Space-resolved vacuum ultraviolet spectrometer system for edge impurity and temperature profile measurement in HL-2A

A 1 m normal incidence vacuum ultraviolet (VUV) spectrometer has been developed for spatial distribution measurement of edge impurity line emission in the wavelength range of 300-3200 A on HL-2A tokamak. A vertical profile of the impurity line emission is measured with a space-resolved slit placed between an entrance slit and a grating of the spectrometer. Two concave 1200 grooves/mm gratings blazed at 800 and 1500 A are set on a rotatable holder in the spectrometer, which gives wavelength dispersion of 0.12 mm/A. A back-illuminated charge-coupled device is used as a detector with an image size of 6.7x26.6 mm2 (26x26 μm2/pixel). An excellent spatial resolution of 2 mm is obtained with good spectral resolution of 0.15 A when the space-resolved slit of 50 μm in width is used. The space-resolved spectra thus provide three radial profiles of emission line intensity, ion temperature, and poloidal rotation. The electron temperature can be measured by the intensity ratio, e.g., CIII 2s2-2s3p (386 A)/2s2-2s2p (977 A). The sensitivity of the spectrometer is calibrated in situ by using the VUV bremsstrahlung continuum radiation emitted from the tokamak plasma. A good performance of the spectrometer system for the edge impurity and temperature profile measurements is presented with results on Ohmic and H-mode discharges.