Experimental achievement of toroidal beta beyond that predicted by Troyon'' scaling

Conference · Thu Sep 01 04:00:00 EDT 1994

OSTI ID:7059623

Taylor, T S ^[1]

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1. General Atomics, San Diego, CA (United States)

Tokamak experiments have made substantial progress toward improving the experimentally achievable beta limit beyond that predicted by Troyon scaling, [beta][sub Troyon] (%) = 2.8 I/aB MA/m/T. These advances in achievable beta have come about from the modification of the plasma profiles, primarily the current density profile, and the utilization of stabilizing conducting structures. Both theory and experiment have shown that the beta limit increases with peaked current density profiles, high [ell][sub i], and broad pressure profiles; scaling of the beta limit [beta][sub max] (%) = 4 [ell][sub i] I/aB has been proposed. Experiments in DIII-D, TFTR, and JT-60U have all confirmed the increase of [beta] with [ell][sub i], using high powered heating and negative current ramps to increase [ell][sub i]. It is recognized that high ell[sub i] is difficult to maintain at high [beta][sub N] in steady-state conditions as a consequence of the profile of the bootstrap current: [beta] is limited by low n external kinks. Profiles with a negative central shear and high edge current density have been proposed that are stable to the low n external kinks provided there is a stabilizing influence from a resistive wall. Experiments from PBX-M and DIII-D provide evidence that wall stabilization is effective and recent experiments at DIII-D have resulted in [beta][sub T] = 12.5% and [beta][sub N] = 4.3 at [ell][sub i] = 0.72 and q[sub 95] = 2.5; conditions that are expected to have a lower beta limit in the absence of wall stabilization.

• Research Organization: General Atomics, San Diego, CA (United States); Oak Ridge National Lab., TN (United States); Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC03-89ER51114; AC05-84OR21400; W-7405-ENG-48
• OSTI ID: 7059623
• Report Number(s): GA-A-21821; CONF-9408176--4; ON: DE95003880
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700412* -- Magnetic Confinement Devices-- (1992-)
BALLOONING INSTABILITY
BETA RATIO
CLOSED PLASMA DEVICES
COMPARATIVE EVALUATIONS
DATA
DESIGN
EVALUATION
INFORMATION
INSTABILITY
KINK INSTABILITY
PERFORMANCE
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PLASMA PRESSURE
PRESSURE GRADIENTS
SCALING LAWS
STEADY-STATE FUSION REACTORS
THERMONUCLEAR DEVICES
THERMONUCLEAR REACTORS
TOKAMAK DEVICES