Performance of an advanced elliptically polarized undulator with shimming

A 4-m-long elliptically polarizing undulator (EPU5.6) device with an Apple-II structure is installed in the Synchrotron Radiation Research Center storage ring. This is the longest EPU device with an Apple-II structure worldwide. The errors of the magnet construction and the assembly process are among the several factors that can degrade the spectral performance. This study describes the mechanical design concept and construction that reduce magnetic field errors to keep high performance of the magnet. The electron orbit distortion in various polarization radiation modes is discussed with reference to a global feedback system and a feed forward table with following gap and phase. The beam dynamic effects are also investigated when the phase and magnetic gap are changed.