Effects of the resonant modes on the magnetic footprint patterns in a tokamak wall

Abstract

Magnetic footprints, or deposition patterns of chaotic magnetic field lines in a tokamak wall, are studied for a configuration with resonant modes due to an ergodic limiter. The formation of magnetic footprints using a nontwist symplectic mapping for a nonmonotonic safety factor radial profile is investigated numerically. The radial position of the resonant mode we focus on changes drastically the magnetic footprints. Deeper resonant modes produce a concentrated field line deposition pattern, whereas a resonant mode closer to the plasma edge yields a broader deposition pattern. Although these shearless equilibria can present robust transport barriers, the magnetic footprints are still present and can deteriorate the plasma confinement quality.