NIMROD Modeling of Poloidal Flow Damping in a Tokamak Using a Drift Kinetic Equation Closure Scheme

Calculations of poloidal flow damping in a tokamak are undertaken using two implementations of the ion drift kinetic equation (DKE) in the extended MHD code NIMROD. The first implementation utilizes a conventional delta-F approach, while the other employs a Chapman-Enskog-like (CEL) ansatz. The CEL ansatz specifies that the n, V, and T moments of the kinetic distortion are identically zero. The closure information needed for the low-order fluid evolution equations are provided by solutions to the ion CEL-DKE written in the macroscopic flow reference frame [1]. Initial value calculations are performed for an axisymmetric-shaped tokamak with an imposed kinetic distortion that initially provides a mean poloidal flow fluid velocity. The computational results are compared with analytic predictions of time-dependent closures for the parallel viscous force and for the poloidal flow damping [2]. The computational results are also compared and contrasted between the two implementations, to verify the consistency, efficiency, and accuracy of each approach. [1] J. J. Ramos, Phys. Plasmas 18, 102506 (2011). [2] A. L. Garcia-Perciante et al, Phys. Plasmas 12, 052516 (2005).