Nonlinear stability of magnetic islands in a rotating helical plasma

Nishimura, S.; Toda, S.; Yagi, M.; Narushima, Y.

doi:10.1063/1.4773041

Cited by 10 publications

(27 citation statements)

References 49 publications

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“…That way, the magnetic perturbation gradually penetrates inside the plasma, which self-consistently adapts in the process. Also this method avoids possible problems with hysteresis effects that could occur if the simulation was started with a fully penetrated magnetic perturbation [23]: the bifurcation from a fully penetrated state to a partially penetrated state might lead to a different plasma response.…”

Section: Physical Modelmentioning

confidence: 99%

Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations

et al. 2013

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The interaction of static Resonant Magnetic Perturbations (RMPs) with the plasma flows is modeled in toroidal geometry, using the non-linear resistive MHD code JOREK, which includes the X-point and the Scrape-Off-Layer. Two-fluid diamagnetic effects, the neoclassical poloidal friction and a source of toroidal rotation are introduced in the model to describe realistic plasma flows. RMP penetration is studied taking self-consistently into account the effects of these flows and the radial electric field evolution. JET-like, MAST and ITER parameters are used in modeling. For JET-like parameters, three regimes of plasma response are found depending on the plasma resistivity and the diamagnetic rotation: at high resistivity and slow rotation, the islands generated by the RMPs at the edge resonant surfaces rotate in the ion diamagnetic direction and their size oscillates. At faster rotation, the generated islands are static and are more screened by the plasma. An intermediate regime with static islands which slightly oscillate is found at lower resistivity. In ITER simulations, the RMPs generate static islands, which forms an ergodic layer at the very edge (ψ ≥ 0.96) characterized by lobe structures near the X-point and results in a small strike point splitting on the divertor targets. In MAST DND geometry, lobes are also found near the X-point and the 3D-deformation of the density and temperature profiles is observed.

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Section: Physical Modelmentioning

confidence: 99%

Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations

et al. 2013

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“…29. In the present study, we focus on an influence of the effective helical ripple rate on the nonlinear stability of RMP-induced magnetic islands.…”

Section: Boundary Condition Of the Poloidal Flow Velocity Ismentioning

confidence: 99%

“…In the following, model equations in the previous work 29 are reviewed, where misprints involved in Ref. 29 are corrected.…”

Section: A Basic Modelmentioning

confidence: 99%

“…By analogy with tokamaks, it has been attempted to explain the self-healing by the shielding effects of helical ripple-induced neoclassical flows. [28][29][30][31][32] Such mechanism works well in explaining characteristics of the self-healing in the LHD: bifurcation and hysteresis characteristics, time scales of transitions faster than those of equilibria, and simultaneous changes of poloidal flow profiles.…”

mentioning

confidence: 95%

“…This point is distinct from a fact that curvature effects due to magnetic axis shifts are of secondary importance for the torque balance. 29 In this study, we clarify how the effective helical ripple rate affects the self-healing mechanism. A magnetic axis shift is associated with multi-helicity characteristics of background magnetic fields, which has not been considered in previous theories for the self-healing.…”

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confidence: 99%

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Roles of effective helical ripple rates in nonlinear stability of externally induced magnetic islands

Nishimura

2015

Physics of Plasmas

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Magnetic islands are externally produced by resonant magnetic perturbations (RMPs) in toroidal plasmas. Spontaneous annihilation of RMP-induced magnetic islands called self-healing has been observed in helical systems. A possible mechanism of the self-healing is shielding of RMP penetration by helical ripple-induced neoclassical flows, which give rise to neoclassical viscous torques. In this study, effective helical ripple rates in multi-helicity helical systems are revisited, and a multihelicity effect on the self-healing is investigated, based on a theoretical model of rotating magnetic islands. It is confirmed that effective helical ripple rates are sensitive to magnetic axis positions. It is newly found that self-healing thresholds also strongly depend on magnetic axis positions, which is due to dependence of neoclassical viscous torques on effective helical ripple rates. V C 2015 AIP Publishing LLC. [http://dx.

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Plasma-induced magnetic responses during nonlinear dynamics of magnetic islands due to resonant magnetic perturbations

Nishimura

2014

Physics of Plasmas

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Resonant magnetic perturbations (RMPs) produce magnetic islands in toroidal plasmas. Self-healing (annihilation) of RMP-induced magnetic islands has been observed in helical systems, where a possible mechanism of the self-healing is shielding of RMP penetration by plasma flows, which is well known in tokamaks. Thus, fundamental physics of RMP shielding is commonly investigated in both tokamaks and helical systems. In order to check this mechanism, detailed informations of magnetic island phases are necessary. In experiments, measurement of radial magnetic responses is relatively easy. In this study, based on a theoretical model of rotating magnetic islands, behavior of radial magnetic fields during the self-healing is investigated. It is confirmed that flips of radial magnetic fields are typically observed during the self-healing. Such behavior of radial magnetic responses is also observed in LHD experiments.

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Nonlinear stability of magnetic islands in a rotating helical plasma

Cited by 10 publications

References 49 publications

Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations

Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations

Roles of effective helical ripple rates in nonlinear stability of externally induced magnetic islands

Plasma-induced magnetic responses during nonlinear dynamics of magnetic islands due to resonant magnetic perturbations

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