Charge Exchange Processes Involving Muticharged Ions: The Quasi-Molecular Approach

Abstract

The physics of multicharged ions has considerably developed during the last years¹. Aside from purely academic and fundamental interest, the initial motivation arose from fusion research. Indeed from simple theoretical arguments it could be predicted that cross sections for charge exchange between highly charged impurities present in tokomak devices, and hydrogen atom would be very large (10^-15–10^-14 cm²). Knowledge of the plasma properties would therefore require measurement of the corresponding cross sections as well as a better understanding of the collision process. A large number of experiments were therefore undertaken to determine the total (all processes included) electron capture cross section for a variety of multicharged ions. In contrast, very little work was devoted to the identification of the states which are effectively populated by the collision process. A similar effort was undertaken in theory, for the collision energy range of interest for nuclear fusion (say few keV/Nucleon). At these energies the electron velocity v is much larger than the collision velocity V so that the electron motion adapts itself adiabatically (or quasi-adiabatically) to the nuclear motion as in a molecule.