Erosion and deposition investigations on Wendelstein 7-X first wall components for the first operation phase in divertor configuration

Dhard, C. P.; Mayer, M.; Brezinsek, S.; Masuzaki, S.; Motojima, G.; König, R.; Pedersen, T. S.; Neu, R.; Hathiramani, D.; Krause, Marco; Ehrke, G.; Ruset, C.; Schwarz-Selinger, T.; Balden, M.; Burwitz, V. V.; Coenen, J. W.; Linsmeier, Ch.; Naujoks, D.; Neubauer, O.; Rack, M.; Tokitani, M.; Oelmann, J.; Liu, Cong; Rasiński, M.; Höschen, D.; Yajima, Miyuki

doi:10.1016/j.fusengdes.2018.12.031

Cited by 17 publications

(12 citation statements)

References 7 publications

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“…2.5 MeV incident protons at normal incidence and a scattering angle of 165° were used, see Figs. 1 and 2 in [15] for typical spectra. A passivated implanted planar silicon (PIPS) detector with a thickness of 300 μm and nominal energy resolution of about 12 keV was used.…”

Section: Analysis Of the Marker Layersmentioning

confidence: 99%

Material erosion and deposition on the divertor of W7-X

et al. 2020

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The net erosion and deposition pattern of carbon from the Test Divertor Unit (TDU) of the stellarator W7-X was determined. Special target elements with marker layers consisting of about 300 nm molybdenum and 5-10 µm carbon on top were used during the operation phase OP 1.2a. The thicknesses of the marker layers were determined by elastic backscattering spectrometry (EBS) using 2.5 MeV protons before and after plasma exposure and laser-induced breakdown spectroscopy (LIBS) on selected target elements after exposure. Scanning electron microscopy (SEM) was used for investigating the surface morphology before and after exposure. Massive erosion of up to 20 µm carbon was observed at the strike line, in total 48±14 g carbon were eroded from the 10 TDUs. The erosion was laterally nonuniform on the micro-scale. Strongly eroded surfaces were considerably smoother as compared to the original material. Only very little deposition of carbon is observed on the TDU: This means that the TDU is a large net erosion source.

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Section: Analysis Of the Marker Layersmentioning

confidence: 99%

Material erosion and deposition on the divertor of W7-X

et al. 2020

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Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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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 11 μm 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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“…A Passivated Implanted Planar Silicon (PIPS) detector with 300 µm thickness and about 12 keV nominal energy resolution was used [5]. Nuclear Reaction Analysis (NRA) was carried out with incident 2.5 MeV 3He ions using the 12 C( 3 He,p0) 14 N and 10 B( 3 He,p1) 12 C reactions. The experimental spectra were evaluated using the software SIMNRA [6].…”

Section: Methodsmentioning

confidence: 99%

“…Forty-four pieces of long term deposition probes of three different types, i.e. Si-wafer, directional material and cavity probes [13,14] were installed at the outboard wall as well as at the pumping gap panels in module 4 (see fig. 1) for monitoring depositions on these low power loaded components.…”

Section: Wafer Probe Holdermentioning

confidence: 99%

Inspection of W 7-X plasma-facing components after the operation phase OP1.2b: observations and first assessments

et al. 2020

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Due to its twisted magnetic field configurations, the orientation of the plasma-facing components of the Wendelstein 7-X stellarator is changed from bean shape to triangular shape along the plasma axis within a module. The plasma-facing components consist of graphite (test divertor units, baffles, head shield tiles, toroidal divertor closures) and stainless steel components (wall panels, pumping gap panels, poloidal closures). In order to document the status of these components as well as to get the first footprints of the plasma-wall interactions that occurred during the plasma campaign, a detailed inspection of the whole plasma vessel after the plasma campaign is of vital importance. Such an inspection was carried out after the operation phase OP1.2b completed in October 2018. A number of observations were made, such as, molten stainless steel drops, melting of a long term probe, deposition on steel panels, arc traces, loosely bound particles and deposition stripes on the plasma vessel hidden behind the graphite tiles. In order to understand the possible causes, their implication and steps to avoid some of these problems for the next phase of machine operation, an assessment was made. The melting events should be avoided in the future, the others are due to usual plasma-wall interaction mechanisms and will be monitored after each campaign.

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Erosion and deposition investigations on Wendelstein 7-X first wall components for the first operation phase in divertor configuration

Cited by 17 publications

References 7 publications

Material erosion and deposition on the divertor of W7-X

Material erosion and deposition on the divertor of W7-X

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

Inspection of W 7-X plasma-facing components after the operation phase OP1.2b: observations and first assessments

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