“…Moreover, mirrors and optical fibers are available to avoid fusion neutron irradiation to detectors. Recently, a local tungsten density in core plasmas of the LHD was successfully assessed with near-UV magnetic-dipole (M1) lines emitted by W 26+ and W 27+ ions [13]. Such visible and near-UV emission lines of highly charged W ions were intensively measured by different research groups, using electron-beam-ion-traps (EBITs): W 7+ -W 9+ [14,15], W 8+ -W 28+ [16], W 11+ [17], W 12+ -W 14+ [18], W 13+ [19], W 24+ -W 25+ [20], W 25+ [21], W 26+ [22,23], W 26+ -W 33+ [24], W 27+ [25], W 28+ [26,27], and W 52+ [28][29][30].…”