Generation and spatial separation of circular polarized FEL radiations by orbit control
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摘要: 研究了在自由电子激光设施中产生高偏振度圆偏振辐射的技术方案。该方案将工作在反向渐变模式的平面波荡器和常规椭圆极化波荡器以前后连接的方式进行排布，并通过波荡器之间的矫正磁铁对电子束进行轨道控制。在平面波荡器部分利用偏转磁铁使电子束偏向传输，所产生线偏振辐射也将偏轴传播，脉冲能量为0.357
${\text{μJ}}$ 。在进入椭圆极化波荡器之前校正电子束的轨道和前进方向，使得带有微群聚结构的电子束沿轴线正向传输，其产生的圆偏振辐射能量为92.39${\text{μJ}}$ 。圆偏振辐射将沿轴向传输，在一定距离后可实现其与线偏振辐射在空间上的分离。通过数值模拟分析了电子束偏转对辐射光性质所产生的影响。Abstract: Circularly polarized radiation in the X-ray region is required by many experimental applications. Such demands can be met at FEL facilities by mounting few helical undulators after the planar undulators. For obtaining high degree of circular polarized radiation, the reverse taper technique is often used, where in the planar section, significant bunching of the electron beam is accumulated while the output linear polarized radiation power is suppressed. This paper investigates the technique of spatially separating the background weak linear radiation by first transversely deflecting the electron beam with dipole kicker magnets in the planar undulator section and correcting its orbit and traveling direction before entering the helical undulators. The resulting linearly and circularly polarized radiations will propagate in slightly different directions and can be separated spatially. Numerical simulations are performed to analyze the impact of electron beam deflection on the radiation properties. -
图 1 用于产生圆偏振辐射的波荡器系统布局
Figure 1. Layout of the undulator system for generation of circularly polarized radiation
图 2 S3FEL的电子束纵向切片能量和流强分布以及切片发射度和能散分布
Figure 2. Slice energy and current and slice emittance and energy spread of the electron beam at S3FEL
图 3 波荡器线内电子束方向传输角度与位置的演化
Figure 3. Current weighted traveling angle and position of the electron beam in the y direction
图 4 在PMU段中线偏振辐射的峰值功率和脉冲能量以及最大群聚因子以及平均群聚因子的演化
Figure 4. Evolution of the peak power and pulse enegy of the linearly polarized radiation and the maximum and average bunching factor in the planar undulators
图 5 线偏振脉冲y方向传播角度与置的演化
Figure 5. Power weighted traveling direction and position of the linearly polarized radiation pulse in the y direction
图 6 在EPU段中圆偏振辐射的峰值功率和脉冲能量以及最大群聚因子以及平均群聚因子的演化
Figure 6. Evolution of the peak power and pulse enegy of the linearly polarized radiation and the maximum and average bunching factor in the elliptical polarized undulators
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