Core barrier formation near integer q surfaces in DIII-D

Journal Article · Tue Aug 15 00:00:00 EDT 2006 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2245579· OSTI ID:20860188

Austin, M E; Gentle, K W ^[1]; Burrell, K H; Waltz, R E; Gohil, P; Greenfield, C M; Groebner, R J; Petty, C C; Prater, R ^[2]; Heidbrink, W W; Luo, Y ^[3]; Kinsey, J E ^[4]; Makowski, M A ^[5]; McKee, G R; Shafer, M W ^[6]; Nazikian, R ^[7]; Rhodes, T L ^[8]; Van Zeeland, M A ^[9]

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1. University of Texas at Austin, Austin, Texas 78712 (United States)
2. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
3. University of California at Irvine, Irvine, California 92612 (United States)
4. Lehigh University, Bethlehem, Pennsylvania 18015 (United States)
5. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
6. University of Wisconsin at Madison, Madison, Wisconsin 53706 (United States)
7. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States)
8. University of California at Los Angeles, Los Angeles, California 90032 (United States)
9. Oak Ridge Institute for Science Education, Oak Ridge, Tennessee 37831-0117 (United States)

Recent DIII-D experiments have significantly improved the understanding of internal transport barriers (ITBs) that are triggered close to the time when an integer value of the minimum in q is crossed. While this phenomenon has been observed on many tokamaks, the extensive transport and fluctuation diagnostics on DIII-D have permitted a detailed study of the generation mechanisms of q-triggered ITBs as pertaining to turbulence suppression dynamics, shear flows, and energetic particle modes. In these discharges, the evolution of the q profile is measured using motional Stark effect polarimetry and the integer q{sub min} crossings are further pinpointed in time by the observation of Alfven cascades. High time resolution measurements of the ion and electron temperatures and the toroidal rotation show that the start of improved confinement is simultaneous in all three channels, and that this event precedes the traversal of integer q{sub min} by 5-20 ms. There is no significant low-frequency magnetohydrodynamic activity prior to or just after the crossing of the integer q{sub min} and hence magnetic reconnection is determined not to be the precipitant of the confinement change. Instead, results from the GYRO code point to the effects of zonal flows near low order rational q values as playing a role in ITB triggering. A reduction in local turbulent fluctuations is observed at the start of the temperature rise and, concurrently, an increase in turbulence poloidal flow velocity and flow shear is measured with the beam emission spectroscopy diagnostic. For the case of a transition to an enduring internal barrier the fluctuation level remains at a reduced amplitude. The timing and nature of the temperature, rotation, and fluctuation changes leading to internal barriers suggests transport improvement due to increased shear flow arising from the zonal flow structures.

• OSTI ID: 20860188
• Journal Information: Physics of Plasmas, Vol. 13, Issue 8; Other Information: DOI: 10.1063/1.2245579; (c) 2006 American Institute of Physics; 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
ALFVEN WAVES
AMPLITUDES
CHARGED-PARTICLE TRANSPORT
DOUBLET-3 DEVICE
ELECTRON TEMPERATURE
EMISSION SPECTROSCOPY
FLUCTUATIONS
ION TEMPERATURE
IONS
MAGNETIC RECONNECTION
MAGNETOHYDRODYNAMICS
PLASMA
PLASMA CONFINEMENT
PLASMA DIAGNOSTICS
PLASMA INSTABILITY
POLARIMETRY
ROTATION
SHEAR
STARK EFFECT
THERMAL BARRIERS
TIME RESOLUTION
TURBULENCE