Design of the Permanent Magnet Diverter for Deflecting Electrons on Wide-Field X-Ray Telescope

The Einstein Probe (EP) Satellite is a mission of Chinese Academy of Sciences, which is planned to be launched at the end of 2022. Its main work is to explore all-sky transient X-ray sources and constantly various X-ray sources. It will carry a Wide-field X-ray Telescope (WXT) and two Follow-up X-ray Telescopes (FXT). It is dedicated to investigate time-domain astronomy and to monitor the sky in the soft X-ray band. For the WXT, the electrons with kinetic energy below 1 MeV will pollute the background when they pass through the optic system. So, it is a key issue to remove the electrons with low energy out of the beam. A Permanent Magnet Diverter (PMD) is designed and fabricated for the WXT. Its main purpose is to separate the background electrons from the X-ray detecting system by re-directing the electrons. In order to minimize the magnetic flux leakage and the magnetic moment, a design of circular magnetic field is proposed by arranging the neodymium iron boron permanent magnet blocks appropriately, which can reduce the length of electron deflecting paths when they pass through the magnetic field region. The total weight is taken into considerations to optimize the structure of the PMD during design. Furthermore, the motion of electrons in the PMD and their entering paths towards the detector are simulated to improve the structure of the PMD. At the end, the eigenfrequency and mode shapes are analyzed to make sure the PMD could work normally on the satellite platform. The design and analysis of the PMD are presented detailed in the paper.