Validation of GBS plasma turbulence simulation of the TJ-K stellarator

Abstract

We present a validation of a three-dimensional, two-fluid simulation of plasma turbulence in the TJ-K stellarator, a low temperature plasma experiment ideally suited for turbulence measurements. The simulation is carried out by the GBS code, recently adapted to simulate 3D magnetic fields. The comparison shows that GBS retrieves the main turbulence properties observed in the device, namely the fact that transport is dominated by fluctuations with low poloidal mode number. The poloidal dependence of the radial $\text{E}\times\text{B}$ turbulent flux is compared on a poloidal plane with elliptical flux surfaces, where a very good agreement between experiment and simulation is observed, and on another with triangular flux surfaces, which shows a poorer comparison. The fluctuation levels in both cases are underestimated in the simulations. The equilibrium density profile is well retrieved by the simulation, while the electron temperature and the electrostatic potential profiles, which are very sensitive to the strength and localization of the sources, do not agree well with the experimental measurements.

Global fluid simulation of plasma turbulence in stellarators with the GBS code

“…GBS [13][14][15] is a three-dimensional, global, two-fluid, flux-driven code that solves the drift-reduced Braginskii equations [16], valid in the high-collisionality regime that often characterizes the plasma boundary of magnetic fusion devices, as well as the core of low-temperature devices such as the TORPEX basic plasma physics experiment [17] or the TJ-K stellarator [12]. GBS evolves all quantities in time, without separation between equilibrium and fluctuating components.…”

“…The simulation results show important differences with respect to tokamak simulations, namely the fact that turbulent transport is dominated by a coherent mode with low poloidal mode number, where the structures are such that their extensions in the radial and poloidal directions are similar. Although such level of coherency and size of the structures is not usual in tokamaks, in stellarators such as TJ-K, a large coherent mode with low poloidal mode number is observed (usually m = 3 or m = 4 in hydrogen and helium discharges) [11], a feature that GBS simulations of TJ-K were able to retrieve [12].…”