Error field measurements with rotating RMP fields for DIII-D H-mode

Abstract Three-dimensional magnetic sensors are employed to identify the amplitude and toroidal phase of error fields (EFs) by analyzing the torque balance for magnetic islands entrained by rotating resonant magnetic perturbations (RMPs) in DIII-D H-mode plasmas. This technique of torque balance allows for efficient identification of EFs, offering a valuable tool for scenario-specific and optimized EF compensation (EFC), and requires only magnetic diagnostics. The torque balance used in this work includes the contribution from electromagnetic torque due to EFs, wall response, RMP fields and viscous torque. Results show that viscous torque plays a crucial role, particularly during locked modes and H-mode plasmas, ensuring accurate data fits with lower residuals. The torque balance technique reveals that L- and H-mode plasmas have distinct EF configurations, consistent with a model-based EF analysis including the ideal magnetohydrodynamic plasma response in IPEC and the SURFMN EF simulation. This technique shows great robustness in measuring the intrinsic EF amplitude regardless of its amplitude or toroidal phase. Repeated discharges with EFC disparities exhibit consistent results of intrinsic EF within a reasonable range near the ‘standard’ EFC. Additionally, the use of a rotating n = 1 RMP offers the advantage of reducing the risk of disruption by entraining saturated magnetic islands. These findings are instrumental for optimizing EF correction in fusion devices, thereby enhancing tearing mode suppression and overall plasma stability.