Influence of the electric and magnetic shears on tokamak transport

Abstract

We applied a non-integrable drift-kinetic model, valid for large aspect ratio tokamaks, to investigate plasma edge particle transport driven by drift waves. Particle transport is obtained from the chaotic trajectories obtained by numerically integrating the canonical equations of motion, for the total flow formed by the equilibrium sheared flow and few dominant resonant drift waves propagating in the sheared equilibrium magnetic field. Thus, we investigate the transport dependence on the radial profiles of the electric and magnetic fields and show that radial particle transport at the plasma edge can be reduced by properly modifying the electric and magnetic shear profiles. For non-monotonic radial electric fields, we also observe non-twist transport barriers with shearless invariants identified by extremum values of the rotation number profiles of the invariant curves. The observed non-twist barriers are modified by the magnetic shear and persist for magnetic shear variations expected in present tokamaks.