Deduction of central plasma parameters from line-of-sight averaged spectroscopic observations

Abstract

A method is presented to deduce central ion temperature and toroidal rotation velocity from line-of-sight averaged x-ray spectra from hot plasmas. The analysis is based on atomic data for the processes that give rise to x-ray spectral lines. Combined with measured electron temperature and density profiles a synthetic spectrum is calculated. The fit of this synthetic spectrum to the observed one gives a new level of accuracy to line-of-sight integrated observations in a considerably extended range of ion temperatures and toroidal rotation velocities. The choice of model for radial profiles for ion temperature and toroidal rotation velocity is shown not to be critical. The concentration of the emitting impurity is deduced from the total line intensity, making use of the absolute calibration of the detector sensitivity. The effective plasma charge Zeff is derived from the absolute level of the continuum radiation. These measurements are based on atomic data for x-ray line and continuum radiation and measured electron temperature and density profiles. The results for ion temperature and toroidal rotation velocity obtained by this analysis are compared with those from visible charge exchange spectroscopy. The observed visible lines are shifted in wavelength, and their width is reduced, due to the velocity dependence of the cross section for the charge transfer from the neutral beam particles to the observed impurities. The theoretically predicted magnitude of these effects is verified. When the results from visible charge exchange spectroscopy are corrected for the cross-section effects, excellent agreement of central ion temperature and rotation velocity with the results of this new analysis is obtained.