Lawrence Berkeley National Laboratory

Time-dependent ion charge state measurements for Pb and Bi cathodic arc plasmas revealed unexpectedly strong differences: the mean Bi ion charge state dropped much stronger and with a longer time constant than the mean Pb ion charge state. It is shown that the difference in thermal conductivity led to much higher vapor pressure for Bi, which in turn much more effectively caused charge exchange collisions. The results have implications beyond Pb and Bi plasmas, most importantly that the "true" charge states as emitted from the cathode spot are higher than what is generally measured and published.