Research of Stability between Driven Stage and Final Stage for RF Power Source of High Intensity Proton Cyclotron

For studying and analyzing the stability between the driven stage and the final stage for the radio-frequency (RF) power source of the high intensity proton cyclotron, the unstable phenomenon observed in the experiment was simulated. The simulation results show that the voltage stand wave ratio (VSWR) in the room temperature and operational status are 1.06 and 6.89, respectively. And the capacitance variation caused by changing the input tuning gap of capacitor is considerable drastic. For solving these problems, the impedance matching simulation, the three-dimensional electromagnetic simulation and the related experiment were performed. Finally, the unwillingly large VSWR of the input port due to the variation of the cathode impedance was suppressed, and the sensitivity of the capacitor was reduced from 10 pF per 0.5 mm to 1 pF per 5 mm.