Thermal analysis of an exposed tungsten edge in the JET divertor

Arnoux, G.; Coenen, J. W.; Базылев, Б.; Corre, Y.; Matthews, G. F.; Balboa, I.; Clever, M.; Dejarnac, R.; Devaux, S.; Eich, T.; Gauthier, E.; Frassinetti, L.; Horáček, J.; Jachmich, S.; Kinna, D.; Marsen, S.; Mertens, Philippe; Pitts, R.A.; Rack, M.; Sergienko, G.; Sieglin, B.; Stamp, M.; Thompson, V.; Contributors, Jet

doi:10.1016/j.jnucmat.2014.11.005

Cited by 16 publications

(20 citation statements)

References 11 publications

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“…1). This top viewing of the IR diagnostic did however mean that during the ILW-1 exposure only the propagation of the heat pulse into the lamella from the side could be observed [7,8].…”

Section: Setupmentioning

confidence: 97%

“…It was shown during multiple experiments [3,4] that deep W melting can cause severe damage to components and can degrade plasma performance [5]. In 2013 experiments [6,7,8] were performed to asses how transient( ms-duration / µ m depth) melting during ELMs (Edge Localised Modes [9,10]) might affect the operation of JET and potentially ITER. The high stored energies of which ITER will be capable means that even with all PFC edges protected, shallow surface melting can still occur under uncontrolled plasma disruptions and ELM transients.…”

Section: Introductionmentioning

confidence: 99%

“…It also opened up questions about the interpretation of Infrared (IR) temperature measurements.Discrepancies were apparent in the JET experiment between the parallel heat flux required to reproduce the misaligned lamella surface temperature and that derived from observations on non-misaligned surfaces. So called mitigation factors, or perhaps more correctly, reduction factors (0.2 for L-mode and 0.4 for Hmode [7,8]) § were derived from these measurements by using the melt layer model MEMOS-3D [15,16,17,18] to generate temperature profiles based on the input heat fluxes and from them producing synthetic signals to compare with the infrared data.…”

Section: Introductionmentioning

confidence: 99%

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Transient induced tungsten melting at the Joint European Torus (JET)

et al. 2017

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Melting is one of the major risks associated with Tungsten Plasma-Facing Components (PFCs) in tokamaks like JET or ITER. These Components are designed such that leading edges and hence excessive plasma heat loads deposited at near normal incidence are avoided. Due to the high stored energies in ITER discharges, shallow surface melting can occur under insufficiently mitigated plasma disruption and so called Edge Localised Modes -Power load transients.A dedicated program was carried out at the Joint European Torus (JET) to study the physics and consequences of W transient melting. Following initial exposures in 2013 (ILW-1) of a Tungsten-lamella with leading edge, new experiments have been performed on a sloped surface (15 • slope) during the 2015/2016 (ILW-3) campaign. This new experiment allows significantly improved Infrared thermography measurements and thus resolved important issue of power loading in the context of the previous leading edge exposures. The new lamella was monitored by local diagnostics: spectroscopy, thermography and high resolution photography in between discharges. No impact on the main plasma was observed despite a strong increase of the local W source consistent with evaporation. In contrast to the earlier exposure, no droplet emission was observed from the sloped surface. Topological modifications

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“…1). This top viewing of the IR diagnostic did however mean that during the ILW-1 exposure only the propagation of the heat pulse into the lamella from the side could be observed [7,8].…”

Section: Setupmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transient induced tungsten melting at the Joint European Torus (JET)

et al. 2017

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“…Because the IR camera viewed the divertor module from top, it could not directly detect the temperature at the melting surface. Instead the local temperature distribution had to be derived by interpretative modelling [17]. To match the IR data, an ad hoc reduction factor was initially assumed for the parallel heat flux to the leading edge [3].…”

Section: Introductionmentioning

confidence: 99%

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

et al. 2018

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Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the Divertor Manipulator II (DIM-II) system [1]. Designed as near replicas of the geometries used also in separate experiments on the JET tokamak [2-4], the samples featured a misaligned leading edge and a sloped ridge respectively. Both structures protrude above the default target plate surface thus receiving an increased fraction of the parallel power flux. Transient melting by ELMs was induced by moving the outer strike point to the sample location. The temporal evolution of the measured current flow from the samples to vessel potential confirmed transient melting. Current magnitude and dependency from surface temperature provided strong evidence for thermionic electron emission as main origin of the replacement current driving the melt motion. The different melt patterns observed after exposures at the two sample geometries support the thermionic electron emission model used in the MEMOS melt motion code, which assumes a strong decrease of the thermionic net current at shallow magnetic field to surface angles [5]. Post exposure ex-situ analysis of the retrieved samples show recrystallization of tungsten at the exposed surface areas to a depth of up to several mm. The melt layer transport to less exposed surface areas leads to ratcheting pile up of re-solidified debris with zonal growth extending from the already enlarged grains at the surface.

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“…Note that similar corrections have been applied to the JET IR data obtained during the tungsten melting experiment [12]. Indeed, the maximum surface temperature ''measured'' by the JET IR system was $2300°C whilst the tungsten lamella was melting, which means that the true temperature around the corner was at least of 3400°C [13]. The final comparisons between TS numerical and experimental IR data are presented in Fig.…”

Section: Thermal Modelling On the Leading Edge And Synthetic Ir Datamentioning

confidence: 99%