A framework for the design of a plasma current and shape controller in next-generation tokamaks

The problem of designing a plasma current and shape control system for a tokamak is dealt with, anal a complete framework based on a validated linearized plasma model is developed. Starting from the equilibrium configurations to control and given the required performance, a procedure for choosing the parameters to control is outlined Then, a method is proposed to evaluate the best performance one could ever expect from a control system, given the actual limitations due to the power supply. A procedure for designing a linear controller is described. The use of a modern multivariable technique, such as the H-infinity theory, allows one to take into account the many existing constraints and to find a trade-off among performance, robustness, and control effort. The methodology proposed is general and can be applied in principle to any tokamak plant. The simulation results refer to the International Thermonuclear Experimental Reactor (ITER) tokamak. A controller designed following almost the same steps has been successfully tested on an existing tokamak.