Turbulent stabilization of the tearing mode in tokamak plasmas
The effect of turbulent electron diffusion from stochastic electron orbits on the stability of low-beta fluctuations is considered through the use of the normal stochastic approximation. A set of coupled, self-adjoint equations is derived for the fluctuation potentials phi-tilde and A/sub parallel/. Solutions to this set of equations describe both unstable finite-..beta.. drift waves when analyzed for high-m modes and the tearing mode when analyzed for low-m modes. For the tearing mode, it is shown that stability is obtained for sufficiently large values of the diffusion coefficient. Provided D/sub e/ approx. 1/n, this implies that a density threshold must be surpassed before the tearing mode is observed. Physically, turbulent electron diffusion prohibits the formation of a perturbed current within a finite region about the rational surface. At higher densities, the inclusion of a finite electrostatic potential phi-tilde gives an additional stabilizing term to the dispersion relation, which physically represents ion inertial effects. This ion inertial effect implies that, in the absence of diffusion, the tearing mode is stabilized for ion betas ..beta../sub i/ above some critical value.
- Research Organization:
- Plasma Fusion Center and Department of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
- OSTI ID:
- 6414734
- Journal Information:
- Phys. Fluids; (United States), Journal Name: Phys. Fluids; (United States) Vol. 29:1; ISSN PFLDA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
700107 -- Fusion Energy-- Plasma Research-- Instabilities
700108* -- Fusion Energy-- Plasma Research-- Wave Phenomena
CLOSED PLASMA DEVICES
ELECTRON DRIFT
EQUATIONS
FLUCTUATIONS
INSTABILITY
LOW-BETA PLASMA
ORBITS
PLASMA
PLASMA DISRUPTION
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
STABILIZATION
STOCHASTIC PROCESSES
TEARING INSTABILITY
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TURBULENCE
VARIATIONS