An Analysis of EUV spectra emitted from highly-charged tungsten ions in JT-60U high-temperature plasmas

Yanagibayashi, Jun; Nakano, Tomohide; Hasuo, Masahiro*; Iwamae, Atsushi; Kubo, Hirotaka; Itami, Kiyoshi

Tungsten is one of the candidates for the divertor material of ITER because of its low retention and low hydrogen inventory. However, it is a problem that tungsten ions accumulated in a core plasma emit intense radiation and cool the plasma. For preparation of investigating the mechanism of the tungsten ion accumulation, Vaccum Ultra Violet (VUV) lines emitted from tungsten ions are identified. A VUV spectrum from a JT-60U plasma ( keV) is observed with a flat-field grazing-incidence spectrometer. The observed spectrum is compared with a theoretical spectrum calculated with Flexible Atomic Code. It is found that the observed peaks around 3 nm are due to transitions between levels of W (), and that those around 5, 6 and 13 nm are due to transitions between levels of W (). It is believed that the former lines are useful to diagnose the tungsten ion accumulation in a high-temperature ( 10 keV) plasma of ITER.