Diffuse and spot mode of cathode arc attachments in a at mospheric magnetically rotating argon arc

Summary form only given. To understand the arc and thermal plasmas, a wide range of numerical simulations based n computational fluid dynamics coupled with electromagnetics have been carried out. Although the LTE models are proved successful to predict plasma temperature, deviations from LTE are experimentally observed, especially around the arc fringe¹. Furthermore, the interaction of plasma with cathode surface plays a key role in the whole discharge processe², ³. To research cathode discharge phenomena with a thermionic, a model including the cathode, the near-cathode layer and the arc column is needed.A typical case is the discharge processes in a atmospheric magnetically rotating argon arc4, 5. Magnetically rotating arcs have been increasingly adopted in dc arc plasma devices for diagnostics and material processing, modern circuit breakers, etc. Many issues remain unclear. One is the spontaneous switching of the dc arc with a thermionic cathode between two distinguished discharge modes: diffuse mode and spot mode. It is noted that, in our simulation the arc column is calculated simultaneously with the near-cathode region and the cathode. Comparative investigation of two modes of attachment of a dc (I=50A,100A) atmospheric pressure arc in argon to a thermionic cathode made of pure tungsten is carried out. Both experimental and computational data reveals that there exist two modes of arc discharge: the spot mode, which has a obvious cathode surface temperature peak in the arc attachment center ; the diffuse mode, which has a flat cathode surface temperature distribution and a larger arc attachment area.