High power test of the ISAC triple gap buncher operating in cw mode

A separated function, variable energy, drift tube linac (DTL) operating in cw mode at 105 MHz is being built for the ISAC radioactive beam facility at TRIUMF. Included in the design are three buncher cavities installed in the first, second and third drift spaces between the five IH tanks. The main requirements of the bunchers are: cw mode, high effective voltage (up to 0.32 MV), large velocity acceptance (1.8-4.1%). The first DTL buncher has been developed at INR and is being tested at TRIUMF. It is a triple gap split-ring RF structure operating at 105 MHz. Signal level measurements give a Q-value of 4300 which is 74% of MAFIA simulation predictions and a resonant frequency within 0.6% of the calculated value. With cooling water flow of 20 l/min the mechanical vibrations were measured to be of the order of 1 μm. Although the design parameters are 56 kV gap voltage and 8 kW nominal power, we demonstrated 85 kV and 16 kW respectively with stable operation