Electron-impact multiple ionization of singly and multiply charged tungsten ions

Cross sections for electron-impact double ionization of W^q+ ions in charge states q=1-6 as well as triple ionization in charge states q=1-4 have been measured using the crossed-beams technique. A new semiempirical formula for multiple ionization of three or more target electrons is in very good agreement with the measurements. Together with previously obtained experimental data for single ionization of tungsten ions, the measured cross sections are used to study the influence of multiple ionization on the W^q+ charge state evolution if tungsten atoms are exposed to an electron flux at 700 eV energy. It is shown that the charge state evolution is significantly influenced by multiple-ionization processes.