Development of Tunable, Precision Permanent Magnet Phase Shifter for X-Ray FEL

In an x-ray free-electron lasers (XFEL), a high quality relativistic electron beam from a linear accelerator traverses an array of undulator magnets to generate a high power x-ray beam by allowing the FEL to reach saturation. In many XFELs, phase shifters haven’t been commonly used or included in their designs. The importance of the phase shifter was recognized only recently. A phase shifter can be constructed using either an electromagnet (EM) or a permanent magnet (PM). EM phase shifters are heavy, complex to operate, and take more valuable longitudinal space between the undulators. Compared to EMs, the PMs have several outstanding advantages, including compactness, lighter weights, simple operation, and low maintenance. This Small Business Innovation Research project will develop a tunable PM-based compact phase shifter for the XFEL. The new design incorporates proven features from the prior work, along with novel field tuning methods, which allow the field strength to be adjusted within a reasonably large range to achieve the desired range of the phase delay control. The PM design without electric currents and power electronics associated with EMs improves reliability by reducing the number of possible points of failure and lowers the operation cost. The compactness makes it possible to use PM phase shifters in the existing XFELs with small gaps between adjacent undulators, as well as in the new XFELs without significantly increasing the FEL length. Phase I will proceed with: (1) Determine the optimum physics parameters for the phase shifter; (2) Conduct design optimizations with concrete magnetic and geometrical parameters of actual PM material produced; (3) Provide solutions to achieve precision tuning of the magnetic fields; (4) Elaborate a design based upon ease of manufacturing and cost comparison analysis; and (5) Fabricate a smaller scale prototype of the optimal magnet design, and characterize the magnet by performing a full set of the field measurements. This phase I project will provide a foundation for the research and development in the next phase Small Business Innovation Research project, which will aim at designing and building a full- size PM phase shifter for an XFEL. This project will significantly provide the potential to bring a paradigm change in accelerator technology, replacing conventional electromagnets for many existing applications and allowing the development of new applications in completely new areas. For example, the PM FEL phase shifters can help significantly improve coherence and power of an XFEL. The proposed use of PM phase shifters will also bring significant cost savings to the construction, operation and maintenance of FEL facilities.