| The 30MeV linac of Institute of Applied Electronics CAEP is a multifunctional experiment platform. Many basic physics researches, such as Free Electron Laser (FEL), can be done on this platform. It is a quite complicated system and involves many fields: accelerator physics, microwave electronics, vacuum physics, low temperature physics and etc. Based on this facility, there are some physics issues' analysis and numeric simulation on the accelerator in this dissertation.First, some theoretical work is done based on L-band RF-GUN (thermionic cathode injector). The electromagnetism field of the accelerator cavity is analyzed, and the movement of electron in the cavity also analyzed. The vibration rule of transverse emittance is acquired when the electron beams move in the accelerator cavity, and the result complies with the numeric simulation. The effect of field strength, initial phase, bunch shape and charge on electron beam transverse emittance is also explored by numeric simulation method. PARMELA including Schottky effect is compiled, the numeric simulation on 30MeV linac injector system is done on the program, and the beam's parameters of the injector system are presented.Alpha-magnet, the beam energy choosing and pulse width compressing element, is a key part of the injector. It plays an important role in 30MeV linac system. The relative physics issues of the a-magnet are discussed in the dissertation. Structures of two kinds a-magnet are presented and compared. The magnetic distribution of a-magnet is presented by analytic way and numeric simulation way.The single particle movement is studied in a-magnet and the movement rule of charged particle in ideal four poles magnetic field also is obtained. Quantificational results of the incidence angle, trajectory length and the maximal distance in x direction are presented for ideal trajectory, and the equation indicates some important characters of a-magnet. Simulation on the a-magnet of 30MeV linac is also done with the GPT code; The movement picture of electron beam in a-magnet is presented; The change of beams emittance, the compression effect of bunch length, change of energy dissipation and achromatic angle of true a-magnet are explored.This chapter mainly introduces some characteristics and properties of the main accelerate stage in 30MeV linac system. Numeric simulation is done based on 30MeV linac structure and the corresponding parts' parameters. The simulate result shows that the design of beamline is reasonable. The beam properties change very small when the drifting distance before the first acceleration stage is changed in the certain ranges. The trajectory of electron, the electronic energy, emittance and the bunch length in the accelerating process are presented. Primary properties parameters are obtained on different positions. Most parameters are better than the experimental results. It indicates that the experiment conditions are not optimized.Technologies of the electron energy recovery is explored, some key technologies in PERL and the phase question in energy recovery process are discussed. Feasibility of the 30MeV linac for energy recovery accelerator is discussed based on simulation. The 30MeV linac can be used as energy recovery accelerator with photo-cathode RF-GUN injector. And multi-cavities photo-cathode injector can not only improve the quality of output electron beam, but also decrease the effect of phase question in the energy recovery process. The studies of such still need to go further.
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