Design of a Short Period Helical Superconducting Undulator

Superconducting technology provides the possibility to develop short period, small bore undulators that can generate much larger magnetic fields than alternative technologies. This may allow an XFEL with optimised superconducting undulators to cover a broader range of wavelengths than traditional undulators. At STFC, we have undertaken work to design and build a prototype helical superconducting undulator (HSCU) module with parameters suitable for use on a future XFEL facility. This work includes the design of a full 2 m long undulator module, including an undulator with 13 mm period and 5 mm inner winding diameter, the supporting cryogenic and vacuum systems required for operation, and quadrupoles, phase shifters and correction magnets for use between undulator sections. We present here the magnetic and mechanical design of the HSCU. The choice of undulator parameters and their influence on the design is discussed. A turnaround scheme to allow continuous winding of the undulator without the need for superconducting joints is also presented. Techniques for winding the undulator are currently being investigated and a short prototype will soon be wound and tested.