X-RAY-DIAGNOSTICS OF TOKAMAK PLASMAS

The paper describes the X-ray diagnostics of central plasma parameters of present large tokamak fusion experiments by means of Johann type c urved crystal spectrometers. These spectrometers have a very high spec tral resolution, lambda/DELTAlambda > 10 000, and are mainly used to d etermine the central ion temperature from Doppler broadening measureme nts of the 1s-2p resonance lines of high-Z helium-like ions. The full diagnostic potential of the spectra of helium-like ions is demonstrate d by the detailed analysis of Fe XXV satellite spectra from a particul ar high temperature tokamak discharge with reactor-like conditions. Th is analysis is based on least squares fit comparisons of the experimen tal data with synthetic spectra, which are constructed from theoretica l predictions. It is found that the satellite spectra which are associ ated with the helium-like resonance lines are in excellent agreement w ith the theoretical predictions. The satellite spectra can therefore b e used for electron temperature measurements, measurements of the diel ectronic recombination rate coefficients and the determination of rela tive 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 poten tial of the X-ray diagnostic for future large tokamaks, such as ITER.