Active control of resistive wall modes in the large-aspect-ratio tokamak

Bondeson, A.; Liu, Yueqiang; Gregoratto, D.; Gribov, Y.; Pustovitov, V. D.

doi:10.1088/0029-5515/42/6/315

Cited by 54 publications

(91 citation statements)

References 23 publications

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“…(Of course, these responses may be modified and perhaps improved by the use of derivative gain and other techniques [8,151, but the simple model serves to illustrate the qualitative differences between detection methods.) More realistic numerical modeling with MARS [ 11,21,22] and VALEN [ 131 gives similar results. In the specific geometry of the DIII-D vacuum vessel, midplane control coils, and sensors, and assuming no plasma rotation, external radial field sensors are predicted to extend the beta limit by about 20% of the difference between the no-wall limit and the ideal-wall limit.…”

Section: Stabilization By Feedback Controlmentioning

confidence: 77%

Resistive wall stabilization of high-beta plasmas in DIII–D

Strait

Bialek

Bogatu³

et al. 2003

Nucl. Fusion

116

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Abstract. Recent DIII-D experiments show that ideal kink modes can be stabilized at high beta by a resistive wall, with sufficient plasma rotation. However, the resonant response by a marginally stable resistive wall mode to static magnetic field asymmetries can lead to strong damping of the rotation. Careful reduction of such asymmetries has allowed plasmas with beta well above the ideal MHD nowall limit, and approaching the ideal-wall limit, to be sustained for durations exceeding one second. Feedback control can improve plasma stability by direct stabilization of the resistive wall mode or by reducing magnetic field asymmetry. Assisted by plasma rotation, direct feedback control of resistive wall modes with growth rates more than 5 times faster than the characteristic wall time has been observed. These results open a new regime of tokamak operation above the free-boundary stability limit, accessible by a combination of plasma rotation and feedback control.

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Section: Stabilization By Feedback Controlmentioning

confidence: 77%

Resistive wall stabilization of high-beta plasmas in DIII–D

Strait

Bialek

Bogatu³

et al. 2003

Nucl. Fusion

116

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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%

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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“…13 Feedback control of the RWM has been carried out in DIII-D, [14][15][16][17][18] HBT-EP ͑High Beta Tokamak-Extended Pulse͒, 19 as well as in EXTRAP T2R reversed field pinch, 20,21 with very encouraging results. Theoretically, a circuit model, 22 cylindrical models, [23][24][25][26][27] and toroidal models [28][29][30][31][32][33] have been developed to study feedback stabilization of the RWM. One of the key understandings is that sensors, measuring the poloidal component of the magnetic field perturbations just inside the vacuum vessel, gives superior control performance to sensors measuring the radial fields.…”

Section: Introductionmentioning

confidence: 99%

Modeling of resistive wall mode and its control in experiments and ITER

Liu

Chu²,

Garofalo³

et al. 2006

Physics of Plasmas

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Active control of the resistive wall mode (RWM) for DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] plasmas is studied using the MARS-F code [Y. Q. Liu, et al., Phys. Plasmas 7, 3681 (2000)]. Control optimization shows that the mode can be stabilized up to the ideal wall beta limit, using the internal control coils (I-coils) and poloidal sensors located at the outboard midplane, in combination with an ideal amplifier. With the present DIII-D power supply model, the stabilization is achieved up to 70% of the range between no-wall and ideal-wall limits. Reasonably good quantitative agreement is achieved between MARS-F simulations and experiments on DIII-D and JET (Joint European Torus) [P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985)] on critical rotation for the mode stabilization. Dynamics of rotationally stabilized plasmas is well described by a single mode approximation; whilst a strongly unstable plasma requires a multiple mode description. For ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], the MARS-F simulations show the plasma rotation may not provide a robust mechanism for the RWM stabilization in the advanced scenario. With the assumption of ideal amplifiers, and using optimally tuned controllers and sensor signals, the present feedback coil design in ITER allows stabilization of the n=1 RWM for plasma pressures up to 80% of the range between the no-wall and ideal-wall limits.

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Active control of resistive wall modes in the large-aspect-ratio tokamak

Cited by 54 publications

References 23 publications

Resistive wall stabilization of high-beta plasmas in DIII–D

Resistive wall stabilization of high-beta plasmas in DIII–D

Magnetic control of magnetohydrodynamic instabilities in tokamaks

Modeling of resistive wall mode and its control in experiments and ITER

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