Orbit simulations of fast-ion transport induced by externally applied 3D magnetic perturbations in the ASDEX Upgrade tokamak.

Abstract

Externally applied 3D magnetic perturbations break the symmetry of the magnetic field in a tokamak and have an impact on the transport of fast-ions, i.e. suprathermal ions. It was shown that the variation of the toroidal canonical momentum gives a measured for the radial transport of fast-ions. In this thesis, experiments of the ASDEX Upgrade tokamak were analyzed in terms of the radial transport of fast-ions. Simulations using the Monte Carlos orbit-following code ASCOT were carried out in order to study the impact of externally applied 3D magnetic perturbations on the topology of the orbits and to quantify the radial fast-ion transport. The results show that when the magnetic perturbations are applied a drift appears (changing the trajectory of the particle) and the transport created depends on the initial pitch angle, radius and energy of the particles and the equilibrium. Also, it is confirmed that the strong correlation between fast-ion losses and impurity toroidal rotation is related to the trapped-passing boundary .