Cogging in the Fermilab Booster

The Fermilab Booster is a rapid-cycling synchrotron which accelerates 84 bunches of protons from 401 MeV to 8 GeV for injection into the Fermilab Main Injector. The entire circumference, i.e., all RF buckets, of the Booster is filled. At extraction, a kicker deflects the beam into the extraction channel. The kicker risetime is long enough so that several of the bunches do not receive the full kick and are deflected instead into Booster magnets, creating radioactive components in the tunnel and radiation at ground level outside. At future Booster intensities and repetition rates, the radiation levels will be unacceptably high. One way of reducing these losses is to create a "notch" of several consecutive unfilled RF buckets. If the beam can be accelerated while tracking and controlling the position of the notch so that the unfilled buckets are aligned with the rising edge of the extraction kicker, losses will be eliminated. We have studied this process and developed an algorithm to count and control RF cycles during the Booster ramp and move ("cog") the notch longitudinally so that it is aligned with the kicker at extraction time. We will describe the relevant parts of the Booster hardware, measurements we have made to understand what controls the total number of RF cycles during a Booster ramp, and the algorithm we intend to use for cogging during the Booster cycle.