Master thesis defense by Aske Olsen

Title: 3D Modelling of Turbulence in a Magnetically Confined Toroidal Plasma

Abstract: In order to accurately describe the dynamics of a fusion plasma 3D-models are essential. However using a simple cartesian coordinate system makes complex fluid models of plasma require a lot of com­putational time. By creating a a set of coordinates aligned with the magnetic field, the number of grid points in the direction of the mag­netic field can be greatly reduced, due to the relatively free motion of charged particles along the magnetic field line.This thesis sets out to investigate plasma dynamics in such a field­aligned coordinate system. Much emphasis has been put on the geom­etry of the investigated system, using a modified version of the simple Hasegawa-Wakatani equations derived using the two-fluid equations. Whereas the original Hasegawa-Wakatani equations include few 3D­effects from the magnetic field, the model investigated in this thesis include more, such as magnetic shear.To create a 3D-model with analytical expressions of the metric, a circle equilibrium solution to the Grad-Shafranov equation was as­sumed, which holds in the large aspect ratio limit.The modified Hasegawa-Wakatani equations was the simulated with the geometric effects of the magnetic field given by the derived metric. To make the numerical simulations the BOUT++ platform was used.