Beam Dynamics Research Of An Electron Linear Accelerator For High Energy Electron Radiography

As one of the candidate methods for high energy density matters diagnosing,studies on the High Energy Electron Radiography(HEER)technology have become a hot topic in recent years.In order to realize the diagnosis of high energy density physics on the high intensity heavy ion accelerator facility,the Institute of Modern Physics(IMP),Chinese Academy of Sciences(CAS)proposed to build the first dedicated platform for HEER experiment in the world.The key part of this platform is an electron linear accelerator(LINAC),which consists of two different guns,either a thermionic cathode RF gun or a photocathode RF gun,for diagnosing different targets.The LINAC with thermionic RF gun is designed for diagnosing static and thick targets,and the LINAC with photocathode RF gun can be used for 4D radiography researching.In this dissertation,beam dynamic simulations of the LINAC are performed by using codes ASTRA,Elegant and GPT.The beam dynamics analysis and the design of the LINAC,which built for HEER studies,are completed.The LINAC in thermionic cathode mode consists of a thermionic cathode RF gun,an alpha magnet and a traveling wave accelerating tube,which is designed to generate high intensity,low energy spread and short pulse-width electron beams.As a key component of bunch compressing and energy filtering in the LINAC,the design of the alpha magnet,the magnetic field distribution of the designed model and the magnetic field measurement results of the constructed alpha magnet were discussed.The transmission of electron beams under space charge force in the three dimensional alpha magnet model is simulated,and the angle of the beam entering the alpha magnet is optimized to reduce the influence of the magnetic field distortion caused by the hole in the mirror plate on beam transmission.Moreover,the transmission process of the high intensity electron beam in the alpha magnet and the interaction between the beams during multi-beam transmission were simulated.The beam with optimized emittance and bunch sizes can be obtained by adding quadrupole magnets between the alpha magnet and the gun.Based on the simulation results of beam transported in an alpha magnet,the design and the beam dynamics of this LINAC were studied.The parameters of the LINAC were optimized,moreover,beam transport in the LINAC with the consideration of space charge effects were analyzed and the parameters of the LINAC were further optimized.The electron Beam with the energy of about 50 MeV,the bunch charge of about 150 pC and the energy spread of about 0.085% can be obtained at the LINAC exit.Furthermore,preliminary tests of the LINAC were completed,and the rationality of the simulation was preliminarily verified.Finally,preliminary studies on the design of the LINAC which working in photocathode mode have been completed.The LINAC parameters under two different longitudinally distributed laser beams were simulated and optimized respectively,and the characteristics of electron beams under different laser beams were compared and analyzed.It is proposed to further optimize the beam emittance by the way of using two emittance compensation solenoid in this LINAC.In the simulation of flat-top laser,it was found that when the bunch charge reduced to 0.4 nC,the beam with energy spread of 0.08% and the emittance of 0.88 ? mm?mrad can be obtained,which can be used for the improvement of spatial resolution in thin target diagnosing.