Charge state and time resolved plasma composition of a pulsed zirconium arc in a nitrogen environment

The species and ion charge state evolution of a pulsed cathodic arc plasma was investigated at different pressures. A zirconium cathode was operated in a nitrogen environment, and the plasma composition was analysed by time-of-flight charge-tomass spectrometry. Large plasma chemistry changes were detected with respect to time and pressure. The 250 μs plasma pulse can be divided in two characteristic phases: a transient phase before 150 μs and a steady state phase for all later times. The measured changes in plasma chemistry in the transient phase at p~10 Torr are explained by charge transfer collisions, while the increasing N fraction in the p>10 Torr range most likely originates from erosion of the nitrided cathode surface. In the steady state phase, a pressure-induced change from higher to lower charge states was observed, which is mainly due to scattering of self-sputtered metal followed by metal ion-atom charge exchange collisions. These results are of importance for