The magnetic island control system is setup following a systematic design approach. The line-of-sight ECE system incorporates magnetic island monitoring and actuation in a single transmission path, thereby minimizing latencies and avoiding the need for geometrical transformations between sensor and actuator. A prototype line-of-sight Electron Cyclotron Emission (ECE) system was developed earlier at the TEXTOR tokamak, Forschungszentrum Jülich, Germany and is used here as the dedicated sensing scheme for feedback control of magnetic islands. Besides the actuators for manipulation of magnetic islands, the feedback control system requires sensors for real-time detection and monitoring of island control variables such as the island location in the magnetic topology, the island’s size and its rotation frequency.

In addition, it will be shown that tailoring of the applied ECRH/ECCD power level via feedback manipulation allows to apply exactly the right amount of power to enforce complete suppression of an island or can be used for the stabilization of a magnetic island at a specific width. This feedback control system allows dynamic island tracking and guarantees stability robustness against uncertainties, disturbances and perturbations. In this work, an advance is made towards a fully autonomous closedloop system that detects magnetic islands, establishes and maintains an accurate alignment between the suppressing ECRH/ECCD and a magnetic island via a feedback controlled steerable mirror and manipulates the applied ECRH/ECCD power in real-time. Suppression experiments, reported earlier, use a fixed alignment and power settings or offer a coarse closed-loop optimization of the alignment of ECRH/ECCD with an island. This is known as Electron Cyclotron Resonance Heating and Current Drive (ECRH/ECCD). The injected millimeter waves induce a local driven current that suppresses the island. For effective magnetic island suppression, localized, high-power millimeter waves must be aligned precisely with the island centre at centimeter accuracy.

Control of magnetic islands allows for high performance plasmas and pulse length extension. Magnetic islands grow nonlinearly, reduce the plasma energy confinement and deteriorate the steady-state operation of tokamaks. At high pressure, however, the magnetic field topology can break-up and magnetic islands are formed. The power produced by the fusion reactions increases with the plasma pressure. In a tokamak, magnetic fields confine a fusion plasma in a topology of toroidally nested magnetic surfaces. A real-time feedback control system has been developed that finds, tracks, suppresses and/or stabilizes resistive magnetic instabilities in a nuclear fusion plasma.

Sight control feedback loop