EUV spectroscopy of Xe ions from the large helical device at the National Institute for Fusion Science for stable plasmas and plasmas undergoing radiation collapse

We have observed EUV spectra of xenon ions from the large helical device (LHD) at the National Institute for Fusion Science in Toki in the wavelength range of 10-17 nm using a high resolution SOXMOS spectrometer. A small quantity of xenon gas was injected into the large helical device. In some cases, the plasma evolution was stable and a steady discharge was obtained for several seconds, but sometimes the plasma underwent radiation collapse and rapid cooling and in this situation the EUV yield was significantly increased. Investigation of the spectra showed that during the heating phase and in a stable plasma, the emission was dominated by ions with open 4s and 4p subshells, while during radiation collapse, the spectra were dominated by lines from species with open 4d subshells. From a comparison of these spectra with theoretical data from atomic structure calculations and also with charge state specific data generated at Tokyo Metropolitan University, it was possible to make tentative assignments of the strongest lines arising from 4d-4f and 4p-4d transitions in Xe XVII and XVIII.