Some nonlinear controls for nonlinear processes in the DIII-D tokamak

In the past few years, much work has been done at various institutions on application of multivariable linear controllers for Tokamak shape control. A great deal has been learned about Tokamak plasma shape control through these studies. Now some of the practical constraints imposed by working Tokamaks must be addressed in order to make the benefits of multivariable control available to working experimental devices. In this paper, we discuss several non linear processes and constraints at DIII-D which must be dealt with as part of the implementation of a routine operational controller. We describe partial solutions to the problems already implemented and point out some characteristics required of future solutions to the remaining problems.