Powering test results of HTS undulator prototype coils for compact FELs at 4.2 K

Short-period and high-field undulators are crucial for the production of coherent light up to X-rays in compact free-electron lasers (FELs). Besides, future colliders like CLIC or FCC-ee demand high-field damping wigglers to reach a low beam emittance. Both applications may benefit from the use of high-temperature superconductors (HTS): magnetic field amplitudes in the range of 2 T become feasible for short periods of 15 mm and smaller with magnetic gaps of 6 mm at 4.2 K. Moreover, potential operation at higher temperatures may relax cryogenic requirements and reduce operational costs. This contribution presents and discusses the powering test results of several HTS undulator prototype coils, designed and manufactured at CERN, made from coated ReBCO tape superconductor. The coil set-up was already described in previous works and is based on non-insulated vertical racetracks with a period length of 13 mm, assembled with iron poles. Powering tests at 4.2 K were performed at KIT to explore the operation at high current densities (2 kA/mm2) and the produced magnetic fields in the iron pole gap.