A periodic table of ion charge-state distributions observed in the transition region between vacuum sparks and vacuum arcs

Ion charge-state distributions have been measured with high time resolution for short (20 μs) and long (250 μs) vacuum discharges of 300 A. Charge-state data for 3 μs after discharge ignition and quasi-steady-state values are given for most conductive elements in a Periodic Table, including data for a few elements (rhodium, europium, and terbium) that were never before reported in the literature. Ion charge states are significantly higher at the beginning of the discharge and decay to their quasi-steady-state arc plasma values. It was found that the mean ion charge states can be fitted by functions of the form Q¯=Q¯_t→∞ [1+A exp(-t/τ)] where A is an enhancement function that depends on the power density. For the present conditions, A~1 and τ~50 μs