Comprehensive Feedback Control of a Tokamak Fusion Reactor

Abstract

Results for the first simulated comprehensive feedback control study for a tokamak operating in the fusion regime are presented. A standard Burning Plasma Experiment (BPX) design is the simulated reactor, but the results apply to any tokamak. Feedback gains are derived for specific classes of dynamic models and control objectives using model-based optimal control. An integrated control approach treats both kinetic and electromagnetic parameters and radial profiles. The control actuators include poloidal field coils, fast-wave and lower-hybrid current drive and heating sources, and pellet fuel injectors. Results show that the strongly coupled plasma parameters provide unintended secondary responses to controller inputs. In particular, attempts to modify the q-profile greatly affect the temperature and density profiles when the transport model incorporates International Thermonuclear Experimental Reactor (ITER) scaling. The hot, highly conductive plasma and poor source penetration in the nominal BPX discharge make the central q-values difficult to regulate. Fusion events also complicate the control efforts. Further, simple plasma circuit models are inadequate to account for a significantly evolving current profile. Proper understanding and use of integrated, model-based feedback control will avoid these pitfalls.