Pedestals and feedback in fusion-plasma relevant sandpile models

Bowie, Craig; Hole, Matthew

doi:10.1063/1.4998793

Cited by 3 publications

(11 citation statements)

References 38 publications

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“…An aspect of pellet pacing in fusion plasmas which is not captured in our model is that pellets for ELM mitigation are typically added at the top of the pedestal -pellets injected into the core are typically used for fuelling rather than pellet pacing. In future work, we propose to adapt a version of the sandpile model which incorporates a pedestal [26] to determine whether that will produce a better comparison with experimental results. Longer term, the extension to a 2D sandpile offers the possibility of capturing the radial-varying poloidal and toroidal twist of the magnetic field.…”

Section: Discussionmentioning

confidence: 99%

Sandpile modeling of pellet pacing in fusion plasmas

Bowie

Hole

2020

Phys. Rev. E

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Sandpile models have been used to provide simple phenomenological models without incorporating the detailed features of a fully featured model. The Chapman sandpile model (Chapman et al Physical Review Letters 86, 2814) has been used as an analogue for the behaviour of a plasma edge, with mass loss events being used as analogues for ELMs. In this work we modify the Chapman sandpile model by providing for both increased and intermittent driving. We show that the behaviour of the sandpile, when continuously fuelled at very high driving, can be determined analytically by a simple algorithm. We observe that the size of the largest avalanches is better reduced by increasing constant driving than by the intermittent introduction of 'pellets' of sand. Using the sandpile model as a reduced model of ELMing behaviour, we conject that ELM control in a fusion plasma may similarly prove more effective with increased total fuelling than with pellet addition.

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Section: Discussionmentioning

confidence: 99%

Sandpile modeling of pellet pacing in fusion plasmas

Bowie

Hole

2020

Phys. Rev. E

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“…The median waiting time, ∆t n , between MLEs is ∼135000, and ∆S max is ∼630000. The energy of the system [32]. For the sandpile chosen, the width of the pedestal, P w , is ∼15/500 cells, meaning that the top of the pedestal is located at n = 485.…”

Section: Dual-fuelled Sandpilementioning

confidence: 99%

“…The resulting pedestal was introduced as a proxy for the pedestal of a fusion plasma in a H-mode plasma [32]. The feedback loops were seen to be analagous to the feedback effects intrinsic to the H-mode pedestal in a fusion plasma [32]. It was suggested that reduction of feedback in the pedestal could result in ELM suppression within a H-mode plasma [32].…”

Section: Introductionmentioning

confidence: 99%

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Sandpile modelling of dual location fuelling in fusion plasmas

Bowie

Hole

2020

Plasma Phys. Control. Fusion

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We modify the Chapman sandpile model (Chapman et al Physical Review Letters 86, 2814) to form comparisons with pellet pacing, which is used to reduce or eliminate ELMs in a fusion plasma. We employ a variation of that model in which a pedestal with feedback is introduced (Bowie and Hole Phys. Plasmas 25, 012511 (2018)), which we further modify to provide for dual fuelling -sand is added both at the centre of the sandpile, and near the edge. We observe that when the additional sand is added at the top of the pedestal, MLEs are largely suppressed. While this suppression comes at a cost by way of reduction in total energy confinement, that reduction is lower than the reduction in MLE size. The trade-off between MLE suppression and reduction in energy confinement depends not only on the amount of extra sand, but also on its precise location relative to the top of the pedestal. We suggest that the approach of constant dual fuelling may be equally applicable to plasmas, and may suggest a strategy for ELM suppression in fusion plasmas. We observe that when the proposed amount of extra sand is added in 'pellets', using frequencies and amounts based on those proposed for ELM suppression for ITER, MLEs are similarly suppressed, although MLEs are not significantly suppressed when the pellet rate does not substantially exceed the MLE frequency. This suggests that pellet injection at the top of the pedestal at small pellet size and high frequency may represent a reasonable physical proxy for our proposed scheme. However, our results suggest that it is not the synchronisation of pellets to ELM frequencies which is the key factor for ELM suppression in this regime, but rather the introduction of additional fuelling at the top of the pedestal.

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“…Further, it is shown that the model has an analytic solution when the fuelling rate is high enough to satisfy two necessary conditions, both of which are identified here. Motivated by pellet injection systems in fusion plasmas, both the original sandpile model, and the modified versions developed here, are then employed to test whether adding 'pellets' of sand to the sandpile can reduce the size 2 C. Bowie [2] of the largest avalanches. Pellets of sand added at the core in the original model are found not to be effective in reducing the size of the largest avalanches.…”

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confidence: 99%

Pedestals and feedback in fusion-plasma relevant sandpile models

Cited by 3 publications

References 38 publications

Sandpile modeling of pellet pacing in fusion plasmas

Sandpile modeling of pellet pacing in fusion plasmas

Sandpile modelling of dual location fuelling in fusion plasmas

Applications of Sandpile Algorithms to Modelling Edge Localised Mode Phenomenology in Magnetically Confined Fusion Plasmas

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