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

A dual-route optical emission spectroscopy (D-OES) diagnostic is newly developed to monitor the optical emission from the X-point plasma region on the HL-2A tokamak. This diagnostic is composed of an imaging system, a beam-splitting system for dual-route measurements, fiber bundles, a spectrometer system, and a 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 a Fulcher band) and highly resolved ${\mathrm{H}}_{\text{α }}$ 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 ${n}_{\mathrm{e}}$ and deuterium temperature $T\text{­}{\text{­}}_{\mathrm{D}}$ in the X-point multifaceted asymmetric radiation from the edge (MARFE) region are derived simultaneously by fitting the measured ${\mathrm{D}}_{\text{α }}$ shape. The density ${n}_{\mathrm{e}}$ is observed to increase from ~$8.7\times10^{18}\mathrm{\ m}^{-3}$ to ~$7.8\times10^{19}\mathrm{\ m}^{-3}$, and the temperature $T\text{­}{\text{­}}_{\mathrm{D}}$ drops from ~14.4 eV to ~2.3 eV after the onset of MARFE in the discharge #38260.