Charge exchange observations and analysis in the dite tokamak

Abstract

Measurements of the enhancement of line intensities from oxygen and carbon ions during beam injection of hydrogen atoms into the DITE tokamak have been made for neutral energies of 25 keV and beam powers up to 2 MW. Observations of the spectrum from O encompass the Lyman series in the XUV region (1 s− n p, n < 9) and Δn = 1 transitions in the VUV and visible regions. The different selection rules for these transitions allow a differentiation between C/X and electron impact excitation of the different ( n, l) states. Using theoretical cross-sections and a cascade model for C/X recombination in to hydrogenic ions, the concentrations of impurity nuclei (eg: O 8+) are determined from the Δn = 1 VUV lines. This analysis is unsuitable for the Lyman series which lack the C/X signature. Their intensity is determined primarily by the ionisation balance, and the excitation from ground state hydrogenic ion. l state mixing is considered. No indication of statistical repopulation of the sublevels is observed for n < 7.