超导开关研究和应用综述

超导开关是实现超导磁体闭环运行的关键部件,也称为持续电流开关(PCS),使超导磁体具有极高的磁场稳定度,广泛应用于核磁共振成像(MRI)、核磁共振谱仪(NMR)、磁浮列车、超导储能系统等技术领域. 文中介绍了超导开关的工作原理和结构组成,综述了用于超导磁体的三类主要超导开关的研究发展现状,比较分析了各自的特点和优势,为...     

High-field (275 GHz) spin-label EPR for high-resolution polarity determination in proteins

The polarity of protein surfaces is one of the factors driving protein-protein interactions. High-field, spin-label EPR at 95 GHz, i.e., 10 times higher than conventional EPR, is an upcoming technique to determine polarity parameters of the inside of proteins. Here we show that by 275 GHz EPR even the small polarity differences of sites at the protein surface can be discriminated. To do so, four single cysteine mutations were introduced at surface sites (positions 12, 27, 42, and 118) of azurin and spin labeled. By 275 GHz EPR in frozen solution, polarity/proticity differences between all four sites can be resolved, which is impossible by 95 GHz EPR. In addition, by 275 GHz EPR, two spectral components are observed for all mutants. The difference between them corresponds to one additional hydrogen bond.     

Review of conductor development for use in high-temperature superconducting cables

Summary This paper reviews and assesses the progress in conductor development across the world in advancing high-temperature superconducting science and technology towards the fabrication of superconducting transmission cables operating at 77 K. Materials, fabrication routes and the feasibility of high-temperature superconducting cables will be discussed. Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.     

ITER 超导馈线系统的设计

ITER( 国际热核试验堆) 采用超导馈线系统传输磁体线圈所需电流、冷却液及数据信号, 并在失超等异常情况, 通过馈线转移磁体能量, 以保护整个磁体系统。介绍了国际热核试验堆超导馈线系统的结构及设计情况, 为同类型超导磁体的馈线设计提供了有益的参考。     

40-T混合磁体外超导磁体CICC摩擦系数测定

40-T混合磁体的建设正在中科院强磁场中心进行,其外超导磁体将由管内电缆导体CICC绕制,并采用4.5K 的超临界氦迫流冷却.CICC的摩擦系数是确定各冷却通道进口压力和流量的重要依据.文中介绍了CICC压降测量平台搭建,并对40-T混合磁体外超导磁体哑缆摩擦系数进行测量;分析了该CICC内的摩擦特性,并拟合出相应的经...     

一种实用的使用铁磁材料匀场的开放式超导MRI磁体的优化方法(英文)

磁共振成像(MRI)系统是一种重要的医学诊断设备。作者提出了一种针对使用铁磁材料匀场的开放式超导MRI主磁场匀场的优化方法。在这种方法中,为了使这种包含非线性铁磁轭结构的MRI磁体产生高均匀度的磁场,集成了改进的多输入多输出负反馈控制理论和有限元方法,来计算匀场区非线性铁磁材料的形状。特别要指出的是,这种方法对初始值的要求不高,一定可以收敛,如果配置得当,可以快速收敛。另外,由于收敛速度快,这种方法也可以应用于大型的非轴对称三维模型优化分析。在文中,作者在一个二维轴对称磁体模型上测试了该方法,表现良好。     

A multifrequency-resonator-based system for high-sensitivity high-field EPR investigations of small single crystals

In this paper, we describe a multifrequency spectroscopic system which is ideally suited to EPR investigations of very small single crystals. Our method utilizes oversized resonant cavities and a continuously tunable vector network analyzer. This system provides excellent sensitivity over a broad frequency range from about 30 GHz up to about 120 GHz, and in magnetic fields up to 33 T.     

35kV/90MVA高温超导限流器低温系统

35kV/90MVA高温超导限流器的低温系统是一个开放式的液氮制冷系统,包括一个环形不锈钢杜瓦、真空绝热管、压力及温度传感器、低温阀门以及监控系统.高温超导磁体放置在杜瓦中;监控系统检测杜瓦内液氮的液面,并控制往杜瓦内进行补液.杜瓦内蒸发的氮气通过真空绝热管道直接排放到大气中.分别对不同工况下的液氮蒸发量进行了测量.进...     

Superconducting wiggler for adone: Design and present status

Summary A superconducting wiggler has been designed and built at Laboratori Nazionali INFN in Frascati, Italy, in collaboration with Ansaldo Componenti-Genova, to be used as an insertion device in the Adone storage ring. It will be used as a light source on the 1.5 GeV, 100 mA electron beam of the accelerator, to produce about 10¹² photons/s/mrad in 0.1% band width, in the short X-ray wavelength range. In order to minimize the electron beam orbit disortion and to obtain the best phase space distribution of the generated synchrotron radiation (a single bright spot), a superconducting dipole, producing a sharp vertical field peak (6 T, 12 cm FWHM), between two normal conducting side dipoles (0.8T), to compensate the field integral, has been manufactured. The s.c. dipole is made up of 2NbTi coils, separated by a central plate and kept together by two 356 kg total weight iron yokes. The magnet gap is 6 cm and the design current is 360A. The system is contained in a warm bore cryostat and cooled by boiling helium at 4.6K. The static cryostat helium consumption is of 41/h and, when the cryomagnet is energized, it is cooled by a 1430S Koch liquefier/refrigerator on line with it through transfer lines. The stored energy is 184 kJ. This paper describes the latest status of the facility and the verification tests.     

High-T c superconducting magnetic bearings for rotation-based devices

Summary A Modified-Melt-Powder-Melt-Growth (MMPMG) technique has been developed for the preparation of melt-textured Y-Ba−Cu−O pellets. To test their performances, the samples were characterized with respect to their microstructure, pinning strength and interaction force with permanent magnets. A superconducting magnetic bearing was built and integrated in a levitating flywheel system for energy storage. Paper presented at the “VII Congresso SATT?, Torino, 4–7 October 1994. Under a Fondazione Confalonieri grant.     

超导电缆的性能检测方法研究

超导电缆与常规电缆在电磁特性上有很大差异。因此,有必要对其试验内容、性能检测方法和试验设备进行研究和规范。文中从超导电缆的电磁特性出发,探讨了超导电缆的试验内容及性能检测方法,并重点介绍了超导电缆交流损耗的测量方法。     

Study on cooling process of cryogenic system for superconducting magnets of BEPCⅡ

In the upgrade project of the Beijing Electron Positron Collider(BEPCⅡ),three superconducting magnets are employed to realize the goal of two orders of magnitude higher luminosity.A cryogenic system with a total capacity of 0.5 kW at 4.5 K was built at the Institute of High Energy Physics(IHEP)to support the operations of these superconducting devices.For preparing the commissioning of the system,the refrigeration process Was simulated and analyrzed numerically.The numerical model Was based on the latest engineering progress and focused on the normal operation mode.The pressure and temperature profiles of the cryogenic system are achieved with the simulation.The influence of the helium mass flow rates to cool superconducting magnets on the thermodynamic parameters of their normal operation is also studied and discussed in this paper.     

Continuous-wave EPR at 275GHz: application to high-spin Fe(3+) systems

The 275GHz electron-paramagnetic-resonance spectrometer we reported on in 2004 has been equipped with a new probe head, which contains a cavity especially designed for operation in continuous-wave mode. The sensitivity and signal stability that is achieved with this new probe head is illustrated with 275GHz continuous-wave spectra of a 1mM frozen solution of the complex Fe(III)-ethylenediamine tetra-acetic acid and of 10mM frozen solutions of the protein rubredoxin, which contains Fe(3+) in its active site, from three different organisms. The high quality of the spectra of the rubredoxins allows the determination of the zero-field-splitting parameters with an accuracy of 0.5GHz. The success of our approach results partially from the enhanced absolute sensitivity, which can be reached using a single-mode cavity. At least as important is the signal stability that we were able to achieve with the new probe head.     

超导纳米线单光子探测系统的时间抖动

超导纳米线单光子探测(SNSPD)器件具有较低的时间抖动特性,可以实现低误码率的QKD和高精度的激光测距。文中对超导纳米线单光子探测系统的时间抖动进行了详细的分析和测量,分析了SNSPD系统各部分对系统抖动的贡献。使用时间相关的单光子计数技术(TCSPC)和示波器的抖动分析软件,分别测量了SNSPD系统的时间抖动,比较了两种方法的优劣。在两种测量方法下,系统总的时间抖动分别约为42ps和31ps,计算后得到单光子探测器件的抖动约为25ps。发现放大器的性能对系统时间抖动影响明显。通过使用不同放大器比较分析了测量得到的时间抖动。     

一种EPR谱图模拟软件的研制

采用Microsoft Visual BASIC 4.0 for Windows 95编写了一个EPR谱图模拟软件.此软件采用鼠标控制命令按键进行程序过程.得到的图象分辨率和色彩优于用其他早期开发的BASIC语言编写的程序,打印的黑白图象质量也很好.运算时间小于20秒.这种软件可用于多种EPR模拟应用,包括自由基EPR谱图的模拟、过渡金属离子E PR谱图的模拟和二维EPR成像的模拟.EPR成像可以彩色强度图、等高线图或三维俯视图来表示.所有的模拟图象均可用激光打印机打印成黑白图片.自由基模拟程序的数据组有2560点.EPR成像的像素一般为128×128点.     

超导磁约束系统中超导磁体涡流损耗的研究

在超导磁约束系统中,超导磁体与射频场、磁场、声场、电场等复合场的兼容耦合是系统稳定运行的关键。探讨了在13.56 MHz频率下的Shoji型天线产生的高频电磁波对超导磁体的影响,高频电磁波会在超导磁体表面产生涡流损耗,进而产生功率损耗并生成热量,导致超导磁体失超。为避免失超现象的发生,在超导磁体室温孔内采用金属屏蔽层进行防护。利用COMSOL软件对整个电磁-射频非线性耦合场进行建模仿真分析,完成了屏蔽层结构的优化选择。基于计算结果,分析讨论了屏蔽层厚度和高度变化对超导磁体上涡流损耗功率的变化影响。通过对超导磁体涡流损耗功率随屏蔽层参数变化进行拟合,最终得到了优化后的屏蔽层参数。     

μ介子转化电子装置超导磁体低温系统(英文)

μ介子转化为电子的试验装置(MECO)将安装在美国布鲁克海文国家实验室的交变磁场梯度同步加速器中。一台4.5K千瓦制冷量的氦制冷设备将为MECO试验中的四个大型的超导螺线管磁体提供冷量,针对MECO中超导磁体的性能特点及要求,主要讨论了该低温系统中每个超导磁体的冷却方法以及相应氦制冷机的流程设计方案。     

Diffusion anisotropy indexes are sensitive to selecting the EPI readout-encoding bandwidth at high-field MRI

Diffusion tensor magnetic resonance imaging (DT-MRI) is generally performed using an echo planar imaging (EPI) acquisition to map directional water diffusion. However, the oscillating magnetic field gradients of the EPI acquisition can result in considerable mechanical vibrations, which lead, in turn, to magnetic field fluctuations causing Nyquist ghosting in the EPI data. The objective of this study was to investigate effects of EPI readout gradient modulation frequency, which is directly associated with the EPI readout bandwidth (BW), on the accuracy of DT-MRI measurements in a high magnetic field system. A spherical water phantom was used to study the relationship between the EPI BW and the Nyquist ghost for a spin-echo EPI acquisition with a matrix size of 128x128, complemented by diffusion sensitization gradients of up to b=800 s/mm(2) along six directions for DT-MRI. Nine volunteers (four males and five females) were studied using EPI at different BW acquisitions. Analysis of variance was used to investigate the EPI BW effects. The phantom studies demonstrated a systematic relationship between BWs and the intensities of Nyquist ghosts. In the human brain studies, EPI BW variations substantially corrupted diffusion anisotropy indexes (i.e., fractional anisotropy and relative anisotropy) (F=10.5, P=.0001) but were unrelated to diffusion-encoding directions (F=0.14, P=.98). It was possible to minimize BW dependence (F=1.48, P=.25) by tuning the modulation frequency of the EPI readout gradient. In conclusion, diffusion anisotropic indexes are sensitive to the readout BW of EPI due to associated Nyquist ghosting. However, the effect can be minimized by tuning the modulation frequency of the EPI readout gradient, that is, the EPI BW, to a range outside the harmonics of mechanical gradient vibrations.     

EAST 外超导母线超导接头的研制

为把电流引线罐从EAST 大厅移到离装置约30m 外的电源大厅,重新设计和制造了连接新旧超导导体间的13 对超导接头。介绍了其中1 对超导接头的结构设计、空隙率的确定、理论直流电阻计算、压降计算和加工装配方案等。为此,制造了1 对超导接头,并进行通电测试,结果表明,所设计的超导接头结构和加工工艺满足EAST 工程的要求。     

Characterization of non-contact torque transfer and switching system for superconducting flywheel

Superconducting flywheel energy storage system can store the energy for a long duration, in that the main body of a flywheel is placed in a vacuum chamber to minimize rotational loss, and is separated from a generation motor. The superconducting flywheel device need a non-contact system which can transfer the rotational torque without contact. A combination of two permanent magnets can transmit the power without contact. We calculated the torque forces and the field distributions of two types of magnetic arrays; repulsive type and Halbach type. Both magnetic circuits have respective inner and outer diameters of 61.5 and 144 mm and consist of eight poles of Fe–Nd–B permanent magnets 30 mm in thickness. We also studied the effects of the number of poles and the size on the transferable torque forces and found that a practical torque transfer and switching systems can be constructed with a combination of permanent magnetic circuits.