Improved modeling of a lower-hybrid wave driven plasma using an extended MHD equilibrium reconstruction on the TST-2 spherical tokamak

Non-inductive plasma start-up is required for a spherical tokamak fusion reactor. Start-up using lower-hybrid current drive has been studied at the TST-2 spherical tokamak. Recently, equilibrium reconstruction based on the extended MHD model was developed to describe the fast electron current dominated equilibrium more accurately. The new equilibrium was applied to a coupled ray-tracing and Fokker-Planck solver based current drive simulation. The simulated total plasma current was within a factor of two of the outer-midplane launch experimental result, but overestimated the experiment by a factor of three for the top launch case. The measured x-ray radiation was substantially greater for the top launch case compared to the outer-midplane launch case despite the similar plasma current. This may indicate that current drive is affected appreciably by the rf induced transport that is a finite-orbit effect neglected in the present current drive simulation.