目标场法在悬浮超导球体的球形线圈设计中的应用

文中把目标场法引入到悬浮超导球体的球形线圈设计中,根据目标场法产生均匀磁场的原理,通过离散化绕组来近似处理球形线圈在超导球体和球形线圈的间隙内产生均匀磁场的电流密度分布规律。利用有限元分析和验证,在超导球体与球形线圈之间的间隙内产生了具有很好均匀性的悬浮磁场,这会明显提高超导球体悬浮的刚度和稳定性。     

电枢参数对电枢超导型高温超导电机性能的影响

高温超导材料存在背景磁场依赖性和各向异性的问题,针对超导感应电机采用双层绕组结构,提出了双重镜像法建立开口矩形槽内漏磁场垂直方向和水平方向的解析模型,利用该模型研究了超导线圈在传输不同电流情况下磁场分布规律,揭示了开口矩形槽电磁结构参数对槽内超导线圈所受表面磁场的影响规律。研究结果表明,适当增大槽宽尺寸可以有效降低超导线圈表面所受最大磁场,传输电流和线圈匝数均能够近乎线性增大超导线圈表面所受最大磁场。     

结构参数对高温超导绕组线圈磁化损耗影响分析

为了研究高温超导电力设备的绕组密度对其磁化损耗的影响,优化绕组线圈结构,减小交流损耗。利用有限元仿真软件,建立了多匝双根单饼线圈绕组的二维轴对称模型。在外加交变磁场条件下,分别改变超导绕组线圈匝数、匝间间距,分析磁化损耗的变化规律。结果表明,线圈间存在屏蔽作用,在一定范围内,超导线圈匝数越多,磁化损耗越小,匝间间距与超导线圈的磁化损耗正相关。     

宽平顶低横向场分量螺线管线圈设计

介绍了非均匀绕线技术和匀场环技术在螺线管线圈设计中的应用。分析表明这两种技术的采用可以减小线圈间隙的磁场波动、屏蔽线圈磁场的横向分量,从而设计出宽平顶低横向场分量的螺线管线圈。针对中国工程物理研究院12 MeV直线感应加速器螺旋管线圈的设计结果表明,非均匀绕线技术可以使线圈间隙处的轴向磁场波动减小约70%,匀场环的采用则能使线圈磁场的横向分量减小96.5%。     

基于边界元方法的超导核磁共振成像设备高阶轴向匀场线圈优化算法

在磁共振成像设备中,为了消除目标区域内的高阶谐波磁场分量,传统方法采用无源匀场,但该方法匀场精度较低,针对性较差,适用于全局匀场,而有源匀场则可以通过优化线圈分布来产生所需要的特定的磁场分布.但是,由于匀场线圈线型的复杂度会随着线圈阶数的增加而增加,难以满足设计需要,因此本文提出了一种用于磁共振成像超导匀场线圈系统的多变量非线性优化设计方法.该方法基于边界元方法,将匀场线圈所产生的磁场与目标磁场之间的偏差作为目标函数,线匝间距、线圈半径等作为约束条件,通过非线性优化算法,得到满足设计要求的线圈分布.通过一个中心磁场为0.5 T的开放式双平面磁共振成像超导轴向匀场线圈的设计案例,说明本方法具有计算效率高、灵活性好的特点.     

高温超导变压器绕组端部分磁环的优化设计与研究

本文采用有限元方法研究了低损耗分磁环对高温超导变压器绕组端部漏磁场分布、线圈所承受的电磁力以及高温超导线圈交流损耗的影响,并以高温超导线圈交流损耗最小和并联超导绕组间环流最小为目标,对分磁环的结构参数进行优化.结果表明,分磁环对提高高温超导变压器的性能有一定的作用.     

基于目标场点法和流函数的磁共振有源匀场线圈设计方法

磁场均匀性是磁共振系统的重要参数,提高磁场均匀性有助于磁共振时域信号的检测和磁共振频域信号分辨率的改善.基于有源匀场连续电流密度分布的思想,采用目标场点法和流函数结合的方法设计匀场线圈,即由毕奥-萨伐尔定律确定磁场分布与电流密度的关系,约束线圈半径和设置约束点后,根据目标场分布逆向求解线圈平面的电流密度分布,再用流函数将电流密度分布离散化处理,得到匀场线圈的绕线位置分布.根据电磁仿真计算结果制作包含一阶与二阶匀场线圈应用于磁共振分析仪,实验验证表明该匀场线圈能有效地改善永磁体核磁共振系统磁场的均匀性.     

高均匀度超导磁体的最佳设计(II)——四次体积最小线圈

为了充分利用四次体积最小线圈组成的超导磁体的中外层绕组的载流潜力,本文提出把磁体绕组分成由两个具有不同电流密度的内外同轴四次体积最小线圈组成.在合理地选择内线圈对总磁场的贡献比例条件下,其最佳设计,当外线圈绕组和内线圈绕阻单位体积的费用之比时,可节省超导材料费42％,当R=1/2时,节省70％,R=1/3时,可节省78％.     

高分辨超导NMR谱仪的匀场

本文详细叙述了超导磁体的磁场分布和匀场线圈的设计。并对匀场电源、匀场线圈的精度和稳定性等要求作了估算。     

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.     

Designing shielded radio-frequency phased-array coils for magnetic resonance imaging

In this paper, an approach to the design of shielded radio-frequency (RF) phased-array coils for magnetic resonance imaging (MRI) is proposed. The target field method is used to find current densities distributed on primary and shield coils. The stream function technique is used to discretize current densities and to obtain the winding patterns of the coils. The corresponding highly ill-conditioned integral equation is solved by the Tikhonov regularization with a penalty function related to the minimum curvature. To balance the simplicity and smoothness with the homogeneity of the magnetic field of the coil’s winding pattern, the selection of a penalty factor is discussed in detail.     

霍尔推力器磁场位形及其优化的数值研究

基于麦克斯韦方程,在轴对称假设下建立了霍尔推力器磁场的数学模型.用有限差分方法对模型进行了离散.给出了数值求解模型的迭代法.通过对模型的数值求解,得到了相应的数值结果.通过对所得数值结果的分析,研究了磁场线圈电流变化对霍尔推力器磁场位形的影响.通过调整磁场线圈电流的大小找到了理想磁场位形.研究表明,对于理想磁场位形,内通道的磁镜比在3—3.5之间,外通道的磁镜比在0.4—0.9之间;增加磁场线圈的电流,出口的磁场强度随着增加,但不能增加磁镜比.通道内部的磁场强度几乎不随着磁场线圈电流的变化而变化. 关键词： 霍尔推力器 磁场位形 磁场线圈电流 磁镜比     

Globally optimal superconducting magnets part II: symmetric MSE coil arrangement

A globally optimal superconducting magnet coil design procedure based on the Minimum Stored Energy (MSE) current density map is outlined. The method has the ability to arrange coils in a manner that generates a strong and homogeneous axial magnetic field over a predefined region, and ensures the stray field external to the assembly and peak magnetic field at the wires are in acceptable ranges. The outlined strategy of allocating coils within a given domain suggests that coils should be placed around the perimeter of the domain with adjacent coils possessing alternating winding directions for optimum performance. The underlying current density maps from which the coils themselves are derived are unique, and optimized to possess minimal stored energy. Therefore, the method produces magnet designs with the lowest possible overall stored energy. Optimal coil layouts are provided for unshielded and shielded short bore symmetric superconducting magnets.     

基于永磁恒定磁场激励的起始磁化曲线测量

现有起始磁化曲线测量系统需绕制励磁线圈和感应线圈,在线应用受限.为此,本文提出了一种基于永磁恒定磁场激励的起始磁化曲线测量原理并搭建了相应测量系统.该系统采用永磁磁化器作为激励磁源,以对称磁化方法在圆柱棒状构件上激励出随轴向位置变化的恒定磁场作为激励磁场;采用阵列霍尔探头测量构件表面不同提离下的轴向和法向磁感应强度;并基于多项式外推法和磁场高斯定理外推法,推算构件与空气分界面上的轴向和法向磁感应强度;进一步地,根据分界面上的磁感应强度获取构件的起始磁化曲线.系统测量结果表明,在永磁恒定磁场激励下,无须励磁线圈和感应线圈即可方便地获取棒状构件的起始磁化曲线,测量误差小于10%,测量误差标准差小于0.01,重复性较好.该系统可为便捷地在线测量棒状构件起始磁化曲线提供新途径.     

3个共轴圆线圈形成的匀强磁场

分析了3个共轴圆线圈形成磁场的均匀性，得到了3个共轴圆线圈形成匀强磁场的条件，并且通过数值计算，全面展示3个共轴圆线圈磁场的均匀性．只要合理配置3个共轴圆线圈的大小、线圈中的电流强度和线圈之间的距离，3个共轴圆线圈的磁场在强度和均匀性方面都优于亥姆霍兹线圈的磁场。     

基于表面磁感应强度的铁磁构件应力恒磁表征方法

便捷获取铁磁承载构件应力对维护基础设施安全具有重要意义.其关键在于准确快速地确定随应力变化灵敏度高、线性度好的表征参数.现有电磁检测法一般在时变磁场线圈激励下,逐点分析实验结果来确定合适的表征参数,会带来线圈发热、涡流影响结果的问题,表征磁参数的确立繁琐.为此,本文提出基于表面磁感应强度的铁磁构件应力恒磁表征方法,采用永磁恒定磁化器产生全局衰减局部均匀的空间变化磁场作激励,用正交磁场测量单元拾取构件表面轴向和法向磁感应强度以表征应力.着重阐述基于表面磁感应强度的应力表征原理：根据退磁场理论、磁场强度切向连续性和磁场高斯定理,建立表面轴向和法向磁感应强度关于应力导函数之间的关系方程.最后开展实验验证.结果表明：根据该关系方程可快速准确地确定随应力灵敏度最高的表面磁感应强度,且其随应力变化线性度较好,拟合优度R²大于0.98,可作为应力表征磁参数.本文所提方法可为在线检测铁磁构件应力提供新途径.     

Effect of large-heat-capacity substances doping of superconducting coils on their dynamic stability

The dependence of the quench currents on the ramp rate was studied for four small NbTi coils. Two pairs of superconducting coils were tested. In one pair the SC 0.85-mm-dia wire with 2970 filaments was used, in the other two coils the SC wire contained 8910 filaments of smaller size. Two coils (with different number of filaments) contained 4.9 vol % of Large-Heat-Capacity Substance (LHCS) in the form of tiny powder evenly distributed over the winding volume, therefore their heat capacity at 4.2 K was an order of magnitude larger than that for coils without LHCS. The LHCS was introduced into the winding in a mixture with epoxy resin (“wet” winding). When the self-magnetic field varied with a rate of ≥5 T/s, premature quenches were observed in the central turns of the undoped coil made of a wire with 2970 filaments. These transitions are likely to be caused by magnetic flux jumps. In the LHCS-doped coil made of the same wire, the quenches took place at currents two to three times higher, since the sample was heated up to a critical temperature because of electrical losses (as confirmed by calculations). Thus, the improved stability of the LHCS-containing coils not only against long-term (0.1–1.0 s) disturbances but also against much shorter (10–100 μs) jumps of the magnetic flux is demonstrated.     

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.     

球形线圈磁场均匀性的研究

研究非密绕球形线圈内部的磁场均匀性质.从圆形电流线圈轴线上的磁场出发,利用叠加原理和Mathematica软件的计算和符号推导功能,得到一个关于线圈内部磁场均匀性与其匝数的定量关系式,在此基础上通过实例说明设计球形线圈磁场均匀区的方法.     

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。