Ionization rate in the presence of runaway electrons

The role of a fast electron population, produced by the strong electric field driving the axial current in a capillary discharge, can be essential in order to justify the appreciable concentration of highly charged C ions (C5+, C6+) as observed in many experiments with low electron temperature. Under the assumption that a quasistationary state is established during the discharge, the runaway electron distribution function is determined analytically for Z(eff) > 1, following the approximated method developed by Lebedev [A. N. Lebedev, Sov. Phys. JETP 21, 931 (1965)]. The strong enhancement of the ionization rate, due to the presence of an electron tail in the energy range of the ionization potential, is then demonstrated. (C) 1997 American Institute of Physics.