Transient Processes during the Initiation and Stabilization of a Diffuse Vacuum Arc Discharge on a Gadolinium Cathode

The processes on the cathode surface prior to the establishment of a diffuse mode of vacuum arc discharge on gadolinium cathode was investigated. Using high-speed video recordings and voltage waveforms, the breakdown process and the ejection of cathode material droplets were examined. The temporal dependences of cathode temperature and discharge voltage after breakdown were analyzed. Characteristic times for the transition to the steady-state diffuse discharge mode were determined. It was found that during breakdown and after, when discharge is unstable, droplets and voltage spikes can occur. Discharge stabilization can be achieved by increasing the cathode temperature, which leads to the transition to a mode with a voltage of about 5 V and the absence of voltage spikes and droplets. These results are significant for the development of a plasma source for the plasma separation of spent nuclear fuel.