多超导线圈并联下的电流分布研究

与多超导线圈串联相比,多超导线圈并联通流的电流分布特性比较复杂。本文提出一种基于H方程和均质化方法的有限元模型,研究了4 YBCO单饼线圈并联下的电流分布,并与场路耦合模型对比。仿真结果表明,多超导线圈并联下的电流分布与各线圈的接头电阻、等效电感和等效超导电阻有关。线圈失超之前,各线圈的等效超导电阻几乎可以忽略,电流分布主要受线圈的接头电阻和等效电感控制;线圈开始失超后,电流分布主要受等效超导电阻影响,电流会重新分配,最终各线圈稳流值与各线圈的临界电流有关。     

大型FFAG磁铁的2维POISSON设计

 为减小边缘场效应，大型固定磁场交变梯度（FFAG）磁铁的磁场分布由修整线圈和磁极形状两者共同来实现。通过2维POISSON模拟计算，确定了修整线圈电流和位置的分布以及磁极形状, 得到了局域磁场梯度指数与设计值之间的最大差异只有0.5％的磁场分布。为提高POISSON模拟计算的效率，POISSON输入文件中有关线圈电流和位置、磁极形状的输入和调整由程序自动完成。     

三相行波磁场中涂层超导线圈的电-磁-力特性研究

随着超导线圈在电力领域中的应用越来越广泛,该文利用有限元仿真软件对处于交变磁场中载流高温超导带材的电-磁-力特性进行了研究,通过超导体的非线性E-J本构关系和基于棱边元法的磁场强度法来求解超导线圈内的电流分布、线圈周围的磁场分布及其受到的电磁力大小等电磁特性,重点研究了在以涂层超导磁体为励磁线圈的直线牵引系统中超导线圈和三相绕组之间的电磁力大小.基于仿真结果,分析了超导线圈内电流分布随气隙的变化关系;线圈周围的磁场分布情况及其对超导线圈临界电流的影响;线圈受到的电磁力随时间和气隙的变化关系等,所得结果为高温超导直线电机的设计和应用提供参考依据.     

对亥姆霍兹线圈磁场分布的分析

利用DH4501D实验仪探究了亥姆霍兹线圈轴线上和轴线外的磁场分布问题。首先通过对单个线圈不同电流下的磁场分布的实验值与理论值对比发现电流大的磁场更接近理论值,更适合用来研究磁场分布问题。然后利用较大电流分别研究了单个线圈以及亥姆霍兹线圈轴线上和轴线外的磁场分布的规律及产生原因。最后利用磁场分布拟合了真空磁导率并与理论值进行了对比。通过对这些问题的研究不仅加深了对毕奥-萨伐尔定律的理解,更加明确了亥姆霍兹线圈的磁场分布规律。     

一种高温超导变压器的优化设计:复合带宽及多间距结构（英文）

高温超导变压器由于具有体积小,交流损耗低等优点而在电网中占有非常重要的作用.本文设计了一种三相1 MVA容量的混合行高温超导变压器,为10 MVA大容量的高温超导变压器的设计提供技术经验.其中,高压绕组采用常规Cu导线;低压绕组采用YBCO第二代高温超导带材,由12个饼并联绕制而成.为了优化其结构,采用了有限元分析方法,在Opera-3D中建立了"磁-路"耦合模型并进行计算.计算结果表明,低压线圈中的电流分布不均匀,导致了材料的浪费并且可能造成线圈损坏.因此,我们采用复合带宽线圈替换相同带宽的线圈,即:12根带材的宽度与其承载的电流的大小成正比.结果给出了复合带宽线圈中每个饼的电流分布情况,表明复合带宽线圈可以应用于变压器中.同时,为了提高低压线圈中电流的均一性,我们提出了多间距结构,并且将实验电流与临界电流的比值定义为电流均一度.结果显示修改后的设计有更好的电流均一性.     

An Optimize Design of HTS Transformer :Multi-Width and Multi-Distance Structure北大核心CSCD

高温超导变压器由于具有体积小,交流损耗低等优点而在电网中占有非常重要的作用.本文设计了一种三相1 MVA容量的混合行高温超导变压器,为10 MVA大容量的高温超导变压器的设计提供技术经验.其中,高压绕组采用常规Cu导线;低压绕组采用YBCO第二代高温超导带材,由12个饼并联绕制而成.为了优化其结构,采用了有限元分析方法,在Opera-3D中建立了“磁-路”耦合模型并进行计算.计算结果表明,低压线圈中的电流分布不均匀,导致了材料的浪费并且可能造成线圈损坏.因此,我们采用复合带宽线圈替换相同带宽的线圈,即:12根带材的宽度与其承载的电流的大小成正比.结果给出了复合带宽线圈中每个饼的电流分布情况,表明复合带宽线圈可以应用于变压器中.同时,为了提高低压线圈中电流的均一性,我们提出了多间距结构,并且将实验电流与临界电流的比值定义为电流均一度.结果显示修改后的设计有更好的电流均一性.     

Bi-2223／Ag超导闭合线圈的制备及其电流衰减特性的研究

本文研究了使用Bi-2223／Ag超导带材制备超导闭合线圈的工艺及超导闭合线圈中电流衰减的特性．在闭合线圈焊接点的制作上，分别采用了超导焊接和普通焊锡焊接两种不同方法．通过测量闭合线圈中心点的磁场衰减过程，观察了这两种闭合线圈中电流衰减的特性．实验发现，使用超导焊接技术制备的闭合线圈，电流衰减与时间的自然对数成线性关系，在线圈局部受损伤的情况下，上述关系仍然成立；使用普通焊锡焊接方法制备的闭合线圈，电流衰减不存在上述关系，但也不是时间的e指数函数．     

MFCG 2维磁流体力学程序中磁场计算的改进

 定子线圈中的电流在空间中产生的磁场是金属导体（套筒）膨胀压缩的主要对象，该磁场直接影响爆磁压缩发生器输出电流脉冲的大小。给出了面电流分布下2维磁场的计算公式，较点电流分布下的磁场公式更能细致准确地反映出磁场的变化。数值结果表明:面电流分布下的磁场公式不仅能准确地描述磁场的变化，而且计算效率大大提高，节约了计算时间。     

跑道型Bi系高温超导双饼线圈I～E特性计算与实验研究

本文使用Ansys有限元分析软件,建立三维跑道线圈模型,考虑超导线截面电流密度的非均匀分布特性,计算Bi系高温超导双饼线圈中各区域磁场分布、临界电流分布、电流密度分布和电场分布,从而计算线圈的I～E关系曲线,为超导线圈提供一个更为准确的检验标准,对照线圈的测试结果,用此程序计算的线圈I～E关系曲线与测试曲线吻合的较好.     

HL-2M 装置极向场线圈的结构设计与制造

介绍了 HL-2M 装置极向场(PF)线圈的结构设计和制造。16 饼 PF 线圈布置在环向场(TF)线圈空腔之 内、真空室外,沿中平面对称分布。PF 线圈采用中空矩形铜导体绕制,其中 PF1~PF4 线圈为双层螺旋绕制结构, 最大运行电流 14.5kA;PF5~PF8 线圈为多层盘式绕制结构,最大运行电流 38~42kA。      

50kA超导变压器初级绕组设计制作及低温通电实验

主要讨论了超导变压器初级绕组的设计、绕制以及低温通电实验,初级绕组主要采用2 942匝NbTi超导股线绕制,并经过真空压力浸渍而成。利用Ansys软件分析了其磁场分布。采用LHe浸泡式制冷,最大电流可达190A,中心场约为2T。     

5 kVA高温超导变压器双饼线圈不同有限元模型对比分析

本文基于5 kVA 高温超导变压器的高压绕组双饼线圈, 运用有限元软件, 完成了均质化建模. 相比于全模型, 采用均质化模型不仅不影响计算精度, 而且大大减少了计算时间, 同时能够快速有效地计算出双饼线圈的磁场分布、 电流密度分布以及线圈交流损耗. 为了验证双饼线圈有限元计算模型的正确性, 本文进行了 H 方程全模型、H 方程均质化模型、T-A 方程全模型及T-A 方程均质化模型下的对比仿真分析. 仿真结果的一致性表明了双饼线圈有限元计算模型的正确性. 本文为后续基于T-A 方程下高温超导变压器均质化模型的研究提供了参考.     

An Efficacious Target-Field Approach to Design Shim Coils for Halbach Magnet of Mobile NMR Sensors

The main magnetic fields of mobile nuclear magnetic resonance (NMR) magnets differ from those of conventional NMR and magnetic resonance imaging (MRI) magnets. In the Halbach magnet, the main field B ₀ is perpendicular to the longitudinal axis, the symmetry of the current distribution with respect to the symmetry of the magnetic field differs from that in conventional target-field applications, and the current distribution on the coil surface cannot be expressed in terms of periodic basis functions. To obtain the winding pattern of the coil, an efficacious target-field approach. The surface of a coil is divided into small discrete elements, where each element is represented by a magnetic dipole. From the stream function of the elements, the resultant magnetic field is calculated. The optimization strategy follows an objective function defined by the power dissipation or efficiency of the coil. This leads to the optimum stream function on the coil surface, whose contour lines define the winding patterns of the coil. This paper shows winding patterns designed of shim coils for Halbach magnet and illustrates the craft of a shim coil using flexible printed circuit board. The performance of the coils is verified by simulating the fields they produce over the sensitive volume.     

Plasma shape optimization for EAST tokamak using orthogonal method

It is necessary to reduce the currents of poloidal field(PF) coils as small as possible, during the static equilibrium design procedure of Experimental Advanced Superconductive Tokamak(EAST). The quasi-snowflake(QSF) divertor configuration is studied in this paper. Starting from a standard QSF plasma equilibrium, a new QSF equilibrium with 300 kA total plasma current is designed. In order to reduce the currents of PF6 and PF14, the influence of plasma shape on PF coil current distribution is analyzed. A fixed boundary equilibrium solver based on a non-rigid plasma model is used to calculate the flux distribution and PF coil current distribution. Then the plasma shape parameters are studied by the orthogonal method. According to the result, the plasma shape is redefined, and the calculated equilibrium shows that the currents of PF6 and PF14 are reduced by 3.592 kA and 2.773 kA, respectively.     

YBCO线圈在低温下的温度仿真分析

近几年,高温超导线材的制造技术已日趋成熟。作为第二代高温超导带材的代表,YBCO在低温下具有的优点使其在超导磁体领域的应用越来越突出。但是在高温超导磁体的运行中会因为受到扰动而失超。为了探讨这个问题,模拟了一个磁体在低温下(20K左右)有加热点扰动时的稳定性情况,即对YBCO线圈在低温下的工作情况进行了模拟仿真。文中根据实验设计的YBCO单饼线圈参数,利用热传导方程和基本电路方程,采用有限元计算方法,模拟出线圈内部的温度分布。分析仿真结果可以为后续实验设计提供参考。     

Inverse design of an organ-oriented RF coil for open,vertical-field,MR-guided,focused ultrasound surgery

The advantages of open, vertical-field, magnetic resonance-guided, focused ultrasound surgery (MRgFUS) are attractive. The inverse technique using the bi-boundary conditions is proposed to design a uterine-oriented intraoperative RF coil with an ultrasound aperture for the MRgFUS system. In the current proposed scheme, the desired magnetic field of the RF coil was set to completely overlap the target organ. The current density distribution on the RF coil surface, accounting for the expected magnetic field, was solved using the inverse technique. The stream function was available through the ‘discretization’ of the current density distribution on the RF coil surface. The coil windings were obtained from the contour plot of the stream function. As a modification of previous designs, the bi-boundary conditions are proposed in the inverse technique for the existence of the ultrasound aperture. Based on the obtained coil windings, a prototype coil was constructed. MR imaging of the phantom and the human body was performed to show the efficacy of the prototype coil. The results of temperature measurement using the prototype coil in a 0.4-T MR system were satisfactory. The performance of the prototype coil improved compared with the previously reported design.     

Design of SC solenoid with high homogeneity

A novel kind of SC (superconducting) solenoid coil is designed to satisfy the homogeneity requirement of the magnetic field. In this paper, we first calculate the current density distribution of the solenoid coil section through the linear programming method. Then a traditional solenoid and a nonrectangular section solenoid are designed to produce a central field up to 7 T with a homogeneity to the greatest extent. After comparision of the two solenoid coils designed in magnet field quality, fabrication cost and other aspects, the new design of the nonrectangular section of a solenoid coil can be realized through improving the techniques of framework fabrication and winding. Finally, the outlook and error analysis of this kind of SC magnet coil are also discussed briefly.     

Multiple Parallel Round Leg Design for Quadrature Birdcage Coil in Ultrahigh-Field MRI

Copper foil has been widely employed in conventional radio frequency (RF) birdcage coils for magnetic resonance imaging (MRI). However, for ultrahigh-field (UHF) MRI, current density distribution on the copper foil is concentrated on the surface and the edge due to proximity effect. This increases the effective resistance and distorts the circumferential sinusoidal current distribution on the birdcage coils, resulting in low signal-to-noise ratio (SNR) and inhomogeneous distribution of RF magnetic (B₁) field. In this context, multiple parallel round wires were proposed as legs of a birdcage coil to optimize current density distribution and to improve the SNR and the B₁ field homogeneity. The design was compared with three conventional birdcage coils with different width flat strip surface legs for a 9.4 T (T) MRI system, e.g., narrow-leg birdcage coil (NL), medium-leg birdcage coil (ML), broad-leg birdcage coil (BL) and the multiple parallel round wire-leg birdcage coil (WL). Studies were carried out in in vitro saline phantom as well as in vivo mouse brain. WL showed higher coil quality factor Q and more homogeneous B₁ field distribution compared to the other three conventional birdcage coils. Furthermore, WL showed 12, 10 and 13% SNR increase, respectively, compared to NL, ML and BL. It was proposed that conductor’s shape optimization could be an effective approach to improve RF coil performance for UHF MRI.     

Performance improvement of a high-temperature superconducting coil by separating and grading the coil edge

In this paper, we establish a model to analyze the transport current performance of a high-temperature superconducting (HTS) coil, considering the dependencies of critical current and n-value of an HTS tape on magnetic field and magnetic field angles. This analysis shows that relatively large electric fields appear at the coil’s edges, preventing improvement in the transport current performance of the coil. To solve this problem, in this paper, we propose a graded coil in which several coil edges of different heights are separated and graded. Analysis of its performance shows that the coil’s critical current increases, thus confirming that there exists an optimum coil cross section at which the stored energy and central magnetic field improve 2.1 times and 45%, respectively, compared with a typical rectangular coil that employs the same total length of the HTS tape. It is recommended that these results of the coil should be applied to SMES.