Multivariable shape control development on the DIII-D tokamak

In this paper, we describe recent work on plasma shape and position control at DIII-D. This control consists of two equally challenging problems the problem of identifying what the plasma actually looks like in real time, i.e. Measuring the parameters to be controlled, and the task of determining the feedback algorithm which best controls these plasma parameters in a multiple input-output system. Recent implementation of the EFIT plasma equilibrium reconstruction algorithm in real time code which produces a new equilibrium estimate every 1.5 ms seems to solve the long-standing problem of obtaining sufficiently accurate plasma shape and position estimation. Stabilization of the open-loop unstable vertical motion is also viewed as a solved problem. The primary remaining problem appears to be how best to command the power supplies to achieve a desired shaping control response. We describe our effort to understand and apply linearized models of plasma evolution to development and Implementation of multivariable plasma controllers.