The evolution of ion charge states in cathodic vacuum arc plasmas: a review

Cathodic vacuum arc plasmas are known to contain multiply charged ions. Twenty years after 'Pressure ionization: its role in metal vapour vacuum arc plasmas and ion sources' appeared in volume 1 of Plasma Sources Science and Technology, this is a great opportunity to re-visit the issue of pressure ionization, a non-ideal plasma effect, and put it in perspective to the many other factors that influence observable charge state distributions, such as the role of the cathode material, the path in the density–temperature phase diagram, the 'noise' in vacuum arc plasma as described by a fractal model approach, the effects of external magnetic fields and charge exchange collisions with neutrals. A much more complex image of the vacuum arc plasma emerges, putting decades of experimentation and modeling in perspective. (paper)