A Compact RF System for a 30-Inch AVF Cyclotron

A high degree of stability, simplicity, and compactness has been achieved with the RF system in operation on a new 30-inch AVF cyclotron. The over-all size of this RF system has been reduced by bending the resonator from the horizontal to the vertical plane so that the RF system extends only 24 inches beyond the cyclotron coils. The resonant structure is a half-wave line terminated in two 120-degree dees. The dee capacity has been reduced by copper plating the cyclotron hill iron, which leaves the full valley gap under a large portion of the dees. The RF frequency, which is the same as the ion rotation frequency, is quickly and easily adjusted from 12.5 to 25 Mc by changing straps in the resonator which is in air. The system is powered by a grounded grid oscillator which uses a single triode. A dee-to-ground voltage of 35 kV at 25 Mc is routinely obtained with 30 kW of dc input to the oscillator. The minimum dee-to-ground gap is ½ inch. Other features of the system include biasing of the entire RF structure to prevent multipacting and a .01 per cent frequency regulation system.