PHOTON SCIENCE

The two high energy X-ray beamlines P07 and P21b at PETRA are equipped with in-vacuum undulators (IVUs). In contrast to conventional undulators, the magnetic structure of IVUs is incorporated into a vacuum chamber with a larger diameter instead of having a flat vacuum chamber with the undulator magnets around it at ambient pressure. These devices allow for smaller gaps and shorter period lengths at the expense of the total magnetic length due to the necessity of flexible taper sections.
The two identical devices for the PETRA beam lines P07 and P21b were built by an industry collaboration of Research Instruments GmbH and Kyma S.p.A. according to DESY’s specifications. They have a magnetic length of 4 m, a period length of 21.2 mm and a deflection parameter K of 1.41 at a gap of 7.0 mm. Their magnet structure is a hybrid design and comprises NdFeB magnets and poles made from a FeCo alloy. The coercivity of the magnet material was further enhanced by a Tb grain boundary diffusion process in order to improve its radiation hardness. To minimize the outgassing of the magnet structure during vacuum conditioning, magnets as well as poles were coated with an approx. 5 μm thick TiN layer. Moreover, the entire magnet structure is covered with a smooth 100 μm thick CuNi foil in order to minimise impedance effects for the electron beam. The magnet girders as well as the flexible taper sections are based on a design by Spring-8 and PSI. They are water cooled to cope with the heat-load due to synchrotron radiation and wake field effects.

Further literature: Reiser, R., Zelenika, S., Ingold, G., Keller, A., Schulz, L., Hara, T. and Kitamura, H., 2002. The Flexible Taper Transitions for an In-Vacuum Undulator. Proc. MEDSI’02, p.323.

Contact: A. Schöps, P. Vagin, M. Tischer