Non-linear magnetohydrodynamic simulations of pellet triggered edge-localized modes in JET

Futatani, S.; Pamela, S.; Garzotti, L.; Huijsmans, G. T. A.; Hoelzl, M.; Frigione, D.; Lennholm, M.

doi:10.1088/1741-4326/ab56c7

Cited by 16 publications

(33 citation statements)

References 25 publications

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“…For all the pellet-triggered ELMs, the most energetic perturbation is the n = 1, followed by the next low n modes. Such result appears to be in agreement with experimental observations at JET [47] and is consistent with previous pellet-triggered ELM simulations with JOREK [27,34]. The energy spectrum of the pellet-triggered ELMs is broad since the pellet-induced helical perturbation is described by low-n modes, and it excites high-n ballooning modes (as described in section 4.2).…”

Section: Toroidal Mode Spectrumsupporting

confidence: 91%

Comparing spontaneous and pellet-triggered ELMs via non-linear extended MHD simulations

Cathey

Hoelzl

Futatani

et al. 2021

Plasma Phys. Control. Fusion

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Injecting frozen deuterium pellets into an ELMy H-mode plasma is a well established scheme for triggering edge localized modes (ELMs) before they naturally occur. This paper presents non-linear simulations of spontaneous type-I ELMs and pellet-triggered ELMs in ASDEX Upgrade performed with the extended MHD code JOREK. A thorough comparison of the non-linear dynamics of these events is provided. In particular, pellet-triggered ELMs are simulated by injecting deuterium pellets into different time points during the pedestal build-up described in A Cathey et al (2020 Nuclear Fusion 60 124007). Realistic ExB and diamagnetic background plasma flows as well as the time dependent bootstrap current evolution are included during the build-up to accurately capture the balance between stabilising and destabilising terms for the edge instabilities. Dependencies on the pellet size and injection times are studied. The spatio-temporal structures of the modes and the resulting divertor heat fluxes are compared in detail between spontaneous and triggered ELMs. We observe that the premature excitation of ELMs by means of pellet injection is caused by a helical perturbation described by a toroidal mode number of n = 1. In accordance with experimental observations, the pellet-triggered ELMs show reduced thermal energy losses and a narrower divertor wetted area with respect to spontaneous ELMs. The peak divertor energy fluence is seen to decrease when ELMs are triggered by pellets injected earlier during the pedestal build-up.

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Section: Toroidal Mode Spectrumsupporting

confidence: 91%

Comparing spontaneous and pellet-triggered ELMs via non-linear extended MHD simulations

Cathey

Hoelzl

Futatani

et al. 2021

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

show abstract

“…For all the pellet-triggered ELMs, the most energetic perturbation is the n = 1, followed by the next low n modes. Such observation appears to be in agreement with experimental observations at JET [46] and is consistent with previous pellet- triggered ELM simulations with JOREK [27,34]. The energy spectrum of the pellet-triggered ELMs is broad since the pellet-induced perturbation is described by low-n modes, and it excites high-n ballooning modes (as described in section 4.2).…”

Section: Toroidal Mode Spectrumsupporting

confidence: 91%

“…Further relevant simulations with JOREK include: spontaneous ELMs with realistic plasma background flows [20], RMP penetration [28,29], investigation of ELM-RMP interactions [30], Quiescent H-Mode [31], triggering of ELMs by vertical magnetic kicks [32], and a direct comparison of the divertor heat fluence caused by spontaneous ELMs to experimental scaling laws [21]. Pellet ELM triggering has also been studied with JOREK before, providing an explanation for the mechanism of pellet ELM triggering by a localised increase of the pressure in the re-heated ablation cloud and including experimental comparisons to JET and DIII-D [33,27,34]. An overview of ELM related non-linear MHD simulations worldwide is given in Ref.…”

Section: Relation To Previous Simulation Workmentioning

confidence: 99%

Comparing spontaneous and pellet-triggered ELMs via non-linear extended MHD simulations

Cathey,

Hoelzl,

Futatani

et al. 2021

Preprint

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Injecting frozen deuterium pellets into an ELMy Hmode plasma is a well established scheme for triggering edge localized modes (ELMs) before they naturally occur. Based on an ASDEX Upgrade Hmode plasma, this article presents a comparison of extended MHD simulations of spontaneous type-I ELMs and pellet-triggered ELMs allowing to study their non-linear dynamics in detail. In particular, pellet-triggered ELMs are simulated by injecting deuterium pellets into different time points during the pedestal build-up described in [A. Cathey et al. Nuclear Fusion 60, 124007 (2020)]. Realistic ExB and diamagnetic background plasma flows as well as the time dependent bootstrap current evolution are included during the build-up to capture the balance between stabilising and destabilising terms for the edge instabilities accurately. Dependencies on the pellet size and injection times are studied. The spatiotemporal structures of the modes and the resulting divertor heat fluxes are compared in detail between spontaneous and triggered ELMs. We observe that the premature excitation of ELMs by means of pellet injection is caused by a helical perturbation described by a toroidal mode number of n = 1. In accordance with experimental observations, the pellet-triggered ELMs show reduced thermal energy losses and narrower divertor wetted area with respect to spontaneous ELMs. The peak divertor energy fluency is seen to decrease when ELMs are triggered by pellets injected earlier during the pedestal build-up.

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“…The magnitude of the peak of the heat flux is similar between the spontaneous ELM and the pellet-triggered ELM, also consistent with the experiment. Furthermore, a toroidally asymmetric heat deposition onto the divertor targets related to pellet-triggered ELMs has been observed in the previous simulations for DIII-D and JET [24,29] consistent with experimental observations [31].…”

Section: Previous Simulationssupporting

confidence: 88%

“…[28]. Afterwards, results based on a spatio-temporally varying pellet ablation model were shown including experimental comparisons to DIII-D [24] and JET [29]. The pellet size requirement for ELM triggering in the stable plasma was found to be ∼ 70% of the minimum pedestal pressure which causes spontaneous ELM.…”

Section: Previous Simulationsmentioning

confidence: 99%

Transition from no-ELM response to pellet ELM triggering during pedestal build-up -- insights from extended MHD simulations

Futatani,

Cathey,

Hoelzl

et al. 2020

Preprint

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Pellet ELM triggering is a well established scheme for decreasing the time between two successive ELM crashes below its natural value. Reliable ELM pacing has been demonstrated experimentally in several devices increasing the ELM frequency considerably. However, it was also shown that the frequency cannot be increased arbitrarily due to a so-called lag-time. During this time after a preceding natural or triggered ELM crash, neither a natural ELM crash occurs nor the triggering of an ELM crash by pellet injection is possible. For this article, pellet ELM triggering simulations are advanced beyond previous studies in two ways. Firstly, realistic ExB and diamagnetic background flows are included. And secondly, the pellet is injected at different stages of the pedestal build-up. This allows to recover the lag-time for the first time in simulations and investigate it in detail. A series of non-linear extended MHD simulations is performed to investigate the plasma dynamics resulting from an injection at different time points during the pedestal build-up. The experimentally observed lag-time is qualitatively reproduced well. In particular, a sharp transition is observed between the regime where no ELMs can be triggered and the regime where pellet injection causes an ELM crash. Via variations of pellet parameters and injection time, the two regimes are studied and compared in detail revealing pronounced differences in the non-linear dynamics. The toroidal mode spectrum is significantly broader when an ELM crash is triggered enhancing the stochasticity and therefore also the losses of thermal energy along magnetic field lines. In the heat fluxes to the divertor targets, pronounced toroidal asymmetries are observed. In case of high injection velocities leading to deep penetration, also the excitation of core modes like the 2/1 neoclassical tearing mode is observed.

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Non-linear magnetohydrodynamic simulations of pellet triggered edge-localized modes in JET

Cited by 16 publications

References 25 publications

Comparing spontaneous and pellet-triggered ELMs via non-linear extended MHD simulations

Comparing spontaneous and pellet-triggered ELMs via non-linear extended MHD simulations

Comparing spontaneous and pellet-triggered ELMs via non-linear extended MHD simulations

Transition from no-ELM response to pellet ELM triggering during pedestal build-up -- insights from extended MHD simulations

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