HIGH POWER TEST OF THE 35 MHZ SPIRAL RE-BUNCHER CAVITY FOR THE TRIUMF ISAC FACILITY

To preserve beam intensity and quality, a 35 MHz spiral two gap re-buncher cavity for the ISAC radioactive beam facility at TRIUMF will operate in cw mode. The spiral at the open end supports the drift tube and has a stem support at the bottom. The spiral is NC machined from solid copper and water pipes are soldered to the inner and outer surfaces and exit via the stem at the bottom. A 2% change in resonant frequency can be obtained by varying the diameter of a spool piece which is part of the stem. The final dimension of the spool piece is obtained from rf signal level measurement. A fine tuner is employed to compensate for the frequency change during operation. The spiral and the end plates are water cooled. The measured mechanical vibrations of the spiral were less than 1 µm with 8 liters/minute water flow. The resonant frequency and Q of the manufactured cavity were within 1 % and 65 % of the value predicted by MAFIA 3D simulation respectively. The cavity has been tested to full power of 1 kW to produce 30 kV on the drift tube. The results of signal level and power tests are reported.