Disruptive instabilities in a poloidal divertor tokamak

Technical Report · Wed Feb 01 04:00:00 EST 1984

OSTI ID:6800679

Osborne, T H

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). If q = 1, sawtooth oscillations are observed in which the disruption (sawtooth crash) itself has an n = m = 1 helical structure. At low toroidal plasma current and high toroidal field, several small sawteeth of period 100 to 200 ..mu..s are superimposed on giant sawteeth of period 1ms. Precursor oscillations with even m and odd n are observed on magnetic loops for both types of sawtooth oscillations. 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 equilibriumm 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 = 600 ..mu..s).

• Research Organization: Wisconsin Univ., Madison (USA)
• DOE Contract Number: AC02-76ET53051
• OSTI ID: 6800679
• Report Number(s): DOE/ET/53051-63; ON: DE84013054
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700107* -- Fusion Energy-- Plasma Research-- Instabilities
CLOSED PLASMA DEVICES
DIVERTORS
ENERGY
INSTABILITY
INTERNAL RING DEVICES
PLASMA DISRUPTION
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
POLOIDAL DIVERTORS
Q-VALUE
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TOKAPOLE DEVICES