A dynamic local bump system for producing synchrotron radiation with an alternating elliptical polarization

To facilitate high-sensitivity soft-X-ray magnetic circular dichroism experiments, we have developed a dynamic local bump system at the SRRC storage ring. This system was devised to vary dynamically the vertical slope of the electron beam in a bending magnet. This variation produces in the electron orbit plane soft-X-rays with an alternating elliptical polarization. The local bump is created by using two pairs of vertical correctors located on each side of the bending magnet. The bump strength coefficient was obtained from both calculated estimation and measured beam response matrix. Control electronics for proper bump strength settings were designed to incorporate the existing orbit corrector function, and a graphical user interface was implemented so that bump amplitude can be easily adjusted. Performance of this system has been characterized and is described in this paper. Disturbance on the stored electron beam orbit was observed while flipping the corrector polarity during elliptical polarization from bending magnet (EPBM) operation. A local feedback loop developed to eliminate such disturbances on other beamlines is also described.