Effects of magnetic perturbations and radiation on the runaway avalanche

Abstract

Electron runaway is seen as one of the main threats to reliable operation of magnetic confinement fusion reactors, and is an issue only predicted to worsen as reactors are scaled up. The runaway phenomenon depends fundamentally on momentum space dynamics, but to simulate large scale systems effective theories which depend only on spatial quantities are often employed. In this thesis, we will address how a momentum space dependent diffusive transport, which appears as a consequence of imperfect confining magnetic fields, can be incorporated into this type of model. A scheme to correct the generation of runaway electrons due to this transport, which incorporates the effect of radiation reaction forces, is proposed. The corrected generation of runaway electrons is formulated as a solution to an integral equation, for which a numerical solver is implemented. The effect of the model is investigated for diffusion coefficients inspired by electron diffusion in stochastic magnetic fields where a reduced generation and a larger critical electric field for the runaway generation is observed.