| With the application of particle accelerators in the field of radiological medicine and nuclear experiments,the compactness of the accelerator structure has become a new requirement for accelerator design.Linear accelerators are often used as injectors for such application accelerators due to high beam quality and ease of injection.The upgrade plan of the first medical heavy ion accelerator(HIMM),designed by Institute of Modern Physics with independent intellectual property rights,will also replace the cyclotron with a linear accelerator as an injector.As an important part of the linear injector,the RF Quadrupole field accelerator(RFQ)is also developed in a compact and miniaturized direction.Based on the upgrade requirements of the HIMM project,the specific design work of HIMM-RFQ has been completed.A fast bunching dynamics design suitable for compact commercial low-intensity RFQ is proposed and the RF structure of the cavity is designed based on the fast bunching dynamics design.Finally,the studies for the cavity structure design and machining have been completed.The whole process of HIMM-RFQ design includes beam dynamics design,RF design,thermal deformation analysis and water cooling system design.According to the requirements of high stability and compactness,as well as the characteristics of its corresponding relatively low current,a beam dynamics design with fast bunching process is proposed for the first time.In the new dynamics design,the Gentle-bunching section and the Shaping section in the traditional four-section design theory of RFQ are redesigned.The length of RFQ is shortened by 17% on the premise that the beam transmission efficiency is guaranteed above 99%.On the other hand,beam acceptance is kept big enough.Error analysis has been made based on the proposed beam dynamics.Through the analysis,it is verified that the beam dynamics has a good tolerance to all kinds of errors.The limit tolerance data of all kinds of errors are obtained to provide a reference for future design.The error analysis includes non-ideal beam parameters and the errors in cavity processing and assembly.Based on the results of beam dynamics,RF structure of the cavity is designed with CST software.And influence of structure parameters on the RF characteristics is analyzed.Fluctuation of the quadrupole field is controlled within ±3.5%,and component of the dipole field is controlled within ±2.5%,by optimizing the parameters of the model structure.The particles tracking in the electric field established by RF simulation has been simulated.It proves that RF design can well meet the beam dynamics design requirements.Based on the RF design results,the cavity thermal and deformation are analyzed.The cavity cooling system design is completed,based on the thermal analysis results.In this paper,the key point of four-rod cavity machining-pole machining is studied.The impact of machining error on particle transmission is analyzed.It proves the feasibility of cavity machining.At the same time,the cold measurement method of cavity and the common errors in cold measurement are analyzed and discussed.This study completes the entire process of RFQ from beam dynamics theory to cavity processing.In the whole design optimization process,the existing basic methods involved RFQ design are adopted.Moreover,on the basis of the existing design methods,innovation and optimization are carried out according to the characteristics of the project.The dynamics and RF design methods,processes,and results can serve as a reference for the application of the same type of accelerator... |
PDF Full Text Request