Material migration and fuel retention studies during the JET carbon divertor campaigns

Coad, J. P.; Rubel, M.; Likonen, J.; Bekris, N.; Brezinsek, S.; Matthews, G. F.; Mayer, M.; Widdowson, A.; Contributors, Jet

doi:10.1016/j.fusengdes.2018.10.002

Cited by 27 publications

(35 citation statements)

References 58 publications

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“…Carbon deposition on the TDU itself is low, see sections 3.1 and 3.2. This is a pronounced difference to tokamaks, where strong carbon deposition in the inner divertor or in remote divertor areas is observed [31,32,33]. Carbon-containing thin layers are observed at various places inside the main chamber of W7-X [34], but total amounts of deposited carbon are not yet available.…”

Section: Discussionmentioning

confidence: 93%

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: Discussionmentioning

confidence: 93%

Material erosion and deposition on the divertor of W7-X

et al. 2020

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“…There are some variations in the deuterium content, but the major result is such that the amounts of fuel trapped in the studied dump plate are small: 1 -4 × 10 17 cm -2 . Such concentrations are considered to be generally low, not only in comparison to JET-C (up to 1 × 10 20 cm -2 [4,5,34]) but also to the data for the JET-ILW divertor, D in the 10 18 cm -2 range [35,36]. It is seen in Fig.…”

Section: Deuterium Retentionmentioning

confidence: 97%

Beryllium melting and erosion on the upper dump plates in JET during three ITER-like wall campaigns

et al. 2019

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Data on erosion and melting of beryllium upper limiter tiles, so-called dump plates (DP), are presented for all three campaigns in the JET tokamak with the ITER-like wall. Highresolution images of the upper wall of JET, show clear signs of flash melting on the ridge of the roof-shaped tiles. The melt layers move in the poloidal direction from the inboard to the outboard tile ending on the last DP tile with an upward going waterfall-like melt structure. Melting was caused mainly by unmitigated plasma disruptions. During three ILW campaigns around 15% of all 12376 plasma pulses were catalogued as disruptions. Thermocouple data from the upper dump plates tiles showed a reduction in energy delivered by disruptions with fewer extreme events in the third campaign, ILW-3, in comparison to ILW-1 and ILW-2. The total Be erosion assessed via precision weighing of tiles retrieved from JET during shutdowns indicated the increasing mass loss across campaigns of up to 0.6 g from a single tile. The mass of splashed melted Be on the upper walls was also estimated using the high-resolution images of wall components taken after each campaign. The results agree with the total material loss estimated by tile weighing (~130 g). Morphological and structural analysis performed on Be melt layers revealed a multilayer structure of re-solidified material composed mainly of Be and BeO with some heavy metal impurities Ni, Fe, W. IBA analysis performed across the affected tile ridge in both poloidal and toroidal direction revealed a low D concentration, in the range 1-4 x 10 17 D atoms/cm 2 .

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“…About 1 g retrieved from the divertor after each of the three experimental campaigns comprising 19 -23 h of plasma operation [5][6][7][8][9], i.e. approximately 150 times less than after JET operation with carbon walls [10]. Particles collected from JET-ILW consist of Be, W, Inconel components from the vacuum vessel wall (Ni, Cr, Fe), carbon from tungsten-coated divertor tiles made of carbon fibre composites (W-CFC) and other materials containing Cu, Mo and other elements (B, Mg, Al, Si) together with N (originating from N 2 puffing for edge cooling), H isotopes and O.…”

Section: Introductionmentioning

confidence: 98%

Micro-analyses of dust particles generated in the JET tokamak with the ITER-like wall

et al. 2020

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Dust generated in JET with the ITER-Like Wall (ILW) was collected from the divertor by vacuum cleaning and examined with ion and electron beam methods. From totally 1 g retrieved after the third ILW campaign (2015-2016) a number of specimens were prepared using sticky (adhesive) carbon tabs. The aim was to determine the distribution and amounts of constituents: from deuterium (D) to W with particular emphasis on the concentration ratio of D to other species. Two classes of particles containing deuterium were identified: (i) rich in Be and (ii) low-Z matrix without Be, that show large C concentrations with some O contribution and minor contributions from heavier elements. The D content in Be-based particles has been at the level not exceeding ≈2 at %, whereas in the C-rich particles, both in small (10-100 µm) and large conglomerates (> 100 µm), the D contribution at the level of about 15 to 20 at % has been detected. W-rich particles are often accompanied by Ni, Cr and Fe and occasionally with Mo. The results clearly indicate that fuel retention in the ILW dust is predominantly associated with residual C, approximately 10-20 times greater retention was found in C-rich objects than in metal-based particles.

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Material migration and fuel retention studies during the JET carbon divertor campaigns

Cited by 27 publications

References 58 publications

Material erosion and deposition on the divertor of W7-X

Material erosion and deposition on the divertor of W7-X

Beryllium melting and erosion on the upper dump plates in JET during three ITER-like wall campaigns

Micro-analyses of dust particles generated in the JET tokamak with the ITER-like wall

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