Role of shielding in modelling cryogenic deuterium pellet ablation

Gál, K.; Belonohy, É.; Kocsis, G.; Lang, P. T.; Veres, G. I.

doi:10.1088/0029-5515/48/8/085005

Cited by 18 publications

(25 citation statements)

References 27 publications

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“…The amplitude of the space and time varying density source is such that the integrated source rate is consistent with the NGS pellet ablation model. 124 Due to limitations on the grid resolution, the pellet density source rate is assumed to be spread over a significantly wider region in space.…”

Section: Elm Control Methods: Pellet Pacingmentioning

confidence: 99%

Modelling of edge localised modes and edge localised mode control

et al. 2015

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Edge Localised Modes (ELMs) in ITER Q ¼ 10 H-mode plasmas are likely to lead to large transient heat loads to the divertor. To avoid an ELM induced reduction of the divertor lifetime, the large ELM energy losses need to be controlled. In ITER, ELM control is foreseen using magnetic field perturbations created by in-vessel coils and the injection of small D2 pellets. ITER plasmas are characterised by low collisionality at a high density (high fraction of the Greenwald density limit). These parameters cannot simultaneously be achieved in current experiments. Therefore, the extrapolation of the ELM properties and the requirements for ELM control in ITER relies on the development of validated physics models and numerical simulations. In this paper, we describe the modelling of ELMs and ELM control methods in ITER. The aim of this paper is not a complete review on the subject of ELM and ELM control modelling but rather to describe the current status and discuss open issues. [

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Section: Elm Control Methods: Pellet Pacingmentioning

confidence: 99%

Modelling of edge localised modes and edge localised mode control

et al. 2015

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“…The ablation model from Ref. [23] is used, where the number of atoms ablated per second for each shard is given by 4.12 • 10 16 (r s [m]) 1.33 (n e [m − 3]) 0.33 T 1.64 e . Here, r s denotes the shard radius.…”

Section: Simulation Setupmentioning

confidence: 99%

First predictive simulations for deuterium shattered pellet injection in ASDEX Upgrade

Hoelzl

Nardon

et al. 2020

Physics of Plasmas

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First simulations of deuterium shattered pellet injection (SPI) into an ASDEX Upgrade H-Mode plasma with the JOREK MHD code are presented. Resistivity is increased by one order of magnitude in most simulations to reduce computational costs and allow for extensive parameter scans. The effect of various physical parameters onto MHD activity and thermal quench (TQ) dynamics is studied and the influence of MHD onto ablation is shown. TQs are obtained quickly after injection in most simulations with a typical duration of 100 microseconds, which slows down at lower resistivity. Although the n=1 magnetic perturbation dominates in the simulations, toroidal harmonics up to n=10 contribute to stochastization and stochastic transport in the plasma core. The post-TQ density profile remains hollow for a few hundred microseconds. However, when flux surfaces re-form around the magnetic axis, the density has become monotonic again suggesting a beneficial behaviour for runaway electron avoidance/mitigation. With 10 21 atoms injected, the TQ is typically incomplete and triggered when the shards reach the q=2 rational surface. At a larger number of injected atoms, the TQ can set in even before the shards reach this surface. For low field side injection considered here, repeated formation of outward convection cells is observed in the ablation region reducing material assimilation. Responsible is a sudden rise of pressure in the high density cloud when the stochastic region expands further releasing heat from the hot core. After the TQ, strong sheared poloidal rotation is created by Maxwell stress, which contributes to re-formation of flux surfaces.

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“…To this end, we consider the strongly shielded NGS model in a Maxwellian plasma [6,7]. The principle of this model is simple, that is, we consider a given heat flux coming down along the field line towards the ablating fragment, the ablation rate of the fragment must be such that it maintains a certain line integrated neutral density along the field line to deplete the incoming heat flux so that the actual flux arriving at the fragment surface is negligible [7]. Hence for a given background electron temperature T e and density n e , the ablation rate for a spherical deuterium fragment with radius r p is…”

Section: The Governing Equations and The Assumptionsmentioning

confidence: 99%

“…The system of interest is described by the reduced non-linear MHD equations combined with a diffusive neutral species, solved by the 3D code JOREK [4,5]. The ablation of the fragments is modelled by the neutral gas shielding (NGS) model [6,7]. To better demonstrate the principle of the MHD destabilization mechanism caused by the SPI, simulations with equatorial injection will be carried out first.…”

Section: Introductionmentioning

confidence: 99%

3D non-linear MHD simulation of the MHD response and density increase as a result of shattered pellet injection

Nardon

Lehnen

et al. 2018

Nucl. Fusion

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The MHD response and the penetration of a deuterium shattered pellet into a JET plasma is investigated via the non-linear reduced MHD code JOREK with the neutral gas shielding (NGS) ablation model. The dominant MHD destabilizing mechanism by the injection is identified as the local helical cooling at each rational surface, as opposed to the global current profile contraction. Thus the injected fragments destabilize each rational surface as they pass through them. The injection penetration is found to be much better compared to MGI, with the convective transport caused by core MHD instabilities (e.g. 1/1 kink) contributing significantly to the core penetration. Moreover, the injection with realistic JET SPI system configurations is simulated in order to provide some insights into future operations, and the impact on the total assimilation and penetration depth of varying injection parameters such as the injection velocity or fineness of shattering is assessed. Further, the effect of changing the target equilibrium temperature or q profile on the assimilation and penetration is also investigated. Such analysis will form the basis of further investigation into a desirable configuration for the future SPI system in ITER.

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Role of shielding in modelling cryogenic deuterium pellet ablation

Cited by 18 publications

References 27 publications

Modelling of edge localised modes and edge localised mode control

Modelling of edge localised modes and edge localised mode control

First predictive simulations for deuterium shattered pellet injection in ASDEX Upgrade

3D non-linear MHD simulation of the MHD response and density increase as a result of shattered pellet injection

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