Design And Optimization Of High Power Traveling Wave Accelerator With Collinear Load

The electron linear accelerator(LINAC),as an injector,plays an important role in the research of free electron laser terahertz source(THz-FEL),for its traveling wave accelerator affecting the quality of electron beam as well as the spectrum and power of THz radiation generated by the whole device.In this paper,aiming at improving the beam quality and ensuring the stable operation of the preliminary designed accelerator with collinear load,the structure optimization simulation and thermal characteristics analysis are carried out.In order to meet the requirement of electron bunch,the beam dynamics simulation under different accelerator feed power is completed by using PARMELA software based on principle of traveling wave accelerator structure and beam dynamics equations.The beam quality parameters satisfying the design requirements are obtained and the power loss of the accelerator tube is calculated by power flow equations.On the other hand,in order to meet the compact requirements of THz-FEL LINAC,according to the equal power distribution principle,the collinear load structure with FeSiAl absorbing material is introduced and designed.After the accelerator tube is designed preliminarily,it is necessary to optimize and simulate the relevant structures.The microwave energy needs to be fed to the accelerator by the input coupler,the performance and structure of which have a great impact on the beam quality.After completing the design and simulation of the single feed coupler based on HFSS,we compared the field asymmetries of single feed eccentric and double feed symmetry structures,and obtained the relevant conclusions.Finally,the thermal characteristics of the double feed symmetry structure is analyzed,which lays the foundation for the future water cooling design.In order to ensure the stable operation of the accelerator,the thermal characteristics of the designed accelerator tube and collinear load are analyzed.The simulation results show that the temperature distribution of the tube meets the requirement,while the temperature gradient and frequency offset of the collinear load are reduced after the optimization.Finally,four experimental load cavities are processed and measured,and the error results verify the feasibility of the design.