Three-dimensional distortions of the tokamak plasma boundary: boundary displacements in the presence of resonant magnetic perturbations

Chapman, I. T.; Bécoulet, M.; Bird, T.; Canik, J.; Cianciosa, M.; Cooper, W. A.; Evans, T.E.; Ferraro, N.M.; Fuchs, C.; Gryaznevich, M.; Gribov, Y.; Ham, Christopher; Hanson, J.M.; Huijsmans, Gta Guido; Kirk, A.; Lazerson, S.; Liang, Y.; Lupelli, I.; Moyer, R. A.; Nührenberg, C.; Orain, F.; Orlov, D. M.; Suttrop, W.; Yadykin, D.; Team, Diii-D; Team, Mast; Team, Nstx; Contributors, Efda‐Jet

doi:10.1088/0029-5515/54/8/083006

Cited by 49 publications

(52 citation statements)

References 63 publications

(98 reference statements)

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“…Although in many cases ideal MHD models predict the experimental plasma response well, in others a resistive model is needed. 39 Two-fluid modeling shows that the plasma response often screens error fields, 40 but error field penetration can occur when the electron fluid velocity at the rational surface is near zero. 41 Linear, resistive modeling in MARS-F, 42 and linear, non-ideal codes such as M3D-C1 41,43 allow the possibility to include nonideal effects such as rotation, resistivity, and two-fluid physics in modeling of error field screening and penetration.…”

Section: B Plasma Response and 3d Equilibriummentioning

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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Section: B Plasma Response and 3d Equilibriummentioning

confidence: 99%

Magnetic control of magnetohydrodynamic instabilities in tokamaks

Strait

2014

Physics of Plasmas

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“…The main conclusion of Ref. [24] is that the measured displacement of the low field side (LFS) midplane boundary depends approximately linearly on the applied resonant field predicted by vacuum field modeling [24]. But it was also observed that in some cases the vacuum modeling clearly underestimates the displacement due to stable ideal kink modes.…”

Section: Introductionmentioning

confidence: 98%

“…The 3D boundary distortion from external MPs has been extensively studied in various machines like ASDEX Upgrade [18,19], DIII-D [20,7,12], MAST [21], JET [22,23] and has been reviewed in Ref. [24]. The main conclusion of Ref.…”

Section: Introductionmentioning

confidence: 99%

Three dimensional boundary displacement due to stable ideal kink modes excited by external n = 2 magnetic perturbations

et al. 2017

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Abstract.In low-collisionality (ν ) scenarios exhibiting mitigation of edge localized modes (ELMs), stable ideal kink modes at the edge are excited by externally applied magnetic perturbation (MP)-fields. At ASDEX Upgrade these modes can cause three-dimensional (3D) boundary displacements up to the centimeter range. These displacements have been measured using toroidally localized high resolution diagnostics and rigidly rotating n = 2 MP-fields with various applied poloidal mode spectra. These measurements are compared to non-linear 3D ideal magnetohydrodynamics (MHD) equilibria calculated by VMEC. Comprehensive comparisons have been conducted, which consider for instance plasma movements due to the position control system, attenuation due to internal conductors and changes in the edge pressure profiles.VMEC accurately reproduces the amplitude of the displacement and its dependencies on the applied poloidal mode spectra. Quantitative agreement is found around the low field side (LFS) midplane. The response at the plasma top is qualitatively compared. The measured and predicted displacements at the plasma top maximize when the applied spectra is optimized for ELM-mitigation. The predictions from the vacuum modeling generally fails to describe the displacement at the LFS midplane as well as at the plasma top. When the applied mode spectra is set to maximize the displacement, VMEC and the measurements clearly surpass the ‡ matthias.willensdorfer@ipp.mpg.de arXiv:1702.03177v2 [physics.plasm-ph] 24 Jul 2017 3D boundary displacement due to stable ideal kink modes excited by external n=2 MPs 2 predictions from the vacuum modeling by a factor of four. Minor disagreements between VMEC and the measurements are discussed. This study underlines the importance of the stable ideal kink modes at the edge for the 3D boundary displacement in scenarios relevant for ELM-mitigation.

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“…Comparative studies in combination with MHD modeling indicate that the highest ELM frequency, the strongest density 'pump-out' and the strongest accompanying reduction in the edge pressure gradient are correlated with the coupling of the stable ideal kink modes to resonant components [7][8][9]. The resulting 3D boundary distortion can be many times larger than expected solely from the MP of the vacuum field [10,11]. It has been argued that the MPs modify the peeling-ballooning mode (PBM) stability by a change of edge bootstrap current due to the 'pump-out' [12] or equilibrium currents around rational surfaces [13].…”

mentioning

confidence: 96%

“…To model ξ r , we employ the 3D ideal MHD equilibrium code VMEC [21]. If no strong resistive MHD modes are active, VMEC is able to predict ξ r at the edge [10,17]. For details about its setup for ASDEX Upgrade discharges and the accuracy of VMEC in the presence of rational surfaces, we refer to Ref.…”

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confidence: 99%

Field-Line Localized Destabilization of Ballooning Modes in Three-Dimensional Tokamaks

et al. 2017

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Field-line localized ballooning modes have been observed at the edge of high confinement mode plasmas in ASDEX Upgrade with rotating 3D perturbations induced by an externally applied n ¼ 2 error field and during a moderate level of edge localized mode mitigation. The observed ballooning modes are localized to the field lines which experience one of the two zero crossings of the radial flux surface displacement during one rotation period. The localization of the ballooning modes agrees very well with the localization of the largest growth rates from infinite-n ideal ballooning stability calculations using a realistic 3D ideal magnetohydrodynamic equilibrium. This analysis predicts a lower stability with respect to the axisymmetric case. The primary mechanism for the local lower stability is the 3D distortion of the local magnetic shear.

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Three-dimensional distortions of the tokamak plasma boundary: boundary displacements in the presence of resonant magnetic perturbations

Cited by 49 publications

References 63 publications

Magnetic control of magnetohydrodynamic instabilities in tokamaks

Magnetic control of magnetohydrodynamic instabilities in tokamaks

Three dimensional boundary displacement due to stable ideal kink modes excited by external n = 2 magnetic perturbations

Field-Line Localized Destabilization of Ballooning Modes in Three-Dimensional Tokamaks

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