Improvement of RF phase ripple by adjusting PFN in BFEL

To realize the saturation output of Beijing Free Electron Laser, the phase stability of RF power in accelerator is required to be less than ± 1° . In this paper, the relations between RF phase variation and the Pulse Form Net (PFN) in modulator of klystron are carefully studied through experiments. In order to meet the requirement of RF phase stability, all 48 sets of the PFN in HV modulator are repeatedly adjusted to obtain optimum result. The results show that the distributed parameters of the PFN take an important part in the stability of RF phase. In the pulse width of 6 s, RF phase ripple from the output of klystron is reduced to ± 1.5° from ± 2.6° before the adjustment; In the pulse width of 4 s, practically used in BFEL, RF phase ripple is only± 1° .