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Title	94: Turbulence Structure and Amplitude Variation with ExB Shear in H-mode Plasmas
Name:	George McKee mckee@fusion.gat.com	Affiliation:	University of Wisconsin
Research Area:	Turbulence & Transport	Presentation time:	Not requested
Co-Author(s):	Burrell, Holland, Petty, Rhodes, Schmitz, Yan	ITPA Joint Experiment :	No
Description:	Determine how the 2D eddy structure of low-wavenumber turbulence as well as its magnitude and spectra vary as a function of rotationally controlled ExB shear in long-duration hybrid H-mode plasmas. Quantify the effects of shear flow on core turbulent and transport.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Determine turbulent eddy structure as a function of Mach number in hybrid discharges by directly measuring eddy correlation function, magnitude, decorrelation rates, and radial & poloidal correlation lengths, in these hybrid discharges with the expanded 2D BES system, as well as the multichannel Doppler reflectometer system. Long-duration, steady hybrid discharges will be employed. The low-amplitude of fluctuations in the core of hybrid plasmas makes their measurement more challenging, but the steady qualities (several seconds) allow for ensemble-averaging of the fluctuation characteristics with good resulting signal-to-noise. This will allow us to examine the improved transport in hybrid discharges, and specifically the Mach number dependence, as well as to more broadly and generally examine the ExB shear effects on turbulence and transport. Discharges similar to those already developed by C. Petty et al. will be used, with the exception that the neutral beams used for beta feedback will be changed to allow for the BES measurements (which require a steady 150 left beam). We will run relatively high q95 (~5.5) to increase turbulence magnitude. Several repeated discharges would be performed for full radial measurements.
Background:	The control and suppression of turbulence by ExB shear is fundamental to confinement physics in toroidally-rotating plasmas. Its explanation in terms of comparing turbulence growth rates and measured ExB shearing rates, and general agreement with simulations, is a significant success in fusion research. Despite this triumph, there remains a lack of fundamental quantitative experimental measurements that link the measured changes in localized core turbulence characteristics with the applied rotation and resulting shear. This experiment aims to resolve this gap. Transport in Hybrid scenario discharges has been shown to depend strongly on the toroidal Mach number (M = v_tor /c_s). By varying the injected neutral beam torque into hybrid plasmas and simultaneously maintaining beta constant via feedback control, the "H-factor" decreases by approximately 20% as the Mach number is reduced from about M=0.5 to M=0.1 (Polizer/Petty-Nuclear Fusion, 2008). This has been shown to be consistent with the a reduction in ExB shearing at lower Mach number from GLF23 modeling. Furthermore, previous measurements of turbulence characteristics in hybrid discharges (McKee, APS-2005) with BES, showed that turbulent eddies exhibit a strongly tilted structure in co-injected hybrid discharges. This is in sharp contrast to the more radially-poloidally symmetric eddy structure typically observed in the core of (rotating or non-rotating) L-mode discharges. The direction of this tilted eddy structure is consistent with the ExB shear flow in these plasmas, although it the shear magnitude didn't appear to be large enough to bring about the measured eddy tilt.
Resource Requirements:	All co and counter-neutral beams
Diagnostic Requirements:	Fluctuation diagnostics: BES, DBS, CECE, ECEI, FIR, PCI, UF-CHERS Full Profile diagnostics
Analysis Requirements:	Transport Analysis; TGLF; GYRO
Other Requirements: