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Collisional Effects on Gyrokinetic Turbulence in Tokamak Edge Plasmas

Author: Emily A. Belli
Requested Type: Poster Only
Submitted: 2015-01-15 11:05:04

Co-authors: J. Candy

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

Abstract Text:
For gyrokinetic studies in the pedestal region, collisions are expected to play a more critical role than in the core and there is concern that more advanced collision operators, as well as numerical methods optimized for the strong collisionality regime, are needed. For this purpose, a new gyrokinetic solver CGYRO has been developed for precise studies of high collisionality regimes. Building on GYRO and NEO, CGYRO uses the NEO pitch angle and energy velocity-space coordinate system to optimize the accuracy of the collision dynamics, particularly for multi-species collisions and including energy diffusion. CGYRO has been benchmarked with GYRO for linear gyrokinetic ITG/TEM/KBM growth rates with a simple Lorentz operator. Comparisons of collision models find that, unlike the case of neoclassical transport, the form of the momentum restoring term does not have a significant effect for the simple cases studied. Finite perpendicular wavenumber corrections are also found to be negligible. In contrast, energy diffusion can reduce the growth rate of the TEM by 10% even for relatively moderate values of collision frequency expected in the tokamak edge. The importance of energy conservation is also demonstrated. Nonlinear terms have recently been included using a new 2D dealiased pseudo-spectral scheme with a communication library reoptimized for simulations of multi-scale high-wavenumber turbulence. Preliminary results of the effects of collisions on nonlinear gyrokinetic turbulence in the edge, including impurities, are presented.

*This work supported in part by the U.S. Department of Energy under DE-FG03-95ER54309 and DE-FC02-06ER54873.

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