Transport studies in the MAST spherical tokamak

Spherical tokamaks (STs) provide a challenging regime for the study of turbulent transport in magnetised plasmas, providing an opportunity to test gyrokinetic and MHD fluid turbulence theory under extreme conditions. The strong field curvature at low aspect ratio has an important influence on micro-stability; both aspect ratio and flow-shear affect transport and at high-β, electromagnetic effects become significant, leading to microtearing instabilities. In this paper, we describe ongoing studies of the dominant transport processes which prevail at low aspect ratio. We present the first non-linear Ion Temperature Gradient (ITG) and Electron Temperature Gradient (ETG) range simulations for MAST using the ORB5 and GYRO models, together with the first results from predictive transport modelling using GLF23 and the next-generation trapped gyro-Landau fluid model TGLF.