The Radiofrequency-Systems of PIA

To decrease the filling-time of positrons into PETRA single bunches of high intensity must be delivered from the DESY-Synchrotron. Therefore the linac injects positrons into an intermediate storage ring PIA, where the particles have to be accumulated and compressed in bunch-length to match the DESY-bucket. A two cavity system, operating on different frequencies was developed and shall be described here. One of these cavities, resonating at the low frequency of 10.4 MHz needs a very strong capacitive load of about 680 pF to keep it at a small volume. This capacity is achieved by coaxial rings, welded to the inner conductor of the resonator. The second cavity resonates at 125 MHz and operates on a pulsed mode for the final bunch compression. It is a reentrant coaxial resonator with a high shunt impedance. During the injection into the PIA-ring the high Q-value must be loaded down by a PIN-switch, to avoid selfbunching into different buckets.