Angularly resolved measurements of ion energy of vacuum arc plasmas

The kinetic energy of ions generated by pulsed vacuum arcs was measured with angular resolution in the interval -90 deg. to +90 deg. with respect to the cathode normal. A current perturbation method in conjunction with drift time measurements was used. Cathode materials included C, Mg, Ti, Cu, Ag, Ta, and Pb with an average arc current of 300 A and 600 μs duration. The measured angular energy distributions are slightly peaked at the cathode normal. Each distribution can be fitted by a superposition of an isotropic component and a cosine function, with the isotropic component dominating. This result is in contrast to plasma jet formation observed by others, which is most likely due to effects of anode geometry and magnetic fields, including the self-field of the current-carrying plasma