Effect of radial pressure corrugations and profile shearing on turbulence in Fusion plasmas

TL;DR

This paper investigates how micro-scale radial corrugations in plasma profiles influence turbulence in fusion devices, revealing a novel turbulence saturation mechanism through profile shearing that reduces transport despite increased linear instability.

Contribution

It introduces a new understanding of how radial pressure corrugations affect ETG mode stability and turbulence saturation via profile shearing in fusion plasmas.

Findings

Radial corrugations split ETG modes into three eigenvalues.

Nonlinear simulations show reduced fluxes despite more unstable modes.

Profile shearing breaks turbulent eddies, lowering transport levels.

Abstract

Microturbulence can produce stationary fine-scale radial corrugations on the plasma density and temperature gradients in magnetic confinement fusion devices. We show that these structures play a significant role in regulating turbulent transport. We focus on the pedestal, studying electron-temperature-gradient (ETG) mode destabilisation and saturation in the presence of radial corrugations on the electron temperature gradient that could result from microtearing turbulence. A linear dispersion relation is derived for a shearless slab case, which indicates that in the presence of a sinusoidal background corrugation, each ETG mode splits into three distinct eigenvalues, with one being the original, one being more unstable and one being less unstable. However, despite the presence of more unstable linear modes, nonlinear gyrokinetic simulations of ETG with corrugated background electron temperature show a reduction of fluxes. Our investigation reveals a radial variation of the phase velocity of the modes that is proportional to the diamagnetic drift velocity and the local pressure gradient. The associated profile shearing breaks the turbulent eddies apart, reducing the transport level. This profile shearing resulting from fine-scale pressure corrugations could be a ubiquitous turbulence saturation mechanism not just in Fusion plasmas, but in Astrophysics and other areas.