Optimization of Electron Storage Ring for Free Electron Laser

1. 考虑到环阻抗分为电阻部分和电感部分，观察到的纵向电子分布被势阱畸变效应扭曲。通过考虑势阱畸变效应的模拟，预测了在负动量压实环上的第一FEL宏脉冲的演化远高于在常规正动量压实环上的第一脉冲。此外，在负动量压实环上，平衡状态下的FEL功率与正动量压实环上的FEL功率相同，即使存在微波不稳定性。用条纹相机观察到，当光学谐振腔处于轻微不稳定状态时，FEL振荡变得不稳定，其宏脉冲结构发生变化。为了保证FEL振荡的稳定，必须严格保持FEL脉冲与电子束的最佳同步。通过检测高次谐波的相位差而不是测量时间偏差，开发了一种反馈系统来保持这种同步。系统运行良好，获得了非常稳定的自由电子激光器。由于FEL振荡稳定，可以精确地观察到FEL相互作用引起的电子束延长。虽然束长明显不强，但考虑到势阱畸变效应，分析得出的FEL诱导能量扩散是非常大的。然而，测量的能量分布与理论预测的一致性并不完美。需要进一步调查。对腔镜进行了优化设计。通过选择合适的涂层材料，可以实现高反射率和高透射率的反射镜。结果，在存储环上提取的FEL功率达到了最高记录（>0.5 W），接下来将进行新的双色实验来研究气体分子的光解离机制。

1. The observed longitudinal electron distribution distorted by a potential-well distortion effect that takes account the ring impedance divided into resistive and inductive parts. The first FEL macropulse evolves on a negative momentum compaction ring is predicted to be much higher than that on conventional positive momentum compaction ring by a simulation including the potential-well distortion effect. In addition, the FEL power at a equilibrated state on the negative momentum compaction ring would reach the same level as that on the positive ring, even the microwave instability exists.2. The FEL oscillation becomes to be unstable and the its macropulse structure is being varied when the optical resonator is slightly unstable, which was evidently observed by using a streak camera. In order to secure stable FEL oscillation, the FEL pulse and the electron bunch should be strictly kept at the best synchronism. A feedback system was developed to keep such synchronism by detecting a phase difference of those higher harmonics instead of measuring time deviation. The system worked very well and excellently stable FEL was obtained.3. Because of stable FEL oscillation, the electron bunch lengthening due to the FEL interaction was able to be precisely observed. Although the bunch lengthening was apparently not strongly, taking the potential-well distortion effect into account, the FEL induced energy spread derived by a analysis was found to be very large. However agreement of the measured energy spread with a theoretical prediction was not perfect. Further investigation is required.4. Optimization of the cavity mirrors was also developed. By using suitable materials for the coating, mirros with both very high refrectance and transmittance were realized. As a results, the highest record of extracted FEL power on the storage rings was achieved (>0.5 W), which is now followed by a new two-color experiment to study the mechanism of photo-dissociation of gas molecules.