Comparisons of linear and nonlinear plasma response models for non-axisymmetric perturbations

Journal Article · Wed May 15 00:00:00 EDT 2013 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4805087· OSTI ID:22228086

Turnbull, A. D.; Ferraro, N. M.; Lao, L. L.; Lanctot, M. J. ^[1]; Izzo, V. A. ^[2]; Lazarus, E. A.; Hirshman, S. P. ^[3]; Park, J. -K.; Lazerson, S.; Reiman, A. ^[4]; Cooper, W. A. ^[5]; Liu, Y. Q. ^[6]; Turco, F. ^[7]

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1. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
2. University of California-San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States)
3. Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831 (United States)
4. Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States)
5. Association Euratom-Confederation Suisse, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Federale de Lausanne, Lausanne (Switzerland)
6. Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB (United Kingdom)
7. Columbia University, 116th St and Broadway, New York, New York 10027 (United States)

With the installation of non-axisymmetric coil systems on major tokamaks for the purpose of studying the prospects of ELM-free operation, understanding the plasma response to the applied fields is a crucial issue. Application of different response models, using standard tools, to DIII-D discharges with applied non-axisymmetric fields from internal coils, is shown to yield qualitatively different results. The plasma response can be treated as an initial value problem, following the system dynamically from an initial unperturbed state, or from a nearby perturbed equilibrium approach, and using both linear and nonlinear models [A. D. Turnbull, Nucl. Fusion 52, 054016 (2012)]. Criteria are discussed under which each of the approaches can yield a valid response. In the DIII-D cases studied, these criteria show a breakdown in the linear theory despite the small 10{sup −3} relative magnitude of the applied magnetic field perturbations in this case. For nonlinear dynamical evolution simulations to reach a saturated nonlinear steady state, appropriate damping mechanisms need to be provided for each normal mode comprising the response. Other issues arise in the technical construction of perturbed flux surfaces from a displacement and from the presence of near nullspace normal modes. For the nearby equilibrium approach, in the absence of a full 3D equilibrium reconstruction with a controlled comparison, constraints relating the 2D system profiles to the final profiles in the 3D system also need to be imposed to assure accessibility. The magnetic helicity profile has been proposed as an appropriate input to a 3D equilibrium calculation and tests of this show the anticipated qualitative behavior.

• OSTI ID: 22228086
• Journal Information: Physics of Plasmas, Vol. 20, Issue 5; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
AXIAL SYMMETRY
COMPARATIVE EVALUATIONS
DAMPING
DISTURBANCES
DOUBLET-3 DEVICE
EDGE LOCALIZED MODES
ELECTRIC DISCHARGES
HELICITY
MAGNETIC FIELDS
MAGNETIC SURFACES
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
PLASMA
PLASMA CONFINEMENT
PLASMA SIMULATION
STEADY-STATE CONDITIONS