Simultaneous Boundary and Distributed Feedback Control of the Current Profile in H-mode Discharges on DIII-D

M.D. Boyer, J. Barton, W. Shi, W. Wehner, E. Schuster, J.R. Ferron, M.L. Walker, D.A. Humphreys, F. Turco, T.C. Luce, R.D. Johnson and B.G. Penaflor

19th IFAC World Congress

Cape Town, South Africa, August 24-29, 2014

Abstract

Control of the current profile in tokamak plasmas has been shown to play an important role in achieving advanced scenarios that could enable steady-state operation. The nonlinearity and spatially distributed nature of the current profile dynamics motivate the use of model-based control designs. In this work, we consider a control-oriented model of the current profile evolution in DIII-D high-confinement (H-mode) discharges, and the problem of regulating the current profile around a desired trajectory. The PDE model is discretized in space with a finite difference method and a backstepping design is applied to obtain a transformation from the original system into a particular target system with desirable properties. The resulting boundary condition control law is complemented with control laws for the available distributed actuators. The combined control strategy uses nonlinear combinations of the total plasma current, total power, and line averaged density as actuators. Simulation and experimental results show the ability of the controller to track desired targets and to reject input disturbances.