Resonant field amplification with feedback-stabilized regime in current driven resistive wall mode

Liu, Yueqiang; Chu, M. S.; In, Y.; Okabayashi, M.

doi:10.1063/1.3455540

Cited by 11 publications

(11 citation statements)

References 21 publications

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“…Another phenomenon pointed out in toroidal simulations (Fig.34, Fig.35 and [14]) is the amplification of the non-resonant harmonics due to the so-called resonant field amplification (RFA). Indeed, the amplitude of the magnetic perturbations in the core is larger with plasma response than in the vacuum modeling, due to the resonant response of a marginally stable kink mode [30]. At the edge, the amplitude of the resonant harmonics m = 10 − 11 (Fig.35) have the same order of magnitude in both vacuum and plasma cases.…”

Section: B Rmp Screening In Itermentioning

confidence: 75%

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: B Rmp Screening In Itermentioning

confidence: 75%

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

et al. 2013

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“…The structure of the current-driven RWM at the plasma surface is similar to what is expected for pressure-driven RWMs and thus could be used for investigation of the RWM interaction with external currents and walls [28]. At the same time the pressure-driven RWM could have quite a different eigenfunction in the plasma core with higher amplitudes of the internal components and a much richer poloidal spectrum [29]. Thus, the plasma-RWM interaction could be quite different for current-driven and pressure-driven RWMs in tokamaks.…”

Section: Rwm Interaction With External Magnetic Fieldsmentioning

confidence: 94%

Physics of resistive wall modes

Igochine

2012

Nucl. Fusion

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The advanced tokamak regime is a promising candidate for steady state tokamak operation which is desirable for a fusion reactor. This regime is characterized by a high bootstrap current fraction and a flat or reversed safety factor profile, which leads to operation close to the pressure limit. At this limit, an external kink mode becomes unstable. This external kink is converted into the slowly growing Resistive Wall Mode (RWM) by the presence of a conducting wall. Reduction of the growth rate allows one to act on the mode and to stabilize it. There are two main factors which determine the stability of the RWM. The first factor comes from external magnetic perturbations (error fields, resistive wall, feedback coils, etc). This part of RWM physics is the same for tokamaks and reverse field pinch (RFP)configurations. The physics of this interaction is relatively well understood and based on classical electrodynamics. The second ingredient of RWM physics is the interaction of the mode with plasma flow and fast particles. These interactions are particularly important for tokamaks, which have higher plasma flow and stronger trapped particle effects. The influence of the fast particles will also be increasingly more important in ITER and DEMO which will have a large fraction of fusion born alpha particles. These interactions have kinetic origins which make the computations challenging since not only particles influence the mode, but also the mode acts on the particles. Correct prediction of the "plasma-RWM" interaction is an important ingredient which has to be combined with external fields influence (resistive wall, error fields and feedback) to make reliable predictions for RWM behavior in tokamaks. All these issues are reviewed in this paper.2

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“…A number of zero-dimensional models for RWM feedback control have been presented in the literature, [121][122][123][124][125][126][127] and can be used to model a wide range of feedback system characteristics. A great deal of physical insight can be obtained from such models, and the simplified version presented here captures their essential features.…”

Section: B Modeling Of Rwm Feedback Controlmentioning

confidence: 99%

“…The same principle applies to the case where the RWM would be unstable without feedback; that is, increasing the gain also reduces the response of a feedback-stabilized plasma to an error field. 127 Sensors that measure the total perturbed radial field, as in this example, approach full compensation of the error field (H ! 0) as the gain increases.…”

Section: B Modeling Of Rwm Feedback Controlmentioning

confidence: 99%

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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Resonant field amplification with feedback-stabilized regime in current driven resistive wall mode

Cited by 11 publications

References 21 publications

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

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

Physics of resistive wall modes

Magnetic control of magnetohydrodynamic instabilities in tokamaks

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