A collisional-radiative model for hydrogen atom including velocity changing collisions

We develop a collisional-radiative model for calculating the velocity distributions of excited hydrogen atoms. In the model, the velocity distributions are approximated using linear combinations of several basis functions which are treated as discrete velocity states, and only charge exchange collisions with proton are considered as velocity changing collisions. The populations in the velocity and excited states are calculated under an assumption of a quasi-stationary state. With the model we derive the velocity distribution of the ground state atoms from that of excited atoms in the n = 3 level observed for an LHD plasma, where n is the principal quantum number. The mean kinetic energy of the ground state atoms is estimated to be 5.6 eV, which is 0.05 eV less than that of the n = 3 atoms.