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

The HBT-EP active mode control 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 fundamental MHD issues associated with disruptions, resonant magnetic perturbations, and SOLC. A two-color multi-energy EUV/SXR tangential array has been used to study internal MHD mode structure. Sawtoothing MHD has been observed correlated with reduced amplitude of 2/1 tearing mode activity. Disruption dynamics and current paths in the SOL and the vacuum vessel have been studied. The scaling of the MHD mode rotation frequency during the current quench phase studied by Myers [NF 58 (2018)016050] has been extended to include HBT-EP data leading to a new drift-frequency based scaling law [Saperstein et al., NF 62 (2022) 026044]. Stable non-disruptive operating space boundaries in HBT-EP have been mapped using a variational autoencoder neural network with a reduced dimensional representation [Wei et al., NF 61 (2021)126063]. A deep-learning-based MHD mode tracking algorithm to process video frames from the upgraded HBT-EP high-speed videography system shows significant improvement over the previous SVD-based method to determine the n=1 mode amplitude and phase.