Observation of EUV spectra from gadolinium and neodymium ions in the Large Helical Device

Abstract

We have observed extreme ultraviolet (EUV) spectra from highly charged gadolinium and neodymium ions in optically thin plasmas produced in the Large Helical Device at the National Institute for Fusion Science. Time evolutions of EUV spectra in the 6–9 nm region following injection of a solid pellet into a hydrogen plasma were measured by a grazing incidence spectrometer with a frame rate of 0.2 s. Three different types of spectral features have been observed depending on the electron temperature. Discrete spectral lines of Ni- and Cu-like gadolinium and neodymium ions were identified when the peak electron temperature was around 2 keV, while some lines of Ag-like gadolinium ions were found in the plasma with temperatures below 240 eV when an unusual hollow plasma was formed. Under the intermediate temperature, a quasi-continuum spectral feature arising from an unresolved transition array from open 4p/4d subshell ions is predominant.