Optimization of the Current Ramp-up Phase in DIII-D via Physics-model-based Control of Plasma Safety Factor Profile Dynamics

J.E. Barton, W.P. Wehner, E. Schuster, T.C. Luce, G.L. Jackson, J.R. Ferron, D.A. Humphreys, A.W. Hyatt

Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)

New Orleans, Lousiana, USA, October 27-31, 2014

Abstract

Simulations and experimental results in DIII-D are presented to demonstrate the potential of physics-model-based control of the q profile to improve the reproducibility of plasma startup conditions by achieving a specified target q profile at the end of the current ramp-up. Three different q profiles (qmin of 1.3, 1.65, 2.1 and q95 of 4.4, 5.0, 6.2, respectively) were specified as targets. A feedforward + feedback scheme is utilized to control the q profile and is constructed by embedding a nonlinear, physics-based model of the q profile dynamics into the control design process. A unique characteristic of the feedforward trajectories obtained by solving the optimization problem is the regulation of the plasma current ramp-up rate to achieve the target q profiles. The feedback controller is employed to add robustness to the control scheme and account for drifts due to external plasma disturbances.