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Author: Emily A. Belli
Requested Type: Pre-Selected Invited
Submitted: 2018-02-20 15:37:06

Co-authors: J. Candy

Contact Info:
General Atomics
P.O. Box 85608
San Diego, CA   92186-5

Abstract Text:
The influence of sonic rotation on gyrokinetic stability and transport is studied, with important implications for heavy impurity dynamics. Sonic toroidal plasma flow, on the order of the ion sound speed, arises in tokamaks due to external torque driven by neutral beam injection and can have a profound effect on the intensity of drift-wave turbulence. It is common in gyrokinetics to consider the weak rotation limit [1], retaining only the ExB flow, Coriolis drift and toroidal rotation shear. However, correct treatment of the sonic rotation regime [2] requires the additional consideration of centrifugal effects. Because of their complexity, these new sonic terms (quadratic in the Mach number), are ignored in most codes and widely-used reduced models of transport. In this work, the impact of rotation on ion and impurity transport is explored with the gyrokinetic code CGYRO and the drift-kinetic code NEO, both of which implement full sonic rotation. It is found that including only weak rotation terms, while neglecting centrifugal terms, leads to a large error. While the ITG drive is dominantly affected by the Coriolis drift, centrifugal drifts and electrostatic trapping corrections induced by the rotation lead to significant modifications to the heavy impurity particle transport. For impurities in a rotating plasma, both gyrokinetic and neoclassical transport must be considered. The turbulent transport is enhanced by the complex interaction between the Mach number and toroidal rotation shear in the drifts, while the neoclassical transport becomes competitive with the turbulent transport through enhanced effective toroidal curvature drifts. This has significant implications, for example, on detrimental core tungsten accumulation in a reactor.

This work was funded by the U.S. DoE under DE-FC02-06ER54873.

[1] R. Waltz, et al., Phys. Plasmas 14, 122507 (2007).
[2] H. Sugama, Phys. Plasmas 5, 2560 (1998).