LINEAR OPTIMAL-CONTROL OF TOKAMAK FUSION DEVICES

The control of plasma position, shape, and current in a tokamak fusion reactor is examined using linear optimal control. These advanced tokamaks are characterized by non-up-down symmetric coils and structure, thick structure surrounding the plasma, eddy currents, shaped plasmas, superconducting coils, vertically unstable plasmas, and hybrid function coils providing ohmic heating, vertical field, radial field, and shaping field. Models of the electromagnetic environment in a tokamak are derived and used to construct control gains that are tested in nonlinear simulations with initial perturbations. The issues of applying linear optimal control to advanced tokamaks are addressed, including complex equilibrium control, choice of cost functional weights, the coil voltage limit, discrete control, and order reduction. Results indicate that linear optimal control is a feasible technique for controlling advanced tokamaks where the more common classical control, relying on the scalar/orthogonalized description, will be severely strained.