In-vessel colorimetry of Wendelstein 7-X first wall components: variation of layer deposition distribution in OP1.2a and OP1.2b

Motojima, G.; Masuzaki, S.; Dhard, C. P.; Krause, Marco; Naujoks, D.; Hayashi, Y.; Brezinsek, S.

doi:10.1088/1402-4896/ab5618

Cited by 7 publications

(6 citation statements)

References 18 publications

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“…Colorimetric analysis [25] performed in-vessel at the end of each operation phase provides non-destructive 2D information about the changes in reflectivity and optical properties of first wall surfaces. A photo of the W7-X vessel interior after OP1.2B, thus integrating for the majority of plasma-facing components the operational time in OP1.2A and B, is shown in figure 3(c).…”

Section: Pfc and Marker Target Elementsmentioning

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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Section: Pfc and Marker Target Elementsmentioning

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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“…Optical reflection measurements were performed on all the panels around the torus. The thickness profile on the wall panels shows a definitive pattern with the thickest deposition around the interface between the modules and the thinnest in the middle of the modules [8]. One such area of thicker deposition on the wall panels close to the toroidal closure along the torus is visible in fig.…”

Section: Wall and Pumping Gap Panels And Poloidal Closuresmentioning

confidence: 90%

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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“…Because that the He GDC for improving wall condition were not necessary any more after boronizations as discussed in [5]. The details of plasma information during OP1.2B such as the magnetic configurations and associated particle and plasma discharge time were summarized in [6,38,39]. The installed location of TM2h6 was at the horizontal divertor target of HM 1u in W7-X and the exact location is shown in figure 1(a).…”

Section: Measured Sample and Experimental Setupmentioning

confidence: 99%

Investigation of boron distribution and material migration on the W7-X divertor by picosecond LIBS

De-you¹,

Brezinsek²,

Yi³

et al. 2022

Phys. Scr.

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One set of horizontal target elements of the Test Divertor Units (TDU), retrieved from the Wendelstein 7-X (W7-X) vessel after the end of second divertor Operation Phase (OP1.2B) in Hydrogen (H), were investigated by picosecond Laser-Induced Breakdown Spectroscopy (ps-LIBS). The Boron (B) distribution, H pattern and the material erosion/deposition pattern on these target elements were analyzed with high depth resolution and mapped in the poloidal direction of W7-X. From the spectroscopic analysis, B, H, Carbon (C) and Molybdenum (Mo) were clearly identified. A non-uniformly distributed B pattern on these divertor target elements was determined by the combination of B layer deposition during the three boronizations and W7-X plasma operation with multiple erosion and deposition steps of B. Like the TDU, the analyzed target elements are made of fine grain graphite, but have two marker layers which allow us to determine the material migration via the ps-LIBS technique. Two net erosion zones including one main erosion zone with a peak erosion depth of 6.5 μm and one weak erosion with a peak erosion of 1.3 μm were determined. Between two net erosion zones, a net deposition zone with width of 135 mm and a thickness up to 3.5 μm at the peak deposition location was determined by the ps-LIBS technique. The B distributions are correlated with the erosion/deposition pattern and the operational time in standard magnetic configuration of W7-X in the phases after the boronizations. The thickness of the containing B layer on these target elements also correlates with the erosion/deposition depth, in which the thickness of the containing B layer varies spatially in poloidal direction between 0.1 μm and 6 μm. Complementary, Focused Ion Beam combined with Scanning Electron Microscopy (FIB-SEM) was employed also to verify and investigate the deposition layer thicknesses at typical net erosion and net deposition zones as well as to identify the three boronizations in depth.

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In-vessel colorimetry of Wendelstein 7-X first wall components: variation of layer deposition distribution in OP1.2a and OP1.2b

Cited by 7 publications

References 18 publications

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

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

Investigation of boron distribution and material migration on the W7-X divertor by picosecond LIBS

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