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NIMROD Solver for Plasma-Neutral Fluid Modeling

Author: Peter C Norgaard
Requested Type: Consider for Invited
Submitted: 2012-12-07 18:31:41

Co-authors: E.T. Meier, U. Shumlak

Contact Info:
University of Washington
4000 15th Ave NE
Seattle, WA   98195

Abstract Text:
NIMROD is being modified to solve fully-coupled neutral particle dynamics with MHD for 3D fusion configurations. Our objective is validated simulation of this model applied to significant processes such as transport and boundary physics that are relevant in both compact and reactor-scale experiments. Consideration of the relatively short mean free path of neutrals colliding with the plasma makes a neutral fluid treatment an acceptable approximation of the Monte-Carlo representation for various regimes. Computational constraints further implicate the utility of a fluid neutral-plasma model for simulation of experimental configurations. To that end, a generalized fluid model was derived from the Boltzmann equation that captures the effects of plasma interacting with a gasdynamic neutral fluid.[E.T. Meier and U. Shumlak, JCP 2012] This model and its underlying assumptions will be presented. It was implemented in the two-dimensional version of the HiFi code and used to study the ELF thruster and coaxial acceleration in the ZaP experiment. These applications and initial validation efforts are also shown. Our present effort is to incorporate this model into the NIMROD pseudospectral / finite element code, which has been used extensively for simulating MHD and multifluid plasma physics. A previous extension to NIMROD was developed for modeling injection of impurity gas to quench a tokamak,[V.A. Izzo et al., POP 2009] however it was limited to coupling through the continuity equation. The goal of this work is implementation of a fully coupled plasma-neutral fluid model, which may be applied to a diverse range of simulation including plasma-wall interaction, energy balance due to charge exchange transport, startup of pulsed configurations, tokamak pedestal formation, or gas injection for refueling or disruption mitigation. The development and implementation of incremental plasma-neutrals will be described, with the final goal of a fully-coupled model where the neutral dynamics are included through a neutral species momentum and energy equation. The hierarchy of plasma-neutral models and the associated linear and implicit leapfrog algorithms which are to be implemented in the NIMROD code as an extension of the existing Hall MHD solver will be discussed.

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