3D field phase-space control in tokamak plasmas

A small relaxation of the axisymmetric magnetic field of a tokamak into a non-axisymmetric three-dimensional (3D) configuration can be effective to control magnetohydrodynamic instabilities, such as edge-localized modes. However, a major challenge to the concept of 3D tokamaks is that there are virtually unlimited possible choices for a 3D magnetic field, and most of them will only destabilize or degrade plasmas by symmetry breaking. Here, we demonstrate the phase-space visualization of the full 3D field-operating windows of a tokamak, which allows us to predict which configurations will maintain high confinement without magnetohydrodynamic instabilities in an entire region of plasmas. We test our approach at the Korean Superconducting Tokamak Advanced Research (KSTAR) facility, whose 3D coils with many degrees of freedom in the coil space make it unique for this purpose. Our experiments show that only a small subset of coil configurations can accomplish edge-localized mode suppression without terminating the discharge with core magnetohydrodynamic instabilities, as predicted by the perturbative 3D expansion of plasma equilibrium and the optimizing principle of local resonance. The prediction provided excellent guidance, implying that our method can substantially improve the efficiency and fidelity of the 3D optimization process in tokamaks.A theoretical and numerical approach, validated by experiments at the KSTAR facility, shows how magnetohydrodynamic instabilities in tokamak plasmas can be efficiently controlled by a small relaxation of the confining field into a 3D configuration.

[1]  A. Kolmogorov.  On conservation of conditionally periodic motions for a small change in Hamilton's function , 1954 .

[2]  V. Arnold.  SMALL DENOMINATORS AND PROBLEMS OF STABILITY OF MOTION IN CLASSICAL AND CELESTIAL MECHANICS , 1963 .

[3]  K. Shaing,et al.  Neoclassical flows and transport in nonaxisymmetric toroidal plasmas , 1983 .

[4]  R. Gruber,et al.  MHD-limits to plasma confinement , 1984 .

[5]  V. Tikhomirov.  On the Preservation of Conditionally Periodic Motions Under Small Variations of the Hamilton Function , 1991 .

[6]  T. C. Hender,et al.  The interaction of resonant magnetic perturbations with rotating plasmas , 1991 .

[7]  H. Zohm.  Edge localized modes (ELMs) , 1996 .

[8]  J. H. Schultz,et al.  The KSTAR project: An advanced steady state superconducting tokamak experiment , 2000 .

[9]  J. Connor,et al.  A review of models for ELMs , 1998 .

[10]  R. L. Haye,et al.  Error field mode studies on JET, COMPASS-D and DIII-D, and implications for ITER , 1999 .

[11]  A. Boozer.  Error field amplification and rotation damping in tokamak plasmas. , 2001, Physical review letters.

[12]  M E Fenstermacher,et al.  Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary. , 2004, Physical review letters.

[13]  Keith H. Burrell,et al.  Edge stability and transport control with resonant magnetic perturbations in collisionless tokamak plasmas , 2006 .

[14]  N Hawkes,et al.  Active control of type-I edge-localized modes with n=1 perturbation fields in the JET tokamak. , 2007, Physical review letters.

[15]  Maxim Umansky,et al.  Stability and dynamics of the edge pedestal in the low collisionality regime: physics mechanisms for steady-state ELM-free operation , 2007 .

[16]  A. Boozer,et al.  Computation of three-dimensional tokamak and spherical torus equilibria , 2007 .

[17]  K. Ikeda.  Progress in the ITER Physics Basis , 2007 .

[18]  Jong-Kyu Park,et al.  Control of asymmetric magnetic perturbations in tokamaks. , 2007, Physical review letters.

[19]  J. S. deGrassie,et al.  Effect of island overlap on edge localized mode suppression by resonant magnetic perturbations in DIII-D , 2008 .

[20]  J. S. deGrassie,et al.  RMP ELM suppression in DIII-D plasmas with ITER similar shapes and collisionalities , 2008 .

[21]  I. T. Chapman,et al.  Toroidal self-consistent modeling of drift kinetic effects on the resistive wall mode , 2008 .

[22]  Massimiliano Mattei,et al.  Principal physics developments evaluated in the ITER design review , 2009 .

[23]  A. Boozer,et al.  Nonambipolar transport by trapped particles in tokamaks. , 2009, Physical review letters.

[24]  T. Osborne,et al.  Validation of the linear ideal magnetohydrodynamic model of three-dimensional tokamak equilibria , 2010 .

[25]  Choong-Seock Chang,et al.  Plasma transport in stochastic magnetic field caused by vacuum resonant magnetic perturbations at diverted tokamak edge , 2010 .

[26]  M. Becoulet,et al.  Role of singular layers in the plasma response to resonant magnetic perturbations , 2011 .

[27]  R. L. Haye,et al.  Error Field Correction in DIII-D Ohmic Plasmas with Either Handedness , 2011 .

[28]  P T Lang,et al.  First observation of edge localized modes mitigation with resonant and nonresonant magnetic perturbations in ASDEX Upgrade. , 2011, Physical review letters.

[29]  Yueqiang Liu,et al.  Observation of lobes near the X point in resonant magnetic perturbation experiments on MAST. , 2012, Physical review letters.

[30]  R. Fitzpatrick.  Nonlinear error-field penetration in low density ohmically heated tokamak plasmas , 2012 .

[31]  R. L. Haye,et al.  Corrigendum: Error field correction in DIII-D Ohmic plasmas with either handedness , 2012 .

[32]  S. G. Lee,et al.  Suppression of edge localized modes in high-confinement KSTAR plasmas by nonaxisymmetric magnetic perturbations. , 2012, Physical review letters.

[33]  R. Waltz,et al.  Theory and simulation of quasilinear transport from external magnetic field perturbations in a DIII-D plasma , 2013 .

[34]  C. Hegna,et al.  Magnetic-flutter-induced pedestal plasma transport , 2013 .

[35]  E. J. Strait,et al.  The importance of matched poloidal spectra to error field correction in DIII-D , 2014 .

[36]  A. Loarte,et al.  Progress on the application of ELM control schemes to ITER scenarios from the non-active phase to DT operation , 2014 .

[37]  X. Garbet,et al.  Mechanism of edge localized mode mitigation by resonant magnetic perturbations. , 2014, Physical review letters.

[38]  T. Osborne,et al.  Pedestal bifurcation and resonant field penetration at the threshold of edge-localized mode suppression in the DIII-D Tokamak. , 2015, Physical review letters.

[39]  J. Park,et al.  Three-dimensional drift kinetic response of high-β plasmas in the DIII-D tokamak. , 2015, Physical review letters.

[40]  S. Haskey,et al.  Observation of a multimode plasma response and its relationship to density pumpout and edge-localized mode suppression. , 2015, Physical review letters.

[41]  Michio Okabayashi,et al.  Extremely low intrinsic non-axisymmetric field in KSTAR and its implications , 2015 .

[42]  A. M. Garofalo,et al.  Advances in the physics understanding of ELM suppression using resonant magnetic perturbations in DIII-D , 2015, Nuclear Fusion.

[43]  X. Ji,et al.  Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak. , 2016, Physical review letters.

[44]  S. G. Lee,et al.  Validation of Toroidal Rotation and Ion Temperature in KSTAR Plasmas , 2016 .

[45]  M. Lanctot.  Impact of toroidal and poloidal mode spectra on the control of non-axisymmetric fields in tokamaks , 2016 .

[46]  H. Yamada,et al.  Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR , 2016 .

[47]  Yueqiang Liu.  Comparative investigation of ELM control based on toroidal modelling of plasma response to RMP fields , 2016 .

[48]  Jae-Min Kwon,et al.  Nonlinear Interaction of Edge-Localized Modes and Turbulent Eddies in Toroidal Plasma under n=1 Magnetic Perturbation. , 2016, Physical review letters.

[49]  M. Becoulet,et al.  Non-linear modeling of the plasma response to RMPs in ASDEX Upgrade , 2017 .

[50]  N. Logan,et al.  Self-consistent perturbed equilibrium with neoclassical toroidal torque in tokamaks , 2017 .

[51]  A. Loarte,et al.  Enhanced understanding of non-axisymmetric intrinsic and controlled field impacts in tokamaks , 2017 .