Gyrokinetic simulations of microturbulence and transport in tokamak plasmas

Abstract: Fusion power is one of few viable and 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. Using high performance computing resources these phenomena can be studied in detail through numerical experiments.

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. With this new wall, new impurities were introduced 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. The change of wall material has also led to a degradation in energy confinement for certain types of discharges at JET. Energy confinement must be optimized in future fusion devices for them to be economically viable. Another important issue for ITER is the refuelling of the plasma through pellet injection. The frozen hydrogen pellets are injected at high speed into the plasma. When they ablate, they perturb the density and temperature profiles. This changes the properties of the microturbulence which might hinder the particles from reaching the core of the plasma.

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.