Relationship between locked modes and thermal quenches in DIII-D

Sweeney, R.; Choi, W.; Austin, M. E.; Brookman, M. W.; Izzo, V.A.; Knölker, M.; Haye, R.J. La; Leonard, A. W.; Strait, E. J.; Volpe, F.

doi:10.1088/1741-4326/aaaf0a

Cited by 43 publications

(57 citation statements)

References 45 publications

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“…Stochasticity is thought to be a possible reason for the thermal collapse and TQ in LM disruptions [17,18]. This work shows that island overlap forms field stochasticity when the island widths are large enough and that it makes the T e evolve much faster as shown in figures 11 and 12.…”

Section: Discussion and Summarymentioning

confidence: 64%

“…In contrast, this exhausted heat flux increases T e from the outside of the 2/1 island region to the plasma edge ( figure 5(b)). This discrepant change in T e on either side of a single LM is usually observed in minor disruptions [17,18]. At saturation, the central T e has decreased by about 20% and the edge T e returns to the initial profile since there is no additional exhaust heat flux from the inner region.…”

Section: Heat Transport With Single Helicity Ef Penetrationmentioning

confidence: 85%

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Fast and pervasive heat transport induced by multiple locked modes in DIII-D

et al. 2018

Nucl. Fusion

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This work presents the impact that multiple island chains co-existent across a tokamak plasma profile have on the heat transport and final temperature of that plasma. Numerical studies using the TM1 code show that error fields (EFs) with multiple poloidal components accelerate the core field penetration compared to pure m/n = 2/1 EF penetration (here m and n are the poloidal and toroidal mode numbers respectively). After field penetration, locked magnetic islands of m/n = 2/1, 3/1 and 4/1 flatten the temperature at the corresponding rational surfaces. The coexistence of these islands significantly enhances the plasma heat transport throughout a wide swath of plasma from the core 2/1 rational surface to plasma edge. The electron temperature T e profile from 2/1 to 4/1 rational surfaces can be nearly flattened even if there is no island overlap, and the temperature inside each island is determined by the boundary temperature at the outboard separatrix of the island. The resulting central T e decreases by more than 50%, in good agreement with experimental observations and much lower than modeling with only a single 2/1 locked island. Further comparisons of the T e profile between numerical modeling and DIII-D experiment indicates that the observed reduction in the edge temperature requires edge island overlap and stochasticity. Numerical scans reveal the T e profile decreases further when large EF amplitudes create larger islands, wider edge stochastic regions and secondary island structures. Scans of the relative phase between EF harmonics reveal that the 3/1 island width is most sensitive to the island phase and the central T e changes with the 3/1 island width. These results indicate that the coexistence of multiple LMs in tokamak plasmas deteriorate thermal confinement more than the sum of their isolated impacts would and that this may be responsible for the fast thermal quench observed prior to major disruptions.

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Section: Discussion and Summarymentioning

confidence: 64%

Section: Heat Transport With Single Helicity Ef Penetrationmentioning

confidence: 85%

Fast and pervasive heat transport induced by multiple locked modes in DIII-D

et al. 2018

Nucl. Fusion

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“…Plasmas which are not quenching that quickly might still develop a TQ a few milliseconds later. On the other hand, a plasma undergoing an incomplete TQ (like cases C or D), might recover in a way comparable to the plasma recovery from partial thermal quenches/minor disruptions [28]. Such a longer term evolution of the plasma is not investigated in the present study.…”

Section: Thermal Quenchmentioning

confidence: 91%

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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“…The initial edge cooling can result from pre-existing locked islands (Sweeney et al. 2018; Du et al. 2019), or from enhanced scrape off layer cross-field transport caused by reaching the density limit (Greenwald 2002), or by an influx of high- impurities that radiate the thermal energy through line emission (Izzo 2006; Sertoli et al.…”

Section: Disruption Dynamics and Loadingmentioning

confidence: 99%

“…In rare cases, the plasma can reheat and the CQ can be avoided (Sweeney et al. 2018; Reinke et al. 2019), indicating the reemergence of confining flux surfaces and the absence of a high impurity density.…”

Section: Disruption Dynamics and Loadingmentioning

confidence: 99%

MHD stability and disruptions in the SPARC tokamak

et al. 2020

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SPARC is being designed to operate with a normalized beta of $\beta _N=1.0$ , a normalized density of $n_G=0.37$ and a safety factor of $q_{95}\approx 3.4$ , providing a comfortable margin to their respective disruption limits. Further, a low beta poloidal $\beta _p=0.19$ at the safety factor $q=2$ surface reduces the drive for neoclassical tearing modes, which together with a frozen-in classically stable current profile might allow access to a robustly tearing-free operating space. Although the inherent stability is expected to reduce the frequency of disruptions, the disruption loading is comparable to and in some cases higher than that of ITER. The machine is being designed to withstand the predicted unmitigated axisymmetric halo current forces up to 50 MN and similarly large loads from eddy currents forced to flow poloidally in the vacuum vessel. Runaway electron (RE) simulations using GO+CODE show high flattop-to-RE current conversions in the absence of seed losses, although NIMROD modelling predicts losses of ${\sim }80$ %; self-consistent modelling is ongoing. A passive RE mitigation coil designed to drive stochastic RE losses is being considered and COMSOL modelling predicts peak normalized fields at the plasma of order $10^{-2}$ that rises linearly with a change in the plasma current. Massive material injection is planned to reduce the disruption loading. A data-driven approach to predict an oncoming disruption and trigger mitigation is discussed.

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Relationship between locked modes and thermal quenches in DIII-D

Cited by 43 publications

References 45 publications

Fast and pervasive heat transport induced by multiple locked modes in DIII-D

Fast and pervasive heat transport induced by multiple locked modes in DIII-D

First predictive simulations for deuterium shattered pellet injection in ASDEX Upgrade

MHD stability and disruptions in the SPARC tokamak

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