Plasma breakdown and runaway modelling in ITER-scale tokamaks

The creation of plasma medium from neutral prefill gas during the breakdown process is not well understood. This motivated the development of a first principles particle-based model, in an attempt to capture the time evolution of the electron growth rate and its velocity distribution. The influence of the prescribed 3D magnetic field geometry on the charged particle growth rate and spatial distribution is also a subject of study. The output of this research work can be categorised into three major areas. First among them is quantifying the resulting ionisation rate (represented by αVe) from each considered scattering angle model and selecting the suitable model for tokamak plasma breakdown simulation. This is followed by an in-depth study on the influence of B${}_{\varphi }$, B${}_{\theta }$ and E${}_{int.}$ on the rate of ionisation as well as the charge and current density spatial distribution in an ITER-scale tokamak. Finally, an attempt to develop a new merging algorithm is done for a full 3D3V particle code to provide a way forward to simulate high number density systems (upward of 10${}^{10}$ m${}^{-3}$). The following three sections provide summaries and outlooks for respective areas. This is then followed by a concluding remark to put the findings into context for ITER's eventual plasma initiation campaign.