Simulating feedback-controlled error field correction

A new model for simulating error field (EF) correction using magnetic feedback is presented. The model makes use of vacuum intrinsic EF and correction coil fields calculated by the SURFMN code [MJ Schaffer, et al., Nucl. Fusion 48 (2008) 024004] and the ideal MHD plasma response field, including drift-kinetic modifications, simulated by GPEC [J-K Park and NC Logan, Phys. Plasmas 24 (2017) 032505]. The vacuum and plasma response fields are restricted to a single toroidal mode n and projected to magnetic sensors, providing coefficients for a scalar model. Solving the model yields correction coil currents that minimize the EF response in the sensors. Comparing the predicted correction currents with recent DIII-D mode control feedback experiments yields ≈50% agreement for n=1 and a large phase disagreement for n=2, indicating possible inaccuracies in the EF source model or suboptimal feedback.