Abstract
Forbidden transitions in the near-UV and visible wavelength of highly charged tungsten (W) ions are potentially useful as novel tungsten diagnostics means of fusion plasmas. Emission lines in 290–360 nm from Wq+ ions interacting with an electron beam of 540–1370 eV are measured, using a compact electron-beam-ion-trap. The charge states of 64 lines are identified as W20+–W29+. A magnetic-dipole (M1) line of W29+ between the excited states (4d84f)[(4d5/2−2)44f7/2]13/2→[(4d5/2−2)44f5/2]13/2 is newly identified; the wavelength is determined as 351.03(10) nm in air. The theoretical wavelength calculated using the multiconfiguration Dirac–Hartree–Fock method is in a good agreement with the measurement.
Highlights
Emission lines of tungsten (W) ions are highly relevant to nuclear fusion energy development because tungsten will be used as plasma-facing in-vessel component materials of ITER (International Thermonuclear Experimental Reactor), being, the primary heavy impurity in the ITER plasma
W measurements in the plasma devices using visible lines were limited to neutral and singly charged ions until visible and near-UV lines emitted by highly charged W ions were observed at the large helical device (LHD), using tungsten pellet injection [9,10,11]
A local tungsten density in core plasmas of the LHD was successfully assessed with near-UV magnetic-dipole (M1) lines emitted by W26+ and W27+ ions [13]
Summary
Emission lines of tungsten (W) ions are highly relevant to nuclear fusion energy development because tungsten will be used as plasma-facing in-vessel component materials of ITER (International Thermonuclear Experimental Reactor), being, the primary heavy impurity in the ITER plasma. A local tungsten density in core plasmas of the LHD was successfully assessed with near-UV magnetic-dipole (M1) lines emitted by W26+ and W27+ 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): W7+ –W9+ [14,15], W8+ –W28+ [16], W11+ [17], W12+ –W14+ [18], W13+ [19], W24+ –W25+ [20], W25+ [21], W26+ [22,23], W26+ –W33+ [24], W27+ [25], W28+ [26,27], and W52+ [28,29,30].
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