Influence of the Radial Electric Field on the Shearless Transport Barriers in Tokamaks

TL;DR

This paper investigates how the radial electric field influences the formation and restoration of shearless transport barriers in tokamaks, using a drift-kinetic model to analyze plasma profile modifications.

Contribution

It introduces a non-integrable drift-kinetic model to study shearless barrier onset and demonstrates how electric field and non-resonant modes can trigger or restore these barriers.

Findings

Shearless barriers can be triggered by modifying electric field profiles.

Non-resonant modes play a key role in barrier onset and restoration.

Proper adjustments can restore broken transport barriers.

Abstract

In tokamaks, internal transport barriers, produced by modifications of the plasma current profile, reduce particle transport and improve plasma confinement. The triggering of the internal transport barriers and their dependence on the plasma profiles is a key nonlinear dynamics problem still under investigation. We consider the onset of shearless invariant curves inside the plasma which create internal transport barriers. A non-integrable drift-kinetic model is used to describe particle transport driven by drift waves and to investigate these shearless barriers onset in tokamaks. We show that for some currently observed plasma profiles shearless particle transport barriers can be triggered by properly modifying the electric field profile and the influence of non-resonant modes in the barriers onset. In particular, we show that a broken barrier can be restored by enhancing non-resonant modes.