Measurement of directed ion velocity in vacuum arc plasmas by arc current perturbation methods

A method of measurement of the ion streaming (or directed) velocity v_i in vacuum arc (VA) plasmas is described. The method is based on the evolution of the ion charge state distribution when the arc current is subjected to a fast perturbation. Two approaches for producing the arc current perturbation were used: the first was by means of a “current spike” and the second by means of a “current zero”. The ion charge state distribution was measured by a time-of-flight method. It has been shown that the directed ion velocities in VA plasmas ν_i≈10⁶ cm/s are determined by the cathode material and are practically independent of the ion charge state Q. Increasing magnetic field increases νv_i , while increasing gas pressure decreases νv_i, and in this case a dependence of νv_i, on Q is observed at elevated gas pressures