Path-oriented early reaction to disruptions in ASDEX Upgrade and TCV in view of the future needs for ITER and DEMO

Routine reaction to approaching disruptions in tokamaks (i.e. sudden current quenches) is currently restricted to machine protection, which obviously remains a basic requirement for ITER and DEMO. However, in future fusion devices, high performance discharge time itself will be very valuable. The ultimate mission is to actively avoid approaching disruptions at an early stage in general, and sustain the discharge whenever possible. To achieve this, the knowledge of the various disruption root causes and the corresponding chain of events towards a disruption, i.e. the disruption path, is vital. For each considered path, physics-based sensors and adequate actuators have to be identified and a hierarchical and specific handling strategy has to be developed. Early detection and reaction facilitates the efficiency of the actuators and enhances the chance for a full recovery. For some disruption paths, experiments have been performed at ASDEX Upgrade and TCV. Disruptions were provoked in ASDEX Upgrade by a high ?N-limit in hybrid scenarios, by a ne-limit both in L and H-modes, and in TCV by impurity injection in ELMy H-modes. For these example discharges, this new approach has been implemented. Based on the gained insight, path-specific strategies will be further developed about sensors (e.g. still rotating modes or radiation rise), actuators (e.g. ECCD at q=2 surface for mode stabilisation or rotating resonant magnetic perturbations for mode entrainment) and their limitations. The hierarchy of action should be discharge recovery to full performance, continuation with a less disruption-prone back-up scenario, controlled discharge termination and in the worst case disruption mitigation. Present ideas on how these schemes can lead to a generalized concept of early handling of approaching disruptions in present devices and their use as a blueprint for ITER and DEMO will be presented.