Sawteeth in MST reversed-field pinch
A dynamo mechanism has been used in astrophysics to explain the self-generation of the magnetic fields observed throughout the universe. This same type of phenomenon is believed to occur in the reversed field pinch (RFP) plasmas. The RFP dynamo has been a major theoretical and experimental investigation since the first observations of the self-reversal process in the early pinch research. A discrete dynamo even has been observed in the experimental RFP plasmas; this event is termed the RFP sawtooth. This phenomenon is similar to the sawtooth phenomenon observed in tokamak plasmas, but the two events differ in many respects. Both events are a results of the inward diffusion of the plasma current density. This radial diffusion peaks the current profiles causing the plasma to become unstable to the m = 1 tearing modes. In the tokamak, it is the (m,n) = (1,1) mode while the RFP, several m = 1 modes can become unstable with the n spectra dominated by the {approx} 2R/a mode. It has been shown theoretically that the nonlinear interaction of these modes can generate the reversed toroidal field in the RFP. During the rise-phase of the sawtooth, the plasma is undergoing a purely diffusive process - no dynamo is occurring during this phase. The dynamo only occurs during the sawtooth crash. During the rise-phase, the m = 1 modes are observed to grow, and nonlinear interactions are observed prior to the sawtooth crash. At the time of the crash, many of the plasma profiles are flattened; these include the current density, the plasma temperature and the plasma density. The flattening of these profiles restabilizes the plasma to the m = 1 tearing modes. This thesis is a study of the RFP sawtooth phenomenon on the MST RFP.
- Research Organization:
- Wisconsin Univ., Madison, WI (United States)
- OSTI ID:
- 5314091
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
REVERSE-FIELD PINCH
SAWTOOTH OSCILLATIONS
COMPUTERIZED SIMULATION
CURRENT DENSITY
MAGNETIC FIELDS
NONLINEAR PROBLEMS
PLASMA DENSITY
PLASMA DRIFT
TEARING INSTABILITY
INSTABILITY
OSCILLATIONS
PINCH EFFECT
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
SIMULATION
700340* - Plasma Waves
Oscillations
& Instabilities- (1992-)