Some aspects of anomalous transport in tokamaks: stochastic magnetic fields, tearing modes and nonlinear ballooning instabilities

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:5673850

Cowley, S C

Various problems in the theory of anomalous transport in tokamaks are investigated. First, as an introduction a general overview of the current theories of confinement is presented. The q greater than one and less than two region is studied since this region is the thermally insulating region of the tokamak. It is shown that stochastic magnetic field transport is not important to the insulating region, because drift tearing modes are stable in this region. A discussion of flux surface breakup is given. It is demonstrated that, in a model with simplified electron dynamics, no breakup occurs. Tearing modes are shown to be stable in an equilibrium without islands and unstable in an equilibrium with islands. It is therefore proposed that tearing modes observed in experiments originate as equilibrium islands, which may be caused by nonaxisymmetry of the device. The nonlinear evolution of ideal ballooning modes in a simple model is investigated. The saturation mechanism is shown to be the flattening of the density gradient by the instability. One surprising feature of the evolution is the lack of mode coupling in the poloidal wavenumber spectrum. The resistive ballooning mode in this model is analyzed; it is shown that, well below ideal marginal stability, resistive modes cause high levels of transport.

• Research Organization: Princeton Univ., NJ (USA)
• OSTI ID: 5673850
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700101* -- Fusion Energy-- Plasma Research-- Confinement
Heating
& Production
700107 -- Fusion Energy-- Plasma Research-- Instabilities
BALLOONING INSTABILITY
CLOSED PLASMA DEVICES
CONFINEMENT
INSTABILITY
MAGNETIC FIELDS
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
STOCHASTIC PROCESSES
TEARING INSTABILITY
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TRANSPORT THEORY