Performance modeling of an elliptically polarizing undulator under magnetic loading

A 3.9-meter-long elliptically polarizing undulator recently has been designed, constructed, and installed in the storage ring at Synchrotron Radiation Research Center (SRRC) to provide an ultra-brilliant polarizing light source in the soft X-ray range. This undulator is the longest such polarizing device ever constructed, accounting for why its backing beams withstand an enormous magnetic force. Conventional deflection compensation scheme cannot be applied to improve the spectral performance owing to dependence of the magnetic loading on the device´s operating modes. This study systematically studies how magnetic loading affects the magnetic field errors of this elliptically polarizing undulator, including numerical calculations and experimental measurements. Ultimately improving the spectral performance of an elliptically polarizing undulator depends on effectively minimizing the deflection sensitivity of the backing beams from the backlash of movable magnetic arrays.