Design of a Fixed Frequency Delta Resonator with Positive Gradient Radial Voltage Distribution

The design of the RF system for the new injector cyclotron for the SIN 600 MeV ring accelerator is described. This open-sector cyclotron is expected to accelerate a 1 mA proton beam of 0.8 MeV to a final energy of 72 MeV. To get a high beam pulse compression, the design goal of the fixed frequency RF system is a positive gradient radial voltage distribution. Different types of resonators were investigated, and a half-wave resonator with a delta-shaped resonant line was found most suitable for the required radial voltage increase of factor 2 to 3. Scaled models of delta resonators of different transmission line shapes were constructed to measure the resonator characteristics. From these results the optimum design was selected to fulfil the required voltage distribution and low power loss.