Magnetic Sensor Performance Evaluation in DIII-D with Magnetic Diagnostic Response Function*

The extensive magnetic diagnostic systems in present tokamaks are comprised of numerous hardware devices. The potential for intermittent hardware failures means that some signal distortion in random channels cannot be completely avoided, and such low-performing signals are difficult to identify in advance of tokamak operation. The magnetic diagnostic response function (MDRF) [1] appears to be an effective method of predicting magnetic sensor response to applied fields and induced vessel fields. The time-dependent Green's function used in MDRF is derived by fitting magnetic measurements obtained from individual coil pulses at varying frequencies. The predicted and measured signals are compared to evaluate magnetic sensor performance and identify malfunctioning channels. This work will be used to identify malfunctioning magnetic channels before plasma formation at DIII-D by utilizing the applied fields from heating, shaping, and 3D coils during the pre-plasma time window t = [-1, 0] sec. The low-performance magnetic channels are flagged in order to inform sensor selection in both real-time and post-shot equilibrium reconstructions, to benefit tokamak operation and improve the accuracy of equilibria-based analysis. The identified faulty sensors are recorded shot-by-shot to aid in troubleshooting the magnetic hardware system.