Plasma fluctuations, local partial Saha equilibrium, and the broadening ofvacuum-arc ion charge state distributions

Charge state distributions (CSD's) of Fe, Co, Zr, Nh, Hf, Ag, Pt, Au ions p roduced at vacuum are cathode spots are investigated without often-used ave raging procedures. Statistical results are used to evaluate the contributio n of fluctuations to the broadening of averaged CSD's, Calculations of Saha equations in the Debye-Huckel approximation are often successful in replic ating experimental CSD's even when using the simple model of "instantaneous freezing." This allows us to use charge state spectrometry as a plasma dia gnostic tool for the dense plasma near tbe cathode spot. Typically, total h eavy particle (atoms and ions) densities and electron temperatures of 10(24 )-10(25) m(-3) and 3-4 eV have been measured this way at the transition zon e from equilibrium to nonequilibrium, the "event horizon." It was also foun d that CSD's for some elements such as Co, Ag, and Hf could not be accurate ly simulated with the assumption of instantaneous freezing. Here, a more gr adual transition to nonequilibrium occurs. This transition can be described by the model of partial local Saha equilibrium. Finally, an axial magnetic field was found to soften the transition to nonequilibrium thus causing br oadening of experimental CSD's.