First Observation of Currents Induced by Alfvén Eigenmodes in a Magnetic Confinement Device.

Instabilities driven by energetic particles normally reduce fusion power, but recent studies find Alfvén eigenmode instabilities can drive "zonal" flows and currents that reduce thermal transport, improving overall performance. Motional Stark effect data from the DIII-D tokamak reveal changes in magnetic pitch angle during the phase when Alfvén-eigenmode nonlinearity drives zonal flows, suppresses microturbulence, and increases the electron and ion temperatures. Measured changes in the safety factor of Δq/q[over ¯]≃5% occur in roughly 20 ms, consistent with a rough estimate based on the measured zonal flow.