Progress on HTS Undulator Prototype Coils for Compact FEL Designs

Compact free-electron lasers require short accelerator structures followed by high peak field and short-period undulators to produce coherent radiation up to hard X-rays. Likewise, future lepton colliders, like CLIC or FCC-ee, require high-field damping wigglers for the creation of low emittance beams. The application of high-temperature superconductor (HTS) in the form of coated REBCO tape to undulators and wigglers enables higher magnetic fields and larger operating margins. This paper discusses the potential of HTS for a superconducting vertical racetrack (VR) undulator coil geometry as well as results of the development work done on a prototype coil, with a period length of 13 mm, wound from coated REBCO tape conductor. Design and assembly aspects as well as first results from powering tests at 77 K are presented and discussed.