Model-based Control of the Current Profile Dynamics in KSTAR: Status, Plans and Needs

E. Schuster, T. Rafiq, W.P. Wehner, H.-S. Kim, S.-H. Hahn, Y.-M. Jeon, M.D. Boyer, S. A. Sabbagh, M.L. Walker, D.A. Humphreys

KSTAR Conference

Muju, South Korea, February 21-23, 2018

Setting up a suitable current profile, usually defined in terms of the safety factor q or the rotational transform ι profiles, plays a critical role in the achievement of advanced tokamak scenarios characterized by high confinement and the non-inductive sustainment of the plasma current necessary for steady-state operation. Robust current profile control algorithms need therefore to be developed to provide reliable access to the conditions necessary to meet the KSTAR steady-state mission. The high dimensionality of this problem, along with the strong nonlinear coupling between magnetic and kinetic profiles motivates the use of model-based control synthesis that can accommodate this complexity through embedding the known physics within the design. Tight regulation of the q profile together with control of some other critical plasma properties such as βN is made possible by combining off-line (feedforward control) and on-line (feedback control) model-based optimization. At the core of both optimization solutions are physics-based, control-oriented models of different complexities (off-line optimization: nonlinear model, on-line optimization: linear model) capturing the dominant physics of the q-profile and βN responses to the available actuators (H&CD systems). This model-based optimal control approach to current profile regulation for steady-state scenario achievement and sustainment has already been demonstrated experimentally on DIII-D. Plans for extending this approach to KSTAR will be discussed.