A space-resolved extreme ultraviolet spectrometer for radial profile measurement of tungsten ions in the Experimental Advanced Superconducting Tokamak

In order to study the radial transport of tungsten ions in long-pulse H-mode discharges, a space-resolved spectrometer working at 30–520 Å has been newly developed to measure a radial profile of the tungsten line emission. The spectrometer is installed behind a long extension vacuum tube connected to a horizontal midplane diagnostic port of EAST tokamak. The long distance between the plasma and spectrometer, 8835.5 mm, enables observation of the radial profile of impurity line emissions in a wide vertical range of −8.5≤Z≤ 40 cm (−0.1≤ρ≤0.6). A good spectral resolution of Δλ0=4−5 pixels at the foot position of spectral line profiles and a high spatial resolution of ΔZ=2.5 cm are obtained in addition to a sufficient temporal resolution, e.g. 50 ms/frame. As a result, accurate radial profiles have been successfully obtained in EAST Ohmic and H-mode discharges for several impurity species such as carbon, oxygen, argon, iron and tungsten. The radial profiles of tungsten line emissions from W42+ – W45+ ions with 4p–4s transitions measured at two wavelength ranges of 45–70 Å and 120–140 Å are analyzed for the ion density evaluation based on the photon emissivity coefficient from ADAS database. The result shows that the density of W43+ – W45+ ions ranges at 2–6 × 108 cm−3 in steady H-mode discharges with Te(0)=3 keV and ne(0)=4 × 1013 cm−3.