Shearless bifurcations in particle transport for reversed shear tokamaks

TL;DR

This paper investigates the formation and breakup of shearless barriers in particle transport within reversed shear tokamaks, revealing bifurcation sequences and their physical implications through numerical simulations.

Contribution

It introduces a novel analysis of shearless bifurcations in tokamak plasma transport using symplectic maps and bifurcation theory, highlighting new insights into barrier dynamics.

Findings

Shearless barriers appear and break up as safety factor profile parameters change.

Multiple shearless curves can form and undergo bifurcations.

Physical consequences of multiple shearless curves are discussed.

Abstract

Some internal transport barriers in tokamaks have been related to the vicinity of extrema of the plasma equilibrium profiles. This effect is numerically investigated by considering the guiding-center trajectories of plasma particles undergoing ExB drift motion, considering that the electric field has a stationary nonmonotonic radial profile and an electrostatic fluctuation. In addition, the equilibrium configuration has a nonmonotonic safety factor profile. The numerical integration of the equations of motion yields a symplectic map with shearless barriers. By changing the parameters of the safety factor profile, the appearance, and breakup of these shearless curves are observed. The successive shearless curves breakup and recovering is explained using concepts from bifurcation theory. We also present bifurcation sequences associated to the creation of multiple shearless curves. Physical consequences of scenarios with multiple shearless curves are discussed.