Expected radiation spectra of a 30-m long undulator in SPring-8

In addition to 44 straight sections of 5 m long, the SPring-8 storage ring comprises four long straight sections of length 30 m. These sections are prepared for insertion devices and highly brilliant quasi-monochromatic photon source is available for experiments in the hard X-ray region. In a simple minded expectation, the brilliance of the undulator radiation is proportional to the square of the number of the undulator period. So that we expect a 60 times higher brilliance from a 30 m long undulator compared with a 4 m long undulator. According to a numerical calculation, however, it turns out that the brilliance is not so high as expected. This is because the brilliance is closely related to the emittance of the electron beam. In this note we study the spectral properties of the synchrotron radiation from a 30 m long undulator