RF cavities for the Positron Accumulator Ring (PAR) of the Advanced Photon Source (APS)

The cavities for the dual frequency system of the APS PAR are described. The system uses two frequencies: a 9.78 MHz fundamental system for the particle accumulation and a 117.3 MHz twelfth harmonic system for the bunch compression. The cavities have been built, installed, tested, and used for storing the beam in the PAR for about a year. The fundamental cavity is a reentrant coaxial type with a capacitive loading plunger and has 1.6 m length. The harmonic cavity is a symmetrical reentrant coaxial type and is 0.8 m long. Ferrite tuners are used for frequency tuning. During the accumulation period, the ferrite tuner of the harmonic cavity works as a damper to disable the cavity. During an injection cycle the 9.78 MHz system accumulates 24 positron bunches in a bucket and the 117.3 MHz system compresses the bunch into a shorter bunch. Measurements were made on the RF properties of the cavities