Removing magnetic pickup from SOL current sensors in HBT-EP

Rogowski coil current sensors have been recently installed on low field side (LFS) diagnostic tiles in three toroidal locations in HBT-EP, for the purpose of determining how scrape-off layer (SOL) currents flow between the plasma and the chamber during discharges. These sensors are attached to the movable walls within the vessel and allow for radial scans of the current. We present numerical methods for removing contributions from external magnetic fields that are picked up by the Rogowski coils due to their imperfect windings. These fields primarily consist of contributions from the equilibrium fields and plasma instabilities, as well as the vertical field, toroidal field, ohmic heating, and non-axisymmetric control coils. The latter can be calibrated using distinct vacuum shots, while the former can be calibrated by shadowing the sensors with other shells and/or limiters during discharges. These calibrations can then be used to compare the amplitudes and directions of the SOL currents relative to the edge magnetic field perturbations.