Mode suppression in HBT-EP using active feedback and a quadrature bias probe array

Suppressing MHD instabilities in Tokamaks is one of the largest challenges facing the fusion community, and to address this, one set of solutions uses sourced electrical currents in the plasma. However, the path these currents take through the plasma and how they couple with MHD modes are not well understood. In this work, we set out to understand the currents' paths and coupling behavior by implementing four directional probes in quadrature in HBT-EP and configuring them to source parallel (co-IP or counter-IP), cross, or perpendicular currents as well as measure plasma rotation. HBT-EP's active feedback system, using a parallelized GPU with 21 \^{A}\textmu s cycle latency, determines the n$=$1 mode phase and then sources phase-locked currents at the probes to couple with and ideally suppress the m$=$2 and m$=$3 modes. Mirnov coils and scrape-off-layer sensors measure the flow of 14 kHz current driven by the probes and provide insight into the current's path, and a resistive Ohm\^{a}\texteuro \texttrademark s law current model is developed and compared to the experimental results.