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

Abstract In order to study the radial transport of tungsten ions in long-pulse H-mode discharges, a space-resolved spectrometer working at 30–520 A has been newly developed to measure a radial profile of the tungsten line emission. The spectrometer is installed behind a long extension vacuum tubeconnected 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 Δ λ 0 = 4 − 5 pixels at the foot position of spectral line profiles and a high spatial resolution of Δ Z = 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 W 42 + – W 45 + ions with 4p–4s transitions measured at two wavelength ranges of 45–70 A and 120–140 A are analyzed for the ion density evaluation based on the photon emissivity coefficient from ADAS database. The result shows that the density of W 43 + – W 45 + ions ranges at 2–6 × 10 8 cm −3 in steady H-mode discharges with T e ( 0 ) = 3 keV and n e ( 0 ) = 4 × 10 13 cm −3 .