EUV Spectra of W¹³⁺ Ions in the Large Helical Device: Recent Progress in Observation of Tungsten Ions in Low to Intermediate Charge State Range for Fusion Plasma Diagnostics

Spectroscopic studies of emissions released from tungsten ions combined with a pellet injection technique have been conducted in the Large Helical Device for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions. Emission lines were explored for the observation of low to intermediate charge states in the range of W¹⁰⁺ to W²⁰⁺, and the line spectra of W¹³⁺ were observed for the first time in fusion plasma experiments. The wavelengths of the observed W¹³⁺ lines were 243.1 Å, 247.6 Å, 248.3 Å, and 249.1 Å in the extreme ultraviolet wavelength range, and all of them were emission from the 4 f ¹³5s² - 4 f ¹³5s5p transitions.