CHARACTERIZATION OF THE ARC CATHODE ATTACHMENT BY EMISSION-SPECTROSCOPY AND COMPARISON TO THEORETICAL PREDICTIONS

Emission spectroscopic diagnostics of electron temperature distributio n and electron number density distribution in the cathode region have been carried out employing an OMA/spectrometer system. Single color an d two color pyrometry of cathode temperature distributions have also b een performed. The experimental results are compared with results of a theoretical model formulated previously to study the are cathode inte raction. The results show that the plasma in the cathode region strong ly deviates from LTE. Thermionic cooling is the major cooling mechanis m of cathodes at high are currents. The work function of 2% thoriated tungsten cathodes increases during arcing due to fast evaporation of t horium from 2% thoriated tungsten cathodes.