Fe-Cu-Nb-Si-B纳米晶体软磁材料中有效磁各向异性的测定

研究了成分为Fe_73.5Cu₁Nb₃Si_13.5B₉的纳米晶体结构的软磁材料的磁各向异性。理论分析及测量结果说明,用趋近饱和的磁化过程可以测定出这种材料中的有效磁各向异性常数,它比晶粒中的磁晶各向异性常数K₁约小一个数量级。 关键词：     

铁磁材料对永磁体磁场分布的影响及悬浮测试

为了研究铁磁材料对永磁体磁场分布的影响,以纯铁与钕铁硼永磁体为研究对象,对添加纯铁后不同组合永磁体磁场进行了测试。结果表明：对直径为80 mm厚度为5 mm的纯铁及边长为10 mm的方形永磁体而言,当纯铁底部永磁体对称排列时,纯铁上表面磁场呈规律性的均匀分布。当永磁体数目为9,边缘距为0时,纯铁上表面中心磁场较大,分布均匀度较高;当纯铁侧面固定永磁体时,组合体表面磁场增强,但增幅不同,表面磁场值越大,磁场增幅越小,磁场均匀度降低;随着距组合体表面高度的增加,纯铁表面中心磁场逐渐减小,磁场均匀度先减小后增加。另外,利用超导样品对均匀区磁场进行了磁悬浮测试,表明该结构实现磁场均匀化的可行性,对后续超导块材平面运动控制的研究具有重要意义。     

李萨如图形法测量软磁材料磁导率

提出了李萨如图形的一个新应用——测量软磁材料磁导率.实验系统由示波器和信号发生器构成,以安培环路定理及法拉第电磁感应定律为理论基础,利用李萨如图形实现了软磁材料磁导率的测量.实验结果给出了在材料未达到饱和磁化的情况下,不同励磁频率下的磁导率测量结果.     

非晶态物理与软磁材料的产业化

由于非晶态材料具有独特的结构和优异的性能,其发现和发展对相关传统材料及其应用领域产生了巨大的冲击和深远的影响.从1960年首次发现非晶合金至今已有40余年,基础研究和应用开发均取得长足进展,特别是作为软磁材料的非晶合金带材已经实现了产业化,并获得了广泛应用.文章综述了非晶态物理方面的一些基本问题,以及非晶软磁合金的发展历程和产业化现状.     

非晶态物理与软磁材料的产业化

由于非晶态材料具有独特的结构和优异的性能，其发现和发展对相关传统材料及其应用领域产生了巨大的冲击和深远的影响。从1960年首次发现非晶合金至今已有40余年，基础研究和应用开发均取得长足进展，特别是作为软磁材料的非晶合金带材已经实现了产业化，并获得了广泛应用。文章综述了非晶态物理方面的一些基本问题，以及非晶办磁合金的发展历史和产业化现状。     

磁场对传导冷却超导磁体系统制冷机的影响

用于传导冷却超导磁体系统的GM制冷机处于强磁场环境中,由于二级蓄冷器的填充材料其性能随外部磁场大小而变化;而且冷头电机本身是永磁电机,电机性能受磁场影响更明显.因此,为了不影响制冷机的性能,需要详细地分析制冷机附近的磁场分布,将制冷机布置在低场区域;但是,高场磁体系统本身磁场强度高、温度裕度低,为了降低磁体运行时的热点温度,不可能将制冷机布置在距离磁体较远的区域,这时就需要对制冷机采取屏蔽措施.本文以正在建造的8T传导冷却超导磁体系统为例,研究了磁场对制冷机位置的影响,并分析了铁磁屏蔽对制冷机附近磁场的屏蔽效果.     

热处理对MgB_2超导体超导电性和显微结构的影响

采用固相反应法常压下制备MgB2超导块材,研究两种不同的热处理工艺(淬火、预热)对MgB:超导电性和显微结构的影响.结果显示淬火有助于细化晶粒,提高样品的临界电流密度;预热在一定程度上提高MgB2样品的致密度和磁通钉扎力,其中随炉升温600℃预热1 h再升至750℃保温0.5 h后淬火的样品自场Jc达到0.586 MA/cm2,不可逆场超过7 T,20 K下在0.8T达到最大钉扎力Fpumax.     

热处理温度对MgB2超导材料的超导电性及微观结构的影响

采用粉末烧结方法在不同温度（650℃，700℃，750℃，800℃，850℃，900℃）制备了MgB2超导块材．采用X射线衍射（XRD）和扫描电镜（SEM）研究了热处理温度对MgB2超导材料的成相及微结构的影响．采用磁化法测定不同温度制备MgB2超导材料的超导电性．结果显示热处理温度对MgB2超导材料的晶粒尺寸、形状和超导电性有明显影响，700℃制备的MgB2超导体具有最高的临界电流密度和最好的磁通钉扎特性，细小的晶粒尺寸是样品磁通钉扎特性改善的原因．     

Matching effect in superconducting NbN thin film with a square lattice of holes

A square hole array is fabricated over a micro-bridge of NbN thin film by electron beam lithography and reactive ion milling. Magneto-resistance is measured across the micro-bridge filled with a hole array near the superconducting transition temperature. It is found that magneto-resistance minima occur when the number of vortices is an integer multiple or a fractional multiple of the number of holes. The temperature and the current dependences of the matching effect are studied.     

1.5 T关节磁共振成像超导磁体的设计、制作与测试

磁共振成像(magnetic resonance imaging,MRI)是当今世界上最先进的医学影像技术之一,现阶段MRI技术正朝着成像质量更清晰、功能更强大、效率更高、个体化更强的趋势发展.与全身MRI设备相比,专科型MRI设备具有体积小、重量轻、成本低、病人舒适度高、成像质量高、功能更强等优点.但是关节专用超导MRI系统需要长度方向上被严格限制的超导磁体在160 mm直径球域(diameter sphere volume,DSV)内产生高均匀度的磁场.本文综合考虑了超导线用量、中心磁感应强度和成像区磁场不均匀度等因素,使用0-1规划和遗传算法相结合的方法设计了一种非屏蔽型1.5 T关节MRI超导磁体,该磁体的室温孔径为280 mm,总长度为520 mm,液氦量为30 L,载流区最大磁场为5.48 T,5高斯线范围为径向3.2 m、轴向2.6 m,160 mm DSV的磁场不均匀度设计值为22 ppm,考虑加工误差及冷缩因素,磁体加工完成并经过被动匀场后的预估值为60 ppm.经过绕制、固化、组装、焊接等工序,该磁体已制作完成.经过3次锻炼后成功励磁到1.5 T,经过被动匀场后160 mm DSV的磁场不均匀度达到50 ppm,各项指标均达到设计目标.     

Gyrotron based on a superconducting magnet

The replacement of conventional pulsed magnetic field coils previously used to generate the intra-cavity B-field with an 11T superconducting magnet is reported. The resulting more stable mm-wave output pulse is shown and the refurbishment requirements of both the field emission, field-immersed, cold cathode and Marx bank spark gaps demonstrated. This system proved to be tunable, oscillating from 20GHz up to 110GHz, with peak power levels of 450kW and 300kW respectively. Other operating parameters were also examined including mm-wave pulse length as a function of anode-cathode position. The pulse length increased from 87±6ns to 310±10ns with a 2.5 cm horizontal transit of the cathode away from the anode. A similar effect was witnessed with the increase of the intra-cavity B-field from 1.00T to 5.00T resulting in the mm-wave pulse duration increasing from 250±40ns. Second harmonic operation of the cavity resulted in 0.5kW of radiation observed at 96GHz. The pulse-to-pulse mm-wave stability coupled with the mode selectivity of the ohmic-Q-dominated cavity resulted in the identification of several oscillating modes including the TE₁₂, cut-off frequency 21.1 GHz, the TE₀₂, cut-off frequency 29.1 GHz, the TE₃₅ at 74 GHz and the TE_14,2, at 88GHz.     

适用于超高灵敏磁测量的新型高效磁屏蔽研究

高效磁屏蔽对于超高精度超导量子干涉仪(SQUID)等超高灵敏器件可靠稳定工作至关重要。实践中一般采用多层的高磁导率笨重复合磁屏蔽,或者用小型的轻量屏蔽桶配合差分式平面梯度计完成超高灵敏信号测量。文章作者提出并实现了一种新型的高性能磁屏蔽装置,采用实时的动态磁补偿与高温超导线圈相结合就可以实现。对该装置磁屏蔽效果进行了数值仿真计算,并实际测量了该屏蔽装置的轴向和横向磁场,装置屏蔽因数最高可达80 dB;实验测量发现,新型装置可以同时有效地屏蔽轴向与纵向磁场干扰。     

A design of novel type superconducting magnet for super—high field functional magnetic resonance imaging by using the harmonic analysis method of magnetic vector potentials

The approach of expanding the magnetic scalar potential in a series of Legendre polynomials is suitable for designing a conventional superconducting magnetic resonance imaging magnet of distributed solenoidal configuration. Whereas the approach of expanding the magnetic vector potential in associated Legendre harmonics is suitable for designing a single-solenoid magnet that has multiple tiers, in which each tier may have multiple layers with different winding lengths. A set of three equations to suppress some of the lowest higher-order harmonics is found. As an example, a 4T single-solenoid magnetic resonance imaging magnet with 4×6 layers of superconducting wires is designed. The degree of homogeneity in the 0.5m diameter sphere volume is better than 5.8 ppm. The same degree of homogeneity is retained after optimal integralization of turns in each correction layer. The ratio B_m/B₀ in the single-solenoid magnet is 30% lower than that in the conventional six-solenoid magnet. This tolerates higher rated superconducting current in the coil. The Lorentz force of the coil in the single-solenoid system is also much lower than in the six-solenoid system. This novel type of magnet possesses significant advantage over conventional magnets, especially when used as a super-high field functional magnetic resonance imaging magnet.     

从磁滞回线了解铁磁性材料的性能

从磁滞回线简要讨论了铁磁性材料的性能及特点,并指出一些大学物理教材在这方面讨论的不妥之处.     

A novel approach to designing cylindrical-surface shimcoils for a superconducting magnet of magnetic resonance imaging

For a superconducting magnet of magnetic resonance imaging (MRI), the novel approach presented in this paper allows the design of cylindrical gradient and shim coils of finite length. The method is based on identification of the weighting of harmonic components in the current distribution that will generate a magnetic field whose z-component follows a chosen spherical harmonic function. Mathematical expressions which relate the harmonic terms in the cylindrical current distribution to spherical harmonic terms in the field expansion are established. Thus a simple matrix inversion approach can be used to design a shim coil of any order pure harmonic. The expressions providing a spherical harmonic decomposition of the field components produced by a particular cylindrical current distribution are novel. A stream function was applied to obtain the discrete wire distribution on the cylindrical-surface. This method does not require the setting of the target-field points. The discussion referring to matrix equations in terms of condition numbers proves that this novel approach has no ill-conditioned problems. The results also indicate that it can be used to design cylindrical-surface shim coils of finite length that will generate a field variation which follows a particular spherical harmonic over a reasonably large-sized volume.     

Spatial variation of superconducting properties of Gd123 Bulk superconductors with magnetic particles addition

Magnetic flux trapping and the homogeneity of the flux pinning are essential problems in the practical application of high-temperature superconductors. We have conducted study on the role of addition of soft magnetic Fe-B alloy particles contribute to the enhancement of the critical current density (J_c) under wide-range of magnetic field. Magnetic flux trapping was enhanced in Gd123 bulk superconductor with suitable amount of magnetic particles addition. In addition, it can be effective as pinning center enhance the J_c of the bulk in both the a–b growth sector and the c-growth sector under magnetic field. However, the T_c of the Gd123 bulk was decreased obviously by addition of magnetic particles. The study on the spatial variation of superconducting properties indicates that the performance of the upper part of the bulk is better than the bottom. By comparing the superconducting properties of the Gd123 bulk with magnetic particles addition and without magnetic particles addition, we concluded that there is a trace of the formation of homogeneous pinning properties in the magnetic particles addition Gd123 bulk.     

迫流冷却二极NbTi超导磁体的研究

首先介绍了导体的测试结果;其次,为评估迫流冷却的二极NbTi超导磁体正常工况下对液氦产生的低温热负荷,基于surf152表面效应单元对线圈盒进行了辐射传热分析;此外,为减小通过线圈盒支撑的传导热负荷并且提高其机械强度,依据线圈盒支撑杆的设计尺寸,提出使用玻璃纤维经过三维编织的各向异性复合材料-G10制作线圈盒支撑杆,从...     

Control application of a superconducting magnet power supply based on EPICS

The superconducting quadrupole magnets （SCQs） are powered by 16 power supplies in the inter- action region of the BEPC Ⅱ. The control application of these power supplies must be interlocked with the quench protection system to protect the superconducting magnet and relevant devices. This paper describes the development procedures of this control application using EPICS and the operating result with the quench protection system on-site.