Ion charge state distributions of alloy-cathode vacuum arc plasmas

Ion charge state distributions (CSDs) of alloy-cathode vacuum arc plasmas have been calculated under the assumption that thermodynamic equilibrium is valid in the vicinity of the cathode spot, and equilibrium CSDs “freeze” when the plasma is rapidly expanding. In this way, experimental data of titanium-hafnium alloy cathode plasmas have been simulated using a generalized system of Saha equations. It was found that the CSDs of titanium and hafnium freeze approximately at the same plasma temperature and density. The freezing parameters depend slightly on the cathode (i.e., plasma) composition. For the example considered, freezing occurs at temperature of T=3.0-3.8 eV and a total heavy (atom and ion) particle density of order 10²⁵ m^-3