Experiments and modelling of external kink mode control using modular internal feedback coils

Abstract

We report on recent advances in modelling and experiments on resistive wall mode feedback control. The first experimental demonstration of feedback suppression of rotating external kink modes near the ideal wall limit in a tokamak is described [1]. This was achieved using an optimized control system employing a low latency digital controller and directly coupled modular feedback coils. The magnitude of plasma dissipation affecting kink mode behaviour has also been experimentally quantified for the first time using measurements of the radial eigenmode structure of the poloidal field fluctuations associated with the rotating kink mode. New capabilities of the VALEN code [2] are also reported. These include the ability to simulate multiple plasma modes and mode rotation in the model of the feedback control loop. Results from VALEN modelling of resistive wall mode feedback control in ITER are also presented, showing a significant improvement in performance with internal coils. Evidence for a lack of mode rigidity in HBT-EP is given, and plans to address this and other issues related to coil coverage and coil modularity are presented.