Long pulse D2 and N2 seeded discharges on the upper actively cooled tungsten divertor of WEST. (24th June 2020)

• Record Type: Journal Article
• Authors: Dittmar, T; Loarer, T; Drenik, A; Bourdelle, C; Brezinsek, S; Desgranges, C; Douai, D; Fedorczak, N; Guirlet, R; Gunn, J; Meyer, O; Laguardia, L; Tsitrone, E
• Other Names: collab.
• Is Part Of: Physica scripta. Volume T171(2020:Jan.)
• Publication Date: 2020-06-24
• Subjects: tungsten divertor -- WEST tokamak -- long pulse operation -- nitrogen seeding -- ammonia formation; Physics -- Periodicals; 530.05
• DOI: 10.1088/1402-4896/ab753f
• Languages: English
• ISSNs: 0031-8949

Abstract

Abstract: A series of L-mode discharges in upper single null configuration with more than 30 s duration were performed in the WEST tokamak with the strike line on actively cooled tungsten-coated divertor components. This series of discharges accumulated 20 min of plasma and a strike point fluence of ≈ 2 × 10 25 m − 2 in two days of operation in attached conditions. The discharges showed good density control, no tungsten accumulation and overall very benign thermal behaviour of the upper divertor. A subset of the discharges were seeded with nitrogen either in the divertor or midplane region to study plasma–wall interaction and associated ammonia formation in this weakly pumped scenario with all-tungsten plasma-facing components. While ammonia signals remained too weak for useful analysis, a strong dependence of nitrogen plasma penetration efficiency and residence time on the injection location was found. This hints towards a currently underestimated plasma-near nitrogen reservoir in these tokamak discharges in divertor configuration.