Frequency control of RF booster cavity in TRIUMF

A booster cavity is used in the TRIUMF cyclotron to increase the energy gain per turn for beam orbits corresponding to energies greater than 370 MeV. It operates at 92.24 MHz, the 4th harmonic of the cyclotron main RF, and at a nominal voltage of 150 kV. Excitation is provided by a 90 kW RF system that is phase locked to the main RF. When the main RF is interrupted due to sparking or other causes, a controller built into the low level frequency source of the booster RF system disables the phase-locked loop, and reconfigures the source as a temperature stabilized oscillator operating at the last locked frequency. When the cyclotron RF is restored it usually will be at a different frequency. The oscillator tunes automatically to this new frequency. The acquisition time is extended by the controller to match the response time of the mechanical tuner in the cavity