Calculation And Research Of The Higher Harmonic Cavity In Storag Ring

In storage ring, a higher harmonic cavity (HHC) can be used to control the bunch length. The beam lifetime in low-medium energy storage ring is typically dominated by Touschek scattering. A particularly attractive option for improving the lifetime is to reduce the Touschek scattering by using a HHC to lengthen the bunch. In addition, a HHC can be used to shorten the bunch in high luminosity storage ring, storage ring FEL and time-resolved synchrotron radiation experiments. This thesis mainly researches on the topic of using a HHC to change the length of the bunch in storage ring, with an example of HLS-II.Based on the Byrd’s analysis model on HHC, the effects of HHC on the beam lifetime and the bunch length are calculated for the uniform fill pattern. The optimum bunch length is39mm and the optimum beam lifetime improvement factor is2.75.We explore the constant detuning and the constant voltage scenarios to guide the operation of the passive HHC. Based on the multibunch single particle model, a tracking code is developed to estimate the mean beam lifetime for the non-uniform fill pattern. According to the parameters of HLS-II, the calculated results show that the passive HHC can’t be used to improve the lifetime for non-uniform fill pattern.Related theories of using a HHC to shorten bunch are also presented in this thesis, and then the optimum conditions are proposed firstly. The results show that the shortest bunch is close to7.00mm. The synchrotron frequency spreads are calculated to explore the effects of the HHC on Landau damping.In this thesis, a novel concept of using a bimodal cavity is proposed to reduce the space and cost in storage ring. Based on the Novosibirisk-shaped cavity, a bimodal cavity is designed for HLS-II and a general design method of the bimodal cavity is introduced. According to the law of the optimum tunings for two operation scenarios, we propose two solutions to implement the tuning of the bimodal cavity. The results show that the beam lifetime using a bimodal cavity is similar with that of using both rf cavity and harmonic cavity.These works may provide a theoretical reference for the design and operation of the HHC in storage ring.