Measurement of EUV Spectra from High Z Elements in the Large Helical Device

Abstract

Extreme ultra‐violet (EUV) emission spectra from highly charged tin, xenon and tungsten ions have been measured in optically thin high‐temperature plasmas produced in the Large Helical Device (LHD) at the National Institute for Fusion Science by using a grazing incidence spectrometer and a tracer‐encapsulated solid pellet (TESPEL) injector. Quasi‐continuous spectral features arising from unresolved transition array (UTA) of open 4d subshell ions were observed for tin, xenon and tungsten around 13.5, 11, and 5 nm, respectively, when edge plasma was cooled sufficiently. The spectral appearance obviously depends on edge electron temperature and atomic number. In the case of intermediate edge temperature, sharp discrete lines from highly charged open 4s or 4p subshell ions are clearly observed for tin and xenon in the longer wavelength side of the UTAs but not the case for tungsten. Assignments of the strong discrete lines have been performed by comparison with other experimental data and the theoretical calculations generated using the Cowan code. In order to interpret the tungsten spectra it was necessary to include the contribution of open 4f subshell ions.