April 15-17

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Author: Ammar H Hakim
Requested Type: Pre-Selected Invited
Submitted: 2019-02-22 12:25:30

Co-authors: N. Mandell, T. Bernard, J. Juno, P. Cagas, B. Srinivasan, G. Hammett

Contact Info:
PPPL
100 Stellerator Drive
Princeton, NJ   08540
USA

Abstract Text:
The Gkeyll project aims to develop a comprehensive open-source computational framework to simulate plasmas at (almost) all scales. In this talk we will present an overview of the project with focus on applications to fusion physics. In particular, we will focus on scrape-off-layer (SOL) turbulence and first-principles calculations of plasma-wall interaction in which the detailed magnetized sheath-physics is resolved. Other applications to kinetic study of shocks will be briefly presented. Gkeyll implements high-order discontinuous Galerkin algorithms that allow robust and efficient solutions to (gyro)kinetic equations. For Hamiltonian systems, Gkeyll uses a finite-element method to update the field equations, while a discontinuous Galerkin method is used for the particles. This allows conserving the total (particle plus field) energy exactly, while ensuring that total momentum is conserved to high-precision. Our schemes also ensure entropy is non-decreasing. A simplified form of the Fokker-Planck operator is implemented using a conservative scheme. The sheath is modeled in two ways. For use in gyrokinetic solver, the sheath is treated as boundary condition constructed to allow current flows into and out of the walls. Coupled to the gyrokinetic solver this allows performing electromagnetic simulations of turbulence on open field-lines in the tokamak SOL. For use in full kinetics, the sheath is treated from first principles, allowing a self-consistent determination of fields and particle fluxes at the wall. Two secondary electron emission (SEE) models are implemented. The first uses a phenomenological fit to compute the emitted electron spectrum. The second is based on a semi-classical approximation of electron mobility inside the wall. The effects of gazing magnetic fields and SEE on sheath physics is studied.

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