First demonstration of rapid shutdown using neon shattered pellet injection for thermal quench mitigation on DIII-D

Commaux, N.; Shiraki, D.; Baylor, L. R.; Hollmann, E. M.; Eidietis, N. W.; Lasnier, C.J.; Moyer, R. A.; Jernigan, T.C.; Meitner, S. J.; Combs, S. K.; Foust, C. R.

doi:10.1088/0029-5515/56/4/046007

Cited by 103 publications

(76 citation statements)

References 18 publications

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“…the dissipation of the energy of fast electrons via Coulomb scattering by increasing the density, is considered to be the main solution. Several techniques directed to this end are extensively investigated in the tokamak community, for instance Massive Gas Injection (MGI) [15][16][17][18][19][20] and shattered pellet injection [21,22].…”

Section: Introductionmentioning

confidence: 99%

Runaway electron mitigation by 3D fields in the ASDEX-Upgrade experiment

Gobbin

Liu

et al. 2017

Plasma Phys. Control. Fusion

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Disruption-generated runaway electron (RE) beams represent a severe threat for tokamak plasma-facing components in high current devices like ITER, thus motivating the search of mitigation techniques. The application of 3D fields might aid this purpose and recently was investigated also in the ASDEX Upgrade experiment by using the internal active saddle coils (termed B-coils). Resonant magnetic perturbations (RMPs) with dominant toroidal mode number n = 1 have been applied by the B-coils, in a RE specific scenario, before and during disruptions, which are deliberately created via massive gas injection. The application of RMPs affects the electron temperature profile and seemingly changes the dynamics of the disruption; this results in a significantly reduced current and lifetime of the generated RE beam. A similar effect is observed also in the hard-X-ray (HXR) spectrum, associated to runaway electron emission, characterized by a partial decrease of the energy content below 1MeV when RMPs are applied. The strength of the observed effects strongly depends on the upper-to-lower B-coil phasing, i.e. on the poloidal spectrum of the applied RMPs, which has been reconstructed including the plasma response by the code MARS-F. A crude vacuum approximation fails in the interpretation of the experimental findings: despite the relatively low β (< 0.5%) of these discharges, a modest amplification (factor of 2) of the edge kink response occurs, which has to be considered to explain the observed suppression effects.PACS numbers:

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Section: Introductionmentioning

confidence: 99%

Runaway electron mitigation by 3D fields in the ASDEX-Upgrade experiment

Gobbin

Liu

et al. 2017

Plasma Phys. Control. Fusion

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“…Several impurity delivery methods have been studied, including gas injection, cryogenic pellet injection (PI), and shattered cryogenic pellet injection (SPI) [9]. Good progress has been made in understanding tokamak rapid shutdowns, with shattered neon pellet injection presently considered the most promising method for rapid shutdown of ITER [10].…”

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confidence: 99%

Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal

et al. 2019

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The first rapid tokamak discharge shutdown using dispersive core payload deposition with shell pellets has been achieved in the DIII-D tokamak. Shell pellets are being investigated as a possible new path toward achieving tokamak disruption mitigation with both low conducted wall heat loads and slow current quench. Conventional disruption mitigation injects radiating impurities into the outer edge of the tokamak plasma, which tends to result in poor impurity assimilation and creates a strong edge cooling and outward heat flow, thus requiring undesirable high-Z impurities to achieve low conducted heat loads. The shell pellet technique aims to produce a hollow temperature profile by using a thin, low-ablation shell surrounding a dispersive payload, giving greatly increased impurity ablation (and radiation) rate when the payload is released in the plasma core. This principle was demonstrated successfully using outer diameter = 3.6 mm, thickness = 40 μm diamond shells holding boron powder. The pellets caused rapid (< 10 ms) discharge shutdown with low conducted divertor heat fluence (~0.1 MJ/m 2 ). Confirmation of massive release of the boron powder payload into the plasma core was obtained spectroscopically. Some evidence for the formation of a hollow temperature profile during the shutdown was observed. These first results open a new avenue for disruption mitigation research, hopefully enabling development of highly effective methods of avoiding disruption wall damage in future reactor-scale tokamaks.

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“…Injection of large amounts of neutral gas has been demonstrated to be effective on today's tokamaks. However, this is insufficient for ITER, and a new technique based on firing shattered pellets of deuterium ice into the plasma is soon to be trialled on JET [22].…”

Section: Disruptionsmentioning

confidence: 99%

The impact of plasma physics on the timescale to a tokamak fusion power plant

Wilson

2019

Phil. Trans. R. Soc. A.

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Some of the main plasma physics challenges associated with achieving the conditions for commercial fusion power in tokamaks are reviewed. The confinement quality is considered to be a key factor, having an impact on the size of the reactor and exhaust power that has to be managed. Plasma eruptions can cause excessive erosion if not mitigated, with implications for maintenance and availability. Disruptions are a major concern—one large disruption could terminally damage the reactor so it is important to understand the loads they impart to the structure, and put in place appropriate protection and an effective avoidance/mitigation strategy. Managing the exhaust of heat and particles from the plasma is likely to be a significant issue, which may be mitigated if an advanced confinement regime can be identified. The advanced divertor structures that may be required to handle the exhaust have a significant impact on the design of a fusion reactor. Three strategies can be identified to take account of the physics challenges, with different implications for the timescale to fusion power: (1) a staged approach with the size of each step determined by our confidence in the predictive capability of our models; (2) a single, big step with contingency built into the design where possible to accommodate the uncertainty in physics predictions and (3) a single big step with optimistic physics assumptions and no contingency, accepting the increased financial and reputational risk that comes with such an approach. This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’.

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First demonstration of rapid shutdown using neon shattered pellet injection for thermal quench mitigation on DIII-D

Cited by 103 publications

References 18 publications

Runaway electron mitigation by 3D fields in the ASDEX-Upgrade experiment

Runaway electron mitigation by 3D fields in the ASDEX-Upgrade experiment

Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal

The impact of plasma physics on the timescale to a tokamak fusion power plant

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