Physics of Intrinsic Rotation in Flux-Driven ITG Turbulence
Authors: S. Ku, J. Abiteboul, P.H. Dimond, G. Dif-Pradalier, J.M. Kwon, Y.Sarazin, T.S. Hahm, X. Garbet, C.S. Chang, G. Latu, E.S. Yoon, Ph. Ghendrih, S.Yi, A. Strugarek. W. Solomon and V. Grandgirard
Abstract: Global, heat flux-driven ITG gyrokinetic simulations which manifest
the formation of macroscopic, mean toroidal flow profiles with peak thermal Mach
number 0.05, are reported. Both a particle-in-cell (XGC1p) and a semi-Lagrangian
(GYSELA) approach are utilized without a priori assumptions of scale-separation
between turbulence and mean fields. Flux-driven ITG simulations with different
edge flow boundary conditions show in both approaches the development of net
unidirectional intrinsic rotation in the co-current direction. Intrinsic torque is shown
to scale approximately linearly with the inverse scale length of the ion temperature
gradient. External momentum input is shown to effectively cancel the intrinsic rotation
profile, thus confirming the existence of a local residual stress and intrinsic torque.
Fluctuation intensity, intrinsic torque and mean flow are demonstrated to develop
inwards from the boundary. The measured correlations between residual stress and two
fluctuation spectrum symmetry breakers, namely E x B shear and intensity gradient,
are similar. Avalanches of (positive) heat flux, which propagate either outwards or
inwards, are correlated with avalanches of (negative) parallel momentum flux, so that
outward transport of heat and inward transport of parallel momentum are correlated
and mediated by avalanches. The probability distribution functions of the outward
heat flux and the inward momentum flux show strong structural similarity.
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Submitted to: Nuclear Fusion (February 2012)
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