Energy dispersion correction of electro-magnets chicane

The XFEL facility of SPring-8 is named SACLA (SPring-8 Angstrom Compact free-electron LAser). The beam operation of the SACLA accelerator was started at the end of February 2011. After four months of beam tuning, 1.2Å X-ray laser was successfully obtained. In the SACLA accelerator, a 1 ns electron bunch produced by the electron gun is compressed to less than 100 fs by using velocity bunching and three bunch compressors in order to obtain a 3 kA peak current at the end of the 8 GeV linac. When the bending magnets of magnetic chicanes have multi-pole field components, energy-dispersion function leaks from the chicane and degrades beam emittance downstream of the bunch compressor. In each bunch compressor of SACLA, two quadrupole magnets are installed at the chicane center to control the dispersion function. In this paper, measured dispersion function and its control by quadrupole magnets are reported. (author)