Radially global neoclassical transport in tokamak pedestals

Abstract: Nuclear fusion has the potential to become a sustainable energy sourcein the foreseeable future. The most developed system for fusion powerproduction is the tokamak, which magnetically confines a plasma at highenough temperature for fusion reactions to take place.Tokamaks operating in the H-mode feature the largest known steadystate density and temperature gradients, located in a region at the edgeof the plasma known as the pedestal. These steep gradients result froma spontaneous reduction in turbulence, and as a result of these steepgradients, the plasma behavior couples between nearby radial locations,and can no longer be evaluated in terms of plasma parameters at a singleradius. The plasma behavior is said to be radially global. This makesit challenging to model the transport of particles, heat, etc., which isneeded to design and evaluate future reactors.In this thesis, we study collisional, radially-global transport in toka-mak pedestals, using numerical methods to solve a drift-kinetic equationfor the distribution of particles in both velocity and configuration space.Particular focus is put on the influence of non-trace impurities, and theeffects of changing the mass and charge of the bulk ions. Order unitydeviations from radially-local results are observed in plasma flows andcross-field fluxes, both in the pedestal and the near-pedestal core. In ad-dition, a significant radial transport of angular momentum arises in theradially-global description, which may have implications for the plasmarotation, which is understood as a crucial component for the transitionto H-mode.