Sawteeth in the MST reversed field pinch

Technical Report · Sat Sep 01 04:00:00 EDT 1990

OSTI ID:5651889

Beckstead, J A

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 early pinch research. A discrete dynamo event 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 result of the inward diffusion of the plasma current density. This causes the plasma to become unstable to the m = 1 tearing modes. It has been shown theoretically that the nonlinear interaction of these modes can generate the reversed toroidal field in the RFP. This thesis is a study of the RFP sawtooth phenomenon on the MST RFP. This includes experimental observations as well as 1-D numerical simulations of the sawtooth rise-time. During the rise-time 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-time, 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 period of the sawteeth is observed to increase with the plasma current, as well as the magnetic Reynolds number, S.

• Research Organization: Wisconsin Univ., Madison, WI (USA)
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: FG02-85ER53198
• OSTI ID: 5651889
• Report Number(s): DOE/ER/53198-167; ON: DE91014288
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700103* -- Fusion Energy-- Plasma Research-- Kinetics
MAGNETIC FIELDS
OSCILLATIONS
PINCH EFFECT
PLASMA DENSITY
PLASMA DIAGNOSTICS
PLASMA SIMULATION
REVERSE-FIELD PINCH
SAWTOOTH OSCILLATIONS
SIMULATION