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

The HBT-EP research program aims to: (i) understand the physics of scrape-off layer currents (SOLC) and interactions between the helical plasma edge and conducting boundary structures, (ii) test new methods for measurement and mode control that integrate optical and magnetic detector arrays with both magnetic and SOLC feedback, and (iii) understand MHD issues from disruptions, resonant magnetic perturbations, SOLC, and disruption mitigation using an in-vessel passive coil. A two-color multi-energy EUV/SXR tangential array has been used to observe the suppression of sawtooth MHD activity correlated with the coupling of an internal 2/1 mode and an external 3/1 kink mode. This is consistent with observations of flux pumping which broadens the current profile as has been seen in hybrid plasmas in DIII-D and JET. A deep-learning-based MHD mode tracking algorithm to process video frames from the upgraded HBT-EP high-speed videography system has been used to determine the n=1 mode amplitude and phase [1]. A real-time application of this algorithm using an FPGA has achieved a latency less than 17 μs, on par with the magnetic sensor GPU-based control system. Measurements from a new set of high-field side halo current diagnostic and control tiles before and during disruptions will be presented, along with plans for runaway electron mitigation coil (REMC) studies.

[1] Y. Wei, et al, PPCF 65 (2023) 074002