Single- and double-electron loss from helium by collisions withv≥v0multiply charged ions

Cross sections for single- and double-electron loss (electron capture plus impact ionization) for ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{q+}$, ${\mathrm{O}}^{q+}$, and ${\mathrm{Au}}^{q+}$ incident on helium have been measured at velocities from $\sim v_0$ to $\sim 10v_0$. The charge state $q$ was varied from 1 to 21, depending on velocity and projectile. The energy and charge-state dependence of the single-loss cross section at the lower velocities is reasonably well described by the model of Olson based on Coulomb interaction between particles and classical trajectory Monte Carlo calculations. The results for ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{+}$, and ${\mathrm{He}}^{++}$ at high velocities are in good agreement with earlier experimental values of Pivovar et al. and with Bethe-Born calculations of Gillespie. The double-loss cross section, which for highly charged projectiles amounts to as much as 60% of the single loss, is found to behave quite differently from the single-loss cross section, both as a function of incident charge and velocity. While single-loss cross sections at velocities between $v_0$ and $2v_0$ are almost independent of energy and proportional to $q$, the double-loss cross sections are approximately proportional to energy and to $q^2$.