Superimposition of Pulses to Steady Arc Discharge in Toroidal Divertor Simulator

Abstract

A pulsed discharge was superimposed to a steady state arc discharge in the toroidal divertor simulator NAGDIS-T. The dynamic response of the plasma was observed with an electrostatic probe and fast framing camera. In the first loop plasma, which is close to the plasma source, the density becomes higher in response to the pulsed discharge, and the emission from the plasma significantly increases. On the other hand, in the second loop plasma, where a recombining plasma is formed, the emission from the plasma disappears in response to the pulse. Just after the pulsed discharge, plasma instabilities were formed and they were propagated from the upstream to downstream at the velocity of ∼10 km/s. After the series of pulsed plasma experiments, arc trails were recorded around the cathode area. On a molybdenum cover of the cathode, unipolar arcing was initiated on the surface. It is likely that the pulsed discharge leads to instabilities and initiate the unipolar arcing consequently.