中国散裂中子源磁铁系统和样机研制

中国散裂中子源(China Spallation Neutron Source, CSNS)快循环同步加速器(Rapid Cycling Synchrotron, RCS)磁铁由24块二极磁铁、48块四极磁铁、16块六极磁铁和若干斜四极磁铁以及校正磁铁组成, 其中二极磁铁和四极磁铁是带直流偏置的25Hz正弦交流励磁, 铁芯和线圈导体将产生不可忽视的涡流效应. 为了积累批量生产磁铁的制造经验, 探索磁铁后期处理和磁场测量方法, 已完成了中空水冷铝绞线试样线圈的研制, 启动了二极磁铁和四极磁铁样机的研制. 本文将对相关进展进行介绍.     

CSNS/RCS交流二极磁铁研制关键技术

针对交流二极磁铁的磁场特性和涡流问题,利用电磁场分析软件对磁铁进行了优化设计和温度场计算,确定了交流二极磁铁关键技术的方案。对交流二极磁铁极头端面采用了罗高斯基曲线和谐波削斜的方法来提高磁铁磁场质量;对铁芯端部和端板进行开槽优化设计,有效切断磁铁端部主要的涡流回路,降低了磁铁温升;磁铁线圈采用铝绞线导线进行绕制,以减少磁铁线圈内的涡流损耗。最后,通过对样机磁铁的测试,磁场均满足物理要求,磁铁温度也控制在安全范围内。     

轴对称高场超导磁体电磁应力有限元分析方法

核磁共振成像和核磁共振谱仪是高场超导磁体的主要应用领域.高场超导磁体通常具有较高的磁场和运行电流,在运行过程中超导线会产生较高的电磁应力,其临界特性将发生退化,影响磁体的稳定性.开展高场超导磁体的电磁应力精确分析显得尤为必要.本文发展了一种快速有效的有限元分析方法,第一步,为整个超导磁体系统建立平均有限元模型,采用传统的电磁-结构耦合方法求解电磁应力,获得最大应力位置;第二步,对最大应力所在的超导线圈建立详细有限元模型,采用单积分-结构分析方法精确求解每一组分中电磁应力.基于该模型研究了500 MHz NMR超导磁体的电磁应力.该分析方法也可以用于超导磁体冷却过程中的热应力分析.为高场超导磁体设计和建造提供有益的理论依据.     

线性瞬态涡流电磁场定解问题解的唯一性和稳定性

线性瞬态涡流电磁场定解问题的主要特点是边界条件使用磁感应强度的法向分量边界条件代替了电场强度的切向分量边界条件，约束方程中忽略了位移电流.这种具有特殊性的定解问题的解是否唯一和稳定对于求解瞬态涡流电磁场而言是一个基本问题.本文在非涡流区引入标量位函数，证明了在推导过程中起重要作用的辅助函数的存在性.通过推导线性瞬态涡流电磁场定解问题的能量估计式，证明了该定解问题的解是唯一的，并且关于初始条件和外源项是稳定的.本结果对于线性瞬态涡流电磁场的求解有一定的指导意义.作为应用，给出了通有单脉冲电流的单匝圆环线圈与球形导体共轴的涡流问题的解析解. 关键词： 瞬态涡流电磁场 能量估计式 唯一性 稳定性     

The eddy current induced in the pulsed bump magnet for the CSNS/RCS injection

The injecton pulsed bending bump magnets of Rapid Cycling Synchrotron (RCS) in China Spallation Neutron Source (CSNS) consist of four horizontal bending (BH) magnets and four vertical bending (BV) magnets. The BH magnets are operated at a repetition rate of 25 Hz and are excited with a trapezoid rectangle waveform with about 1.6 milliseconds duration. The eddy current is induced in BH magnets and in the end plates it is expected to be large, so the heat generation is of our great concern. In this paper, the eddy current loss of the BH magnet has been investigated and calculated by using a coupling method of 3D electromagnetic and thermal analysis. The accuracy of the analysis is confirmed by testing the prototype BH magnet. The end plate temperature of the BH magnet provided with slit cuts has been decreased obviously and met the requirements.     

基于电磁谐振分离的宽带低雷达截面超材料吸波体

基于超材料的电磁谐振特性, 设计、制作了一种极化无关的宽带低雷达散射截面 (radar cross section, RCS)超材料吸波体. 通过场分布和反演法分析了其吸波机理, 利用波导法和空间波法测试了其吸波率和RCS特性. 理论分析表明: 在平面波的作用下, 该吸波体对某一吸波频率在不同的位置分别提供电谐振和磁谐振, 对不同的吸波频率, 利用不同的介质层提供主要的能量损耗, 从而有效减弱了电磁耦合, 保证了宽频带的强吸收特性. 实验结果表明: 设计的三层结构吸波体吸波率达90%以上的带宽是单层结构的4.25倍, RCS减缩10 dB以上的带宽为5.1%, 其单元尺寸为0.17λ, 厚度仅为0.015λ. 该吸波体的低RCS特性还具有极化无关、宽入射角的特点, 且通过改变吸波体的夹层结构可以实现工作带宽的灵活调节. 关键词： 超材料吸波体 雷达散射截面 宽带 电磁谐振     

14T全身超导MRI磁体的技术挑战——大规模应用强场超导磁体未来十年的发展目标之一

本文首先综述了大规模应用的超导磁体,依赖并推动铌三锡Nb3Sn导线技术进步,向更强磁场发展的趋势.着重分析了超高场14 T全身MRI磁体的挑战性技术.选择青铜Nb3Sn导线,采用Nb3Sn线圈和NbTi线圈相结合的混合结构,对14 T全身MRI磁体进行了电磁概念设计和热稳定性及失超保护仿真分析,并简要阐述了14 T全身MRI磁体在应力、接头和匀场方面的关键问题.根据分析结果认为:1)Nb3Sn导线是14 T全身MRI磁体需要面临的首要挑战性问题—作为最佳选择的青铜Nb3Sn导线,其现有产品的性能指标离14 T全身MRI磁体的要求尚存在有一定的差距;2)14 T全身MRI磁体的失超保护涉及线圈的铜超比设计、运行电流同线圈电感的协调配置、被动保护的分段策略和主动保护的失超触发控制以及主动屏蔽结构磁体在失超过程中的逸散磁场限制等多个十分复杂的环节,是最具挑战性的综合性技术.     

Study of eddy current power loss in an RCS vacuum chamber

In a Rapid Cycling Synchrotron (RCS), power loss due to an eddy current on the metal vacuum chamber would cause heating of the vacuum chamber. It is important to study the effect for estimating eddy current induced power loss and temperature growth. Analytical formulas for eddy current power loss for various types of vacuum chambers are derived for dipole and quadrupole repectively. By using the prototype of dipole of CSNS/RCS, an experiment was done to test the analytical formula. The derived formulas were applied to calculating the eddy current power loss on some special structures of an RCS vacuum chamber.     

一种磁场优化结构电磁超声传感器设计*

为了进一步增强电磁超声检测技术在管道厚度测量领域的检测能力,该文对电磁超声传感器(EMAT)的结构进行了优化。提出了多磁铁对称分布型EMAT,能实现更小的磁铁体积,产生更强的表面剩磁强度。采用在硅钢表面开槽的方式限制涡流形成的区域,解决了涡流对测量的影响。建立厚度测量实验系统,对比出单磁铁型与多磁铁对称分布型EMAT在不同提离距离上检测信号的变化规律。结果表明,多磁铁对称分布型结构可通过增强EMAT的偏置磁场达到信噪比更优的效果。采用耐高温探头外壳和钐钴磁铁,提高了EMAT探头在高温环境下的检测性能。     

紧凑型自由电子激光THz源上四极磁铁的设计及测量

基于自由电子激光（FEL）的太赫兹源具有高功率、高效率、波谱范围宽且连续可调、波束质量好等显著优点,目前是获得最高输出功率的方法。紧凑型太赫兹源使整体装置小型化,减少了装置成本和占用空间,但依然可以提供高功率、高品质的太赫兹波束,是一种便利可靠的用户装置。由于空间限制,FEL上的磁铁要尽可能地减小其尺寸,并仍能满足束流参数设计要求。本文设计的四极磁铁磁轭孔径与有效长度,其中2块是64 mm100 mm,另外3块是45 mm100 mm。这些四极磁铁的磁场梯度可以达到0.6~1.9 Tm-1。采用Poisson和Oprra-3D软件进行四极磁铁的二维和三维仿真计算,设计优化四极磁铁的结构,并测量了加工完成后的四极磁铁的磁场。     

中国散裂中子源旋转线圈测量系统研制

中国散裂中子源(CSNS)加速器主要由一台直线加速器、一台快循环加速器以及低能、高能输运线组成。针对CSNS加速器部分直流磁铁研制了一套旋转线圈测量系统。对系统的研制方案、功能、精度、完成的磁铁类型以及部分测量结果进行介绍。该系统解决了CSNS批量磁铁之间的不同中心高度、质量、有效长度、磁场强度的兼容性难题。经过测试运行,积分场测量重复性误差好于±0.02%,空间谐波重复性误差好于0.005%,磁中心测量重复性误差好于±0.03 mm,顺利完成了中国散裂中子源工程150台多种类型磁铁的检测任务。     

Analytical solutions of transient pulsed eddy current problem due to elliptical electromagnetic concentrative coils

The electromagnetic concentrative coils are indispensable in the functional magnetic stimulation and have potential applications in nondestructive testing.In this paper,we propose a figure-8-shaped coil being composed of two arbitrary oblique elliptical coils,which can change the electromagnetic concentrative region and the magnitude of eddy current density by changing the elliptical shape and/or spread angle between two elliptical coils.Pulsed current is usually the excitation source in the functional magnetic stimulation,so in this paper we derive the analytical solutions of transient pulsed eddy current field in the time domain due to the elliptical concentrative coil placed in an arbitrary position over a half-infinite plane conductor by making use of the scale-transformation,the Laplace transform and the Fourier transform are used in our derivation.Calculation results of field distributions produced by the figure-8-shaped elliptical coil show some behaviours as follows:1) the eddy currents are focused on the conductor under the geometric symmetric centre of figure-8-shaped coil;2) the greater the scale factor of ellipse is,the higher the eddy current density is and the wider the concentrative area of eddy current along y axis is;3) the maximum magnitude of eddy current density increases with the increase of spread angle.When spread angle is 180,there are two additional reverse concentrative areas on both sides of x axis.     

Measurement of the magnetic-field parameters of the NICA Booster dipole magnet

Serial assembly and tests of dipole and quadrupole magnets of the NICA Booster have started at the Laboratory of High Energy Physics of the Joint Institute for Nuclear Research (JINR). The accelerator is fitted with Nuclotron-type magnets with a superconducting winding and an iron yoke for shaping the needed magnetic field. The design of magnets for NICA was optimized (based on the experience gained in constructing and operating the JINR Nuclotron) for the production of magnetic fields of the required configuration in terms of the beam dynamics in the accelerator and the collider. Measurements of parameters of the field of each magnet are expected to be performed in the process of assembly and testing of each module of the magnet-cryostat system of the NICA Booster and Collider. The results of magnetic measurements for the NICA Booster dipole magnet are presented.     

CCT型超导组合磁体样机结构设计

基于斜螺线管型(Canted-Cosine-Theta,简称CCT)线圈结构,研制了一台四极与六极组合的超导磁体样机,它的四极和六极梯度场分别为22 T/m和120 T/m2.该组合型磁体的好场区范围为Φ0.16 m × 1.3 m,有效长度为1.3m.其中四极与六极磁体均采用两层骨架结构,每层骨架的线槽内并排放置多层...     

磁约束等离子体推进器高温超导磁体系统的电磁计算

在地面实验中磁约束等离子体推进器磁体系统是靠四个NbTi低温超导磁体提供磁场,现在设计依靠G-M制冷机传导制冷的由Bi2223超导带材绕制成的四个高温超导磁体替代以前的四个低温超导磁体.本文利用ANSYS有限元分析软件进行电磁计算,得出高温超导磁体的参数。     

Electronic Structure and Electromagnetic Properties for 2D Electromagnetic Functional Materials in Gigahertz Frequency

Two‐dimensional (2D) materials exhibit massive potential for research and development in the scientific world due to the unique electrical, optical, thermal, and mechanical properties. Particularly, they have received intensive attentions in the microwave absorption (MA) and electromagnetic interference (EMI) shielding. Herein, the structure and electronic state of 2D materials are examined systematically, and the origination of electromagnetic (EM) response is shown, including electron transport, dipole relaxation, magnetic resonance, and eddy current. Furthermore, the latest research progress of 2D materials in EM field is introduced, and the application prospect and limitation are highlighted.     

准矩形截面强流相对论带状电子束的传输

提出利用准矩形截面带状电子束传输强电流.相对于目前广泛采用的椭圆形截面带状电子束,在大横纵比,即电子束的宽度(横向)远大于厚度(纵向)的情况下,其厚度沿横向更加均匀,利用冷阴极爆炸发射容易产生.该电子束利于高功率微波发生器中腔体模式的控制和束波作用效率的提高,如果利用模块化的结构还可使阴极及聚焦磁铁在宽度上的扩展更加容易.首先给出了准矩形截面带状电子束空间电荷场的典型分布,然后根据该分布和束匹配的方法对相互独立的周期会切磁铁和边聚焦磁铁分别进行了设计.其中边聚焦磁铁的磁化方向与以往的纵向不同,为横向磁化,其激励的边聚焦磁场在电子束宽边的边缘附近的梯度更大,有利于横向的束匹配.最后根据理论分析的结果进行了粒子模拟.结果表明,300keV,3kA的准矩形截面强流相对论带状电子束可以在0.163T的周期会切磁场和0.064T的横向磁化边聚焦磁场中稳定传输,电流传输效率大于98%.     

HT-7托卡马克低杂波天线的涡流及电磁力分析

用有限元方法详细分析并计算了HT 7超导托卡马克等离子体实验装置上低杂波天线壁上的涡流分布、感应磁场位形和天线所受电磁力.针对难以求解的磁场耦合问题,采用了新的迭代算法.具体的分析方法和计算结果对于研究复杂电磁环境下金属板上的涡流及其所受电磁力的分布具有一定的借鉴价值.     

Preliminary Study on Measurement of Magnetic Center of Quadrupoles Using Quadrupole Shunt for Hefei Storage Ring

The theoretical analysis of the DC K-modulation of quadrupole for the beam-based alignment method is presented. It is shown that the shift of the orbit,when the focussing strength of one quadrupole magnet is changed,can be described by the perturbed or unperturbed linear lattice parameters. The beam-based alignment system is constructed using DC K-modulation of quadrupole. In order to use the beam-based alignment method one must be able to individually adjust the strength of the quadrupole magnet. So,a switchable shunt resistor is installed on quadrupole to bypass 1%-2.5% magnet current and some solid-state relays are used to switch the shunt resistor in this beam-based alignment system. To improve the measurement accuracy,two methods are used. First method is that beam positions in measured quadrupole magnet are moved by local bump of beam closed orbit using the corrector magnets. Second method is that the root-mean-square of difference in closed orbit is fitted by a parabola function. The system can be not only used to position the beam in the magnetic center of quadrupoles,but also to measure the β function in quadrupole magnets. Some preliminary measurement results are given for Hefei 800MeV electron storage ring. These experimental results show that this system is valid to position the beam to the center of the quadrupole magnets and measure the β function at Hefei Light Source.     

放电过程中脉冲磁体的热传导

 对脉冲磁体放电过程中的热传导进行理论分析与实验测试,结果表明：对于短脉冲磁体,采用绝热模型与考虑热传导后的模型所得计算结果相近,并且二者均与实验测量得到的结果相符;对于长脉冲磁体,由于热传导时间相对较长,绝热模型计算得到的温升与考虑热传导后模型得到的温升有较大差别。通过理论分析可知：无论是短脉冲磁体还是长脉冲磁体,放电过程中的热传导只对磁体温升分布有较大影响,而对磁场波形则几乎没有影响。