曙光一号自由电子激光器束调节研究

简单介绍了曙光一号自由电子激光器实验布局．着重就束调节方案进行了数值模拟和实验研究，给出了束流调试结果,并进行了分析；当进入摇摆器的束流为950A，摇摆器磁场为0.31T，在摇摆器长度为2．4m的位置,获得了50MW的饱和功率，经变参数实验后输出功率提高到140MW．     

曙光一号自由电子激光实验的理论分析

对曙光一号自由电子激光实验方案和结果进行了系统的理论分析和数值计算。首先用实测的束流发射度ε＿Ｎ＝０．３６～０．６３ｒａｄ·ｃｍ论证了电子束可以不经调制而由束流传输段直接进入摇摆器达到有效产生自由电子激光。其次用编制的三维电子束传输程序模拟２ｋＡ强流束从加速器出口到摇摆的器入器传输过程。最后根据实测参数，使用ＣＥＢＱ程序和ＷＡＧＦＥＬ程序，对曙光一号ＡＳＥ实验、功率放大实验和磁场失谐曲线进行的计算表明，曙光一号束流发射度大约在印ε＿Ｎ＝０．６１～０．８ｒａｄ·ｃｍ附近；ε＿Ｎ＝０．８ｒａｄ·ｃｍ时，上述实验与曲线的理论计算基本一致；曙光一号双向聚焦摇摆器设计是成功的；从功放结果分析，磁控管输入摇摆器的ＴＥＯ１模的功率约为５０Ｗ，并对下一轮实验提出了改进意见。     

曙光一号自由电子激光器(FEL)电子束发射度的分析

对曙光一号自由电子激光装置电子束发射度的测量值进行了深入的分析。严格地计算了不同发射度的束流在摇摆器内的传输,计算了发射度对激光功率的影响。由此得出,曙光一号自由电子激光器可以省去9米长的束流选择段。     

曙光一号自由电子激光装置的设计研究

曙光一号自由电子激光装置(SG-1 FEL)是一台高功率毫米波段自由电子激光放大器,它由3.5MeV直线感应加速器、电子束调制系统、变参数摇摆器和微波种子源等部件组成。本文扼要叙述了SG-1 FEL的物理设计和主要技术参数,并重点分析了各主要部件的实验研究、计算模拟,以及物理设计和结构的特点。     

毫米波圆柱波导自由电子激光放大器的数值模拟

本文以单粒子理论为基础，在不计空间电荷效应的近似条件下推导了带轴向引导磁场的三维圆柱波导非线性模拟方程组。用CAGFEL程序计算、分析了在带入口区、常数摇摆器条件下两组不同物理参数的自由电子激光放大器的物理模型。计算结果可靠，物理图象合理。对于其中的第二组参数还着重考查了光波频率、输入功率和摇摆器场振幅改变对输出功率和效率的影响。上述这些计算结果对0．7MeV 自由电子激光放大器的设计和实验具有一定的参考价值。     

3.3MeV直线感应加速器性能改进

主要介绍曙光一号（ＳＧ－１）自出电子激光器中３．３ＭｅＶ直线感应加速器的系统改进及实验结果，改进后系统的稳定性、同步性和可靠性以及束品质都有很大改善，进入摇摆器的束流比改进之前提高了数十倍，并获得了大于１０ＭＷ的放大自由电子激光输出功率。     

变参数自由电子激光放大器的设计方法

据自由电子激光原理,利用变参数摇摆器设计可以大幅度提高自由电子激光放大器的效率,在分析文献中所提出的“单电子共振”和“磁场指数下降法”基础上,提出了变参数摇摆器的“多电子自洽设计和最佳选择”的设计方法。经数值计算证明,所提出的方法明显优于其它方法。     

喇曼型无引导场自由电子激光实验的理论计算

用三维程序CAGⅡ对西南应用电子学研究所在EPA-74脉冲加速器上所作的FEL(自由电子激光)实验进行了数值模拟,分析计算了输入功率、摇摆器磁场振幅、自发辐射频率、电子能量、束流强度和发射度等参数变化时对饱和位置、饱和功率和效率的影响。在对实验参数中的电子能量作合理调整的条件下,数值模拟的增益系数大约为70dB/m,是实验值的80％。因此饱和位置比实验推后20％到40％。饱和功率高出大约3倍。经折算后大约为1MW,与实验结果比较接近。考虑到实验的复杂情况可认为理论结果同实验结果基本符合。     

曙光一号自由电子激光强流电子束的数值模拟

根据曙光一号自由电子激光实验的需要，将国外二维ＥＢＱ程序发展为三维强流束数值模拟程序（ＣＥＢＱ）。ＣＥＢＱ既能计算轴对称问题，还能计算磁四极子、束流偏轴和斜入射等三维问题。对强流束的自生电磁场效应，与ＥＢＱ程序一样，只考虑线性近似而略去了高阶项。使用ＣＥＢＱ程序对曙光一号装置进行了计算，对摇摆器入口处的椭圆形挡板进行了论证。数值结果表明，椭圆形档板对提高束流品质，有效地产生自由电子激光是必要的。这一结果和第二轮曙光一号实验的测量结果基本一致。     

圆极化变参数摇摆器中电子的稳定性研究

采用圆极化变参数摇摆器能延缓自由电子激光器件进入饱和,提高束波互作用效率。通过计算电子运动的柯尔莫哥洛夫熵来研究变参数摇摆器自由电子运动的稳定性。研究结果表明:摇摆器无论采用正坡度还是负坡度,平衡态电子的柯尔莫哥洛夫熵值均小于零,稳定性均比无坡度时好,但电子的运动轨迹趋于发散;当有激光场存在时,正坡度破坏电子运动的稳定性,负坡度改善电子运动的稳定性。其结果为电子运动稳定性的进一步研究提供参考。     

Nonlinear simulation of a high-power, collective free-electronlaser

Results obtained with the three-dimensional nonlinear analysis and simulation code, ARACHNE, and a recent 33.4-GHz, collective, free-electron laser (FEL) amplifier experiment are compared. The experiment has demonstrated power levels of 61 MW (≈27% efficiency) without recourse to tapered magnetic fields, using a 750-keV/300-A electron beam with a nominal axial energy spread of 1.5% propagating through a cylindrical drift tube in the presence of a helical wiggler and an axial guide magnetic field. Significant differences in the character of the emission were found, depending on the direction of the guide magnetic field. When the wiggler and guide fields were parallel, observed power levels reached approximately 4 MW for both the strong and weak guide field regimes, but vanished in the neighborhood of the magnetic resonance. However, the maximum power was observed in the reversed field case when the wiggler and guide fields were antiparallel. In this case, no resonant enhancement in the transverse velocity is expected to occur; however, a significant reduction in the output power occurred in the neighborhood of the antiresonance. The ARACHNE simulation is in substantial agreement with the experiment     

磁场预增强的锥型波荡器

研究了波荡器磁场增强对提高自由电子激光器效率的影响。模拟计算发现采用磁场增强波荡器能使自由电子激光器的效率提高到１７．６％，采用磁场预先增强而后又增弱的锥型波荡器则能获得高达４３．３￥的输出效率，自由电子激光器的功率得到进一步的提高。     

Amplification and superradiant emission from a 33.3 GHz freeelectron laser with a reversed axial guide magnetic field

A new regime of free-electron laser (FEL) operation using a helical wiggler field and a reversed axial guide magnetic field is reported. The orientation of the axial field is such as to oppose the electron rotation imparted by the helical field. The 33.3-GHz FEL amplifier is driven by a mildly relativistic electron beam (750 kV 300 A, 30 ns) and generates 61 MW of radiation with a 27% conversion efficiency. The results are compared with those obtained when the axial guide field is in its conventional orientation, where considerable loss of power and efficiency is observed     

曙光一号自由电子激光自发辐射放大的理论计算

曙光一号自由电子激光装置用自发辐射放大(ASE)机理,在毫米波波段测得了数百毫瓦的光信号输出。利用三维WAGFEL程序,结合曙光一号直线感应加速器型自由电子激光放大器参数,详细地分析了自发辐射放大的增益、输出功率随电子束的质量(包括束流能散度、流强、发射度等因素)的变化情况,给出了相应的定标关系;并且考察了摇摆场随机误差对自发辐射放大功率的影响。最后对自发辐射放大的实验结果进行了分析。     

Measurements of microwave power and frequency in a pulsed freeelectron laser amplifier

We report output power and frequency measurements of a pulsed free electron laser (FEL) operating as an amplifier at 35 GHz, without guiding field. The experiment used an induction linac, which delivers an 800-A relativistic electron beam (2.2 MeV) with a flat-top of 40 ns into the helical wiggler. The input signal furnished by a 35-GHz magnetron source is amplified to power levels of the order of 80 MW. The experimental results are in good agreement with our simulations. Frequency chirping is observed, and its behavior as a function of the basic FEL parameters is discussed     

毫米波自由电子激光的数值模拟和实验的比较

从波导管毫米波自由电子激光器的设计要求出发,根据Livermore实验室FRED程序的物理思想,编制了空间三维的数值模拟程序(WAGFEL)。为了检验程序的可靠程度,结合ELF装置的实际参数,进行了数值模拟并和实验结果进行了比较。结果表明,把Wiggler磁场B_w增大300 Gs后,WAGFEL程序的模拟结果和Livermore实验室的实验结果基本符合。模拟使用的全部参数,除B_w增大300Gs外,都是ELF的实际参数。模拟时峰值磁场B_w=4050Gs,实验测量峰值磁场B_w=3720Gs,相差在8％左右。WAGFEL程序可以用来从事毫米波自由电子激光器的设计以及基本物理问题的研究。     

Electric-Wiggler-Enhanced Three-Quantum Scattering and the Output Power Affected by this Scattering in a Free-Electron Laser

We derive the cross section of scattering through the three-quantum interaction of an electron with the incident laser field, the emitted photon, and an axial electrostatic field produced by the magnetic wiggler in the magnetic wiggler acting as the sole zeroth-order perturbing classical field in the first free-electron laser （FEL）. In the derivation, we apply quantum-wiggler electrodynamics （QWD）. We find that this scattering predominates the usual two-quantum scattering. The output power of spontaneous free-electron two-quantum Stark emission driven by the above electrostatic field attenuated by the three-quantum scattering agrees within a factor of 10 with the measured power in the case of the first FEL.