基于螺线管扫描法进行电磁叠加场中热发射度测量的仿真分析

在一种猝发高重频的X射线自由电子激光（XFEL）装置中，由于受到光阴极注入器内补偿螺线管与电子枪之间特殊结构的限制，阴极附近电场与磁场为叠加状态。实验中需要对阴极热发射度进行测量，而测量热发射度常用的螺线管扫描法基于几何发射度不变的前提，无法直接应用于电磁场叠加的结构。针对这一问题，考虑到归一化过程可以剔除电场对发射度的影响，基于此，研究归一化相空间中应用的螺线管扫描法，并通过仿真计算与分析，最终证明该方法适用于电磁叠加场中阴极热发射度的测量。

Simulation of the solenoid scan method used in overlapping field for thermal emittance measurement

In one high repetition frequency X-ray free electron laser (XFEL) equipment, the electron gun and compensate solenoid have special structure in the photoinjector, thus the electric field and the magnetic field overlaps near the cathode. The thermal emittance of the cathode should be measured in the experiment. The solenoid scan method used to measure the thermal emittance is not suitable for the overlapping field, because it works effectively only when the rms emittance keeps constant. As the normalized phase space can avoid the influence of the electric field, we tried to use the solenoid scan method in normalized phase space. Using simulation code to do simulations and analysis, we finally demonstrate that this method is feasible for measurement of thermal emittance of the photoinjector which has overlapping field.