Nuclear Techniques ›› 2014, Vol. 37 ›› Issue (04): 40103-040103.doi: 10.11889/j.0253-3219.2014.hjs.37.040103


Digital I/Q technology used for magnetron frequency control

ZHONG Shaopeng ZHAO Minghua ZHANG Junqiang   

  1. (Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jiading Campus, Shanghai 201800, China)
  • Received:2014-01-17 Revised:2014-02-20 Online:2014-04-10 Published:2014-04-11
  • Contact: Shao-Peng


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.

Key words: Digital I/Q, Phase detection, Magnetron, Automatic frequency control (AFC), Cavity