Research On The Related Technology Of High Power Compact THz Source Electron Beam Based On FEL

R&D of a high power and compact THz source based FEL has been done by the cooperation of NSRL (National Synchrotron radiation Laboratory)/USTC (University of Science and Technology of China) and HUST (Huazhong University of Science and Technology). The facility consists of an intense electron gun, an external thermionic cathode and independently tunable cells (ETC-ITC) microwave electron gun, an accelerating tube and focusing system, a beam transport line, a beam measurement system and so on. This paper includes R&D of an ETC-ITC microwave electron gun, quasi-S2E beam simulation of the injector, beam commissioning, and beam parameter measurements. Meanwhile, an optimal design of the bi-periodic structure of the standing wave accelerating based on genetic algorithm has discussed in this paper also.The main characteristic of the ETC-ITC is no coupling between two cells. One of the most significant features of ETC-ITC is that electron sources are emitted from an external diode DC gun which nearly eliminated the back-bombardment effect. And the other is that the microwave power, total power from klystron is appropriately divided into two parts bypower divider and is independently fed into each cell with proper phase via phase shifter and waveguide system. The high quality beam is generated at the exit of ETC-ITC. The structure of ETC-ITC is simply and compact without compensating coil and a-Magnet. According to beam dynamics simulation, the shape of cylindrical symmetry and size of each cell are chose. The design of ETC-ITC and coupler are simulated with 3D electromagnetic simulation software. It was fabricated in NSRL workshop. Then the microwave parameter of the ETC-ITC such as frequency, coupling coefficient etc are measured. In order to measure the electric field distribution along the axis, an automatic measurement system is developed with the National Instruments Laboratory Virtual Instrumentation Engineering Workbench (Labview) software and a standard cylindrical cavity is fabricated and used to verify the measurement system. The simulation and the experiment results of the parameter of each cell are agreement well.Quasi S2E is used for beam dynamics simulation where the electron source and ETC-ITC with CST PARTICLE STUDIO(?)(CST PS); linac with ASTRA code and beam load effect with self-programming; transport line with MADX and ELEGANT code. Because of the different parts with different code, the data transfer between the various codes is particularly important. Thus the programming interface is required according to the input and output parameters of different code. The simulation results of the LINAC outlet:beam energy of 12.3 MeV, energy spread of 1‰, the transverse emittance about 14.3 πmm mrad, bunch charge about 210 pC.After the installation of the facility of THz light source, there are several procedures before formally beam test, such as:electron gun activation, cavity tuning, and conditioning of the LINAC including waveguide system. And then according to the results of beam dynamic simulation, beam parameter are measured. Fast beam current transformer (FBCT) is used to measure macro beam current, the analysis magnet is used to measure the beam energy and energy spread, the phase method is used to measure bunch length, the quadrupole magnet is used for measuring the transverse emittance. At the end of microwave conditioning, the emission current of cathode and the current of exit of ETC-ITC are measured with the filament current and high voltage of DC gun. We have observed radiance lead by beam at the Flagl, the energy bar of the end of analysis magnet, the beam bar of the end of beam line. Meanwhile, the macro-pulse beam current of TORI and TOR2 are measured with FBCT. By means of changing the phase shifter of two cells and linac, the feeding power of two cells and linac, the filament current and high voltage of DC gun, we can get the higher quality beam parameter.Now the LINAC has been commissioning successfully. Preliminary measurement parameters are:the center energy of beam is of 12.76 MeV; the energy spread is of 3.2‰; bunch length is of 3.7 ps; macro-pulse current is of 0.7 A.The bi-periodic structure of standing wave accelerating tube is studied in this paper. The traditional method is replaced by genetic algorithm for optimizing the accelerating structure. The shunt impedance increased by 17.6%. We have designed a 6 MeV tube and coupler based on the optimal result of genetic algorithm and performed beam dynamics.