A DYNAMIC LOCAL BUMP SYSTEM FOR PRODUCING SYNCHROTRON-RADIATION WITH AN ALTERNATING ELLIPTIC POLARIZATION

To facilitate high-sensitivity soft X-ray magnetic circular dichroism experiments, a dynamic local bump system has been developed at the SRR C storage ring. This system was devised to vary dynamically the vertic al slope of the electron beam in a bending magnet, producing, in the e lectron orbit plane, soft X-rays with an alternating elliptical polari zation. The local bump was created by using two pairs of vertical corr ectors located on each side of the bending magnet. The bump strength c oefficient was obtained both from calculated estimation and from measu red beam-response matrices. Control electronics for proper bump streng th settings were designed to incorporate the existing orbit-corrector function. A corresponding graphic user interface was implemented so th at the bump amplitude could be easily adjusted. The performance of thi s system is presented. Disturbance on the stored electron beam orbit w as observed while flipping the corrector polarity during EPBM (ellipti cal polarization from bending magnets) operation. A local feedback loo p, developed to eliminate such disturbance on other beamlines, is also described.