Beam decelerations with variable momentum compaction in the Fermilab Antiproton Accumulator

For the study of charmonium resonances above and including the χc0, Fermilab experiment E-835 required an intense and stochastically cooled antiproton beam with kinetic energies from 8 GeV (the injection energy of the Accumulator) down to 4 GeV. We developed a scheme in which the momentum compaction factor of the machine was changed as the antiprotons were decelerated, so that the energies of interest to the experiment were kept above transition. The scheme was used during the E-835 10-month run of the year 2000. Here we describe the design criteria, operational procedures and diagnostic tools we used to exploit the machine as an efficient antiproton decelerator. The machine performance during data taking is also discussed, in relation to the main experimental requirements.