A dual-route optical emission spectroscopy diagnostic with wide spectral range and high wavelength resolution on HL-2A tokamak

Abstract A dual-route optical emission spectroscopy (D-OES) diagnostic is newly developed to monitor the optical emission from X-point plasma region on the HL-2A tokamak. This diagnostic is composed of imaging system, beam splitting system for dual-route measurements, fiber bundles, spectrometer system, control and acquisition system. One route is used to obtain wide-spectral-range spectra, and the other route is used to acquire high-wavelength-resolution line shapes. The spectral resolution of the wide-range spectrometers is 0.8 nm with a coverage of 800 nm (@200-1000 nm). The spectral resolution of the high-resolution spectrometer is 0.01 nm with a coverage of 6 nm (@200-660 nm). The spatial resolution of each route of D-OES is about 4 cm with 11 channels. The temporal resolution is 16 ms at maximum in the single-channel mode. Wide-range spectra (containing Balmer series and Fulcher band) and highly resolved H_α line shapes are obtained by D-OES in the hydrogen glow discharge in the lab. D-OES measurements are carried out in the high-density deuterium experiments of HL-2A. The electron density n_e and deuterium temperature T_D in the X-point MARFE region are derived simultaneously by fitting the measured D_α shape. The density n_e is observed to increase from ~8.7×10^18 m^(-3) to ~7.8×10^19 m^(-3) and the temperature T_D drops from ~14.4 eV to ~2.3 eV after the onset of MARFE in the discharge #38260.