Design of the RF cavity and power amplifier for the Fermilab antiproton source

In the Fermilab program for production of an intense antiproton beam, trains of 82 short antiproton bunches (1 nsec) separated by 18.8 nsec are produced with a large momentum spread about a mean energy of 8.9 GeV. The bunch trains are delivered to a Debuncher ring where a 3% momentum bite is reduced to about 0.2% by exchanging momentum spread for time spread. This exchange is a two step process involving synchrotron rotation of the bunches in mismatched buckets followed by adiabatic debunching. During the bunch rotation the rf system is required to provide a stable rf voltage of 5 MV at 53.1035 MHz for 60 251sec, or about 35 turns. Then the voltage must be lowered to 98 kV within about 56 251sec to match the rotated distribution. The voltage is then reduced to 5 kV in about 12 msec for final adiabatic debunching of the antiprotons. The process is repeated at a 2 second repetition rate. The rf voltage is to be generated by eight rf cavities in a long straight section. Each cavity, when excited with 112 KW of rf power, will generate a peak voltage of 625 kV. Each cavity is excited by a self contained power amplifier mounted directly on top of the cavity to minimize rf interference with nearby high sensitivity stochastic cooling systems. The cavity, 90.9 cm dia. and 182.6 cm long, is made of aluminum and completely evacuated. The rf power is fed into the cavity through ceramic vacuum feedthrus through a top plate. Details of the cavity and amplifier design as well as prototype cavity measurement are presented