Discovery of stationary operation of quiescent H-mode plasmas with net-zero neutral beam injection torque and high energy confinement on DIII-D

Journal Article · Sun May 15 00:00:00 EDT 2016 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4943521· OSTI ID:22600234

Burrell, K. H.; Chen, X.; Garofalo, A. M.; Groebner, R. J.; Muscatello, C. M.; Osborne, T. H.; Petty, C. C.; Snyder, P. B. ^[1]; Barada, K.; Rhodes, T. L.; Zeng, L. ^[2]; Solomon, W. M. ^[3]; Yan, Z. ^[4]

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1. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
2. University of California-Los Angeles, Los Angeles, California 90024 (United States)
3. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
4. University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

Recent experiments in DIII-D [J. L. Luxon et al., in Plasma Physics and Controlled Nuclear Fusion Research 1996 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H{sub 98y2} international tokamak energy confinement scaling (H{sub 98y2} = 1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggered in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers E × B rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbulence to increase. In the H-mode edge, a narrow transport barrier usually grows until MHD instability (a peeling ballooning mode) leads to the ELM heat burst. However, the increased turbulence reduces the pressure gradient, allowing the development of a broader and thus higher transport barrier. A 60% increase in pedestal pressure and 40% increase in energy confinement result. An increase in the E × B shearing rate inside of the edge pedestal is a key factor in the confinement increase. Strong double-null plasma shaping raises the threshold for the ELM instability, allowing the plasma to reach a transport-limited state near but below the explosive ELM stability boundary. The resulting plasmas have burning-plasma-relevant β{sub N} = 1.6–1.8 and run without the need for extra torque from 3D magnetic fields. To date, stationary conditions have been produced for 2 s or 12 energy confinement times, limited only by external hardware constraints. Stationary operation with improved pedestal conditions is highly significant for future burning plasma devices, since operation without ELMs at low rotation and good confinement is key for fusion energy production.

• OSTI ID: 22600234
• Journal Information: Physics of Plasmas, Vol. 23, Issue 5; Other Information: (c) 2016 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BALLOONING INSTABILITY
BEAM INJECTION
BEAMS
DOUBLET-3 DEVICE
EDGE LOCALIZED MODES
HEAT
H-MODE PLASMA CONFINEMENT
IAEA
LIMITING VALUES
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
PLASMA
PRESSURE GRADIENTS
ROTATING PLASMA
SHEAR
STABILITY
THERMONUCLEAR REACTORS
TORQUE
TRANSPORT THEORY
TURBULENCE