X-ray diagnostics of tokamak plasmas

Abstract

The paper describes the x-ray diagnostics of central plasma parameters of present large tokamak fusion experiments by means of Johann type curved crystal spectrometers. These spectrometers have a very high spectral resolution, λ/Δλ > 10 000, and are mainly used to determine the central ion temperature from Doppler broadening measurements of the 1s-2p resonance lines of high-Z helium-like ions. The full diagnostic potential of the spectra of helium-like ions is demonstrated by the detailed analysis of Fe XXV satellite spectra from a particular high temperature tokamak discharge with reactor-like conditions. This analysis is based on least squares fit comparisons of the experimental data with synthetic spectra, which are constructed from theoretical predictions. It is found that the satellite spectra which are associated with the helium-like resonance lines are in excellent agreement with the theoretical predictions. The satellite spectra can therefore be used for electron temperature measurements, measurements of the dielectronic recombination rate coefficients and the determination of relative ion charge-state abundances. Discrepancies between experiment and theory are, however, observed for the intensity ratios of the helium-like lines. Also discussed are atomic physics data needs and the potential of the x-ray diagnostic for future large tokamaks, such as ITER.