High-speed digital mode control feedback on magneto-hydrodynamic instabilities in the HBT-EP tokamak

Ideal magneto-hydromagnetic (MHD) instabilities set the limit on sustainable pressures in advanced tokamak devices, which are the leading candidates for viable fusion reactor concepts. Active feedback control of these instabilities may present a route to high-pressure operation with burning plasmas and is therefore of intense interest. The feedback system on the HBT-EP tokamak uses magnetic pick up and control coils which are arranged in what is called a "mode control" configuration and are coupled via a set of high-speed digital processors. Experiments are presented which show that this system is capable of suppressing these instabilities even when they are near the ideal limit. The effects of transfer function phase shifts, loop latency, and control coil coverage of the feedback system are characterized and shown to be critically important.