In practice however, not all the available RF buckets are occupied in a given spill. For a start the RF monitor is active between T5 and T6 which is 23 seconds of which the slow spill occupies 19.27 seconds plus 0.67 seconds of prespill. When fully loaded with beam it contains 12 booster batches which occupy 84 buckets each and are spaced 1 bucket apart. The remaining 94 buckets are left empty. This gap is called the abort hole.
Further reductions occur as a result of uneven extraction and missing booster batches.
This is somewhat higher than what we normaly see. The reason for the discrepancy is that the micro-structure of the spill is not very uniform and hence the bucket occupancy is not well described by a Poisson distribution. The loss of events due to non-Poisson fluctuations in bucket multiplicity can be expressed in terms of the spill deadtime, the measured hadronic fraction, and the optimal hadronic fraction one would obtain if the spill were purely Poisson. In order to maximize our data taking rate we need to keep the hadronic fraction as high as possible so as to reduce the deadtime generated while reading out uniteresting events. One way of doing this is to monitor the spill structure.