Online Betatron Tune Feedback in the HLS-II Storage Ring
The betatron tune of a storage ring is a critical parameter in the design process and for user operation. A proportional–integral–differential (PID)-based feedback system is developed for the Hefei light source II (HLS-II) storage ring to stabilize the betatron tune. This feedback system adopts a tune knob using global mechanism, which can precisely adjust the tune. A simulation using an intelligent algorithm is carried out to optimize the PID coefficients. Online experiments show that this system can effectively correct the tune shift, which is caused by the gap change of insertion devices and other factors. The tune feedback system can improve the tune stability to the order of  $10^{-4}$ , which can be employed as a useful tool for stable operation of storage ring-based light sources. This paper reports the details of the development of this tune feedback system. Some simulation and online experiment results are also presented.