Gyrokinetic simulations of turbulent particle and heat transport in tokamaks

Licentiatavhandling, 2015

Fusion power is one of few viable sustainable means of energy production. The tokamak is arguable the most mature technology to magnetically confine fusion plasmas. In these devices, heat and particle transport is dominated by small-scale turbulent fluctuations. Recent advances in high performance computing have made it possible to study these phenomena in detail. The Joint European Torus (JET) is currently the largest tokamak in operation. Recently, the plasma facing components of JET were changed from carbon to metal — beryllium and tungsten. This in order to better align with the design foreseen for ITER, a next-generation device under construction in Cadarache in France. The change to this so-called ITER-like wall at JET has had several consequences. Firstly, it introduces new impurities into the plasma. Impurities, any ion that is not a reactant in the fusion reactions, are detrimental to the fusion power as they dilute the plasma and can radiate energy. It is therefore important to study the transport of impurities and how it is affected by different operational parameters, such as the cross-sectional shape of the plasma. Secondly, the change of wall material has led to a degradation in energy confinement for certain types of discharges at JET. Energy confinement must be optimized in future fusion devices in order for them to be economically viable. The present thesis aims at an improved understanding of these urgent issues by means of gyrokinetic simulations of particle and heat transport driven by Ion Temperature Gradient (ITG) and Trapped Electron (TE) mode turbulence.