Toward integrated digital control of the DIII-D tokamak

An integrated digital controller for the DIII-D tokamak is being developed to simultaneously control plasma equilibrium parameters using modern multiple-input-multiple-output (MIMO) techniques. It is anticipated that this controller will eventually replace the current mixed analog and digital controller, allowing all aspects of DIII-D plasma control to be incorporated into a single digital system. In this paper, we describe the technical approach and engineering problems associated with development of a digital controller using modern control techniques. The hardware capability to apply modern control methods is enabled by recent development of a real-time digital data acquisition and control system for DIII-D. Recent work in simulating plasma control with MIMO techniques has demonstrated that such methods can be successfully applied to the control of tokamak plasmas. Perturbed equilibrium techniques have been shown to provide accurate and rapidly computable estimates of the linear, axisymmetric, ideal magnetohydrodynamic plasma response. Integration of these hardware and analytical capabilities will produce a uniquely flexible, accurate, and robust plasma control system which can be readily applied to high performance next-generation tokamaks. The DIII-D device itself provides an ideal testbed for implementation and evaluation of multivariable tokamak control strategies