H-Mode density limit disruption avoidance in ASDEX Upgrade, TCV and JET

In recent years a strong effort has been made to investigate disruption avoidance schemes in order to aid the development of integrated operational scenarios for ITER. Within the EUROfusion programme the disruptive H-Mode density limit (HDL) has been studied on ASDEX Upgrade, TCV and JET. This paper presents the results from these studies in the view of the plasma control system (PCS). The successful migration of disruption avoidance schemes based on direct measurements as well as state space based HDL observers across the devices has been demonstrated. HDL disruption avoidance using continuous control is now routinely available at TCV and ASDEX Upgrade, using both observer types. Exception handling based disruption avoidance has been utilized on all three devices. All three control systems allowed the implementation of the desired schemes with minimal adaptions, implementing the equivalent detection algorithms. Using the same experimental methodology it is confirmed that the XPR/MARFE movement, which is preceding the disruptive HDL, is similar on all three devices. The main difference lies in the associated times scales which increase with machine size. This would be beneficial for large devices, such as ITER and DEMO, since it would give the control system more time to apply the appropriate disruption avoidance action. As actuator auxiliary heating, gas flow and plasma shaping have been successfully demonstrated. This work gives input for the requirements of future tokamak control systems which should enable the necessary disruption avoidance schemes. All disruption avoidance schemes developed during the studies can be implemented in the ITER PCS with its currently foreseen capabilities.