Measurement and Modeling of Magnetron Injection Lock to the Stable Bandwidth

Particle accelerators use radio frequency driving forces to accelerate particles close to the speed of light. The RF driving force emits microwaves that cause alternating positive and negative electric fields in RF cavities surrounding the particle beam. Many particle accelerators use klystrons as wave amplifiers for the particle beam, but magnetrons are less costly and more efficient to use. For a magnetron’s output signal to be stabilized, it must be frequency locked to an external signal. However, as power level of the magnetron increases, the frequency pushing characteristic changes the resonant frequency of the magnetron and the locking bandwidth around it. The pushing characteristic is inherent in magnetrons, but the locking bandwidth can be increased to account for changes in the resonant frequency of the magnetron. The locking bandwidth was measured with an injection frequency of 2.439 GHz using a frequency spectrum analyzer for a magnetron with and without an RF cavity at the magnetron test stand at Jefferson Lab. Analysis of experimental data in relation to previously proposed theoretical models and comparison of Chen to Adler model for best fitting of experimental data will be given.