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摘要: 束流分配系统是自由电子激光装置中至关重要的一部分，它可以将直线加速器产生的电子束团分配至不同的波荡器中。提出了一种基于上海软X射线自由电子激光装置的束流分配系统设计方案。针对该方案，详细介绍了三维从头至尾的束团跟踪模拟以及在传输过程中的束流动力学分析，模拟结果表明，该束流分配系统设计可以保证束流发射度增长小于8%，同时可以保证峰值电流、能散以及束团长度在经过该分配系统时未受到破坏。此外，针对束团在直线加速器中的微束团不稳定性和抖动也进行了分析。Abstract: In this article, a feasible switchyard design is proposed for the Shanghai soft X-ray Free Electron Laser (SXFEL) facility. In the proposed scheme, a switchyard is used to transport the electron beam to different undulator lines. Three-dimensional start-to-end simulations have been carried out to research the beam dynamic during transportation. The results show that the emittance of the electron beam increases less than 8%, meanwhile, the peak current, the energy spread and the bunch length are not spoiled as the beam passes through the switchyard. The microbunching instability of the beam and the jitter of the linear accelerator (linac) are analyzed as well.
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Key words:
- switchyard /
- resistive wall effects /
- microbunching instability /
- jitter
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Figure 4. Longitudinal wakefield behind a point charge in a round, metallic pipe with various radii (s is inner length of bunch)
Figure 5. Variation of central energy along beam for various pipe radii at exit of FODO cells
Figure 6. Emittance evolution through the switchyard (a) and energy and current distributions at exit of switchyard (b)
Table 1. Main linac parameters of SXFEL
electron beam energy/GeV peak current/A charge/pC bunch length
(FWHM)/fstransverse normalized emittance/(mm·mrad) repeat frequency/Hz 1.5 700 500 ~700 1 50 
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Table 2. Summary of trajectory jitters
mechanism RMS error Ax/% Ay/% corrector current 5×10-4 5 7 bend current 5×10-5 2 0 quad vibration 150 nm 5 8 quad current 2×10-4 5 4 quad misalignment 200 μm kicker 5×10-4 12 0 septum 1×10-5 4 0 CSR+σz jitter 5% 10 0 total (RMS) 18 11
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