The brightest x-ray source:: A very long undulator at SPring-8

A long undulator is a direct way to create a brilliant synchrotron radiation source. However, the length of undulators has been bounded by technical limitations and available space in accelerators. The first long undulator was developed at SPring-8, which is a third-generation synchrotron radiation facility equipped with four 30-m-long straight sections, making it the most brilliant x-ray source in the world. The magnets are placed inside a vacuum chamber and this makes it possible to arrange 780 periods continuously for 25 m. The absolute flux and spectrum of the output radiation were measured and compared with theory. The observed spectrum is in a good agreement with theory once the electron beam orbit was corrected for geomagnetic fields. (C) 2002 American Institute of Physics.