First wall erosion by arcing

In high temperature plasma experiments arc tracks are found on all wall areas in close contact with the plasma. The craters of such arc tracks, which are the same as for vacuum arcs, were investigated in more detail. The investigation was done with an optical microscope and a scanning electron microscope. Crater diameter and crater depth from vacuum arcs on clean cathode surfaces were measured for Cu, W, Al and Fe. Crater dimensions were determined from probes exposed to one single arc discharge moving across the probe surface due to a cross magnetic field. Controlled parameters were arc current and cathode temperature; their influence on crater size was investigated. Cleaning of the tungsten cathode surface was achieved by heating in vacuum. In other cases such as with copper cathodes simultaneous heating and exposure to a glow discharge was necessary to obtain reproducible surface conditions. Crater size was determined by statistical methods. The most probable diameter of the measured distribution curve is representative for the processes involved.