significant parameters affecting the electron density. Collector temperature, cesium vapor pressure, and interelectrode spacing were less important. Complete electron density profiles and electron temperature profiles were obtained and compared to conditions characteristic of local thermodynamic equilibrium (LTE). A representative case indicated the measured temperature, 2600°K, was only 200°K higher than required for complete LTE in the region of the peak electron density. This corresponds to an electron density approximately 45 percent below the equilibrium value.