Toroidal studies of sawtooth oscillations in tokamaks
Sawtooth oscillations in present-day tokamaks exhibit some features that can not be fully explained by the Kadomtsev model. In addition to double or compound sawteeth thought to be caused by multiple q=1 surfaces in the plasma, observed crash times are much faster than the predictions of the simple Kadomtsev reconnection process. Since the time scales involved appear to be too short for a resistive mode, Wesson has suggested that a pressure-driven ideal kink mode could be the responsible instability mechanism. This mode is always unstable in a cylinder for q{sub 0} < 1, and p' < 0, where q{sub 0} is the safety factor on axis, and p' is the radial pressure gradient, but was generally believed to be stabilized by toroidal effects for typical values of {beta}{sub pol}. However, studies of low-shear systems with q{approx}1 for a substantial portion of the plasma column indicate that n=1 mode is in fact unstable for {beta}{sub pol} {>=} 0. Numerical studies with their toroidal MHD code CTD, which solves the full, non-reduced, compressible, nonlinear MHD equations without any expansions in the inverse aspect ratio, indicate that this ideal instability can be triggered by small changes in the q-profile. Using CTD and including ohmic heating plus parallel and perpendicular transport, the author has recently produced periodic sawtooth oscillations where the plasma column does relax to a symmetric state after each crash. 6 refs., 2 figs.
- OSTI ID:
- 5705319
- Journal Information:
- IFS Newsletter; (USA), Vol. 6:2; ISSN 0306-0500
- Country of Publication:
- United States
- Language:
- English
Similar Records
Investigation of magnetic reconnection during a sawtooth crash in a high temperature tokamak
Sawtooth studies with [ital q]-profile measurements on TFTR (abstract)
Related Subjects
PLASMA MACROINSTABILITIES
NUMERICAL ANALYSIS
TOKAMAK DEVICES
ASPECT RATIO
C CODES
EIGENFUNCTIONS
GEOMETRY
JOULE HEATING
KINK INSTABILITY
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
PLASMA WAVES
PRESSURE GRADIENTS
THEORETICAL DATA
TOROIDAL CONFIGURATION
ANNULAR SPACE
CLOSED CONFIGURATIONS
CLOSED PLASMA DEVICES
COMPUTER CODES
CONFIGURATION
DATA
ELECTRIC HEATING
FLUID MECHANICS
FUNCTIONS
HEATING
HYDRODYNAMICS
INFORMATION
INSTABILITY
MAGNETIC FIELD CONFIGURATIONS
MATHEMATICS
MECHANICS
NUMERICAL DATA
PLASMA HEATING
PLASMA INSTABILITY
RESISTANCE HEATING
SPACE
THERMONUCLEAR DEVICES
700107* - Fusion Energy- Plasma Research- Instabilities