Probe measurement of residual plasma of a magnetically confined high-current vacuum arc

The electron temperature and the ion density of residual plasma of a magnetically confined high-current vacuum arc were measured using the electrostatic (Langmuir) probe method. Measurements were performed in a vacuum-triggered gap with a OFCu cathode of 40 mm in diameter and an anode of 100 mm in diameter, separated by a gap of 30 mm. The arc current formed a sinusoidal wave having a half-period of approximately 1 ms and a peak value ranging from 1 kA to 5 kA. An axial magnetic field was supplied by either a DC field coil or an AMF-type electrode. It was found that the electron temperature of residual plasma did not depend on current peak current gradient and space remained in a constant range of 2.2-3.0 eV. Radial distribution of ion density was diffusive, in contrast to the parabolic confined distribution of the steady state arc. The characteristics obtained in the DC magnetic field and in the AMF electrode were identical except for the ion density at current zero.