用于频域方法测量超短电子束纵向分布的Kramers-Krnig变换研究

Research of Kramers-Krnig relationship for reconstruction of ultrashort electron longitudinal bunch profile by means of frequency domain measurements

Kramers-Krnig(K-K)变换方法被广泛地应用于频域测量中还原超短电子束团分布,成为分析电子束团形状、长度等参量的有效工具.研究发现,利用该方法分析电子束参量时,自相干曲线基底的选择、低频损耗与高频截止及插值外推位置的选择,对束团参量有重要的影响.以清华大学加速器实验平台采用相干渡越辐射测试束团长度为例,分析了上述参量的选取对测量结果的影响,讨论了选择K-K变换的关键物理参量的方法.

Kramers-Krnig （K-K） relationship is widely used in diagnostics of longitudinal bunch distribution with frequency domain measurement,and it has been used as a powerful tool in analysis of bunch profile and length.The study results show that the bunching beam parameters are severely affected by the choosing of the baseline of autocorrelation curve,power loss at low frequency and cutoff at high frequency,as well as extrapolation point,etc.As an example,the longitudinal bunching length is measured by means of coherent transition radiation in accelerator laboratory of Tsinghua University.We analyze the influence of the choice of parameters on measured experiment results and discuss the method of choosing the key parameters for the K-K transform.