Indirect phase locking of RF clock to the beam for BNL Booster BPM system

The beam position monitoring (BPM) system for the BNL Booster consists of 48 main pick-up electrodes (PUE) symmetrically distributed around the ring and two special PUE's for the transverse dampers. The BPM system utilizes An integrator that is AC coupled to the PUE. In order to eliminate the cumulative error in the signal from the PUE introduced by the AC coupling, a base line restorer (BLR) is used to reestablish a reference value between the bunches. Three signals phase locked to the beam, 48 x fREV and both quadrature components of fRF, are needed to insure that the triggers to the BLR's occur between bunches. The triggers for the main PUE's require a clock at 48 times the revolution frequency as well as the RF frequency to time their occurrence. The quadrature components of RF frequency are used in a phase shifter to produce the triggers for the damper PUE's. By making use of direct digital synthesis technology, they were able to produce all three signals locked to the beam using only a single phase locked loop