Tess Bernard, UT-Austin

"Validating a Gyrokinetic Model of Plasma Turbulence in the Texas Helimak"

Abstract: Simple magnetized torus (SMT) experiments, such as the Texas Helimak, use vertical and toroidal field coils to create open, helical magnetic-field-line configurations with curvature and shear. With dimensionless parameters and magnetic geometry similar to the scrape-off-layer (SOL) of fusion devices, SMT’s can be used to compare analytic and numerical models of SOL turbulence to experimental data. Prior to this work, only fluid simulations had been performed of the Helimak. Using the computational plasma physics framework Gkeyll, we present the first continuum gyrokinetic simulations of plasma turbulence in the Texas Helimak. The device has features similar to the scrape-off layer region of tokamaks, such as bad-curvature-driven instabilities and sheath boundary conditions on the end plates, which are included in our model. A bias voltage can be applied across conducting plates to drive ExB flow and study the effect of velocity shear on turbulence suppression. We performed simulations of grounded and limiter-biased scenarios and made detailed comparisons with experimental data. Simulations captures key features of experimental data, and we also discuss how including additional physical and geometric effects could further improve agreement. Overall, results demonstrate good progress towards modeling turbulence on helical, open-field lines in tokamak SOL-like conditions with gyrokinetic equations.