Influence of the radial electric field on the shearless transport barriers in tokamaks

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 which is 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 the particle transport driven by drift waves and to investigate the shearless barrier 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 barrier onset. In particular, we show that a broken barrier can be restored by enhancing non-resonant modes. Published under license by AIP Publishing.