Optimization, real-time simulation and feedback control of tokamak plasma profiles on TCV

Introduction Control of plasma profiles is an essential ingredient in tokamak operation, in particular to access improved confinement regimes where the safety factor (q) profile plays a major role in determining plasma confinement and stability. This paper shows how physics models of profile transport can be used for improved plasma profile control methods. We show two distinct applications. In the first, a physics model is used to aid in the real-time reconstruction of the q profile, providing spatial and temporal accuracy beyond the limits imposed by diagnostic hardware constraints. This paradigm has been implemented in the TCV tokamak real-time control system and is able to provide real-time estimates of the q profile every 1ms. The reconstructed profiles have then been used in a feedback controller for the internal inductance. The second application is in determining the optimal time evolution (trajectories) of tokamak plasma actuators such as to reach a prescribed set of profiles at the final time while satisfying constraints during the transient. This technique is applied to determine the optimal trajectories of Ip and auxiliary power Paux required to reach a stationary hybrid q profile at the end of a TCV plasma current ramp-up phase.