Ion energies in vacuum arcs: A critical review of data and theories leading to traveling potential humps

A summary of the 2014 Dyke Award presentation is given. Ion energy data and theories are reviewed. It is shown that the potential hump theory can be reconciled with the gasdynamic acceleration theory by considering traveling potential humps, each of which is associated with an explosive emission event. Using information from pulsed laser plasma expansion, it is appears natural and consistent to have traveling humps whose heights are related to the local power dissipation of the explosive plasma-forming events. In this way, ion velocities (energies) are material-dependent following the Cohesive Energy Rule and exhibit fractal (statistical) features.