Non-resonant magnetic braking on JET and TEXTOR

Sun, Yuan; Liang, Y.; Shaing, K. C.; Liu, Y.Q.; Koslowski, H. R.; Jachmich, S.; Alper, B.; Alfier, A.; Asunta, O.; Buratti, P.; Corrigan, G.; Delabie, E.; Giroud, C.; Gryaznevich, M.; Harting, D.; Hender, T. C.; Nardon, E.; Naulin, V.; Parail, V.; Tala, T.; Wiegmann, C.; Wiesen, S.; Zhang, T.; Contributors, Jet‐Efda

doi:10.1088/0029-5515/52/8/083007

Cited by 50 publications

(58 citation statements)

References 49 publications

(128 reference statements)

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“…8, compensation of the n ¼ 3 error in NSTX increases the rotation and improves the stability to resistive wall modes at high beta. 15 JET experiments with n ¼ 1 perturbations have also shown good agreement with NTV predictions of braking, 80 account the calculated plasma response. In the case of an applied n ¼ 1 "error field" that is compensated by another n ¼ 1 coil set with a different geometry, non-resonant NTV braking by the uncompensated poloidal harmonics may decrease 63 or increase 63,81 depending on the geometry of the error field and compensation coils, and on the strength of the kink-resonant plasma response to the external fields.…”

Section: E Limitations Of Single-mode Modelssupporting

confidence: 64%

Magnetic control of magnetohydrodynamic instabilities in tokamaks

Strait

2014

Physics of Plasmas

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Externally applied, non-axisymmetric magnetic fields form the basis of several relatively simple and direct methods to control magnetohydrodynamic (MHD) instabilities in a tokamak, and most present and planned tokamaks now include a set of non-axisymmetric control coils for application of fields with low toroidal mode numbers. Non-axisymmetric applied fields are routinely used to compensate small asymmetries (δB/B∼10−3 to 10−4) of the nominally axisymmetric field, which otherwise can lead to instabilities through braking of plasma rotation and through direct stimulus of tearing modes or kink modes. This compensation may be feedback-controlled, based on the magnetic response of the plasma to the external fields. Non-axisymmetric fields are used for direct magnetic stabilization of the resistive wall mode—a kink instability with a growth rate slow enough that feedback control is practical. Saturated magnetic islands are also manipulated directly with non-axisymmetric fields, in order to unlock them from the wall and spin them to aid stabilization, or position them for suppression by localized current drive. Several recent scientific advances form the foundation of these developments in the control of instabilities. Most fundamental is the understanding that stable kink modes play a crucial role in the coupling of non-axisymmetric fields to the plasma, determining which field configurations couple most strongly, how the coupling depends on plasma conditions, and whether external asymmetries are amplified by the plasma. A major advance for the physics of high-beta plasmas (β = plasma pressure/magnetic field pressure) has been the understanding that drift-kinetic resonances can stabilize the resistive wall mode at pressures well above the ideal-MHD stability limit, but also that such discharges can be very sensitive to external asymmetries. The common physics of stable kink modes has brought significant unification to the topics of static error fields at low beta and resistive wall modes at high beta. These and other scientific advances, and their application to control of MHD instabilities, will be reviewed with emphasis on the most recent results and their applicability to ITER.

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Section: E Limitations Of Single-mode Modelssupporting

confidence: 64%

Magnetic control of magnetohydrodynamic instabilities in tokamaks

Strait

2014

Physics of Plasmas

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“…As shown in Figs. 5(f) and 5(g), the evaluated electron fluid perpendicular rotation, ω e⊥ , and E ×B one, ω E×B , near the pedestal top becomes very close to 0 after the application of RMPs because of rotation braking [30][31][32]. According to recent plasma response theories [11] and modelings [8,10,22], the resonant harmonics near the pedestal top, where ω e⊥ ≈ 0, may penetrate.…”

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confidence: 90%

Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak

et al. 2016

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Evidence of a nonlinear transition from mitigation to suppression of the edge localized mode (ELM) by using resonant magnetic perturbations (RMPs) in the EAST tokamak is presented. This is the first demonstration of ELM suppression with RMPs in slowly rotating plasmas with dominant radio-frequency wave heating. Changes of edge magnetic topology after the transition are indicated by a gradual phase shift in the plasma response field from a linear magneto hydro dynamics modeling result to a vacuum one and a sudden increase of three-dimensional particle flux to the divertor. The transition threshold depends on the spectrum of RMPs and plasma rotation as well as perturbation amplitude. This means that edge topological changes resulting from nonlinear plasma response plays a key role in the suppression of ELM with RMPs. DOI: 10.1103/PhysRevLett.117.115001 Magnetic reconnection and the resultant topological change play an important role in plasma dynamics in both laboratory and space plasma physics research. The formation of an edge stochastic magnetic field caused by resonant magnetic perturbations (RMPs) is believed to be the reason for the suppression of periodic crash events near the plasma edge known as the edge localized mode (ELM) observed in the DIII-D tokamak [1]. The ELM causes transient heat loads to the plasma facing components and may degrade them on the next generation fusion device like ITER [2]. The reduction of free energy in the edge pressure gradient and current because of field stochasticity moves the plasma into a stable regime against the ELM [3]. This successful experiment motivated ELM control using RMPs in many other tokamaks [4][5][6][7]. However, the plasma response effect usually shields the external applied RMPs and may significantly reduce the magnetic field stochasticity [8][9][10][11], which makes this mechanism questionable. Different from topological change, the linear peelinglike magneto hydro dynamics (MHD) response has been found to play an important role in ELM control [12][13][14]. Nonlinear plasma response has been observed in the JET totamak [15]. The possible formation of a magnetic island near the plasma edge [16] with a toroidal Fourier mode number n ¼ 1 during ELM suppression by using n ¼ 2 RMP has been recently observed on DIII-D [17]. However, the key difference between ELM suppression and mitigation and the different roles of linear and nonlinear plasma response on ELM suppression are still not clear.In this Letter, we report the first observation of full ELM suppression using low n RMPs in slowly rotating plasmas with dominant radio-frequency (rf) wave heating, which is potentially important for the application of this method for a future fusion device. This is the first observation of full ELM suppression using RMPs in the medium plasma collisionality regime in EAST, and it expands beyond the previous observations of ELM suppression on DIII-D [1,3] and KSTAR [7]. It is found that not only the formation of a magnetic island near the edge [17] but also a critical leve...

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“…The knowledge of various mechanisms and corresponding torques driving the toroidal plasma rotation is therefore crucial for operation control of these fusion experiments. Dedicated experimental studies at NSTX [1], DIII-D [2] and JET [3,4] have shown a strong dependence of the plasma rotation on non-axisymmetric magnetic perturbations (e.g., from coils for mitigation of edge localized modes (ELMs), from toroidal field (TF) coil ripple and from error fields). The observed changes in plasma rotation were in agreement with theoretical predictions for the torque produced by ‡ See http://www.euro-fusionscipub.org/mst1 non-resonant non-axisymmetric magnetic perturbations, which are based on analytical and semi-analytical approaches [5,6,7].…”

Section: Introductionmentioning

confidence: 99%

Effect of 3D magnetic perturbations on the plasma rotation in ASDEX Upgrade

Martitsch

Kasilov

Kernbichler

et al. 2016

Plasma Phys. Control. Fusion

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The toroidal torque due to the non-resonant interaction with external magnetic perturbations (TF ripple and perturbations from ELM mitigation coils) in ASDEX Upgrade is modelled with help of the NEO-2 and SFINCS codes and compared to semi-analytical models. It is shown that almost all non-axisymmetric transport regimes contributing to neoclassical toroidal viscosity (NTV) are realized within a single discharge at different radial positions. The NTV torque is obtained to be roughly a quarter of the NBI torque. This indicates the presence of other important momentum sources. The role of these momentum sources and possible integral torque balance measurements are briefly discussed.

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Non-resonant magnetic braking on JET and TEXTOR

Cited by 50 publications

References 49 publications

Magnetic control of magnetohydrodynamic instabilities in tokamaks

Magnetic control of magnetohydrodynamic instabilities in tokamaks

Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak

Effect of 3D magnetic perturbations on the plasma rotation in ASDEX Upgrade

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