| To meet the requirements of the THz source based on the free electron lasers (FEL-THz),the photoinjector has to provide electron beams with some good characters such as low emittance,high peak intensity and low scattered energy. Therefore, focus on high quality electron gun design is increasing worldwide. Photocathode RF electron gun becomes the first choice for FEL-THz,for its unique advantage.This article is intended to carry out some design and research on L-band photocathode RF electron gun.At the beginning of theis,development of the free electron lasers and electron gun is briefly introduced.Then the beam dynamics in photocathode microwave gun is discussed.Besides,some relative issues which cause the increase of tranverse emittance are analyzed in detail. Finally, the principles and methods of compensation due to space charge effects emittance growth were described in detail.Secondly, it introduces the overall design concept and cavity structure of the L-band photocathode microwave electron gun. Microwave Characteristics is studied,using a two-dimensional electromagnetic field simulation software (POISSON Spearfishes) and A three-dimensional electromagnetic field simulation software (CST-STUDIO).The relationship of the field distribution and the two main mode frequencies were analyzed.In addition, analysis of the impact of the resonance frequency of various structural parameters were discussed.Finally, this article elaborate beam tracking and optimization of process parameters. Finally, it elaborated beam tracking and optimization of process parameters. Combining the beam dynamics theory and the design needs in energy spread, emittance and other requirements to achieve,we focus our discussion on the initial distribution of the bunch and laser drive phase, accelerating gradient through the entire cavity.A series of independent optimization is carried out especially on the initial radius bunch, bunch charge amount, the compensation coil magnetic field strength. |
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