April 4-6

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Author: Andrew Spencer
Requested Type: Poster
Submitted: 2022-03-04 16:42:30

Co-authors: E.D.Held, J.R.Jepson, J-Y.Ji

Contact Info:
Utah State University
4415 Old Main Hill
Logan, UT   84322-4
United States

Abstract Text:
Recent work has led to improvements in NIMROD's continuum drift kinetic (DK) solver and subsequent coupling of closures into its extended MHD model. Namely, improved accuracy in the calculation of the collision operator [1] and a calculation of poloidal flow damping in tokamak geometry using high order FE grids in pitch angle to resolve the trapped-passing-boundary in velocity space [2]. Tight coupling between the fluid equations and electron and ion DK equations demands a careful treatment of the time-centering to implicitly advance the system of equations over large time steps. The fluid advance in NIMROD is numerically stabilized by a semi-implicit approach that uses the ideal-MHD operator to allow for large timesteps compared to the compressional Alfven wave propagation time. In this approach, the center-of-mass flow is staggered in time from the remaining fluid quantities. One approach that builds on the success of this leap-frog method is to center the electron and ion velocity distribution functions such that one is advanced simultaneously with the ion flow and the other is advanced simultaneously with the remaining fluid quantities. The goal of this work is to determine the optimal centering of each distribution function in the context of NIMROD's existing fluid model. Preliminary results that focus on the collisional effects of the Spitzer electrical conductivity and thermalization problems and the collisional/free-streaming effects of temperature flattening across a growing magnetic island are presented.
This research is supported by the U.S. Department of Energy grant nos. DE-FG02-04ER54746 and DE-SC0018146.
[1] J. A. Spencer, et. al., J. Comput. Phys., 450, 110862 (2022).
[2] J. R. Jepson, et. al., Phys. Plasmas, 28, 082503 (2021).