Disruptive instabilities in a poloidal divertor tokamak

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1984

OSTI ID:5055922

Osborne, T H

Relaxation oscillations in the plasma pressure, that appear as sawtooth oscillations on collimated soft x-ray detectors, are observed in all Tokapole II discharges. These instabilities exhibit characteristics which are unexpected from the usual picture of disruptive instabilities in polidal divertor tokamaks without a close fitting conducting shell. Tokamak discharges are observed with safety factor, q, as low as 0.5 over most of the current channel within the poloidal divertor separatrix. These discharges show sawtooth oscillations, but magnetic probe measurements indicate the central q values, instead of relaxing to 1, remain nearly fixed. The q = 1 surface for this case is very near the separatrix, and there is a small oscillation in q near the q = 1 surface which is time correlated with the sawtooth oscillations. The observation of discharges which maintain q < 1 is at variance with the usual resistive MHD theory of sawtooth oscillations. These discharges have poor energy confinement ({tau}{sub E} < 50 {mu}s). As the plasma current is increased with the toroidal magnetic field constant, the giant sawteeth become less regular. At large enough plasma current, only small sawtooth oscillations are observed, these show an m = n = 1 precursor in the soft x-ray. An MHD equilibrium code predicts that the q = 2 surface is very near the divertor separatrix for this case. This suggests that the m = 2, n = 1 disruption may be eliminated by the proximity of the q = 2 surface and the separatrix. These discharges have good energy confinement time ({tau} {approx equal} 600 {mu}s).

• Research Organization: Wisconsin Univ., Madison, WI (USA)
• OSTI ID: 5055922
• Country of Publication: United States
• Language: English

Related Subjects

440000* -- Instrumentation
440101 -- Radiation Instrumentation-- General Detectors or Monitors &amp; Radiometric Instruments
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
47 OTHER INSTRUMENTATION
CALCULATION METHODS
CLOSED PLASMA DEVICES
DATA
EXPERIMENTAL DATA
INFORMATION
INTERNAL RING DEVICES
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
OSCILLATIONS
PLASMA PRESSURE
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TOKAPOLE DEVICES