Measurement of Single Bunch Purity in the SRS

During single bunch operation of the Daresbury SRS it is necessary to reduce the population of empty r.f. buckets to less than 1 part in 103. Measurement of the bunch intensity is by single photon counting using the synchrotron light emitted by the electrons. This technique is described, which is capable of resolving relative intensities of 1 part in 104 at the bunch spacing of 2 ns.