Modelling of Alternative Divertor Power Exhaust

Controlled nuclear fusion on Earth is one of the most powerful technological dreams devised by humanity. The prospect of an artificial star on our planet could offer reliable, clean, and widely accessible energy for all, using the most common element in the universe as fuel. Despite all its prospects, an economic fusion power plant has not yet been developed, due to the enormity and complexity of the challenges in the way of such a feat. In tokamaks, where a high temperature plasma is confined using strong magnetic fields, one of the most pressing issues is that of plasma exhaust. As these fusion devices become more powerful and better confined, the peak heat and particle loads on surrounding surfaces is enough to erode and damage even the strongest materials.

The focus of this thesis is the study of alternative divertors, one proposed solution to the tokamak exhaust challenge. By modelling edge plasmas under different shapes, conditions, and magnetic and physical geometries, this work furthers the understanding of how these different geometric features can influence divertor performance. The process of detachment, characterised by significant power and pressure loss in an edge plasma, is a key focal point for this modelling work.

By developing and extending reduced models, and comparing them to hundreds of 2D simulations of alternative divertors, good agreement is found in terms of the predicted impacts of divertor features on detachment. These models are also compared with experiment, where certain broad predictions and ideas from reduced modelling seem present in experimental data. The agreement is not perfect, and when it comes to the movement of so-called detachment fronts, the location of these fronts is much more stable in 2D simulations and experiment than the reduced modelling. Notwithstanding, this work provides first of a kind verification of a reduced physics framework to understand the control of divertor detachment.