The measurement and interpretation of Ne VII spectral line intensity ratios

Abstract

Results are presented for the measurement, using the branching ratios calibration method, of the spectral intensities of Ne VII lines emitted from a theta -pinch plasma whose electron temperature and density have been found by laser scattering and other methods. Taking the principal resonance line as the reference line, the comparisons of predicted and measured line ratios show good agreement for lines with upper terms 2s3s 1S, 2s3d 1D, 2s3d 3S, 2s3p 3P, 2s3d 3D and 2p3s 3P. The theoretical excitation rate coefficient from 2s2 1S to 2s3p 1P, X(2s2 1S, 2s3p 1P), appears about a factor two too low. For the 2s2p 3P-2p2 3P line, the theoretical ratio is slightly higher than the experimental ratio while for 2s2p 1P-2p2 1D the average experimental ratio is 58% of the theoretical one. An experimental upper limit for X(2s2p 1P-2p2 1D) was deduced for two different plasma conditions. One of the results was consistent with theory. For the intercombination line ratio and for X(2s2p 3P, 2p2 3P), X(2s2p 3P, 2s3d 3D) and X(2s2p 3P, 2p3s 3P) evaluated from ratios involving the intercombination line, there is about a factor three between theory and experiment. A reduction in the intercombination line intensity because the calibration line C III 2p2 1D-2s3p 1P A value is too high by a factor of three would reconcile this. In Ne VII the theoretical A value of 2p2 3P-2s3p 3P is a factor of six higher than the experimental value.