Basin Entropy and Wada Property of Magnetic Field Line Escape in Toroidal Plasmas with Reversed Shear

Abstract

The structure of magnetic field lines in toroidal fusion plasmas, as in tokamaks and stellarators, represents the lowest-order description of the plasma particle behavior, up to finite Larmor and drift effects. Tokamaks with reversed magnetic shear typically present internal transport barriers that help to improve confinement through a partial or total reduction of the particle transport across magnetic surfaces. In this work, we investigate numerically particle escape in tokamaks with reversed shear in order to identify fractal structures affecting transport. These structures are quantitatively evaluated using two basic measures: the basin entropy and the Wada property.