Congratulations to Bhavin Patel, a York Fusion CDT student who successfully defended his thesis at viva on 25 March 2021. Bhavin’s thesis is entitled ‘Confinement physics of a steady state net electric burning spherical tokamak‘ and his supervisors are Professor Howard Wilson & Dr David Dickinson. An abstract from Bhavin’s thesis is below.
“This work examines the feasibility of a spherical tokamak capable of generating net electricity, which was called BurST for Burning Spherical Tokamak. Different steady state scenarios were examined and areas of operating space were ruled out by different operational limits such that a baseline scenario at 1GW was determined. The feasibility of driving the auxiliary current using neutral beam injection was examined and a suitable configuration was designed such that all the auxiliary power was driven with 94MW. Next the linear micro-stability was examined to understand which types of turbulence will be prevalent in BurST like plasmas. Kinetic ballooning modes (KBMs) and micro-tearing modes (MTMs) were found to the dominant modes. Flow shear was able to wipe out the KBMs and certain MTMs but other MTMs were resilient against it. However, these MTMs were stabilised by the density gradient such that a new equilibrium was designed with a more peaked density profile. This equilibrium was marginally stable to all the modes found, suggesting operating at neoclassical levels of transport may be possible. Finally, the validity of the TGLF quasi-linear model was examined in a BurST regime. It was not possible to obtained converged nonlinear BurST simulations as the MTMs found required multi-scale resolution, but the the TGLF model was tested in progressively more challenging regimes. In low beta ITG regimes, the quasi-linear approximation was found to be valid, but the saturation rule needs development in a high aspect ratio tokamaks. For electromagnetic turbulence like MTMs, it was found the the quasi-linear approximation needs further development”.