On the ion energy distribution of high current arcs in vacuum

With the experiments presented in this paper, applications of a retarding field analyzer (RFA) for the measurement of the ion energy E _i in a vacuum arc plasma are discussed. The examined plasma was produced by a sinusoidal half-wave vacuum arc current. The experiments were concentrated on evaluating the plasma parameters at the last three milliseconds before current zero. In a current range from 300 A_rms to 10 kA_rms, the ion energy distributions and their peak values were evaluated. With the increase of the arc current, a decrease of the ion energy was found. By additional investigations of the angular distribution of the ion energies, a transition from a collision dominated interelectrode plasma to a freely expanding plasma was observed, depending on the arc current