Electron-beam enhancement of ion charge state fractions in the metal-vapor vacuum-arc ion source

摘要

We report demonstrations of ion charge-state enhancement for an electron-beam metal-vapor vacuum-arc (E-MEVVA) ion source. Results with a lead cathode yielded a maximum ion charge state of Pb~(7+), which implies an ionization potential of at least 130 eV. Electron current densities j=70 A/cm~(2) and ionization times τapprox=100 μs produced jτ=9.2×10~(-3) C/cm~(2) (5.8×10~(16) electrons/cm~(2)). Standard analysis for these conditions indicates—somewhat surprisingly—that successive single (stepwise) ionization accounts for the present observations, even though the charge states are substantially higher than most previous results with MEVVA-based ion sources.