Controlling a DEMO reactor with a sparse set of diagnostics

The development of the diagnostic and control (D&C) system for a future tokamak demonstration fusion reactor (DEMO) is facing unprecedented challenges. On the one hand, the DEMO D&C system has to provide high reliability, since any loss of plasma control may result in damage of the inner wall of the machine. Moreover, high accuracy of the D&C system is needed in order to operate near operational limits, where the power output of the reactor is maximised. On the other hand, space restrictions for the implementation of diagnostic components in the blanket (optimization of the tritium breeding rate), and lifetime issues for the front-end components (neutron and gamma radiation, heat loads, erosion and deposition) will limit the performance of measurements, while the capabilities of the available actuators (poloidal field coils, external heating and fuelling) are limited as well. As part of the European DEMO conceptual design studies, the development of the D&C system has recently been launched [1]. An initial understanding of the prime choices of diagnostic methods and actuators applicable to DEMO has been obtained, and the conditions for controllability of the DEMO plasma are being analysed quantitatively by numerical simulations. First results and plans for future R&D will be presented.