Reduced length design of 9.8 MHz RF accelerating cavity for the Positron Accumulator Ring (PAR) of the Advanced Photon Source (APS)

A 9.8-MHz RF accelerating cavity is developed for the first harmonic system in the APS PAR and an aluminum unit is tested. The design goal is 40 kV at the accelerating gap, Q-factor of /spl sim/7,000 for the accelerating mode, 1.2-m diameter, 1.6-m length with good mechanical strength and stability. The design employs no dielectric or ferrite loading for tuning. The cavity is a plunger-loaded reentrant coaxial structure; the end of the inner conductor facing the wall has a piston-shaped loading structure which consists of a circular disk and a cylinder. The RF characteristic of the cavity was investigated using the URMEL-T and MAFIA programs. Compared with a coaxial structure with lumped element capacitive loading, this design gives improved RF characteristics.<
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