Effectiveness and constraints of using the refueling system to control fusion reactor burn

A specialized 0-dimensional plasma simulation code has been developed and used to study the possibility of controlling the burn condition of an ITER-type fusion reactor by modulating the refueling rate. A robust feedback controller is synthesized; the values of feedback gains are obtained by an ℋ_∞ design. Simulation shows that, for burn control, modulating the refueling rate could be a better mechanism than, for example, modulating the auxiliary heating power, because the former can stabilize larger perturbations and obtain a higher Q-value. Specifically, using ITER/CDA tokamak parameters, it is found that modulating refueling rate alone can stabilize ±10% perturbations in temperature, as long as the controller delay due to the finite time required for fresh fuel to diffuse into the plasma center region is not much larger than the energy confinement time