Magnetic flutter effect on validated edge turbulence simulations

TL;DR

This study demonstrates that magnetic flutter significantly stabilizes edge turbulence in plasma simulations, reducing transport by over 50%, and highlights its importance for accurate predictive modeling in magnetic confinement devices.

Contribution

The paper introduces the inclusion of magnetic flutter effects in validated edge turbulence simulations, revealing its stabilizing influence on turbulence and transport.

Findings

Magnetic flutter reduces turbulent transport by more than a factor of 2.

Flutter stabilizes drift-Alfvén waves, decreasing phase shifts in fluctuations.

Including flutter is essential for accurate edge turbulence predictions.

Abstract

Small magnetic fluctuations ($B_1/B_0 \sim 10^{-4}$) are intrinsically present in a magnetic confinement plasma due to turbulent currents. While the perpendicular transport of particles and heat is typically dominated by fluctuations of the electric field, the parallel stream of plasma is affected by fluttering magnetic field lines. In particular through electrons, this indirectly impacts the turbulence dynamics. Even in low beta conditions, we find that $E\times B$ turbulent transport can be reduced by more than a factor 2 when magnetic flutter is included in our validated edge turbulence simulations of L-mode ASDEX Upgrade. The primary reason for this is the stabilization of drift-Alfv\'en-waves, which reduces the phase shifts of density and temperature fluctuations with respect to potential fluctuations. This stabilization can be qualitatively explained by linear analytical theory, and appreciably reinforced by the flutter nonlinearity. As a secondary effect, the steeper temperature gradients and thus higher $\eta_i$ increase the impact of the ion-temperature-gradient mode on overall turbulent transport. With increasing beta, the stabilizing effect on $E\times B$ turbulence increases, balancing the destabilization by induction, until direct electromagnetic perpendicular transport is triggered. We conclude that including flutter is crucial for predictive edge turbulence simulations.