High-Temperature Superconducting Undulators for Future X-ray Free Electron Laser Systems

A free electron laser (FEL) can be used to produce high intensity X-rays, or other monochromatic radiation for a number of purposes. Two primary components, in terms of size and expense, of an FEL system are an electron accelerator and undulator. Reducing undulator period without reducing its magnetic field would allow a reduction in the electron beam energy and potentially reduce the total cost and complexity of FELs. In this paper, finite-element modeling and experimental approaches were used to investigate the feasibility of using high-temperature superconducting (HTS) conductor to create tunable, liquid nitrogen cooled undulators with shorter periodicity. A prototype undulator with three periods was fabricated and tested. Hiperco 50 A structures with machined grooves were used as the magnetic cores. Commercial YBCO tapes were used to wind the magnetizing coils in the grooves of the magnetic core. The undulator was tested and measured in subcooled liquid nitrogen at 65 K. Peak magnetic fields of 0.77 T with a periodicity of 14 mm were attained. Our simulations indicate that by using optimally processed magnetic core and HTS wires, fields of 1 T or higher can be achieved.