Cooling and heating of channelled ion beams

Abstract

Experiments showing a transverse cooling or heating of channelled ions have been interpreted in terms of electron capture and loss processes between the projectile ions and the target. Reversibility is violated as the projectile captures electrons from occupied bound states and looses them to unoccupied weakly bound or continuum states. If, on the average, capture by the ion occurs at smaller distances from the target atoms than loss, then the transversal kinetic energy of the ion is reduced and vice versa. The impact parameter dependence of transition probabilities for capture and loss is determined by scale factors which depend in turn on the relative velocity and the binding energies of the transferred electrons in the projectile and in the crystal, respectively. The resulting rules for the appearance of cooling and heating in terms of the crystal atom and projectile ion species and the projectile velocity agree with experimental observations.