Development of an automatic frequency measurement system for RF linear accelerator magnetrons

An X-band [9300 MHz] magnetron frequency measurement system was developed for the electron linear accelerators at the Korean Atomic Energy Research Institute (KAERI). The measurement and the display of the RF frequency during the accelerator operation time is a crucial factor for continuous operation for two key reasons. Firstly, if the RF frequency of the magnetron is not known, then the amount of frequency tuning cannot be known, and the appropriate RF power cannot be supplied to the accelerating-structure. Second, values including the accelerating-structure’s coolingwater temperature setting, the solenoid-magnet’s cooling-water temperature setting, and the tuning of the source’s (magnetron’s) frequency can be undertaken because the RF frequency is used as the reference. A key component of the accelerator is the accelerating-structure. The volume of the accelerating-structure changes according to the environment’s temperature; there, the resonance frequency of the accelerating-structure varies. When the resonance frequency of the accelerator is changed, the output becomes unstable, and a low beam energy is obtained. Accordingly, was developed a magnetron frequency-measuring device in order to stabilize the accelerator’s operation. The results of the test demonstrate that the measurement’s accurate up to 100 kHz, which enables the provision of an accurate RF power to the accelerating -structure. In this paper, we discuss the RF frequency measurement system for the magnetron to enable a more stable accelerator operation in a linac.