Development Of Control System For HLS Higher Harmonic Cavity And Related Researches

A passive 4th harmonic RF cavity,also called high harmonic cavity(HHC)in this dissertation,was installed in the storage ring of the Hefei Light Source(HLS)in its major maintenance and improvement.This cavity is used to increase the Touschek lifetime and suppress beam instabilities.The HHC is used to be monitored and controlled by an analog control module provided by its manufacturer.However,this module did not meet the requirements of the commissioning and operation of the HLS.Based on the HLS control system and the HHC analog control module,we developed a HHC control and feedback system to stabilize and adjust the cavity voltage.A number of researches were conducted using this control and feedback system.Firstly,this dissertation introduces the longitudinal motion of electrons in a storage ring.The relevant equations are of importance for understanding the behavior of electrons in the longitudinal phase space,and also are the physical basis for studying higher harmonic cavity.Energy gain and loss determine the distribution of the electron beam in the phase space.The electron bunch can be lengthened or shortened by adjusting the relative phase advance and voltage ratio of the fundamental and harmonic cavities.The lengthened bunch has less Touschek scattering effects,thus a longer beam lifetime.Secondly,the HHC remote control system of the HLS is comprehensively introduced.The hardware and software development of the HHC remote control are introduced in detail,including the selection of equipment types,wiring methods and the development of the low-level control program,EPICS IOC database development,GUI development,etc.The operation results of the HHC control system are then given.Then,the HHC voltage feedback system is introduced in detail.The cavity voltage signal collected by the analog control module is relatively noisy,which makes the driving motor move too frequently when the HHC operates in the fixed cavity voltage mode,and leading to damage of the motor.For this purpose,a cavity voltage feedback system is developed based on EPICS.This work includes analyzing the frequency spectrum of the HHC voltage signal,conditioning the cavity voltage sampling signal,and developing feedback schemes using EPID record.A series of tests are performed for this feedback system.Finally,using the HHC voltage control system,a number of experimental studies are conducted to analyze the impact of the HHC on the bunch length,beam lifetime,emittance,and synchronous oscillation frequency.The experimental results are in accordance with the theoretical analysis,which shows that the HLS higher harmonic cavity can be used to effectively improve the Touschek lifetime and suppress beam instability.