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  Bahrdt, J.; Bäcker, H.-J.; Dirsatt, M.; Frentrup, W.; Gaupp, A.; Just, D.; Pflückhahn, D.; Scheer, M.; Schulz, B.; Weingartner, R.; Grüner, F.; O'Shea, F.: Cryogenic Design of a PrFeB-Based Undulator. In: Proceedings IPAC 10. First International Particle Accelerator Conference, Kyoto, Japan, 23 - 28 May, 2010, 2010. - ISBN 978-92-9083-352-9, p. 3111-3113
  http://accelconf.web.cern.ch/AccelConf/IPAC10/papers/wepd012.pdf

Abstract:
A PrFeB-based cryogenic undulator has been built at Helmholtz-Zentrum Berlin (HZB) in collaboration with the Ludwig-Maximilian-University München (LMU). LMU will operate the undulator at a laser plasma accelerator at the Max-Planck-Institut für Quantenoptik in Garching. The 20-period device has a period length of 9mm and a fixed gap of 2.5mm. The operation of a small gap device at a high emittance electron beam requires stable magnetic material. A high coercivity is achieved with PrFeB-material cooled down to 20-30K. In this paper we present the mechanic, magnetic and cryogenic design and compare predictions with measured data.