Preliminary results of absolute wavelength calibration of imaging X-ray crystal spectrometer on EAST

Abstract

Imaging X-ray crystal spectrometers (XCS) are currently operating on several major tokamaks to provide profiles of ion temperature and rotation velocity. In order to acquire absolute rotation velocity, several indirect methods were pursued previously, however the direct and effective method is to use known X-ray lines for wavelength calibration. One way to produce standard spectral lines is X-ray fluorescence, which could be excited by X-rays from tokamak plasmas. As part of the upgrade of XCS system on EAST, wavelength calibration was studied using cadmium's L-shell lines, namely Lα1 line (3.9564Å) and Lα2 line (3.9650Å) as the reference wavelength. The Geant 4 code was used to optimize foil thickness to achieve a reasonable X-ray fluorescence intensity. The Cd foil was placed between the beryllium window and crystal and could be retracted to provide in situ wavelength calibration. The detailed arrangement and preliminary wavelength calibration results of imaging X-ray crystal spectrometer on EAST are presented, plus the calibration using MHD frequency.