Inclusion of charge-exchange dynamics in a collisional-radiative model for magnetic fusion plasmas

The charge-exchange processes are usually not included in the collisional-radiative (CR) model of atomic processes in plasmas. However, they are known to be important for impurity dynamics in magnetic fusion plasmas, for both steady-state power exhaust and disruption mitigation. One particular interesting scenario for disruption mitigation is the use of hydrogen injection to purge high-Z impurities in the post-thermal-quench plasma that has already completed the Ohmic-to-runaway current conversion. This is previously understood as the result of enhanced recombination due to the additional electron cooling. Here we investigate the additional role of charge-exchange, both with the same species and between different species. To this end, we first present the single electron total and state selective charge-exchange cross-sections for N^q+ (q = 1-7), Ne^q+ (q = 1-10), Ar^q+ (q = 1-18) colliding with H and H₂ in ground state using the multichannel Landau-Zener and molecular orbital close-coupling methods. The main emphasis here is to systematically explore the charge-exchange dynamics in the low-energy regime typical of a post-thermal-quench plasma. The calculated charge-exchange rate coefficients will be incorporated in the extended version of the CR program to study the ionization balance of impurity ions. More broadly, this CR model with charge-exchange will also be important to determine the impurity transport fluxes and the electron energy dissipation. The radiative power in this mixture of light and heavy atoms can also be quantified for the purpose of both plasma cooling and runaway current dissipation.