Impedance-Matching Network Box of the RF Power Amplifier for the RFT-30 Cyclotron

RFT-30 is a 30-MeV prototype cyclotron for radioactive isotope (RI) production, neutron generation, and fundamental research. Charged particles are accelerated by using a radio-frequency (RF) cavity and a high-power RF signal transmitted by an RF amplifier. This paper describes the impedance-matching network box of an RF power amplifier for an RFT-30 cyclotron. The impedance-matching process is an essential procedure for maximizing the RF amplifier’s performance with respect to efficiency and stability. In a dummy load test, the impedance value remains almost constant. However, in terms of beam loading, the impedance varies because of the vacuum and water/air cooling. These effects make the resonance conditions different; thus, the RF amplifier’s operation becomes unstable. In this work, an impedance-matching network box with a stub-line inductor, which is applied to the cathode of the power amplifier (PA) tube, is proposed. A calculation for the impedance-matching network box was performed and then simulated through optimization processes. In addition, the stub-line inductor measurement and the RF performance when using this matching network box are described.