INVESTIGATION OF C-V LINE RATIO VARIATIONS IN A TOKAMAK WITH AN APPLICATION TO NEUTRAL HYDROGEN MEASUREMENT

Significant differences in the ratio between the He-like carbon triplet lines 1s2s3(S)S(1)-1s2p(3)P(2) (2271.59 Angstrom) and 1s2p(3)S(1)-1s2p(3)P(0,1) (2278.41 Angstrom) have been observed in line of sight measurements across the TJ-I tokamak. Such variations, which deviate from the 2(3)P level statistical ratios,have not been reported for this line ratio in similar fusion plasmas. We show that such differences can be explained by charge exchange, involving collisions between H-like carbon ions and neutral hydrogen atoms, while ruling out excitation and deexcitation by electron collisions and line blending effects. Finally we discuss similar transitions in other low Z ions and propose monitoring these variations as a spectroscopic tool for estimating relative neutral concentrations in plasmas.