On the Effects of Tokamak Plasma Edge Symmetries on Turbulence Relaxation

TL;DR

This paper investigates how symmetries at the tokamak plasma edge influence turbulence behavior, using a simplified model to analyze the effects of magnetic X-point symmetries and mode interactions on turbulence relaxation and transport.

Contribution

It introduces a simplified 3D model for edge turbulence, explores the impact of X-point symmetries, and reveals resonance effects that challenge perturbative solutions.

Findings

Turbulence relaxes to a 2D axisymmetric profile influenced by initial conditions.

X-point symmetries can alter turbulent transport properties.

Resonance between modes prevents a simple perturbative solution.

Abstract

The plasma edge of a tokamak configuration is characterized by turbulent dynamics leading to enhanced transport. We construct a simplified 3D Hasegawa--Wakatani model reducing to a single partial differential equation for the turbulent electric potential dynamics. Simulations demonstrate how the 3D turbulence relaxes on a 2D axisymmetric profile, corresponding to the so-called interchange turbulence. The spectral features of this regime are found to be strongly dependent on the initialization pattern. We outline that the emergence of axisymmetric turbulence is also achieved when the corresponding mode amplitude is not initialized. Then, we introduce the symmetries of the magnetic X-point of a tokamak configuration. We linearize the governing equation by treating the poloidal field as a small correction. We show that it is not always possible to solve the electric potential dynamics following a perturbative approach. This finding, which is due to resonance between the modes of the background and the poloidal perturbation, confirms that the X-point symmetries can alter the properties of turbulent transport in the edge region.