This paper reports x-ray crystal spectroscopy (XCS) on highly charged ions of tungsten impurity within the Large Helical Device (LHD) under plasma conditions with a central electron temperature around 4 keV. By combining measured spectra with Flexible Atomic Code (FAC) calculations and a collisional radiative model weighted by ADAS ionization and recombination rates, emission lines from W43+ to W47+ charge states were systematically identified in the 3.7–4.0 Å band. The dataset was constructed by integrating 10 discharges to cover the entire wavelength range, using tungsten introduced reproducibly via coaxial W pellet injection. Notably, the W47+ line at 3.7691 Å extends the highest charge state observed to date in the LHD. Leveraging the high dispersion characteristics of XCS, three diagnostics directly relevant to ITER-class edge/pedestal plasmas with Te of several keV were demonstrated: (i) simultaneous measurement of multiple charge states via EUV-x-ray co-observation. This enables monitoring the evolution of tungsten charge state distribution in response to electron temperature variations, supporting impurity transport studies and operational monitoring. (ii) Ion temperature estimation from the Doppler width of the W46+ 3.8784 Å line showing a core peak, including error propagation via determination of instrument functions and cross-comparison with the charge exchange recombination spectroscopy. (iii) An electron temperature indicator based on the W46+ 3.8784/3.8956 Å intensity ratio. This exhibits strong sensitivity to Te, and FAC calculations reproduced the observed Te dependence of the line intensity ratio in the Te range of 3–5 keV.
Bright EUV lines emitted by highly ionized tungsten ions as diagnostic indicators of the tungsten transport in ITER core plasmas (Te > 7 keV)