HBT-EP Program: MHD Dynamics and Active Control through 3D Fields and Currents

The HBT-EP active mode control research program aims to: (i) advance understanding of the effects of 3D shaping on advanced tokamak fusion performance, (ii) resolve important MHD issues associated with disruptions, and (iii) measure and mitigate the effects of 3D scrape-off layer (SOL) currents through active and passive control of the plasma edge and conducting boundary structures. SOL current measurements have been used to study SOL dynamics and current-sharing with the vacuum vessel wall during kink-mode growth and disruptions. Asymmetric vessel currents are observed to reach ~5% of the pre-disruption plasma current during the current quench, and have been analyzed in the context of several disruption models. A multi-chord extreme UV/soft X-ray array is being installed to provide detailed internal mode structure information. A GPU-based low latency control system using 96 inputs and 64 outputs to apply magnetic perturbations for active control of kink modes has been extended to control plasma toroidal rotation through feedback on the voltage of a biased electrode in the plasma edge. Applying high voltage and current to the probe induces strong poloidal flow shear and a transition into biased H-mode.