In-situ wavelength calibration system for the X-ray Imaging Crystal Spectrometer (XICS) on W7-X

An in-situ wavelength calibration system for the X-ray Imaging Crystal Spectrometer (XICS) on W7-X has been developed to provide routine calibrations between plasma shots. XICS determines plasma flow profiles by measuring the Doppler shift of x-ray line emission from high charged impurity species. A novel design is described that uses an x-ray tube with a cadmium anode placed in front of the diffracting spherically bent crystal to provide calibration lines over the full detector extent for the spectrometer channels. This calibration system can provide a relative wavelength accuracy of 3x10^-7 angstroms, corresponding to 50 m/s in the W7-X system over the wavelength range of 3.95 to 4.00 angstroms. An absolute wavelength calibration of 1x10^-5 angstroms (1 km/s) is expected based on the known cadmium wavelengths and the absolute positioning of the hardware. This independent calibration system can be used on both stellarators and tokamaks. Experimental and simulated results are shown along with expected results and a complete design of the calibration hardware to be installed in the W7-X XICS system.