Theoretical and experimental study of a new single-coil superconducting   miniundulator
  The first pre-prototype of a single-coil superconducting miniundulator has been built and studied. Its basic specifications include 10 main periods and two end compensation periods, a period length of 7 mm, and a gap of 2 mm. The design is based on a racetrack-like coil configuration that is subsequently compressed to form the gap region with the spatially alternating currents flowing perpendicularly to the electron beam above and below the midplane. Operation up to an excitation current slightly beyond 400 A before quenching resulted in a peak magnetic flux density on axis of about 1 T and an undulator parameter of K about 0.65. 
Joe Kulesza, Dave Waterman, Neil Roscup, Cao Zheng Diao, Alex Deyhim,   Herbert O. Moser
physics.acc-ph