Burn control strategies using plasma elongation in DEMO

In this paper, a feedback control algorithm to reduce the DEMO fusion power fluctuations due to the presence of possible disturbances and unpredicted events is proposed. Fluctuations can be limited controlling temperature and densities of the different plasma species by means of a set of actuators like electron cyclotron resonance heating, fuelling rate modulation and/or impurity injection. However, electron cyclotron resonance heating is expensive in terms of power cost and impurities are difficult to control because it is hard to remove them from the core. A possible alternative is to use plasma shape as a virtual actuator and in particular elongation through plasma shape magnetic control. This work exploits the possibility to use elongation modifications in a coordinated way with electron cyclotron resonance heating power, and electron density, for real time control. The integrated control scheme implements a supervised control allocation strategy and accounts for constraints coming from actuator limits as maximum elongation, maximum ECRH power or maximum electron density, but also on other key plasma parameters like plasma safety factor and Greenwald density limit. Numerical results of the overall control scheme to compensate the effect of uncontrolled argon injection and tungsten flake event are obtained within the DEMO flight simulator based on Fenix.