抑制自由电子激光微聚束不稳定性的可逆电子束加热
Reversible electron beam heating for suppression of microbunching instabilities at free-electron lasers
摘要：
由于在现有和未来的X射线自由电子激光（FEL）中高亮度电子束的压缩而导致的微聚束不稳定性的存在导致可达到的激光性能的限制，并且使得利用光学跃迁辐射的束成像是不可能的。不稳定性可以通过引入额外的能量扩展来抑制，即，“加热”电子束，如通过在直线加速器相干光源处的激光加热器系统的成功操作所证明的。增加的能量扩展对于自放大自发发射FEL通常是可容忍的，但限制了诸如播种的先进FEL方案的有效性。在本文中，我们提出了一个可逆的电子束加热系统的基础上，两个横向偏转射频结构（TDS）的上游和下游的磁聚束压缩机弯道。在第一个TDS中引入额外的能量扩展，抑制微聚束不稳定性，然后在第二个TDS中消除。通过计算和模拟，包括相干同步辐射的影响，我们证明了微聚束增益抑制的可行性。可接受的电子束和射频抖动的确定，和固有的选择，诊断和在线监测的电子束的纵向相空间进行了讨论。
英文摘要：
The presence of microbunching instabilities due to the compression of high-brightness electron beams at existing and future X-ray free-electron lasers (FELs) results in restrictions on the attainable lasing performance and renders beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e., "heating" the electron beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of advanced FEL schemes such as seeding. In this paper, we present a reversible electron beam heating system based on two transverse deflecting radio-frequency structures (TDSs) up and downstream of a magnetic bunch compressor chicane. The additional energy spread is introduced in the first TDS, which suppresses the microbunching instability, and then is eliminated in the second TDS. We show the feasibility of the microbunching gain suppression based on calculations and simulations including the effects of coherent synchrotron radiation. Acceptable electron beam and radio-frequency jitter are identified, and inherent options for diagnostics and on-line monitoring of the electron beam's longitudinal phase space are discussed.
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