Plasma–surface interaction in the stellarator W7-X: conclusions drawn from operation with graphite plasma-facing components

BrezƖnsek, S.; Dhard, C. P.; Jakubowski, M.; König, R.; Masuzaki, S.; Mayer, M.; Naujoks, D.; Romazanov, J.; Schmid, K.; Schmitz, O.; Zhao, D.; Balden, M.; Brakel, R.; Butterschoen, B.; Dittmar, T.; Drews, P.; Effenberg, F.; Elgeti, S.; Ford, O.; Fortuna-Zalesna, E.; Fuchert, G.; Gao, Y.; Goriaev, A.; Hakola, A.; Kremeyer, T.; Krychowiak, M.; Liang, Y.; Linsmeier, Ch; Lunsford, R.; Motojima, G.; Neu, R.; Neubauer, O.; Oelmann, J.; Petersson, P.; Rasinski, M.; Rubel, M.; Sereda, S.; Sergienko, G.; Sunn Pedersen, T.; Vuoriheimo, T.; Wang, E.; Wauters, T.; Winters, V.; Zhao, M.; Yi, R.; the W7-X Team,

doi:10.1088/1741-4326/ac3508

Title: Plasma–surface interaction in the stellarator W7-X: conclusions drawn from operation with graphite plasma-facing components

Journal Article · Thu Dec 02 00:00:00 EST 2021 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ac3508· OSTI ID:1828773

; Dhard, C. P.;

;

; Schmid, K.;

;

; Brakel, R.;

;

; Elgeti, S.;

;

W7-X completed its plasma operation in hydrogen with island divertor and inertially cooled test divertor unit (TDU) made of graphite. A substantial set of plasma-facing components (PFCs), including in particular marker target elements, were extracted from the W7-X vessel and analysed post-mortem. The analysis provided key information about underlying plasma–surface interactions (PSI) processes, namely erosion, transport, and deposition as well as fuel retention in the graphite components. The net carbon (C) erosion and deposition distribution on the horizontal target (HT) and vertical target (VT) plates were quantified and related to the plasma time in standard divertor configuration with edge transform ι = 5/5, the dominant magnetic configuration of the two operational phases (OP) with TDU. The operation resulted in integrated high net C erosion rate of 2.8 mg s^-1 in OP1.2B over 4809 plasma seconds. Boronisations reduced the net erosion on the HT by about a factor 5.4 with respect to OP1.2A owing to the suppression of oxygen (O). In the case of the VT, high peak net C erosion of 11μm at the strike line was measured during OP1.2B which converts to 2.5 nm s^-1 or 1.4 mg s^-1 when related to the exposed area of the target plate and the operational time in standard divertor configuration. PSI modelling with ERO2.0 and WallDYN-3D is applied in an interpretative manner and reproduces the net C erosion and deposition pattern at the target plates determined by different post-mortem analysis techniques. This includes also the ¹³C tracer deposition from the last experiment of OP1.2B with local ¹³CH₄ injection through a magnetic island in one half module. The experimental findings are used to predict the C erosion, transport, and deposition in the next campaigns aiming in long-pulse operation up to 1800 s and utilising the actively cooled carbon-fibre composite (CFC) divertor currently being installed. The CFC divertor has the same geometrical design as the TDU and extrapolation depends mainly on the applied plasma boundary. Extrapolation from campaign averaged information obtained in OP1.2B reveals a net erosion of 7.6 g per 1800 s for a typical W7-X attached divertor plasma in hydrogen.

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Research Organization:: Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE; German Research Foundation (DFG); EUROfusion Consortium

Contributing Organization:: W-7X Team

Grant/Contract Number:: AC02-09CH11466; 633053; 10415657; SC0014210

OSTI ID:: 1828773

Journal Information:: Nuclear Fusion, Vol. 62, Issue 1; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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