Since 2021, the Experimental Advanced Superconducting Tokamak (EAST) has been in continuous operation under a full tungsten divertor environment. Several line emissions from Ni-like W46+ ions were observed in the wavelength range of 7–8 Å in EAST device using extreme ultraviolet (EUV) spectrometers. The W46+ spectra became observable after a tungsten burst suddenly occurred in L-mode plasma with electron cyclotron resonance heating and lower-hybrid wave heating. The W46+ line emissions were precisely identified through spectral analysis using flexible atomic code and NIST database. The line identification in the W46+ spectra includes two E1 transitions at 7.026 Å and 7.173 Å, an E2 transition at 7.607 Å and blended line at 7.93 Å. The blended line is composed of E2 and M3 transitions at 7.928 Å and 7.937 Å, respectively. The temporal evolution of the intensity of such line emissions was investigated with tungsten concentration (CW = nWne−1) and electron temperature. Statistical analysis results indicate that observation of the W46+ spectral lines becomes possible at CW ⩾ 1.0 × 10−4 and Te ⩾ 4.0 keV. The radial intensity profile of W46+ line emissions was also measured using space-resolved EUV spectrometers, and the local emissivity profile was analyzed with Abel inversion method. As a result, the density profile of W46+ ions was successfully obtained using photon emissivity coefficients in the ADAS database.
Evaluation of tungsten influx rate and study of edge tungsten behavior based on the observation of EUV line emissions from W6+ ions in HL-2A