3D nonlinear magnetohydrodynamic simulations of macroscopic internal instabilities in tokamak plasmas

This work is aimed at advancing the theoretical understanding of magnetic flux pumping in Hybrid tokamak discharges. To this end, long-term 3D nonlinear magnetohydrodynamic simulations in toroidal geometry are performed by means of the high-order finite element code M3D-C1. The simulations result in either a sawtooth-like reconnection cycling behavior or in sawtooth-free stationary states with a helical core where magnetic flux pumping prevents the central safety factor from decreasing below unity. It is analyzed in detail how the flux pumping mechanism, in which a dynamo effect plays an important role, works and under which conditions it sustains itself.