| 1. |
- Corre, Y., et al.
(författare)
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Testing of ITER-grade plasma facing units in the WEST tokamak: Progress in understanding heat loading and damage mechanisms
- 2023
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 37
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Tidskriftsartikel (refereegranskat)abstract
- Assessing the performance of the ITER design for the tungsten (W) divertor Plasma Facing Units (PFUs) in a tokamak environment is a high priority issue to ensure efficient plasma operation. This paper reviews the most recent results derived from experiments and post-mortem analysis of the ITER-grade PFUs exposed in the WEST tokamak and the associated modelling, with a focus on understanding heat loading and damage evolution. Several shaping options, sharp or chamfered leading edge (LE), unshaped or shaped blocks with a toroidal bevel as foreseen in ITER, were investigated, under steady state heat fluxes of up to 120 MW⋅m−2 and 6 MW⋅m−2 on the sharp LE and top surface of the block, respectively. A very high spatial resolution (VHR) infrared (IR) camera (0.1 mm/pixel) was used to derive the temporal and surface distribution of the temperature and heat load on the castellated tungsten blocks for different geometric alignment and plasma conditions. Photonic modelling was required to reproduce the IR measurements in particular in the toroidal and poloidal gaps of the mono-block (MB) stacks where high apparent temperatures are observed. Specular reflection is found to be the dominant emitter in these parts of the blocks. W-cracking was observed on the leading edge of the blocks already within the first phase of plasma operation, during which the divertor was equipped with unshaped PFUs, including some intentionally misaligned blocks. Numerical analysis taking into account softening processes and mechanical stresses, revealed brittle failure due to transients as the dominant failure mechanisms. Ductile failure was observed in one particular block used for the melting experiment, therefore under extremely high steady state heat load conditions. W-melting achieved on actively cooled PFU exhibits specific features: shallow melting and slow melt displacement. Plasma exposure of pre-damaged PFUs at various damage levels (crack network and melted droplets) was carried out under high heat load conditions with several hours of cumulated plasma duration. IR data and preliminary surface analyses show no evidence of significant degradation damage progression under these conditions.
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| 2. |
- Paschalidis, Konstantinos, et al.
(författare)
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Melt dynamics with MEMENTO — Code development and numerical benchmarks
- 2023
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 37
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Tidskriftsartikel (refereegranskat)abstract
- The new numerical implementation of the MEMOS-U physics model, fully validated in multiple EUROfusion sponsored experiments, is presented. The computational tool - MEMENTO (MEtallic Melt Evolution in Next-step TOkamaks)- is able to address fusion-relevant melting scenarios that feature complex plasma-facing component geometries, involve intricate plasma wetting patterns and are characterized by vast spatio-temporal scale separations. The high level architecture of the code is discussed and numerical benchmarks of the heat transfer, fluid dynamics and current propagation solvers are presented.
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| 3. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Experiments and modelling on ASDEX Upgrade and WEST in support of tool development for tokamak reactor armour melting assessments
- 2022
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- The risk of metallic armour melting constitutes a major concern for ITER and DEMO. Combined computational and experimental effort has led to a successful understanding of melt dynamics in present-day tokamaks, but there remain unexplored melting regimes of relevance to future reactors. Analysis of recent poor-versus -efficient thermionic emitter sample exposures in ASDEX-Upgrade and ITER-like actively cooled tungsten leading edge exposures in WEST is presented. The coupled thermal response and melt dynamics is modelled with the new MEMENTO code employing the MEMOS-U physics model which has no adjustable parameters. In the weak Lorentz force regime accessed in the exposures, very close agreement between modelling and experiments is achieved not only for the deformation profiles, but also for the additional, unique to these experiments, constraints; simultaneous thermal response of two different materials in ASDEX-Upgrade and in-situ detection of melt build-up in WEST.
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| 4. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Metallic melt transport across castellated tiles
- 2024
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 64:3
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Tidskriftsartikel (refereegranskat)abstract
- In future fusion reactors, extended melt pools in combination with strong plasma-induced accelerations, suggest that the metallic melt could reach the gaps between castellated plasma-facing components, potentially accompanied by profound changes in their mechanical response. The first results of a combined experimental and modelling effort to elucidate the physics of melt transport across gaps are presented. Transient melting of specially designed tungsten samples featuring toroidal gaps has been achieved in ASDEX Upgrade providing direct evidence of gap bridging. Detailed modelling with the MEMENTO melt dynamics code is reported. Empirical evidence and simulations reveal that the presence of gaps can be safely ignored in macroscopic melt motion predictions as well as that the re-solidification limited melt spreading facilitates gap bridging and leads to poor melt attachment. The findings are discussed in the context of ITER and DEMO.
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| 5. |
- Vignitchouk, Ladislas, et al.
(författare)
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Remobilized dust dynamics and inventory evolution in ITER-like start-up plasmas
- 2023
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing Ltd. - 0741-3335 .- 1361-6587. ; 65:1
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of remobilized metallic dust are simulated with the MIGRAINe code in low-power ITER discharges meant to emulate reactor start-up environments. The particle size and speed distributions are varied along with plasma profiles to investigate the influence of initial and background parameters on high-Z impurity production by vaporization as well as long-term in-vessel dust inventory evolution over the course of consecutive discharges. Simulation output data regarding beryllium remobilization can be integrated into more global ITER models to guide the operation of dust diagnostics and facilitate the compliance with nuclear safety restrictions, while results on tungsten particles serve as a basis for first assessments of dust dynamics in DEMO.
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