25T超导磁体优化中线圈数量影响分析

20 T以上强磁场在高场科学工程中有着不可替代的作用. 电工研究所正在研制一个25 T全超导磁体系统, 包括15 T背景磁场和10 T高温超导内插磁体. 在磁体的设计和优化中, 线圈的数量和种类对于最终优化结果十分关键. 为了研究磁体数量和磁体相关参数的关系, 计算了20 组不同的线圈组合下磁体的优化结果. 优化中除了考虑必要的限制条件以外, 还采用了一种结合局部优化算法和全局优化算法的方法. 通过对比分析发现, 线圈数量和磁体造价之间, 存在一个“V”形的关系. 更进一步地, 本文分析了不同超导体在磁体中应该贡献的最佳磁场, 以及背景磁体统一供电给优化结果带来的影响.     

无绝缘高温超导跑道型磁体设计

环向场磁体是ITER托卡马克装置中的核心部分,采用无绝缘高温超导磁体技术能使其产生更高的稳态场。文中介绍了无绝缘高温超导磁体技术的原理和特点,并以跑道型磁体为着手点,使用不同的超导带材,利用有限元法设计无绝缘高温超导磁体,总结了线圈个数与布局对磁体临界电流和中心磁场的影响。该磁体在20K下可产生的稳态磁场约为3.59T。     

45T混合磁体外超导磁体失超保护系统设计北大核心CSCD

由中国科学院强磁场科学中心建成的混合磁体包含着内水冷磁体和外超导磁体两大部件,目前已经成功达到40T的中心磁场,在下一轮实验将冲击45T磁场.作为中国磁场强度最高的稳态强磁场装置,其失超保护系统合理的设计是该磁体安全运行的重要保证.本文详细介绍了45T混合磁体外超导磁体失超保护系统设计,主要包括:同绕线、二次补偿、失超保护电路以及失超保护参数的选取.同时对混合磁体在运行调试期间外超导磁体出现的两次失超与保护动态过程也进行了分析与讨论.     

45T混合磁体外超导磁体失超保护系统设计

由中国科学院强磁场科学中心建成的混合磁体包含着内水冷磁体和外超导磁体两大部件,目前已经成功达到40T的中心磁场,在下一轮实验将冲击45T磁场.作为中国磁场强度最高的稳态强磁场装置,其失超保护系统合理的设计是该磁体安全运行的重要保证.本文详细介绍了45T混合磁体外超导磁体失超保护系统设计,主要包括:同绕线、二次补偿、失超保护电路以及失超保护参数的选取.同时对混合磁体在运行调试期间外超导磁体出现的两次失超与保护动态过程也进行了分析与讨论.     

中国科学院近代物理研究所磁体工程进展概述(英文)

本文着重论述了中国科学院近代物理研究所目前正在研制的三大磁体工程,它们包括重离子治癌工程(HIMM),强流重离子加速器(HIAF)工程,以及加速器驱动次临界系统(ADS)。在HIMM工程中的常规磁体建设中,着重介绍了联合运用钝化槽与活极头两项技术改善磁场品质的设计方法,并且运用Opera-3D设计软件,对该类高场常规磁体进行了数值分析,进一步地测量了该磁体磁场分布情况,相关的测量结果与数值模拟结果吻合良好。而对于正在处于预研阶段的HIAF工程中的快脉冲超导二极磁体,讨论了超导磁体的前期设计与结构优化技术,包括CACC超导线缆的结构设计,80 K冷屏与线圈盒结构的优化,力-磁耦合结构计算方法等。而在嬗变核废料处理的C-ADS注入器II中,核心部件是具有高磁场(高达7～8 T)的多层复合超导螺线管磁体结构,介绍了其在励磁和失超过程中相关磁学和力学多场实验测试工作。这些相关的设计和测量技术将为中国科学院近代物理研究所自主研制的磁体工程的物理和结构设计提供方法和指导。     

一种永磁磁共振中磁体涡流场的测量方法

磁共振成像（Magntic Resonance Imaging,MRI）技术是一种先进的医疗影像技术.在MRI系统中,通过梯度线圈电流快速切换方向,对待测区域施加梯度磁场,产生的梯度磁场会在其周围的金属体内激发出变化的涡旋电场,进而导致金属体内闭合的回路中产生对原来的梯度电流起抑制作用的感生电流,也就是我们所说的涡流.本文介绍了一种测量磁体涡流场的方法,结合电磁感应定律,设计了一种磁体涡流场测量装置,通过硬件采集以及软件处理的方法,将理想梯度场与实际磁场进行相减并将波形实时呈现,实验结果表明该方法可实现对磁体涡流场的测量.     

脉冲强磁场技术发展现状与趋势

脉冲强磁场是现代科学研究的重要工具,因其可以较容易地实现50 T以上磁场,因而在最近20年快速发展。最高磁场强度已经由70 T左右发展到目前的100 T,磁场波形也由以前单一的短脉冲发展到现在的长脉冲、平顶脉冲、长短合成脉冲等多种波形。随着电源与控制技术的发展,脉冲强磁场技术也在一定时间内实现了高稳定度磁场,拓宽了脉冲强磁场的实用范围;同时,脉冲磁体技术发展催生出能快速冷却的、具有高重频和异形结构的脉冲磁体,以满足X射线实验、中子实验和太赫兹实验要求。文章详细介绍了脉冲强磁场技术的发展现状与发展趋势,还介绍了武汉国家脉冲强磁场科学中心的磁场技术。     

内/外部励磁方式下高温超导环的俘获场特性

高温超导磁体在闭环运行时,可以提供稳定磁场,但是由于高温超导带材无法实现无阻焊接,成为高温超导磁体闭环运行的技术瓶颈.本文利用第二代高温超导带材制备闭环超导环,采用内部励磁和外部励磁对超导环进行励磁,在液氮温度中(77 K)测量超导环的中心俘获磁场.结果表明超导环在内部励磁俘获的磁场值比外部励磁俘获的磁场值高;外部励磁中,超导环中插入铁芯柱能提高俘获场;内部励磁中,超导环在螺线管闭环运行俘获的磁场值比开环运行俘获的磁场值高.结果对于高温超导闭环磁体励磁和高温超导带材磁通动力学研究具有很重要参考价值.     

高温超导磁体临界电流影响因素的研究

临界电流值是描述Bi2223高温超导带材性能的一个基本参数,在一定的温度条件下,Bi2223高温超导带材的临界电流是带材所在位置磁场大小和磁场方向的函数,其短样的临界电流值可以通过四引线法测量,单根超导带材的自场很小,磁场对临界电流的影响可以忽略.高温超导磁体的临界电流被定义成引发该磁体失超的最小电流,高温超导磁体的自场比单根超导带材的自场要大得多,磁体各个位置的磁场大小和方向各不相同,很难用理论的方法准确计算磁体的临界电流.对于高温超导磁体而言,除了磁场的影响因素以外,绕制磁体所用的超导带材自身的均匀性也是影响其临界电流的一个重要因素.本文对这两个因素进行探讨,并着重讨论高温超导带材自身的均匀性对临界电流大小的影响,本文的结论可以为高温超导磁体的设计、磁体绕制时带材的选择、磁体运行时安全工作电流的确定提供帮助.     

基于近似解析法的超导储能磁体设计

降低超导储能磁体的研制成本一直是控制超导磁储能系统(Superconducting Magnetic Energy Storage, SMES) 总成本的重要手段之一. 本文考虑在一定磁体结构参数范围内, 磁体产生的最大磁场值可以采用级数进行 表示, 磁体的电感值可以采用线性函数表示, 给出了超导储能磁体磁场能量的近似解析表达式, 提出了一种基于近 似解析法的超导储能磁体设计方法. 该方法以储能磁体的线材用量最小作为设计目标, 在给定超导线材参数和临界电流特性曲线, 以及磁体储能总量要求的情况下, 依据此方法可快速的得到成本最优时所对应的磁体结构参数.将近似解析法优化和采用传统的有限元软件 Ansys 仿真优化进行对比分析, 结果表明采用近似解析法进行磁体优化更加方便快捷, 节省了大量计算时间.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.