Scrape-off-layer current measurements during disruptions in HBT-EP

Non-axisymmetric halo currents that occur during tokamak disruptions can result in significant asymmetric forces on the vessel, potentially causing damage to components. Understanding the generation and rotation of these currents is important for establishing design requirements for high-current devices to tolerate disruptions. A new set of halo current diagnostic tiles has been installed on the high-field-side of the HBT-EP tokamak, in regions where there is strong plasma-wall contact and current flow during disruptions. Two tile arrays are built as electrically-isolated blade limiters with poloidal resolution and separate toroidally-facing collection areas. Arrays are located at 2 toroidal locations separated by Δφ=96°, integrating over 6 poloidal regions with Δθ~12° resolution to measure narrow poloidal contact areas. We present the first disruption current measurements from these tiles. Strong localized electron currents to tiles correlate with magnetic perturbations, and are observed to rotate poloidally from tile to tile. Cathode spots form on tiles in some cases, leading to strong local electron emission. Plans for biasing the tiles and for expanding the system to a set of four equally-spaced arrays are also described.