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

The beam position monitoring (BPM) system for the Brookhaven National Laboratory (BNL) booster consists of 48 main pick-up electrodes (PUEs) symmetrically distributed around the ring and two special PUEs for the transverse dampers. The BPM system utilizes an integrator that is AC coupled to the PUE. The operation of the design relies upon the use of direct digital synthesis. 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 are needed to insure that the triggers to the BLRs occur between bunches. The triggers for the main PUEs require a clock of 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 PUEs. By making use of the direct digital synthesis technology, all three signals produced were locked to the beam by using only a single phase locked loop.<>