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brower_epr_invited_02_15_2013v3.pdf2013-02-21 18:44:58David Brower

Direct Evidence for Magnetic Fluctuation-Driven Intrinsic Flow in a Toroidal Plasma

Author: David L Brower
Requested Type: Consider for Invited
Submitted: 2012-12-07 10:00:37

Co-authors: W.X. Ding, L. Lin, A. Almagri, B. Chapman D. J. Den Hartog, J.S. Sarff

Contact Info:
2515 Speedway (C1500)
Austin, TX   78712-1

Abstract Text:
Exploiting fluctuation-driven torque is highly desirable for ITER where the efficiency of externally applied torque will likely be limited. Plasma pressure fluctuations, electric field fluctuations and magnetic field fluctuations have been long observed in various magnetic confinement configurations and can all play a role in intrinsic plasma flow. Electric and magnetic field fluctuations can act on plasma flow via the Reynolds stress or Maxwell stress, respectively. In addition, the interaction between plasma parallel pressure and magnetic field fluctuations (e.g., tearing instabilities, energetic particle modes) can also generate a net torque (kinetic stress) that drives plasma flow, ( ). This stress stems from the divergence of the magnetic-fluctuation-driven momentum flux, and <…> denotes flux surface average. Direct experimental evidence of the kinetic stress and its relation to intrinsic flow has been observed in the MST reversed field pinch. Using advanced polarimetry and differential interferometry techniques, measurements of the torque amplitude, direction and spatial distribution are made in the plasma core. The toque is approximately 0.5 N/m3 (co-current direction) at r/a~0.2 which is comparable to the observed flow acceleration, ρdV/dt. Both the kinetic stress and plasma parallel flow vary in direction with minor radius, changing sign about the mid-radius. The saturation mechanism of flow is qualitatively consistent with the stochastic magnetic field induced damping. When magnetic fluctuations are suppressed by current profile control, the flow is observed to decrease on MST. These results strongly indicate the fluctuation-driven kinetic stress plays important role in plasma flow in MST.

Characterization: 1.4,2.0

Groups 1.4 and 2.0

University of Texas

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR2013)
February 12-15, 2013
Fort Worth, Texas

EPR 2013