Progress of space-resolved EUV spectrometer system in HL-2A

The space-resolved extreme ultraviolet (EUV) spectrometer is developed in HL-2A for impurity monitoring and transport study. The system mainly consists of an entrance slit, a space-resolved slit, a varied-line-spacing holographic grating and a charge-coupled-device (CCD). The CCD detector is mounted on a movement system which is remotely controlled, enabling the impurity line emission measurement in the wavelength range of 30 ∼ 600 Å. The angle of incidence of EUV spectrometer is 87°, and high spectral resolution, i.e 0.22 Å at 200 Å, is obtained by use of the entrance slit with width of 30 μm. The spectrometer is installed at the upper side of the midplane of HL-2A machine to observe the impurity lines emitted from the lower half of plasma. In order to quantitatively analyze the impurity behavior, the absolute calibration of the vertical positions in the obtained impurity emission profiles have to be done. Recently, a metal bar with width of 5 mm is installed at the diagnostic port as a reference for vertical position calibration. Due to the principle of grating in the EUV spectrometer, the optical paths between the grating and the detector are different at different wavelength positions. Therefore, the absolute calibrations of the vertical positions have to be carried out at different wavelengths. Based on the absolute vertical position calibration, the spatial distributions of EUV impurity line emissions are obtained by Abel inversion analysis. (authors)