Background: Low-energy electrons linear accelerator with magnetron as power source has been more widely used in medical

radiation

X-ray detection and other fields. Purpose: The aim is to control magnet’s operating frequency in an industry accelerator. Methods: A set of automatic frequency control (AFC) system is developed by using digital I/Q technology combined with Field-Programmable Gate Array (FPGA). Microwave signal generated by the magnetron tube accelerates the electron beam in accelerator

the magnetron frequency stability is important for beam energy

energy spread and emittance. But magnetron is an oscillator with its frequency affected by temperature

vibration

load-pull effect

which will produce frequency drift

the AFC system

which includes travelling wave phase control and dual-cavity frequency discriminator

can stabilize frequency accurately. Results: Experimental results show that the frequency drift could be detected through phase discrimination and then be used for feedback control to achieve effective magnetron frequency control. In machine commissioning frequency drift is controlled within 1 kHz

to meet the requirement of less than 500 kHz. Conclusion: The theory and engineering design of digital I/Q technology proposed in the paper provide a feasible and achievable solution in the magnetron frequency control.Cited