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

Coenen, J. W.; Matthews, G. F.; Krieger, K.; Iglesias, Daniel; Bunting, P.; Corre, Y.; Silburn, S.; Balboa, I.; Базылев, Б.; Conway, N. J.; Coffey, I.; Dejarnac, R.; Gauthier, E.; Gaspar, J.; Jachmich, S.; Jepu, I.; Makepeace, C.; Scannell, R.; Stamp, M.; Petersson, P.; Pitts, R.A.; Wiesen, S.; Widdowson, A.; Heinola, K.; Baron-Wiechec, A.; Contributors, Jet

doi:10.1088/1402-4896/aa8789

Cited by 23 publications

(19 citation statements)

References 41 publications

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“…The validity of the geometric projection for the calculation of the parallel power flux at JET, called into question by the first leading edge experiment, was tested experimentally in a second transient melt study using an alternative lamella design with a protruding sloped surface facing the toroidal field allowing direct IR observation of the slope surface [20]. The conclusion of this work, and of the detailed new thermal analysis [19], is that the optical approximation (i.e.…”

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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Section: Introductionmentioning

confidence: 99%

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

et al. 2018

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“…For an all-W ITER divertor, detailed studies have been performed and are given in refs. [36][37][38][39][40][41]. It was established that melting can and will be a potentially limiting factor and needs to be controlled by shaping and plasma control.…”

Section: From Carbon To Tungstenmentioning

confidence: 99%

Fusion Materials Development at Forschungszentrum Jülich

Coenen

2020

Adv Eng Mater

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Material issues pose a significant challenge for the design of future fusion reactors. From a historic point of view, the material mix used for the first wall of a fusion reactor has continually evolved, from original steel vessels to carbon and other low-Z materials such as beryllium to tungsten as the primary candidate for a reactor's first wall armor and divertor material. For materials considered for fusion applications, a highly integrated approach is necessary. Resilience against neutron damage, good power exhaust, and oxidation resistance during accidental air ingress are design relevant issues while deciding on new materials or improving upon baseline materials. Neutron-induced effects, e.g., transmutation adding to embrittlement, retention, and changes to thermomechanical properties, are crucial to material performance. In this contribution, the recent progress (2013-2019) in fusion materials development for current and future fusion devices, at Forschungszentrum Jülich GmbH, with activities focussing on advanced materials and their characterization is given. It is a continuation and extension of the work given by Coenen et al.

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“…They are heavily bombarded by energetic particles during plasma shots. Consequently, the temperature of the leading edge could reach the melting point of tungsten, resulting in the movement of molten tungsten in the direction of j × B [17][18][19]. By tilting and shaping of the castellated structure, and by changing its angle with respect to the field line, leading edges can be hidden from the plasma particles.…”

Section: Damage and Melting Test Of Tungsten Blocks By Power Loading mentioning

confidence: 99%

“…It was also found that the molten droplets of W were directed towards the high field side due to j × B force as reported in Refs. [17][18][19].…”

Section: Damage and Melting Test Of Tungsten Blocks By Power Loading mentioning

confidence: 99%

A brief summary of tungsten technology development in Korea

Hong

2020

Tungsten

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A review of tungsten technology development in Korea is briefly given. According to the upgrade plan of Korea superconducting tokamak advanced research (KSTAR) tokamak associated with Korean fusion energy R&D program, graphite plasma-facing components will be replaced with tungsten-based ones to handle the high-peak heat load caused by an increase of heating power up to 26 MW. Brazing technique to bond tungsten was developed and tungsten blocks were manufactured. Blocks were installed at the central divertor in KSTAR and exposed to high heat flux. Under high heat flux and long-pulse discharge, tungsten blocks were severely damaged. Molten tungsten materials show movements towards the high field side, which is j×B direction. The COMSOL ® modeling described the melting event quantitatively well. The failure of a water cooling system with a metal wall environment during a long-pulse plasma operation is very critical.

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

Cited by 23 publications

References 41 publications

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

Fusion Materials Development at Forschungszentrum Jülich

A brief summary of tungsten technology development in Korea

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