A conceptual model of the magnetic topology and nonlinear dynamics of ELMs

Evans, T.E.; Yu, J. H.; Jakubowski, M.; Schmitz, O.; Watkins, J.G.; Moyer, R. A.

doi:10.1016/j.jnucmat.2009.01.209

Cited by 31 publications

(38 citation statements)

References 10 publications

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“…It has been found, that the wetted area of ELMs during non RMP H-mode discharge depends on ELM size in terms of the power deposited to the inner divertor leg. This is consistent with recently proposed mechanism for ELM behaviour given in [23], that temperature losses due to an initial peeling-ballooning instability, conducted along opened magnetic field lines due to a small pre-existing perturbation leads to a temperature difference at the end point of the field lines at the inner and outer divertor targets. The resulting thermo-electric currents are supposed to be capable to amplify explosively the existing magnetic field perturbation.…”

Section: Introdctionsupporting

confidence: 92%

Overview of the results on divertor heat loads in RMP controlled H-mode plasmas on DIII-D

et al. 2009

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Abstract. In this paper the manipulation of power deposition on divertor targets at DIII-D by application of resonant magnetic perturbations (RMPs) for suppression of large Type-I edge localized modes (ELMs) is analysed. We discuss the modification of the ELM characteristics by the RMP applied. It is shown, that the width of the deposition pattern in ELMy H-mode depends linearly on the ELM deposited energy, whereas in the RMP phase of the discharge those patterns are controlled by the externally induced magnetic perturbation. It was also found that the manipulation of heat transport due to application of small, edge resonant magnetic perturbations (RMP) depends on the plasma pedestal electron collisionality . We compare in this analysis RMP and no RMP phases with and without complete ELM suppression. At high , the heat flux during the ELM suppressed phase is of the same order as the inter-ELM and the no-RMP phase. However, below this collisionality value, a slight increase of the total power flux to the divertor is observed during the RMP phase. This is most likely caused by a more negative potential at the divertor surface due to hot electrons reaching the divertor surface from the pedestal area along perturbed, open field lines and/or the density pump out effect.

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Section: Introdctionsupporting

confidence: 92%

Overview of the results on divertor heat loads in RMP controlled H-mode plasmas on DIII-D

et al. 2009

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“…As described in Ref. 27, the pulse is conducted toward the target plates and, e.g., in the DIII-D tokamak, arrives at the outer target plate before it reaches the inner target plate. The heat pulse instantaneously increases the electron temperature T e on the outer target relative to the inner target plate.…”

Section: Model and Reference Statementioning

confidence: 99%

“…25 Based on a conceptual model 27,28 that describes the states of the edge plasma and the pedestal magnetic topology following the linear growth phase of a peeling-ballooning instability, a numerical model was implemented. 29 The model (and the numerical simulation discussed in this paper) does not extend beyond the initial nonlinear growth phase.…”

Section: Introductionmentioning

confidence: 99%

Effect of thermoelectric current splitting on the magnetic topology in DIII-D

2011

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An extended model is proposed to describe the magnetic topology during appearance of edge localized modes (ELMs). It is applied to an ELMing H-mode in a lower single null discharge at DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)]. The process of flux tube formation is discussed based on a previously proposed two-step model. Large currents, as found in measurements in DIII-D, are assumed running through newly formed large flux tubes. Two different realizations of the current distribution within the tubes are compared, namely a single filament in each tube and a scenario where the current in each tube is split into subfilaments. The latter scenario is shown to be the more realistic distribution because it leads to much better agreement with infrared camera observations. It is demonstrated that stripe patterns in the divertor heat flux produced by an ELM in the DIII-D tokamak can be reproduced numerically by taking into account the magnetic perturbation caused by the thermoelectric current subfilaments.

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“…ELM divertor traces [22][23][24][25] are also compatible with a homoclinic tangle. Both show multiple spiraling nonaxisymmetric stripes of plasma heating on the divertor surfaces.…”

Section: Introductionmentioning

confidence: 99%

Magnetic X-points, edge localized modes, and stochasticity

Sugiyama

Strauss

2010

Physics of Plasmas

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Edge localized modes ͑ELMs͒ near the boundary of a high temperature, magnetically confined toroidal plasma represent a new type of nonlinear magnetohydrodynamic ͑MHD͒ plasma instability that grows through a coherent plasma interaction with part of a chaotic magnetic field. Under perturbation, the freely moving magnetic boundary surface with an X-point splits into two different limiting asymptotic surfaces ͑manifolds͒, similar to the behavior of a hyperbolic saddle point in Hamiltonian dynamics. Numerical simulation using the extended MHD code M3D shows that field-aligned plasma instabilities, such as ballooning modes, can couple to the "unstable" manifold that forms helical, field-following lobes around the original surface. Large type I ELMs proceed in stages. Initially, a rapidly growing ballooning outburst involves the entire outboard side. Large plasma fingers grow well off the midplane, while low density regions penetrate deeply into the plasma. The magnetic field becomes superficially stochastic. A secondary inboard edge instability causes inboard plasma loss. The plasma gradually relaxes back toward axisymmetry, with diminishing cycles of edge instability. Poloidal rotation of the interior and edge plasma may be driven. The magnetic tangle constrains the early nonlinear ballooning, but may encourage the later inward penetration. Equilibrium toroidal rotation and two-fluid diamagnetic drifts have relatively small effects on a strong MHD instability. Intrinsic magnetic stochasticity may help explain the wide range of experimentally observed ELMs and ELM-free behavior in fusion plasmas, as well as properties of the H-mode and plasma edge.

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A conceptual model of the magnetic topology and nonlinear dynamics of ELMs

Cited by 31 publications

References 10 publications

Overview of the results on divertor heat loads in RMP controlled H-mode plasmas on DIII-D

Overview of the results on divertor heat loads in RMP controlled H-mode plasmas on DIII-D

Effect of thermoelectric current splitting on the magnetic topology in DIII-D

Magnetic X-points, edge localized modes, and stochasticity

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