脉冲线积分场测量系统的研制

介绍了脉冲线测量插入件磁场一二次积分的原理和测量装置的组成,分析了重力、噪声和反射波等因素对测量精度的影响,并采用对称安装金属线、夜间测量、油滴吸收反射波等方法减小了这些因素对测量的影响。脉冲线测量系统的测量结果与霍尔点测法相比符合得较好。利用该装置对实验室即将投入应用的电磁型圆极化波荡器进行了测量,验证了校正线圈和主线圈电流之间的关系。     

纯永磁波荡器基波与谐波磁场的三维计算与测试

 对标淮的纯永磁波荡器进行了三维磁场的有限元计算,给出了纯永磁波荡器的基波与谐波磁场的幅值与相位,并与测试结果进行对比,结果表明,标准的纯永磁波荡器谐波磁场幅值比基波幅值低两个数量级。     

High energy gain of trapped electrons in a tapered, diffraction-dominated inverse-free-electron laser

Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an inverse-free-electron-laser (IFEL) accelerator experiment. A 14.5 MeV electron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and field amplitude. The Rayleigh range of the laser, approximately 1.8 cm, is much shorter than the undulator length yielding a diffraction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.     

Choice of the parameters of a magnetic undulator

The total output power of undulator radiation is investigated as a function of the constructional parameters of the undulator and its supply current. Calculations are presented of the magnetic field in the undulator, and the optimum undulator dimensions for maximum magnetic field intensity per unit length of the system are calculated. It is shown that the total radiated power of the charged particles depends on the undulator periodicity.     

大块永磁铁低温剩磁测量技术研究

通过对霍尔探头低温标定系统改进, 建立了大块永磁铁低温剩磁测量系统(CRMS). 以尺寸为40 mm×40 mm×10 mm的矩形NdFeB永磁铁(N50M)为例, 对低温剩磁测量方法进行了研究, 结果表明, 影响低温剩磁测量可靠性主要因素有: 霍尔探头低温标定, 霍尔探头位置, 温度漂移与材料低温热膨胀等. 如果测量方法一样, 永磁铁低温剩磁测量重复性好于0.1%. 实验为低温波荡器等高精度永磁装置大块永磁铁低温剩磁测量与研究创造了条件. 关键词： 大块永磁铁 低温剩磁 测量误差 低温波荡器     

Efficiency and sideband observations of a Raman FEL oscillator witha tapered undulator

Power and spectral measurements are reported from the Columbia Raman free-electron laser (FEL) oscillator experiment. High-power radiation pulses (~12 MW, 100 ns) are generated at a wavelength of ~2.5 mm, using a 750-kV electron beam injected into a helical undulator. The undulator is made up of a 40-cm long constant-period (1.45 cm) section followed by an equal length of tapered undulator. The period is decreased by 7.6% in such a way that the on-axis field remains constant. It is reported that the taper allows an increase in total power efficiency from ~4 to ~12%. Most noteworthy is that the tapered undulator reduces the sideband radiation compared with a constant-period undulator FEL which is studied in the same configuration. The power was measured calorimetrically and compared with the results of a 1-D Raman code. The reduction of sideband power observed in the experiment was consistent with computational results obtained with a 2-D sideband code     

混合型波荡器的3维优化

 以波荡器辐射波和共振电子能及混合型波荡器的解析计算为基础，通过3维磁场的有限元计算，在欧洲光源横向优化基础上，给出了同步辐射和自由电子激光用混合型波荡器纵向优化参数，进而给出了用于DUV FEL混合型波荡器的设计计算参数。加侧位和顶部永磁块后，峰值磁场分别提高到0.722T和0.773T，辅助以1μm量级分辨率的磁间隙调节机械系统，磁场分辨率好于10^-4T量级。     

FEL undulator with permanent ferromagnetic magnets

A terahertz FEL ferromagnetic undulator has been created. The length of the undulator period is 9 cm with the number of the periods at 27. By means of the selection and redistribution of magnetic elements, the spread of the amplitudes of the magnetic field was reduced to 7%. Additional windings of the magnetic elements were used to compensate for residual spread. The required focusing gradient of the magnetic field was obtained as a result of the relative displacement of alternating poles with an opposite charge of the magnetic field along the x axis. Parameters of undulator, including the focusing properties in the horizontal plane, were investigated.     

Influence of a constant magnetic field on the radiation of a planar undulator

The influence of a constant magnetic field on the radiation of a planar undulator is studied analytically with the use of generalized Bessel functions. The behavior of on-axis radiation intensity in the undulator and the influence of a magnetic field on off-axis radiation are investigated. The critical magnitude of the constant component of the magnetic field, which has a significant effect on the motion of electrons in the undulator, is calculated analytically. The examples of several planar undulators are discussed, and the influence of the Earth’s magnetic field on their spectrum is evaluated.     

An analysis of undulator optimization in self-seeding free electron lasers

A simple analysis is given for the optimum length of undulator in a self-seeding free electron laser(FEL).The obtained relations show the correlation between the undulator length and the system parameters.The power required for the seeding in the second part of the undulator and the overall efficiency of monochromatizating the seeding determine the length of the first part of the undulator;the magnitude of seeding power dominates the length of the second part of the undulator;the whole length of the undulator in a self-seeding FEL is determined by the overall efficiency for getting coherent seed,and is about half as long again as that of SASE,not including the dispersion section.The requirement of the dispersion section strength is also analyzed.     

Probing the anisotropy constants of SmCo5 and PrCo5 by Hall resistance measurements in pulsed high magnetic fields up to 47 T

In order to assess the anisotropy constants of highly anisotropic thin film samples with anisotropy fields well above 10 T, Hall resistance measurements were conducted in pulsed magnetic fields. These measurements also deliver the anomalous Hall data, which are proportional to the perpendicular magnetisation. This specific approach combines the high field values obtainable by pulsed fields with a measurement technique sensitive enough to be applied to thin film samples. Two epitaxial Rare Earth-Cobalt thin films with large in-plane uniaxial magnetocrystalline anisotropy at room temperature were studied. The resulting anisotropy fields and constants are discussed with respect to measurements on single crystals and similar films investigated in quasi-static magnetic fields well below the anisotropy field. The present technique proved to be very valuable to highly anisotropic samples, as the approach to saturation is fully monitored and the data thus provides a more extended view on the hard axis magnetisation process.     

Giant hysteresis of magnetoresistance in the quantum hall effect regime

A simple system consisting of a two-dimensional electron gas with a narrow conducting wire is studied. In this system, a giant hysteresis of both longitudinal and Hall magnetoresistances in the quantum Hall effect regime is observed for even and odd filling factors v of the Landau levels. At v = 1 and v = 2, the giant hysteresis occurs in the background of the zero-resistance plateau, and the width of the hysteresis loop in a magnetic field is comparable to the plateau width. At the entry to the hysteresis region, the magnetoresistance varies in a threshold manner; i.e., a magnetically induced breakdown of the quantum Hall effect takes place. It is shown that the system under study reflects the relaxation processes in the two-dimensional electron gas adjacent to the wire and, therefore, represents an effective instrument for investigating the hysteresis phenomena in the two-dimensional electron gas itself. An unusual “anticoercive” behavior of the hysteresis is revealed. A comparative analysis of the results obtained and the experimental data on the long relaxation of eddy currents and on the ferromagnetic state of the quantum Hall liquid indicates the common physical origin of these effects.     

W波段同轴静磁波荡器自由电子激光优化设计

基于同轴静磁波荡器的自由电子激光主要利用环形电子束与同轴TE模式的相互作用产生电磁辐射,是一种重要的毫米波辐射源。分析了同轴结构作用区内外半径、工作模式、电子束电压、波荡器周期等参数对辐射频率的影响规律,研究了电子束平均半径的选取原则和束波互作用腔的设计方法,设计了辐射频率在W波段的基于同轴静磁波荡器的自由电子激光,并进行了粒子模拟,在电子束电压为720 kV,电子束流为1 kA的情况下,获得了频率107 GHz、辐射功率35 MW的TE01模,束波转换效率为4.9%,束波作用腔总长度小于200 mm,同轴静磁波荡器的磁场幅度0.34 T。     

双丝脉冲MIG焊接电弧光谱诊断及热源耦合机理分析

搭建了双丝脉冲MIG焊接试验系统,为了分析研究双丝脉冲MIG焊接的热源耦合机理以及电弧温度场,采用光谱技术对其电弧进行了诊断分析,采用中空探针法进行等离子体的辐射采集,得到电弧等离子体的光信号,利用Boltzmann图法计算了双丝脉冲MIG焊接电弧等离子体的电子温度,得出了电弧等离子体的电子温度分布规律,并结合电信号采集和高速摄像技术对电弧进行了综合分析。研究创新之处在于结合了电弧的高速摄像图片信息和电弧等离子体的光信号对双电弧耦合机理进行分析,对电弧温度场进行了较为直观的分析研究。试验结果表明,在本试验条件下焊接过程实现了推挽式输出,实现了一脉一滴的过渡方式;两个电弧在焊接过程中在磁场的作用下相互吸引,向中心发生了偏移,在双电弧的几何中心形成了新的热源中心,并且电弧发生上飘现象;双电弧电子温度整体呈倒V型分布,在双电弧几何中心位置,距工件表面3 mm的位置电弧电子温度最高,为16 887.66 K,比最低温度11 963.63 K高大约4 900 K。     

交叉型波荡器软X射线自由电子激光极化控制的影响因素

 交叉型波荡器是一种实现软X射线自由电子激光极化控制的有效方式。以自放大自发辐射自由光电子激光为例,采用统计的方法系统地分析了交叉型波荡器软X射线自由电子激光极化控制的影响因素。通过对光场相干长度、光脉冲两分量之间相对滑移长度和光场分量平均功率差异等的分析,给出了优化交叉型波荡器极化控制方案遵循的原则,即：辐射场相干时间尽可能长,光场分量相对滑移长度尽可能短,辐射场分量功率差异尽可能小等。该原则为交叉型波荡器软X射线自由电子激光极化控制方案的优化提供了依据。     

Theoretical and numerical analysis of electron motion in a three-dimensional undulator field

The results of numerical calculations of electron trajectories in the three-dimensional ideal magnetic field of an undulator are given. These trajectories can be regarded as exact results in our case. It is shown that, in a series of cases, results of the calculation of trajectories using approximate analytical formulas significantly differ from those obtained using numerical methods. The obtained numerical results show that the influence of the undulator on the dynamics of the electron beam is very complicated and cannot be reduced only to the focusing properties of the undulator magnetic field or wiggler.     

药芯焊丝脉冲TIG电弧增材制造电弧特性研究

对药芯焊丝脉冲TIG电弧增材制造电弧特性展开研究。利用高速摄像拍摄不同熔敷层脉冲电流条件下的电弧与熔滴过渡图片,对高速摄像图片进行分析,发现焊丝熔化过程存在“滞熔”现象,导致熔滴过渡存在渣桥过渡与液桥过渡两种接触过渡方式,在脉冲峰值电流较小的50/100 A电流参数下,出现熔滴断续的渣桥过渡的频率最高。熔滴过渡影响电弧温度场与药粉成分在电弧中的分布,利用光谱诊断分析熔敷过程中在不同脉冲峰值电流与脉冲基值电流条件下电弧温度场及药粉成分在电弧中的分布。利用点阵法测量得到各点光谱数据,根据Boltzmann图法计算各点温度,将各点温度拟合得到完整电弧温度场,结果表明,焊丝从钨极轴线前（左）侧送入,吸收电弧热量并且对电弧有扰动作用,电弧前侧温度低于电弧后（右）侧,电弧前侧尺寸稍小于后侧;随着熔敷层数增加,降低峰值电流,电弧收缩,高温区面积相对减小,低温区面积相对增大。电弧最高温度区域出现在钨极下方1~2 mm的范围,大约为13 000~15 000 K,脉冲峰值电流越大则最高温度区域面积越大。在脉冲基值电流时期,由于电流小,电弧面积相比于峰值时期要小得多,焊丝与电弧相互作用减弱,电弧温度场基本关于钨极轴线对称分布。选择药芯焊丝中特有的Na元素的NaⅠ589.6 nm谱线对其分布点进行标记,拟合绘出不同脉冲峰值电流与基值电流下药粉元素在电弧中的分布情况,结果表明,电流越小,药粉运动高度越低,在不同的脉冲峰值电流下药粉均没有沾染到钨极上,在不同的脉冲峰值电流与脉冲基值电流下 Na元素均偏电弧后侧分布,说明焊丝自电弧前侧送入熔池后,在电弧前侧的电弧中没有出现药粉强烈的喷发现象,而是进入熔池进行冶金反应。接触过渡解决了碱性焊丝工艺性差的问题,电弧较为稳定,避免药粉喷发损伤钨极,熔敷过程稳定进行。     

Effect of the correction of the motion of relativistic electrons in a magnetic undulator on the properties of undulator radiation

The properties of undulator radiation of electrons in a planar undulator with an arbitrary number of periods of the magnetic field and with correcting sections along the ends of the undulator are investigated. It is shown that in setups with relatively large number of periods of the field, the emission of particles in the correcting sections has a large effect on the general characteristics of undulator radiation of electrons in the setup. The experiment confirmed the basic assumptions of the theory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 52–58 November, 1981.     

Magnetic design and modelling of a 14 mm‐period prototype superconducting undulator

The magnetic design of a ten‐period (each period 14 mm) prototype superconducting undulator is reported using RADIA. The results of modelling the magnetic flux density are presented in an analytical formula. The dependence of the field integrals and phase error on the current density and undulator gap has been calculated, and temperature curves are determined for the models and are compared with earlier reported Moser–Rossmanith fits.     

CAEPXFEL波荡器束线初步物理设计

中国工程物理研究院计划开展XFEL光源的研制,主要通过电子束在波荡器中的辐射特性产生硬X射线。根据理论分析和数值模拟,在电子束最高能量可达12GeV的实际条件下,初步设计了一条间隙可调的真空外波荡器束线,波荡器分为25段,每段长3.86m,间隙7~10mm,周期长度25.4mm,磁场0.636~1.03T,束线总长120m左右,辐射光子能量为3~25keV。