Study on the Resonant Cavity for Low-level RF System at the PBP-CMU Electron Linac Laboratory

This research aims to investigate characteristics of the resonant cavity, which is a part of the radio-frequency (RF) power system of the electron linear accelerator (linac) at the PBP-CMU Electron Linac Laboratory, Chiang Mai University. A resonant cavity is used to resonate the RF wave of the desired frequency by exploiting the relation between the cavity dimension and the resonant frequency. The resultant RF wave from the resonant cavity is later amplified in RF amplifier and klystron. Finally, it is used to accelerate electron beam in the linac that has a specific operating frequency. Simulations of the electric and magnetic field patterns inside the resonant cavity as well as the resonant frequency were performed by using the program SUPERFISH. Meanwhile, measurements of the resonant frequency for the real cavity were done with a spectrum analyzer. The relation between the cavity length and the resonant frequency was experimentally studied. The study results showed that our resonant cavity has TM012 mode and the resonant frequency has a negative linear correlation to the cavity length. This cavity has an inner radius of 6.892 cm. The resonant frequency of the cavity can be varied by adjusting its length. The optimal cavity length, which produces the RF waves of 2856 MHz, obtained from the measurement was 13.48 cm.