Analysis of Unsteady Charge Kinetics of Helium in the Initial Phase of Plasma Discharge in LHD

The proposed analysis of the unsteady kinetics of helium is based on data and conclusions from the spectroscopic study of helium behavior in the LHD stellarator, specifically on the fact that, in the initial phase of plasma discharge, the behavior of impurities is primarily determined by atomic ionization-recombination (IR) processes rather than particle transport. The temporal evolution of the emission ratios of the spectral lines HeI (447.1 nm) and HeII (468.6 nm) has been used to calculate the time dependence and magnitudes of the recombination rates of helium ions, as well as the temporal evolution of the charge state distribution accompanying the three consecutive stages of discharge initiation: the onset of ECR heating, the injection of helium gas, and the activation of neutral beam heating. It has been found that charge exchange processes with a large number of neutral hydrogen atoms, particularly in excited states, contribute significantly to recombination. Owing to the high values of IR rates for helium, the relaxation time of its charge distributions to quasi-steady-state distributions is less than 0.2 ms, which allows for a simplification of the detailed analysis of helium charge kinetics in the LHD and enables it to be conducted within the framework of a quasi-steady-state problem.