Research On High - Frequency System Upgrade And Related Physics Of Hefei Light Source Storage Ring

HLS Ⅱ has been upgraded during last two year, the beam quality and stability has been great improved. The emittance of beam is below40nm*rad, and the current is up to300mA.The thesis is about the RF system upgrade. The replacement of the tetrode amplifier by high power solid state amplifiers (SSA), and the development of digital low level RF (DLLRF) system, and the upgrade of software and hardware of RF control system are included in this thesis. The design of RF system is also introduced in thesis. The offline testing of key components, the installation of SSA and DLLRF are both done during the upgrade. Then the online testing and operating with beam are implemented.By investigating the SSAand DLLRF technology, the upgrade program of HLS Ⅱ RF system is decided.In the development of SSA, considering the efficient and upgrade in the future, two output mode (30kW/40kW) of SSA are both designed to satisfy the requirement of RF power.48amplifier units which are combined through8*6way, are used in30kW mode. The other combining method is8*8, and64amplifier units are used. The high power test platform is structured to measure the character of amplifier units, combiner and the output of SSA The gain of amplifier unit is25±0.1dB. After adjustment, the phase shift is less than±0.2°,and the SWR is less than1.02. The maximum output power under two output mode, are33kW and44kW respectively. The long-term inspection of SSAstability is done after installation. The fall of output power caused by broken amplifier units are also measured, which is very close to theoretical value. It means that that the manufacture of combiner and splitter is successful. We found that the broken circulator may also cause the huge decline of output power in some special condition, which is already proved by relevant experiment.A DLLRF offline test platform is build to establish parameter of DLLRF system. The maximum gain of DLLRF is30dB. During the long-term test, the stability of amplitude and phase were less than±1%and±0.1°, which meet the design requirements.The software and hardware of RF control system are both upgrade. Fluke2680A data acquisition is applied to measure the parameters of SSA components, such as the temperature, current, voltage of amplifier units and flux of water cooling board. The control program is compiled by Lab View. The monitor and control function of signal source, DLLRF, interlock, Fluke2680A data acquisition, power meter, are intergraded together by this control program. The communication with EPICS and remote control are both implemented by this control program.The installation and commissioning of the RF system are completed. Currently, the SSA takes the8*6mode, and the output power is30kW. The relationship between low-level loop parameters and beam stability are studied. After the adjustment of DLLRF parameters, amplitude stability is less than±1%, respectively, phase stability is less than±0.1°under high beam current and high field condition. The stable operation with460mA are achieved.The interaction between RF noise and beam are studied. The noise in the RF system will excited the beam longitudinal oscillations, and debase the quality of the beam. The effects of RF noise has always been concerned by accelerator laboratories all over the world. Presently, some of the effective method have already been developed, such as Pedersen models and iterative equations and so on. Longitudinal oscillations changes the field caused by the beam, the change of field affects the beam movement in turn, the relationship between them is more complicated. Existing methods have conducted a number of approximations, in the case of low current and small perturbations is very effective, but in the case of high current and strong disturbance, these methods will produce large errors. This paper bases on the original theory, improves the theory. According to the transient pulse response model, it calculates the change of transient field caused by RF cavity beam oscillation (without any approximation) turn by turn, and monitors the longitudinal movement of beam.We developed a simulation program to analyze the longitudinal movement of the beam in phase-modulated RF field, the calculation results are close to relevant experimental data. For example, calculations show that when the phase modulation frequency is in the vicinity of the synchronous oscillation frequency, the synchronous oscillation will be excited, this conclusion is consistent with the experimental results.