Simulations of 3D currents in SPARC for magnetic sensor placement optimization and impact analysis

Magnetic fields produced by three dimensional currents in the vacuum vessel and other conducting structures in SPARC will impact the magnetic sensor signals required for plasma control and analysis of MHD modes. To determine the effects of these currents on the SPARC magnetic sensor set, the thin-wall current modeling tool ThinCurr [1] is used, along with CAD-derived models of the vacuum vessel walls, port plugs, and thermal shields (termed “parasols”) to simulate 3D eddy current distributions induced by models of MHD modes. These simulations are used to inform the optimal placement of an array of Mirnov sensors designed to detect high frequency modes, as well as determine the effects of sensor parasol thickness and location. The results of ThinCurr simulated, high frequency Alfven eigenmodes show that eddy currents induced in nearby conducting structures have a substantial impact on the sensor signals when placed in close proximity, but that signal attenuation due to distance from the simulated mode was also a competing factor at these short, centimeter ranges. This analysis advises sensor placement by addressing the competing need to both shield and support the magnetic sensors, while simultaneously ensuring appreciable signal strength for MHD mode detection, which is necessary for successful SPARC operation.

[1] C. Hansen et al. 2025 Comput. Phys. Commun. 315 109713