Predicting Ion Charge State Distributions of Vacuum Arc Plasmas

Multiply charged ions are present in vacuum
arc plasmas. The ions are produced at cathode spots,
and their charge state distributions (CSDs) depend on
the cathode material but only little on the arc current
or other parameters as long as the current is relatively
low and the anode is not actively involved in the
plasma production. There are experimental data of
ion CSDs available in the literature for 50 different
cathode materials. The CSDs can be calculated based
on the assumption that thermodynamic equilibrium is
valid in the vicinity of the cathode spot, and the
equilibrium CSDs "freeze" at a certain distance from
the cathode spot (transition to a non-equilibrium
plasma). Plasma temperatures and densities at the
"freezing points" have been calculated, and, based on
the existence of characteristic groups of elements in
the Periodic Table, predictions of CSDs can be made
for metallic elements which have not yet been used as
catqode materials.