Suppression and control of magnetic islands in toroidal plasmas

Journal Article · Thu Aug 01 04:00:00 EDT 1991 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.859595· OSTI ID:5660889

Hegna, C C; Bhattacharjee, A ^[1]; Nakamura, Y; Wakatani, M ^[2]

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1. Department of Applied Physics, Columbia University, New York, New York 10027 (USA)
2. Plasma Physics Laboratory, Kyoto University, Kyoto, (Japan)

Magnetic islands play an important role in determining the stability and confinement properties of toroidal plasmas. The nonlinear growth of magnetic islands can lead to major disruptions in tokamaks. In stellarators, which do not have a continuous symmetry, the formation of magnetic islands can set equilibrium beta limits. In the first part of this paper, a novel method is proposed for reducing drastically the size of {ital m}=2, {ital n}=1 islands in tokamaks by introducing a beamlet of energetic ions just outside the {ital q}=2 surface via parallel neutral-beam injection. A simple physical picture is given of the nonlinear stability of a tearing mode in the Rutherford regime in the presence of energetic ions. This physical picture is supported by a kinetic calculation in the long mean-free-path regime in which the effect of bootstrap currents and resistive interchanges are retained. Estimates show that the energy of the beamlet required for the suppression is a small fraction of that used for Ohmic or beam-heating of the background plasma. In the second part of the paper, an equilibrium beta limit is obtained for stellarators by calculating the island widths induced by finite plasma pressure; the widths are then constrained by the criterion of island overlap. The theory is applied to the Heliotron-E device (Nakamura {ital et} {ital al}., Phys. Fluids B {bold 2}, 2528 (1990)). It is shown that some aspects of the experimental observations on internal disruptions in Heliotron-E can be interpreted as signatures of the equilibrium beta limit.

• DOE Contract Number: FG02-86ER53222
• OSTI ID: 5660889
• Journal Information: Physics of Fluids B; (United States), Journal Name: Physics of Fluids B; (United States) Vol. 3:8; ISSN 0899-8221; ISSN PFBPE
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700107* -- Fusion Energy-- Plasma Research-- Instabilities
ANNULAR SPACE
BETA RATIO
BOOTSTRAP CURRENT
CLOSED CONFIGURATIONS
CLOSED PLASMA DEVICES
CONFIGURATION
CONFINEMENT
CURRENTS
ELECTRIC CURRENTS
EQUILIBRIUM
FLUTE INSTABILITY
INHIBITION
INSTABILITY
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC ISLANDS
MEAN FREE PATH
NONLINEAR PROBLEMS
PLASMA
PLASMA CONFINEMENT
PLASMA DISRUPTION
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PLASMA PRESSURE
SPACE
STELLARATORS
TEARING INSTABILITY
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TOROIDAL CONFIGURATION