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 electron beam in a bend magnet, producing, in the electron orbit plane, soft-X-rays with an alternate elliptical polarization. The local bump was created by using two pairs of vertical correctors located on each side of the bend magnet. Bump strength coefficient was obtained from both calculated estimation and measured beam response matrix. Control electronics for proper bump strength settings was designed to incorporate the existed orbit corrector function. Corresponding graphic user interface was implemented so that bump amplitude can be easily adjusted. Performance of this system is presented. Disturbance on the stored electron beam orbit was observed while flipping of corrector polarity during EPBM operation. A local feedback loop developed to eliminate such disturbance on other beamlines is also described.