Development of a Robust Current Profile Feedback Controller in DIII-D*

Setting up a suitable current profile has been demonstrated to be a key condition for one candidate advanced tokamak scenario with improved confinement and steady-state operation. A control-oriented model of the current profile evolution in DIII-D was recently developed for the plasma current ramp-up and early-flattop phases [1] and used to synthesize open-loop control schemes tested both in simulations and experiments [2]. A robust closed-loop controller is proposed to regulate the current profile under the presence of model uncertainties in the plasma resistivity. Using the POD/Galerkin technique, the control-oriented PDE model is reformulated into a low-dimensional ODE model that preserves the dominant dynamics, and an $H_\infty$ controller is designed to minimize the regulation/tracking error. A Corsica-based simulation assessment is presented. \vskip6pt\noindent [1] Y. Ou, et al., Fusion Engin. Design {\bf 82} (2007) 1153. \par\noindent [2] Y. Ou, et al., Plasma Phys. Control. Fusion {\bf 50} (2008) 115001.