Finite-beta effects on the nonlinear evolution of the (m = 1; n = 1) mode in tokamaks
The stability and evolution of ISX-B-like plasmas are numerically studied using a reduced set of resistive magnetohydrodynamic (MHD) equations. For a sequence of equilibria stable to ideal modes, the n = 1 mode changes from a tearing branch to a pressure-driven branch as ..beta../sup p/ is increased. When this mode is unstable at low beta, it is just the (m = 1;n = 1) tearing mode. Higher n modes also become linearly unstable with increasing ..beta../sub p/; they are essentially pressure driven and have a ballooning character. For low values of beta the instability is best described as a ..beta../sub p/ distortion of the (m = 1;n = 1) tearing mode. This mode drives many other helicities through toroidal and nonlinear couplings. As ..beta../sub p/ is increased, the growth of the m = 1 island slows down in time, going from exponential to linear before reconnection occurs. If ..beta../sub p/ is large enough, the island saturates without reconnection. A broad spectrum of other modes, driven by the (m = 1;n = 1) instability, is produced. These results agree with some observed features of MHD activity in ISX-B.
- Research Organization:
- Oak Ridge National Lab., TN (USA)
- DOE Contract Number:
- W-7405-ENG-26
- OSTI ID:
- 5543335
- Report Number(s):
- ORNL/TM-8063; ON: DE82007124
- Country of Publication:
- United States
- Language:
- English
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MHD activity in the ISX-B tokamak: experimental results and theoretical interpretation
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Related Subjects
700107* -- Fusion Energy-- Plasma Research-- Instabilities
FLUID MECHANICS
HIGH-BETA PLASMA
HYDRODYNAMICS
INSTABILITY
ISX TOKAMAK
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC ISLANDS
MAGNETOHYDRODYNAMICS
MECHANICS
NONLINEAR PROBLEMS
PLASMA
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
TEARING INSTABILITY
THERMONUCLEAR REACTORS
TOKAMAK TYPE REACTORS