EFFECT OF THE B DRIFT DIRECTION ON PLASMA EDGE PROPERTIES AND THEL-H TRANSITION ON DIII-D

Conference · Mon Jul 01 04:00:00 EDT 2002

OSTI ID:804698

CARLSTROM, T N ^[1]; GROEBNER, R J; McKEE, G R; MOYER, R A; RHODES, T L; ROST, J C; NEVINS, W M

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1. General Atomics

The power threshold for the L-H transition, P{sub TH}, is low when the ion {del}B drift is toward the X-point and increases significantly when it is away from the X-point. In order to study the cause of this effect, we have compared lower single-null (LSN) discharges with upper single-null (USN) discharges where the ion {del}B drift direction is down in both cases. Since many plasma parameters change with input power, we have made comparisons at the same power level (PTOT=2.3 MW). For these experiments, the LSN discharge is just below PTH (2.7 MW) and the USN discharge is far from P{sub TH} (6.8 MW). We have measured various properties of the edge plasma in an attempt to identify changes that may be responsible for the difference in P{sub TH} for the two cases. The equilibrium flux surfaces and diagnostic measurement locations are shown. The most pronounced difference is the reversal and the increased shear in the poloidal group velocity of the density fluctuations near the plasma edge [1]. These results complement a previous study where the plasma configuration was held fixed and the toroidal field was reversed [2]. In that study, differences in the divertor and X-point plasma were measured. In the present work, the X-point could not be located in the range of the divertor Thomson scattering diagnostic due to top/bottom symmetry issues, and those measurements are not available.

• Research Organization: GENERAL ATOMICS (US)
• Sponsoring Organization: (US)
• DOE Contract Number: AC03-99ER54463
• OSTI ID: 804698
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CONFIGURATION
DIVERTORS
DOUBLET-3 DEVICE
FLUCTUATIONS
MAGNETIC SURFACES
PLASMA
SHEAR
SYMMETRY
THOMSON SCATTERING
VELOCITY