Undulator Development for SPring-8-II

After the construction of the X-ray free electron laser facility SACLA, which achieved first lasing in 2011 1 T. Ishikawa, Nature Photon. 6, 540 (2012)Crossref], Web of Science ®] , Google Scholar]] and has been successfully operated for nearly four years, SPring-8 has now turned to upgrading its storage ring to further enhance the light source performance in terms of brilliance. In this “SPring-8-II” project, a new lattice structure composed of five bending magnets has been chosen 2 SPring-8-II Conceptual Design Report (2014), available from http://rsc.riken.jp/pdf/SPring-8-II.pdf Google Scholar]] in order to reduce the horizontal emittance, which, in turn, requires us to shorten the straight sections available for undulators by roughly 1 m. In addition, the electron energy will be reduced down to 6 GeV from the current 8 GeV for further reduction of the emittance. This upgrade plan is not necessarily compatible with the existing undulators in SPring-8 and thus most of them need to be replaced with new ones optimized for operation in the new ring in order to maximize the brilliance. This raises a number of technical challenges toward realization of SPring-8-II, including considerable reduction of the manufacturing cost and further shortening of the magnetic period of undulators. In this article, we report relevant R&;D activities to overcome these challenges, together with a new concept to enable a flexible polarization control, which is one of the important options in synchrotron radiation (SR) beamlines.