A 35 MHz spiral re-buncher cavity for the TRIUMF ISAC facility

A full-scale prototype of a 35 MHz re-buncher cavity was built for the ISAC project at TRIUMF. The re-buncher will be operated in cw mode to maintain the beam intensity and quality. Due to the longitudinal space limitation in the beam line, a compact spiral structure was constructed and investigated to determine its parameters. Natural frequencies and vibration amplitudes were measured. Vibration amplitudes of the spiral structure with 10 liter per minute water flow are two orders of magnitude lower than the allowable values. Measurements also show that the shunt impedance of the structure is 370 k/spl Omega/ with a Q of 2740 at a resonant frequency of 39.5 MHz. MAFIA simulation predicts the resonant frequency, Q and shunt impedance to be 39.8 MHz, 5520 and 686 k/spl Omega/ respectively. Due to poor rf contacts of the prototype cavity, the measured Q is much less than that predicted by MAFIA, however, R/Q values of the prototype and simulation are 135 and 124 respectively. Construction details and final dimensions of the spiral for 35 MHz will also be presented.