Key Technologies Research And Development Of Beam Position Monitor In Linear Acceleration Section For SHINE

Shanghai high repetition frequency free electron laser(SHINE)project is under construction in China is a CW hard X-ray FEL user facility,including an 8 GeV of superconducting linear accelerator,three undulator lines,three optical beam line and the fir st ten experiment stations.It will provide 0.4-25 kev photons within the scope of energy after completion.As an important tool in the debugging,testing and operation,the beam diagnosis system plays a key role in the operation and optimization of FEL.B ased on the physical characteristics and design requirements of the linear accelerator,the multielectrode BPM system was selected as the beam position measurement tool,and the position resolution requirements reached 10μm@100pC for Stripline BPM and 200μm@10pC for Button BPM.In order to optimize the measurement accuracy and ensure the project progress of the multielectrode BPM system on SHINE,this project study the optimal design method of the multielectrode BPM system,give suggestions for the BPM design and provide the theoretical support.Starting from the principles of multielectrode BPM,this research has discussed the technical difficulties and constraints in the design and development process of multielectrode BPM.The conventional configuration and application range of multielectrode type BPM system have be defined based on the realistic conditions.Furthermore,the key parameters that affect the position measurement resolution of the multielectrode BPM system were summarized,and their influence trends were discussed.Finally,the mathematical relationship between them and the measurement resolution of the BPM system was given.The research has been advanced in three stages:1.Combining basic theory,beam experiments and engineering experience,the key parameters in the multielectrode BPM system have been refined,and the ways and ways they exert their influence in the induction electrode BPM system were analyzed.Moreover,the electrode-sensing BPM system is divided into four parts: electrode pickup,analog front end,signal acquisition module and digital signal processing module.Starting from the theoretical model,the physical parameters that may matter in each part have been summarized and extracted.For key parameters that cannot be directly determined or quantitatively described by existing theories,such as front-end noise or passband range,an approximate mathematical model of its influence trend under target conditions has been given through calibration experiments or simulation experiments,and its applicable scope was delineated.2.After the key parameters of the system are determined,the signal acquisition and processing process under different parameter combinations of the sensing electrode type BPM system was simulated by mathematical software,and the corresponding system measurement resolution was calculated by Monte Carlo method.The correctness of the simulation software has been verified by beam experiments on the SXFEL device.3.The quantitative relationship between each key parameter and the measurement resolution of the system was summarized into an empirical formula.Based on the simulation software to generate a wide range of simulation results,the influence trend of key parameters was fitted and described with the corresponding mathematical model.In this process,the scope of use and constraints of the empirical formula have also been discussed.On this basis,in view of the difficulties in the development of the induction electrode type BPM in SHINE,the optimal design direction of the system has been given by the mathematical model.The developed SHINE device linear accelerator coldBPM prototype achieved SNR of48.7dB under the target conditions and met the physical design requirements of SHINE,which corresponds to a SNR of 34.5dB.This result verified the validity of the mathematical model.This topic focuses on the sensing electrode type BPM system on the FEL,and a series of studies have been carried out on how to improve the measurement accuracy of the system.The main innovation is to provide a systematic design optimization tool for the multielectrode BPM,and finally complete the description of the system’s integrity with a digital model.