Development of Charge eXchange Recombination Spectroscopy (CXRS) edge plasma diagnostic system for International Thermonuclear Experimental Reactor (ITER)

Charge eXchange Recombination Spectroscopy (CXRS) is a powerful diagnostic tool for hot plasmas, widely used on modern tokamaks and stellarators for measuring ion temperature, rotation velocity, and low-Z impurity concentration. Three CXRS diagnostics, observing different plasma regions, will be implemented on the ITER (International Thermonuclear Experimental Reactor) tokamak. In this paper, one of the ITER diagnostics, CXRS Edge, is described. An overview of its hardware, including a diagnostic neutral beam, a light collection system consisting of four in-vessel mirrors, vacuum windows, lens assemblies, fiber bundles, an alignment system, and back-end equipment (spectrometers, calibration equipment, and instrumentation and control) is presented. Laboratory tests of several manufactured mock-ups are described. The process of the diagnostic preparation for operation and specifics of measurement data analysis for CXRS on ITER is reviewed. A calibration system using a retroreflector, developed for remote calibration of the CXRS Edge diagnostic, is presented. CXRS modeling approaches and results are outlined. Non-statistical errors, their influence on parameters measurement, and possible solutions are also discussed.