ITER core imaging X-ray spectroscopy: Atomic physics issues

The Core Imaging X-Ray Spectrometer (CIXS) will be employed for measurements of the ion temperature and of the toroidal rotation velocity, T i and v ϕ , respectively, as a function of the radius of ITER plasmas. The diagnostic is based on precision determinations of the Doppler broadening, centroid shift, and intensity of the lines of highly ionized heavy impurities using a curved Bragg crystal spectral disperser and imager. The ions under consideration for the diagnostic are those of tungsten, krypton, xenon, iron, and argon. A detailed discussion is given of the need for atomic physics experiments and calculations involving the primary diagnostic lines and their collisional and dielectronic satellites. Such experiments and calculations define the instrument parameters, determine the diagnostic uncertainties, and provide paths for extending the diagnostic capabilities to measure impurity concentrations, electron temperature, and ion transport parameters. Enabling the diagnostic to measure radially dependent ion transport coefficients, in particular, requires a large amount of high-quality atomic data in the form of reliable excitation, ionization, and recombination rate coefficients as well as ionization balance calculations which make use of these data. Because core imaging spectrometers are being developed and implemented on present-day magnetic fusion devices, much of the atomic data are already needed and can be tested in the analysis of existing spectra recorded by these diagnostics.