PROTOTYPE PHOTON POSITION MONITORS FOR UNDULATOR BEAMS AT THE ADVANCED LIGHT-SOURCE

Design criteria are described, and test results are presented, for prototype undulator beam position monitors at the Advanced Light Source (ALS). The design is based on monitors presently in use at the National Synchrotron Light Source, Brookhaven National Laboratory, with modifications to account for the widely varying and large K values of the undulators to be installed at the ALS. In particular, we have modified the design to simplify the thermal engineering and we have explored techniques to suppress the response of the monitors to soft photons, below 100 eV, so that the beam position can be determined by measuring the higher energy photons which are better collimated.