Plasma and Fusion Research

Volume 17, 2402022 (2022)

Regular Articles


Spatial Profiles of NeVI-NeX Emission in ECR-Heated Discharges of the Large Helical Device with Divertor Detachment Induced by RMP Application and Ne Impurity Seeding
Tetsutarou OISHI1,2), Masahiro KOBAYASHI1,2), Hiromi TAKAHASHI1,2), Yuki HAYASHI1), Kiyofumi MUKAI1,2), Shigeru MORITA1,2), Motoshi GOTO1,2), Yasuko KAWAMOTO1), Tomoko KAWATE1,2,3), Suguru MASUZAKI1,2), Chihiro SUZUKI1,2), Gakushi KAWAMURA1,2), Gen MOTOJIMA1,2) and Ryosuke SEKI1,2)
1)
National Institute for Fusion Science, National Institutes of Natural Sciences, 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan
2)
Department of Fusion Science, The Graduate University for Advanced Studies, SOKENDAI, 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan
3)
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
(Received 9 December 2021 / Accepted 18 February 2022 / Published 22 April 2022)

Abstract

In the Large Helical Device, the divertor detachment has been attempted by application of resonant magnetic perturbation (RMP) field and Ne gas puffing in electron cyclotron resonance- heated discharges for compatibility of high central electron temperature and low divertor heat load. Two kinds of divertor detachment phases were observed. The first one appeared transiently just after the Ne gas puffing (1st detachment), and the second one appeared steadily in the latter half of the discharge (2nd detachment). Space-resolved extreme ultraviolet spectroscopy revealed that NeVI-NeVIII emissions increased slightly outside the last closed flux surface (LCFS), while NeIX and NeX emissions increased inside the LCFS in the 1st detachment phase. Although in the 1st detachment the divertor heat load was significantly reduced, the central electron temperature also decreased because the Ne ions were penetrated inside the LCFS as a radiation source. In the 2nd detachment phase, NeVI-NeVIII emissions increased outside the LCFS while NeIX and NeX emissions kept low intensity inside the LCFS. In this phase, low divertor heat load and high central electron temperature were obtained simultaneously because the Ne ions were localized outside the LCFS as a radiation source. The profile measurements of Ne emission show that the edge island structure created by the RMP application impacts on the impurity emission distribution, where the peak of the emission shifts radially stepwise as the detachment proceeds.


Keywords

plasma spectroscopy, extreme ultraviolet, vacuum ultraviolet, magnetically confined fusion, impurity seeding, resonant magnetic perturbation, divertor detachment

DOI: 10.1585/pfr.17.2402022


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