Multiple-vacancy production in the rare gas atoms He, Ne, Ar, Kr and Xe by 1.4 MeV/u highly stripped ion impact is studied. From a recoil-ion-projectile-ion coincidence experiment charge-state distributions of target ions were obtained distinguishing between pure ionization and capture of up to three electrons by projectile ions N6+,7+, Fe12+,15+,20+,21+, Kr18+, Gd37+, and U30+,36+,41+,44+,48+. For high-charge-state projectiles the relative fractions of recoil ions for concomitant electron capture and ionization are found to be independent of projectile charge or species.

Multiple-vacancy production in Ar atoms by 1.4-MeV/u highly stripped ion impact is studied. From a recoil-ion--projectile-ion coincidence experiment charge-state distributions of Ar ions were obtained distinguishing between pure ionization and capture of up to three electrons by ${\mathrm{N}}^{6+}$,7+, ${\mathrm{Fe}}^{12+}$,15+,20+,21+, ${\mathrm{Kr}}^{18+}$, ${\mathrm{Gd}}^{37+}$, and ${\mathrm{U}}^{30+}$,36+,41+,44+,4 $^{8+}$ ions. With increasing projectile charge state the relative abundances of multiply charged recoil ions increase. However, for high-charge-state projectiles, the relative fractions of recoil ions for concomitant electron capture and ionization are found to be independent of projectile charge or species. To interpret the data, classical trajectory Monte Carlo calculations have been made assuming the applicability of the independent-electron model. The calculations indicate the dominant electron capture is from the L-shell of Ar while the ionization process includes both the L- and M-shell electrons. The use of a common ionization potential inherent in the application of the independent-electron model is not adequate for the high degrees of ionization obtained in the investigated collisions; the cross sections for the production of high recoil-ion charge states are overestimated. Nevertheless, the calculated total cross sections for ionization and electron capture are in reasonable agreement with the available experimental data.

Electron-capture, ionization, and recoil-ion-production cross-sections are measured and calculated for fast highly charged projectiles in hydrogen and rare-gas targets. Recoil-ion-production cross-sections are found to be large; the low energy and high charge states of the recoil ions make them useful for subsequent collision studies.

Cross sections for single-electron capture and for impact ionisation of Feq+ (q=10,15,20,25) ions incident on atomic hydrogen have been calculated in the energy range 50 to 1200 keV amu-1 using a classical-trajectory Monte Carlo method. Cross sections for the same processes for Feq+ ions incident on molecular hydrogen have been measured for q=11-22 at 1100 keV amu-1, for q=9 at 277 keV amu-1, and for q=12 and 14 at 262 keV amu-1. The experimental cross sections for molecular hydrogen divided by two are in excellent agreement with the calculated atomic hydrogen cross sections. Scaling laws for the cross sections with q, the charge state of the incident ion, are discussed. The scaling with q is not found to follow the q2 law predicted by the binary-encounter theory.

Impurities such as C, N, O, Fe, and Mo in a confined plasma reduce the penetration of the energetic neutral deuterium or hydrogen beam injected for heating or fueling the plasma, thus affecting the energy- and fuel-deposition profiles. New calculations, confirmed by recent experimental results, show that previous estimates of the reduction of neutral beam penetration due to impurities in the plasma were overly pessimistic. Until recently, the cross sections used to calculate beam attenuation had been assumed to be q/sup 2/times the cross section for H/sup +/ + H obtained from the Born approximation, where q is the charge state of the ion. This led to very large cross sections for large values of q, and thus to very stringent requirements on the acceptable level of impurity ions in the plasma.