Simulation of pellet ELM triggering in low-collisionality, ITER-like discharges

Wingen, A.; Lyons, Brendan; Wilcox, R.S.; Baylor, L. R.; Ferraro, N.M.; Jardin, S.C.; Shiraki, D.

doi:10.1088/1741-4326/ac34d7

Cited by 2 publications

(8 citation statements)

References 36 publications

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“…The most unstable mode can be found near n = 23. In the linear workflow, see [11], n = 9 was found to be the most unstable mode for this case, which can still be seen in the time average here as well by the increased growth rate around n = 9 compared to n = 7 and n = 11. However, during the time evolution, which is only captured by the nonlinear workflow, high-n ballooning modes grow significantly stronger, resulting in the large growth rates for n > 20.…”

Section: Finding a Threshold For Pellet Elm Triggeringsupporting

confidence: 51%

“…Note that in the linear workflow the perturbation is fixed and profiles do not evolve. More details are found in [11] and appendix. In all cases, thresholds simulated by M3D-C1 successfully separate (within error bars) events where a pellet fails to trigger an ELM in the experiment from events where another pellet successfully triggers an ELM.…”

Section: Diii-d Experimental Threshold and Model Validationmentioning

confidence: 99%

“…Pellet size thresholds for ELM triggering in a plasma with peeling limited pedestal were simulated for the first time [11] using the M3D-C1 code [12]. A linear workflow was conceived and applied to DIII-D, showing how thresholds vary with plasma conditions and injection locations.…”

Section: Introductionmentioning

confidence: 99%

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Prediction of pellet mass thresholds for ELM triggering in low-collisionality, ITER-like discharges

Wingen,

Wilcox,

Lyons

et al. 2024

Nucl. Fusion

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In ITER, pellets are calculated to require more than 8 times the mass than currently planned to reliably trigger ELMs. Unmitigated heat flux impulses from edge-localized modes (ELMs) are intolerable in ITER at full power and current. Therefore, ITER operation relies on multiple approaches to control ELM heat fluxes. One method is pellet ELM pacing to instigate small rapid ELMs with low heat flux. Predicting the performance of pellet pacing is critical for ITER, which is expected to operate in a regime with a low-collisionality, peeling-limited pedestal. However, to trigger ELMs the local pressure increase in the expanding pellet cloud pushes the equilibrium over the ballooning stability limit. In this work, linear and nonlinear M3D-C1 simulations are used to predict pellet mass thresholds in DIII-D discharges and ITER scenarios with peeling-limited pedestals. It is found that the distance of the equilibrium's operational point from the ballooning branch of the pedestal stability boundary strongly changes thresholds. Linear M3D-C1 simulations find a strong dependence of the pellet mass threshold on the poloidal injection location for ITER's 15 MA, Q=10 scenario. The required pellet mass at the planned injection locations is 8 to 17 times larger than currently considered. However, such linear simulations do not include pellet ablation physics or time evolution of density and temperature. A new scheme of 2D nonlinear simulations, coupled with linear stability analysis at various steps throughout the nonlinear time evolution, was developed to include such physics and improve on the linear results. These new nonlinear-to-linear simulations confirm previous findings. This result suggests that pellet ELM triggering in ITER could require pellets much larger than those currently planned, which makes ELM-pacing operationally challenging. On the other hand, fueling pellets injected from the high-field side will likely not unintentionally trigger ELMs in an otherwise ELM-stable plasma.

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Section: Finding a Threshold For Pellet Elm Triggeringsupporting

confidence: 51%

Section: Diii-d Experimental Threshold and Model Validationmentioning

confidence: 99%

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Prediction of pellet mass thresholds for ELM triggering in low-collisionality, ITER-like discharges

Wingen,

Wilcox,

Lyons

et al. 2024

Nucl. Fusion

Self Cite

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“…Therefore modeling of the pellet ELM triggering process and integrated ELM pacing scenarios will be increasingly important to understand how this process will extrapolate to next-step devices. The JOREK code has been used to estimate the distribution of ELM heat fluxes using non-linear MHD calculations [30,31], and the M3D-C1 code has been used to estimate the necessary pellet size to trigger an ELM in low collisionality, peeling-limited plasma conditions [39]. Detailed integrated simulations of pellet ELM-paced scenarios have demonstrated a reduction in ELM energy loss for pellet frequencies sufficiently faster than the natural ELM frequencies in JT-60SA [49], and have made estimates of the core performance enabled by pellet pacing in ITER under various assumptions [50].…”

Section: Discussionmentioning

confidence: 99%

“…When a pellet is injected, the stability determination becomes three dimensional, which is not handled properly by the ELITE code, and changes on a fast timescale relative to diagnostic frequencies. The naive expectation is that the operating point of the flux tube with an ablating pellet would shift to the right in figure 5(c), toward higher pressure gradients, but the high fidelity modeling of these dynamics is left to other studies [39].…”

Section: Pedestal Stability Analysismentioning

confidence: 99%

Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D

Wilcox¹,

Baylor²,

Bortolon³

et al. 2021

Nucl. Fusion

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Edge localized modes (ELMs) are triggered using deuterium pellets injected into plasmas with ITER-relevant low collisionality pedestals, and the resulting peak ELM energy fluence is reduced by approximately 25-50% relative to natural ELMs destabilized at similar pedestal pressures. Cryogenically frozen deuterium pellets are injected from the low-field side of the DIII-D tokamak at frequencies lower than the natural ELM frequency, and heat flux is measured by infrared cameras. Ideal MHD pedestal stability calculations show that without pellet injection, these low collisionality pedestals were limited by their current density (peeling-limited) rather than their pressure gradient (ballooning-limited). ELM triggering success correlates strongly with pellet mass, consistent with the theory that a large pressure perturbation is required to trigger an ELM in low collisionality discharges that are far from the ballooning stability boundary. For sufficiently large pellets, both instantaneous and time-integrated ELM energy deposition measured by infrared cameras is reduced with respect to naturally occurring ELMs at the inner strike point, which is the position where it is largest for natural ELMs. Energy fluence at the outer strike point is less effected. Cameras observing both heat flux and D-alpha emission often find significant toroidally asymmetric striations in the outboard far scrape-off layer resulting from ELMs that are triggered by pellets. Toroidal asymmetries at the inner strike point are similar between natural and pellet-triggered ELMs, suggesting that the reduction in peak heat flux and total fluence at that location is robust for the conditions reported here.

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Simulation of pellet ELM triggering in low-collisionality, ITER-like discharges

Cited by 2 publications

References 36 publications

Prediction of pellet mass thresholds for ELM triggering in low-collisionality, ITER-like discharges

Prediction of pellet mass thresholds for ELM triggering in low-collisionality, ITER-like discharges

Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D

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