Experimental characterization of emittance growth induced by the nonuniform transverse laser distribution in a photoinjector
Experimental characterization of emittance growth induced by the nonuniform transverse laser distribution in a photoinjector
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光注入器中非均匀横向激光分布引起的发射度增长的实验表征
DOI：
10.1103/physrevstab.5.094203
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发表时间：
2002
影响因子：
--
通讯作者：
V. Yakimenko
中科院分区：
文献类型：
--
作者：
F. Zhou;I. Ben;M. Babzien;X. Chang;A. Doyuran;R. Malone;Xuelong Wang;V. Yakimenko
来自光注入器的高亮度电子束的发射率受到照射阴极的激光束的横向和纵向分布的影响。非均匀激光束产生非均匀电子束分布，其发射度在等离子体周期的时间尺度上增长。在布鲁克海文加速器测试设施进行了实验，以研究横向不均匀激光束导致的发射率增长。制造激光掩模以产生各种激光分布。当激光分布强烈偏离均匀分布时，观察到显着的发射率增长。对于柱对称、非均匀分布，实验结果与 PARMELA 模拟一致。对于均匀和非均匀光束，发射度对束团电荷的依赖性是线性的，作为束团电荷的函数。对于均匀光束，发射度测量与 PARMELA 模拟的预测非常吻合，但分析方法高估了结果。对于非均匀光束，分析估计值约为测量值的 70%。对于非圆柱对称、非均匀光束，我们观察到发射率与均方根激光不均匀性成线性比例，并且完全均匀光束的最佳发射率在 0.5 nC 时外推为 $1.07\ifmmode\pm\else\textpm\fi{}0.13\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$。
The emittance of a high-brightness electron beam from a photoinjector is affected by the transverse and longitudinal distributions of the laser beam illuminating the cathode. A nonuniform laser beam generates a nonuniform electron-beam distribution that experiences emittance growth on a time scale of the plasma period. Experiments were performed at the Brookhaven Accelerator Test Facility to investigate the emittance growth due to transversely nonuniform laser beams. Laser masks were fabricated to generate various laser distributions. Significant emittance growth was observed as the laser distribution deviated strongly from a uniform distribution. For cylindrically symmetric, nonuniform distributions, experimental results agree with PARMELA simulations. The emittance dependence on the bunch charge is linear as a function of the bunch charge for both uniform and nonuniform beams. For a uniform beam, the emittance measurements agree well with the predictions from PARMELA simulations, but the analytical approach overestimates the results. For nonuniform beams, analytical estimates are about 70% of the measurements. For noncylindrically symmetric, nonuniform beams, we observed that the emittance is linearly proportional to the rms laser nonuniformity and the best emittance for a perfectly uniform beam is extrapolated to be $1.07\ifmmode\pm\else\textpm\fi{}0.13\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ at 0.5 nC.