Beam position monitors for Duke FEL storage ring

The Duke FEL storage ring is a 1 GeV electron ring, which is designed for driving UV-VUV free electron lasers. The ring has been in operation since November of 1994 but the beam position monitors (BPMs) were connected and operated just recently. The BPM pick-ups are 4 stripline electrodes. In order to reduce the higher-order-mode loss excited by the stored beam at the BPM pick-up area, the BPM vacuum chamber is designed with 4 grounding strips between the electrodes that have the same diameters as the electrode. This design allows the electron beam to see a much smoother vacuum chamber at the BPM area. The pick-up signals are processed by Bergoz´s electronic modules, which give X/Y outputs directly. Each BPM has its own process module and 34 modules have been connected to the EPICS control system. The beam orbit now can be displayed and corrected through EPICS in the control room. The system performance and the test data are presented in this paper