Excited impurity species and plasma transport

The authors discuss the role of charge exchange in collisions between protons and thermally excited impurity ions in modifying the cross-field transport of hydrogen. It is assumed that electron collisions with partially stripped impurity ions maintain a population of highly excited, highly charged ions, which produce neutral hydrogen by charge exchange with plasma protons, and that the diffusion of this hydrogen modifies cross-field transport of both electrons and protons. This effect is shown to be small. In order to discuss this phenomenon, empirical fits to a large number of effective rate coefficients were used, and these are recorded in an appendix.