Global flux-driven simulations of plasma turbulence in the boundary of stellarators*

We present the first 3D, global, two-fluid, flux-driven simulations of plasma turbulence in stellarator configurations [1]. We consider a 5-field period stellarator with a vacuum magnetic field constructed using the Dommaschk potentials. The simulations are carried out with the GBS code [2], which solves the two-fluid drift-reduced Braginskii equations. In contrast to tokamak simulations and experiments, but in agreement with W7-X measurements, coherent filamentary structures are essentially bound to a flux surface. The radial particle and heat transport are mainly driven by a field-aligned mode with low poloidal wavenumber, in contrast to smaller size turbulent structures observed in tokamaks. Confidence in these simulation results is increased by the first validation of a simulation of boundary turbulence in a stellarator configuration, where GBS retrieves the main turbulence properties of the TJ-K stellarator [3]. The peculiar features of stellarator turbulence are investigated through a set of turbulence simulations in magnetic configurations that smoothly transition from a tokamak to a stellarator.

[1] A. J. Coelho et al, NF 62, 074004 (2022)

[2] P. Ricci et al., PPCF 54, 124047 (2012)

[3] A. J. Coelho et al, PPCF accepted (2023)