Simulation of Charged Particle Orbits in Fusion Plasmas

Abstract

When designing a fusion device, knowledge of the particle motion inside the fusion plasma is crucial. The charged plasma particles are confined inside the device using a strong magnetic field, which influences particle motion. Particle trajectories can therefore be obtained by numerically solving the equations of motion for a charged particle in the confining magnetic field. With the simulation tool developed as a part of this project, charged particle orbits are studied. Especially, the properties of the so called banana and passing orbit topologies are studied and the observed results explained using theoretical models. We find expressions that approximately describe the width of the banana and passing orbits and the location of the banana orbit’s mirror points. The orbit dependence on mass, charge and energy is investigated and an expression for the particle’s deviation from a field line is derived. Also, the cause for banana orbits forming is studied and their occurrence is shown to depend on how the particle’s velocity vector is directed. Finally, the two computational methods used, where either the particle or its guiding-center is followed, are compared with respect to both energy conservation and computational time. The guiding-center approach is shown to greatly reduce computational cost.