Neoclassical tearing modes and their control

Journal Article · Mon May 15 00:00:00 EDT 2006 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2180747· OSTI ID:20783110

La Haye, R J ^[1]

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1. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)

A principal pressure limit in tokamaks is set by the onset of neoclassical tearing modes (NTMs), which are destabilized and maintained by helical perturbations to the pressure-gradient driven 'bootstrap' current. The resulting magnetic islands break up the magnetic surfaces that confine the plasma. The NTM is linearly stable but nonlinearly unstable, and generally requires a 'seed' to destabilize a metastable state. In the past decade, NTM physics has been studied and its effects identified as performance degrading in many tokamaks. The validation of NTM physics, suppressing the NTMs, and/or avoiding them altogether are areas of active study and considerable progress. Recent joint experiments give new insight into the underlying physics, seeding, and threshold scaling of NTMs. The physics scales toward increased NTM susceptibility in ITER, underlying the importance of both further study and development of control strategies. These strategies include regulation of 'sawteeth' to reduce seeding, using static 'bumpy' magnetic fields to interfere with the perturbed bootstrap current, and/or applying precisely located microwave power current drive at an island to stabilize (or avoid destabilization of) the NTM. Sustained stable operation without the highly deleterious m=2, n=1 island has been achieved at a pressure consistent with the no-wall n=1 ideal kink limit, by using electron cyclotron current drive at the q=2 rational surface, which is found by real-time accurate equilibrium reconstruction. This improved understanding of NTM physics and stabilization strategies will allow design of NTM control methods for future burning-plasma experiments like ITER.

• OSTI ID: 20783110
• Journal Information: Physics of Plasmas, Vol. 13, Issue 5; Other Information: DOI: 10.1063/1.2180747; (c) 2006 American Institute of Physics; 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
BOOTSTRAP CURRENT
DESIGN
DISTURBANCES
ECR CURRENT DRIVE
EQUILIBRIUM
ITER TOKAMAK
KINK INSTABILITY
MAGNETIC FIELDS
MAGNETIC ISLANDS
METASTABLE STATES
MICROWAVE RADIATION
MODE RATIONAL SURFACES
NEOCLASSICAL TRANSPORT THEORY
NONLINEAR PROBLEMS
PERFORMANCE
PLASMA
PLASMA CONFINEMENT
PLASMA PRESSURE
PRESSURE GRADIENTS
SAWTOOTH OSCILLATIONS
STABILIZATION
TEARING INSTABILITY