Approximation error in the rate coefficients of neutral-ion interactions (Q800800)

A study of the error introduced by commonly used approximations of average Maxwellian reaction rate coefficients is presented. Reactions examined are charge exchange and ionization between neutral atoms and ions of a plasma containing hydrogen isotopes and helium. Since some approximations considered have a complementary character, in the sense that one fails in some ranges where the other is successful, it is possible to select in each range the appropriate approximation in order to achieve the required accuracy. A particular combination of methods is suggested which has been tested in Monte Carlo problems with the aim of investigating both its cost and its efficacy.