With permanent magnet undulator operation at cryogenic temperatures, the magnetic field and coercivity can be increased, allowing for shorter periods of high magnetic fields. The first full-scale (2 m length, 18 mm period) hybrid cryogenic undulator [1] with PrFeB [2] magnets working at 77 K was installed at SOLEIL in 2011. Photon spectra data, which agreed well with magnetic measurements, were employed for precise alignment and taper optimisation. The second and third 18 mm PrFeB cryogenic undulators, converted to a half-pole/magnet/half-pole configuration, were optimised without magnet or pole shimming after assembly, however mechanical sorting and certain geometrical modifications were performed prior to ass...
With permanent magnet undulator operation at cryogenic temperatures, the magnetic field and coercivity can be increased, allowing for shorter periods of high magnetic fields. The first full-scale (2 m length, 18 mm period) hybrid cryogenic undulator [1] with PrFeB [2] magnets working at 77 K was installed at SOLEIL in 2011. Photon spectra data, which agreed well with magnetic measurements, were employed for precise alignment and taper optimisation. The second and third 18 mm PrFeB cryogenic undulators, converted to a half-pole/magnet/half-pole configuration, were optimised without magnet or pole shimming after assembly, however mechanical sorting and certain geometrical modifications were performed prior to assembly. A systematic mistake in the individual magnets on the third U18 was also corrected. In-situ testing benches, comprising
