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

To facilitate high-sensitivity sofi-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 vertica l slope of the electron beam in a bending magnet. This variation produ ces in the electron orbit plane soft-X-rays with an alternating ellipt ical polarization. The local bump is created by using two pairs of ver tical 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 str ength settings were designed to incorporate the existing orbit correct or function, and a graphical user interface was implemented so that bu mp amplitude can be easily adjusted. Performance of this system has be en characterized and is described in this paper. Disturbance on the st ored electron beam orbit was observed while flipping the corrector pol arity during elliptical polarization from bending magnet (EPBM) operat ion. A local feedback loop developed to eliminate such disturbances on other beamlines is also described. (C) 1998 Elsevier Science B.V. All rights reserved.