Preliminary result and initial analysis on radial profiles of impurity line emissions measured with EUV spectrometer on HL-2A

A space-resolved extreme ultraviolet (EUV) spectrometer has been developed on HL-2A to monitor the impurity behavior and to study the impurity transport. A gold-coated varied-line-spacing (VLS) holographic grating with curvature of 5600 mm is adopted as a dispersion component and a back-illuminated charge-coupled device (CCD) with size of 6.6x26.6 mm² (1024x256 pixels) is utilized to record the spectral image. A two-stage wavelength scanning system is designed to enable the measurement in wider wavelength range of 30-600Å. The line of sight of the spectrometer is inclined to a downward direction to measure an entire profile of the impurity line emission at lower half (0≤Z≤-40 cm) of HL-2A tokamak plasmas. The vertical profile of line emissions from several impurity spices such as carbon, oxygen, iron, copper and molybdenum is successfully observed with a good spatial resolution. The vertical profile of CIV (312Å) measured from limiter and divertor discharges show a slight different radial location at the peak intensity position. The intensity of CIV significantly increases in the limiter configuration because the graphite is used as the limiter material and further increases when the auxiliary heating of ECRH and NBI is turned on. A similar result is also observed in the CVI emission. When the discharge encounters the H-mode transition, the vertical profile of CIV and CVI indicates a substantial change. A preliminary result on the vertical profile of several impurity spices observed from a variety of discharges is presented with an initial analysis. (author)