Multi-fluid Plasma Modelling

Abstract

Contemporary plasma fusion experiments use significant power injection for plasma heating. The injected power selectively heats only part of the plasma, which then transfers its energy to the rest of the plasma through collisions. Continuous power injection gives rise to a dynamic equilibrium whereby part of the plasma has a higher energy than the bulk of the plasma. Current plasma fluid treatments assume that the velocity distribution of each particle species is described by a Maxwell-Boltzmann distribution function, and so may not be accurate for plasmas with a significant energetic component. A new method of modelling toroidally-symmetric plasma equilibria is derived in this thesis: multi-fluid plasma modelling. In this model, the non-Maxwellian plasma is decomposed into an arbitrary number of energy-resolved fluids. Each fluid is charge-neutral, can have arbitrary rotation, and is described by a Maxwellian distribution function. To investigate the model numerically, it is implemented as a modification to an existing single-fluid plasma equilibrium code. The modified code is then used to investigate the effect of an energetic component on the plasma equilibrium. We find that the influence of the energetic component can be significant if it has large toroidal flow (or flow-shear). The plasma equilibrium is, however, relatively robust to variations in the energetic component’s toroidal flow and pressure profiles.