Development of vacuum ultraviolet spectroscopy for measuring edge impurity emission in the EAST tokamak

The dominant wavelength range of edge impurity emissions moves from the visible range to the vacuum ultraviolet (VUV) range, as heating power increasing in the Experimental Advanced Superconducting Tokamak (EAST). The measurement provided by the existing visible spectroscopies in EAST is not sufficient for impurity transport studies for high-parameters plasmas. Therefore, in this study, a VUV spectroscopy is newly developed to measure edge impurity emissions in EAST. One Seya-Namioka VUV spectrometer (McPherson 234/302) is used in the system, equipped with a concave-corrected holographic grating with groove density of 600 grooves mm(-1). Impurity line emissions can be observed in the wavelength range of lambda = 50-700 nm, covering VUV, near ultraviolet and visible ranges. The observed vertical range is Z = -350-350 mm. The minimum sampling time can be set to 5 ms under full vertical binning (FVB) mode. VUV spectroscopy has been used to measure the edge impurity emission for the 2019 EAST experimental campaign. Impurity spectra are identified for several impurity species, i.e., lithium (Li), carbon (C), oxygen (O), and iron (Fe). Several candidates for tungsten (W) lines are also measured but their clear identification is very difficult due to a strong overlap with Fe lines. Time evolutions of impurity carbon emissions of CII at 134.5 nm and CIII at 97.7 nm are analyzed to prove the system capability of time-resolved measurement. The measurements of the VUV spectroscopy are very helpful for edge impurity transport study in the high-parameters plasma in EAST.