Experimental Verification of a Permanent Undulator for a Strong Helical Field

A helical undulator composed of a permanent magnet structure with a spiral surface, called a twin helix undulator (THU), was designed, built, and experimentally verified to produce a strong helical field of up to 1 T. This THU design, for insertion devices with a permanent magnet structure, is capable of providing the highest helical field for such devices, but with the same period length and gap conditions. The prototype THU built in this work has a period length of 20 mm and a round gap of 5.5 mm. The measurement results show that it can provide a peak helical field up to 1.043 T. In addition to explaining the magnetic field characteristics of the THU and other permanent magnet helical undulators, this article provides a complete explanation of the process of designing, building, measuring, and verifying the prototype THU.