Classical many-body-approach to transverse cooling and heating in ion channeling

An ion is said to be channeled if the energy associated with its transverse motion relative to a crystal axis or plane is below a critical value of the corresponding axial or planar crystal potential. The most fundamental rule in channeling, the so-called Rule of Reversibility, states that the probability for de-channeling is the same as for re-channeling, i.e. the feeding-in of non-channeled ions into a channeled motion. However, experiments have shown unexpected strong violations of this rule – and are still lacking a theoretical understanding. Depending on the experimental conditions a strong flux enhancement (referred to as transverse cooling) along crystal directions was observed as well as strong flux reductions (transverse heating). We herewith present a detailed quantitative model explaining the experimentally found results, including the transition from cooling to heating. In contrast to other methods, our approach does not depend on any free parameters, which also proves its general applicability for describing many aspects in the theoretically difficult regime of the interaction of heavy ions with solids, where charge exchange processes dominate.