Ergodicity of gyrofluid edge localised ideal ballooning modes

TL;DR

This paper uses nonlinear gyrofluid simulations to analyze the magnetic field structure during edge localized ideal ballooning modes, revealing the development and evolution of ergodic magnetic regions throughout the instability.

Contribution

It provides a detailed analysis of the ergodic behavior of magnetic fields during ELMs using gyrofluid models, highlighting the nonlinear evolution of magnetic island formation and ergodicity.

Findings

Small scale magnetic islands form during linear growth phase.

Ergodic magnetic regions develop near the end of linear phase.

Ergodicity decreases during turbulent nonlinear phase with lower plasma beta.

Abstract

The magnetic field structure associated with edge localised ideal ballooning mode (ELM) bursts is analysed by nonlinear gyrofluid computation. The linear growth phase is characterised by the formation of small scale magnetic islands. Ergodic magnetic field regions develop near the end of the linear phase when the instability starts to perturb the equilibrium profiles. The nonlinear blow-out gives rise to an ergodisation of the entire edge region. The time-dependent level of ergodicity is determined in terms of the mean radial displacement of a magnetic field line. The ergodicity decreases again during the nonlinear turbulent phase of the blow-out in dependence on the degrading plasma beta in the collapsing plasma pedestal profile.