Research And Design Of The Microwave Micro-pulse Electron Gun

Initiating the multipacting effect in a microwave cavity can be treated as a kind ofelectron source, namely micro-pulse electron gun (MPG). By using the phase focus-ing mechanism, it is easy to yield short pulse and high current electron beams at theexit of anode without using the pre-bunchers or bunchers, thereby simplify the accel-erator system. In addition, the gun has no requirement for timing and laser system ascompared with photoinjectors, hence the MPG becomes a more cost-effective system.Based on the facts as mentioned above, It is of considerable importance in industry orFEL use in the future.One of the main objectives in the micro-pulse electron gun is the multipactingresearch, which is recognized as a research innovation. Based on this background, thedissertation gave a review of the research progress of the multipacting. Due to the elec-tromagnetic field distribution difference between the parallel plate and the MPG, thedetails of multipacting researches in the parallel plate and the MPG were summarized,respectively. In addition, the resonance condition and the phase focusing mechanismwere also discussed in the paper. Moreover, a novel multipacting model was proposedhere to simplify the progress of the multipacting effect in the parallel plate. The newmodel divided the electron cloud into three parts at saturation, and it was studied indetail using both an analytical approach and particle-in-cell (PIC), which is expectedto improve the quality of beams.The optimizations of the RF parameters and cavity structure were discussed inthis dissertation. The RF parameters by using the theoretical analysis combined with software simulations. For the design of cavity structure, the innovations were conclud-ed to two points:1) Double-side shaped cavity;2) Double-grid electrode structure.The double-side shaped cavity was carefully designed to confine multipacting effectwithin the spatial range of electrodes, which avoiding the secondary emission damagein the copper wall. It was found that increasing the number of impacts for electronsuntil to saturation is important to attain high quality bunches, while at the expense oflosing out-of-phase electrons. Hence a novel electrode structure composed of two gridelectrodes in the system was studied in detail in order to improve the performance ofthe gun.The engineering design of the gun and the results of RF experiments were p-resented in the dissertation. Tuning, choker and electrodes transfer system were de-signed to validate the feasibility of MPG. We reviewed the theory of microwave mea-surement, and the RF test experiments were carried on the test system, then the testresults including the frequency, Q value and coupling coefficient were shown in thelast part. The microwave measurement results show a very low coupling coefficient,and a plug is inserted into the straight waveguide that are connected to the downstreaminput waveguide in order to increase the coupling coefficient.The high power experiments are an important part of the gun research. A highpower platform was built in the mine of the SDUV, and it is consists of a power split-ter, the water cooling system, the vacuum system and the beam diagnostics system. Itis easy to obtain the high power experiments data from the beam diagnostics systemwhich monitored by a6GHz oscilloscope.