Improved feedback control of wall stabilized kink modes with different plasma–wall couplings and mode rotation

A new algorithm for feedback control of rotating, wall-stabilized kink modes in the High Beta Tokamak-Extended Pulse (HBT-EP) device maintains an accurate phase shift between the perturbation and the measured rotating mode through current control, with control power emphasizing fast rotation and phase jumps over fast amplitude changes. In HBT-EP, wall-stabilized kink modes become unstable above the ideal wall stability limit, and feedback suppression is aimed at delaying the onset of discharge disruption through reduction of the kink mode amplitude. Performance of the new feedback algorithm is tested under different experimental conditions, including variation of the plasma–wall coupling, insertion of a ferritic wall, changing mode rotation frequency over the range of 4–8 kHz using an internal biased electrode, and adjusting the feedback phase-angle to accelerate, amplify, or suppress the mode. We find the previously reported excitation of the slowly rotating mode at high feedback gain in HBT-EP is mitigated by the current control scheme. We also find good agreement between the observed and predicted changes to the mode rotation frequency and amplitude. When ferritic material is introduced, or the plasma–wall coupling becomes weaker as the walls are retracted from plasma, the feedback gain needs to be increased to achieve the same level of suppression. When mode rotation is slowed by a biased electrode, the feedback system still achieves mode suppression, and demonstrates wide bandwidth effectiveness.

[1]  M. Mauel,et al.  Design and installation of a ferromagnetic wall in tokamak geometry. , 2015, The Review of scientific instruments.

[2]  M. Mauel,et al.  Active and passive kink mode studies in a tokamak with a movable ferromagnetic walla) , 2015 .

[3]  E. Strait,et al.  Magnetic control of magnetohydrodynamic instabilities in tokamaks , 2015 .

[4]  A. Hyatt,et al.  Tokamak operation with safety factor q95 < 2 via control of MHD stability. , 2014, Physical review letters.

[5]  L. Marrelli,et al.  Self-organized 3D equilibrium formation and its feedback control in RFX-mod , 2014 .

[6]  V. Pustovitov,et al.  Ferromagnetic effects in the theory of slow and fast resistive wall modes in tokamaks , 2014 .

[7]  B. DeBono.  How Rotation affects Instabilities and the Plasma Response to Magnetic Perturbations in a Tokamak Plasma , 2014 .

[8]  M. Mauel,et al.  Measurement of 3D plasma response to external magnetic perturbations in the presence of a rotating external kink , 2013 .

[9]  L. L. Lao,et al.  Overview of physics results from the conclusive operation of the National Spherical Torus Experiment , 2013 .

[10]  M. Mauel,et al.  Adaptive control of rotating magnetic perturbations in HBT-EP using GPU processing , 2013 .

[11]  M. Mauel,et al.  Adaptive feedback control of rotating external kink modes in HBT-EP , 2013 .

[12]  M. Mauel,et al.  Multimode observations and 3D magnetic control of the boundary of a tokamak plasma , 2013 .

[13]  Gerald A. Navratil,et al.  High-speed, multi-input, multi-output control using GPU processing in the HBT-EP tokamak , 2012 .

[14]  M. Mauel,et al.  High resolution detection and excitation of resonant magnetic perturbations in a wall-stabilized tokamaka) , 2011 .

[15]  M. Mauel,et al.  The high beta tokamak-extended pulse magnetohydrodynamic mode control research program , 2011 .

[16]  R. Bell,et al.  Effect of collisionality on kinetic stability of the resistive wall mode. , 2011, Physical review letters.

[17]  Allen H. Boozer,et al.  Control of non-axisymmetric toroidal plasmas , 2010 .

[18]  Chris Llewellyn Smith,et al.  The path to fusion power† , 2007, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[19]  M. Mauel,et al.  A Kalman filter for feedback control of rotating external kink instabilities in the presence of noisea) , 2009 .

[20]  R. Fitzpatrick,et al.  Stability of the resistive wall mode in HBT-EP plasmas , 2006 .

[21]  K. Tritz,et al.  Active stabilization of the resistive-wall mode in high-beta, low-rotation plasmas. , 2006, Physical review letters.

[22]  D. A. Humphreys,et al.  Model-based dynamic resistive wall mode identification and feedback control in the DIII-D tokamak , 2006 .

[23]  J. Manickam,et al.  Control of the resistive wall mode with internal coils in the DIII–D tokamak , 2005 .

[24]  B. G. Penaflor,et al.  Plasma shape control on the National Spherical Torus Experiment (NSTX) using real-time equilibrium reconstruction , 2005 .

[25]  G. A. Navratil,et al.  Dynamics and control of resistive wall modes with magnetic feedback control coils: experiment and theory , 2005 .

[26]  M. Mauel,et al.  Suppression of rotating external kink instabilities using optimized mode control feedback , 2005 .

[27]  J. B. Lister,et al.  Feedback and rotational stabilization of resistive wall modes in ITER , 2005 .

[28]  R. Fitzpatrick.  A simple model of the resistive wall mode in tokamaks , 2002 .

[29]  E. D. Fredrickson,et al.  Resistive wall mode dynamics and active feedback control in DIII-D , 2001 .

[30]  Gerald A. Navratil,et al.  Modeling of active control of external magnetohydrodynamic instabilities , 2001 .

[31]  Michio Okabayashi,et al.  ACTIVE FEEDBACK STABILZATION OF THE RESISTIVE WALL MODE ON THE DIII-D DEVICE , 2000 .

[32]  Gerald A. Navratil,et al.  Suppression of resistive wall instabilities with distributed, independently controlled, active feedback coils , 2000 .

[33]  Allen H. Boozer,et al.  Feedback equations for the wall modes of a rotating plasma , 1999 .

[34]  J. Greene,et al.  Effect of toroidal plasma flow and flow shear on global magnetohydrodynamic MHD modes , 1995 .

[35]  J. Finn.  Resistive wall stabilization of kink and tearing modes , 1995 .

[36]  E. J. Strait,et al.  Stability of high beta tokamak plasmas , 1994 .

[37]  Bondeson,et al.  Stabilization of external modes in tokamaks by resistive walls and plasma rotation. , 1994, Physical review letters.

[38]  R. Fitzpatrick,et al.  Interaction of tearing modes with external structures in cylindrical geometry (plasma) , 1993 .