In situ observation of tungsten plasma-facing components after the first phase of operation of the WEST tokamak

Diez, M.; Corre, Y.; Delmas, E.; Fedorczak, N.; Firdaouss, M.; Grosjean, A.; Gunn, J.; Loarer, T.; Missirlian, M.; Richou, M.; Tsitrone, E.; Team, the WEST

doi:10.1088/1741-4326/ac1dc6

Cited by 21 publications

(9 citation statements)

References 19 publications

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“…No failure occurred on the PFUs during phase 1 but microscopic observations carried out after the C3 campaign revealed a variety of damage on the PFUs including cracking, optical hot spots, melting formation (figure 22). The main results are reported in [50,51]. It has to be noted that the thermal response of misaligned leading edges of ITER-grade PFUs, analysed with 3D finite elements modelling and IR imaging, is in agreement with the optical approximation of the parallel heat flux [52].…”

Section: First Evidence Of Damagesmentioning

confidence: 60%

Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

Bucalossi

2022

Nucl. Fusion

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WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017–2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m−2 were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described.

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Section: First Evidence Of Damagesmentioning

confidence: 60%

Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

Bucalossi

2022

Nucl. Fusion

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“…In addition, melting of the W limiter plate by transient heat flux during disruption has also been observed in the T-10 tokamak [20,21]. Moreover, the transient heat flux during plasma disruption also caused melting of the leading edges of W/Cu monoblocks in WEST [26]. All of the above melting phenomena during disruption illustrate that the transient heat flux during disruption is high enough to induce a large temperature rise, thus resulting in the melting of W PFCs.…”

Section: Melting Phenomenon On W/cu Flat-type Pfcs At the Domementioning

confidence: 86%

“…All of the above melting phenomena during disruption illustrate that the transient heat flux during disruption is high enough to induce a large temperature rise, thus resulting in the melting of W PFCs. Meanwhile, the small solidified spherical particles and sea-wave surface shown in figure 18 is very different from that induced by steady-state loading during L-mode discharges [27], and more similar to the disruption-induced melting in WEST [26] and the residual surface after high pulsed flux loading tests [53]. The migration of the molten layer along the toroidal direction also implies that the molten layer was subjected to an extremely strong plasma stream [54].…”

Section: Melting Phenomenon On W/cu Flat-type Pfcs At the Domementioning

confidence: 90%

“…Thus, the in situ melting phenomena in the W divertor in EAST and WEST can provide direct experience for the future ITER divertor. In situ melting phenomena of chamfered edges were observed on W/Cu monoblocks in WEST, which has been attributed to the transient heat flux during plasma disruptions [25,26]. In EAST, during real-time monitoring of melting phenomena, many droplets ejected from upper W divertor targets were identified due to the leading-edge-induced high steadystate heat loads [27][28][29].…”

Section: Introductionmentioning

confidence: 99%

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In situ melting phenomena on W plasma-facing components for lower divertor during long-pulse plasma operations in EAST

et al. 2023

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Tungsten (W) is one of the most promising plasma-facing materials (PFMs) for future fusion device. Although its melting point is the highest among all the metals, it still has great risk of melting under extremely high plasma heat fluxes, which is a big concern for the ITER and future reactors. Actively-cooled W plasma-facing components (PFCs) with both monoblocks and flat-type structure have been successfully installed in the lower divertor of the EAST tokamak since 2021, which provide a good opportunity for direct comparison of damage mechanism for the two types of PFCs. Various in-situ melting phenomena on the lower divertor have been observed by CCD cameras, which are further verified by Post-mortem inspections. Severe melting even exfoliation of the edge beveled W plates on some W/Cu flat-type components at horizontal outer targets were observed. A large number of droplets were ejected during long-pulse operations, which induced the significant increase of W impurity and total irradiation in the core plasma, and thus greatly deteriorated the plasma performance and even cause disruptions. Two different shaping structures of flat-type PFCs show different position of melting and corresponding mechanisms. Few slight melting has been found on the sharp leading edges of W/Cu monoblocks at the inter-cassette modules for horizontal targets with small droplets ejection, which is much improved compared to that occurred on the upper W divertor, illustrating that the application of large-sized bevel chamfer at inter-cassette modules was generally effective. In addition, an unexpected melting phenomenon on the dome plate was attributed to the extreme transient heat flux during disruption with runaway electrons. The application of both types of W/Cu PFCs for divertor provides important experiences and lessons for engineering design and optimization of divertor PFCs in future fusion devices.

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“…For the same wavelength and temperature, the surface state shows a strong influence with a large increase of the emissivity with the micro crack and cracks network, by a factor up to 4. However, the samples used in this study did not see plasma operation that could have modified the surface state through plasma surface interaction (erosion, deposition and possible damages) [15][16][17]. As a second step, an in-situ method has been developed to assess the emissivity evolution of the WEST divertor PFUs [18].…”

Section: Introductionmentioning

confidence: 99%

Overview of the emissivity measurements performed in WEST: in situ and post-mortem observations

Gaspar¹,

Corre²,

Rigollet³

et al. 2022

Nucl. Fusion

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This paper summarizes the emissivity measurements performed on the plasma facing units (PFU) of the WEST lower divertor during the first phase of WEST running with a mix of actively cooled ITER-like PFUs made of bulk tungsten and inertially cooled PFUs made of graphite with a coating of tungsten. In-situ assessment of the emissivity and laboratory measurements after removing the W-coated graphite and ITER-grade PFUs from the WEST device are shown. The measurements exhibit a complex pattern with strong emissivity variation as function of space and time mainly explained with the variation of magnetic equilibrium (strike point location) as well as the plasma performances during the experimental campaigns. The exposed ITER-grade PFU exhibits sharp spatial variation of the emissivity from 0.05 to 0.85 at a monoblock scale (12mm) at the transition of the erosion (strike point location) and deposition (next to the strike point location) areas on the high field side. In the low field side, the emissivity varies from 0.12, at the strike point location, to 0.2 few cm away in the low field side direction. This emissivity range after exposure is much higher than the emissivity variation of unexposed PFU with emissivity from 0.09 to 0.15. In-situ observation performed on the W-coated graphite PFU shows a rapid evolution, typically few pulses, of the emissivity in the inner and outer strike point location. The whole spatial distribution is discussed as well as his variation due to the plasma operation from the start-up of WEST to the removal of the tungsten (W) coated graphite components.

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In situ observation of tungsten plasma-facing components after the first phase of operation of the WEST tokamak

Cited by 21 publications

References 19 publications

Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

In situ melting phenomena on W plasma-facing components for lower divertor during long-pulse plasma operations in EAST

Overview of the emissivity measurements performed in WEST: in situ and post-mortem observations

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