Monday, May 3, 2021
Abstract: Understanding turbulent transport physics in the tokamak edge and scrape-off layer (SOL) is critical to developing a successful fusion reactor. The dynamics in these regions plays a key role in achieving high fusion performance by determining the edge pedestal that suppresses turbulence in the high-confinement mode (H-mode). Additionally, the survivability of a reactor is set by the heat load to the vessel walls, making it important to understand turbulent spreading of heat as it flows along open magnetic field lines in the SOL. Large-amplitude fluctuations, magnetic X-point geometry, and plasma interactions with material walls make simulating turbulence in the edge/SOL more challenging than in the core region, necessitating specialized gyrokinetic codes.
Further, the inclusion of electromagnetic effects in gyrokinetic simulations that can handle the unique challenges of the boundary plasma is critical to the understanding of phenomena such as the pedestal and edge-localized modes, for which electromagnetic dynamics are expected to be important.
In this talk, we demonstrate the first capability to simulate electromagnetic gyrokinetic turbulence on open magnetic field lines. This is an important step towards comprehensive electromagnetic gyrokinetic simulations of the coupled edge/SOL system. By using a continuum full-f approach via an energy-conserving discontinuous Galerkin (DG) discretization scheme that avoids the Ampere cancellation problem, we show that electromagnetic fluctuations can be handled in a robust, stable, and efficient manner in the gyrokinetic module of the Gkeyll code. We then present results which roughly model the scrape-off layer of the National Spherical Torus Experiment (NSTX), and show that electromagnetic effects can affect blob dynamics and transport in high beta regimes. In particular, stabilizing effects related to magnetic-field-line bending can lead to steeper pressure gradients and a narrower heat flux width on the end-plates.
Bio: Noah Mandell recently started as a DOE FES/ORISE postdoctoral fellow under the supervision of Dr. Nuno Loureiro at MIT PSFC. He received his PhD earlier this year from Princeton University, where he worked with Dr. Greg Hammett on electromagnetic gyrokinetic simulations of tokamak scrape-off layer turbulence. Noah is one of the primary developers of the Gkeyll code.