X-ray Free Electron Laser at SPring-8

Abstract

In the late 1990s, when linac-based X-ray free electron lasers were discussed as the “next” generation synchrotron light source in the US and Europe, we were in the middle of the commissioning of SPring-8, which was inaugurated in 1997. SPring-8 is a 3rd generation X-ray synchrotron radiation facility similar to, but a little larger than, the European Synchrotron Radiation Facility (ESRF) in Grenoble and the Advanced Photon Source (APS) in Argonne. These 3rd generation sources are optimized to use undulators as the primary radiation sources. One remarkable feature of SPring-8 is the adoption of newly developed “in-vacuum” undulators as the standard device. Most undulators in other facilities at that time were “out-of-vacuum” types, which equipped permanent magnet arrays for periodical electron beam deflections out of the UHV chamber of the accelerator. The in-vacuum undulator stores the permanent magnet arrays inside the UHV chamber so that the gap between the arrays could, in principle, be closed as narrow as you like. Additional remarkable features of SPring-8 compared with other 3rd generation X-ray synchrotron radiation facilities are its long, straight sections for long undulators as well as the possible long beamlines up to 1000 m. The four long, straight sections were implemented both for the future longer undulators with higher brightness and for possible R&D toward free electron lasers using the storage ring.