激光斜入射光阴极对束流质量的影响及其优化

Influence of laser oblique incidence on beam quality and optimization

针对美国布鲁克海文国家实验室(BNL)型的光阴极微波电子枪,模拟了不同分布状态的驱动激光脉冲斜入射光阴极对束流质量的影响,给出了改变注入相位和补偿线圈磁场强度对发射度的优化结果。结果表明:光斑椭圆化将会导致发射度的大幅增长,优化效果不理想;波前不同步导致的发射度增长对于纵向高斯分布的脉冲可以得到理想的优化。对于斜入射引起的光斑椭圆化和波前不同步问题给出了光学校正方法及部分测量结果。此外,模拟结果显示,对于横向均匀分布的激光脉冲,适当椭圆度的光斑比圆形光斑更有利于提高电子束质量。

In allusion to Brookhaven National Laboratory（BNL） type photocathode RF gun,we simulated and optimized the influence of drive laser oblique incidence on beam quality.Different distributions of drive laser were considered.We optimized the transverse emittance by tuning the injection phase and magnetic field intensity of compensating coil.The ＂elliptical spot＂ caused serious increase of transverse emittance,which can not be optimized well.Whereas,the increase caused by ＂time slew＂ could be optimized well for Gaussian distribution pulse in temporal direction.We also presented an optical method to calibrate the ＂elliptical spot＂ and ＂time slew＂ problem on the photocathode and partial measurement results.The simulation results show that： for drive laser with uniform transverse distribution,an elliptical spot with appropriate ellipticity is more favorable than a circular one for improving the beam quality.