US Patent 10485089 Helical permanent magnet structure and undulator using the same

A helical permanent magnet structure includes at least one magnet assembly. The magnet assembly includes a plurality of permanent magnets and poles. The permanent magnets are with a magnetization direction, and formed as helical shape and arranged as a helical surface, the center of the helical surface has a longitudinal passage for being passed through by a charged particle. The poles are with the same amount of the permanent magnets, wherein the poles are magnetized by the permanent magnets and absorb on one side of the permanent magnets.