Design and performance of the mini-magnets for FXT onboard EP mission

Purpose: Mini-magnets of FXT are designed to deflect low-energy electrons that are incident into the camera aperture area, preventing them from reaching the focal plane detector and thereby reducing the noises they generate.
Methods: By employing a combination of theoretical calculations and experimental measurements, the parameters of the FXT mini-magnets were obtained, including magnetic field distributions, magnetic moment results, and electron deflection efficiency.
Results: The structural and magnetic models of the optimized mini-magnets are presented. Distributions of magnetic field intensity on different planes within the camera aperture are compared with the measured results from the FXT flight models (FMs). The results for the total and separated magnetic moment of two sets of FMs are also provided. Additionally, the deflection efficiency for 25 keV electrons is calculated under various incident conditions.
Conclusion: The FMs of mini-magnets show good performance, with the measured values of magnetic field distributions being highly consistent with the theoretical values. A perfect result for total magnetic moment of less than 10 mA·m² has been achieved, far better than requirement of 100 mA·m². The calculated electron deflection efficiency reached over 99.88%, effectively fulfilling the objective of deflecting electrons in space.