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

Abstract

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 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\xa0cm ( − 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 \xa0cm 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 ×\xa0108 cm−3 in steady H-mode discharges with T e ( 0 ) = 3 keV and n e ( 0 ) = 4 ×\xa01013 cm−3.