自场下高温超导MCP BSCCO-2212电流引线失超过程电磁特性研究

本文研究了大电流自场条件下,采用熔化铸造工艺(MCP)制备的BSCCO-2212高温超导电流引线失超过程电磁特性.在磁通粘滞流动模型的基础上,推导出二维磁通粘滞流动平衡方程式,得到了磁流阻状态下的电流密度、磁通密度和磁流阻率分布;应用二维场量分布进一步得到了平均磁流阻率随电流密度和温度的变化特性.计算结果对于电流引线安全保护设计、提高电流引线载流能力具有重要意义.     

熔融织构YBCO块材磁通动力学参量的磁光图像研究

通过磁光图像研究熔融织构ＹＢＣＯ块材的剩余磁感应强度在空间的分布和随时间的变化,推算出样品的局域有效激活能Ｕ（ｘ,ｔ）和局域电流密度Ｊ（ｘ,ｔ）以及对数时间尺度ｔ０．实验结果表明在此样品中Ｚｅｌｄｏｖ磁通蠕动模型Ｕ＝Ｕｃｌｎ（Ｊｃ／Ｊ）仍然是有意义的     

GdBCO超导体的顺磁性及低温下磁通分布的动态观测

本文研究了100～300K之间Gd1．8Ba2.4Cu3．4O7-δ（简写为GdBCO）超导体的顺磁性，对GdBCO的磁化强度随磁场和温度的变化分别在100K和0．1T进行了测试，GdBCO的顺磁性遵从朗之万顺磁性理论．在磁光显微镜下，低温12K场冷下，我们观察了从0mT～29mT磁通线进入GdBCO的超导体的过程，以及磁通线在GdBCO超导体中的分布。     

三维光晶格中玻色凝聚气体基态波函数及干涉演化

基于Gross-Pitaevskii方程，运用有效化学势概念，研究了囚禁在组合势(由磁阱和三维光 晶格组成)中玻色凝聚气体在三维光晶格中的分布规律，并由此得到玻色凝聚气体的归 一化基态波函数.在取消组合势和仅取消光晶格而保留磁阱的两种情况下，运用传播子方 法求解出玻色凝聚气体密度分布的解析表达式.取消组合势后，理论计算所得到的玻色凝聚 气体聚随时间的演化规律与Greiner等的实验结果相一致.仅取消光晶格而保留磁阱时，研 究表明玻色凝聚气体的干涉模式呈现周期性的振荡行为.此外，在磁阱为各向异性的情况下 ， 关键词： 玻色凝聚气体 磁阱 光晶格 干涉模式     

通道内空气热磁对流的协同分析

为研究通道内空气热磁对流的流动规律,用数值模拟方法,研究了磁场作用下二维模型水平通道内的流动换热过程,获得了通道内的磁通密度分布和空气温度轴向分布,在此基础上,建立了一维通道内空气热磁对流的数学模型,就温度场和磁场的相对关系对水通道内热磁对流过程的影响进行了数值计算,获得了通道内不同温度场、磁场以及其不同相对位置下的通道空气流量,并讨论了磁极形状对空气流量及其变化的影响。     

四注行波管周期永磁聚焦系统的优化设计

根据电子注参数、布里渊磁场公式及周期聚焦系统轴向磁通密度峰值经验公式,计算出永磁聚焦系统轴向峰值磁通密度,利用Ansoft Maxwell 3D软件建立了四注行波管周期永磁聚焦系统仿真模型,对模型结构尺寸进行了参数化分析,研究了周期永磁聚焦系统结构尺寸对聚焦系统通道内磁通密度的影响,确定了磁聚焦系统结构最佳尺寸配合,优化设计出了四注行波管周期永磁聚焦系统。其电子注通道中心轴线上轴向磁通密度峰值B_z=309 mT,横向磁通密度B_t=2.86 mT,B_t/B_z=0.92%。     

二维磁通随机钉扎系统动力学行为的数值模拟

本文利用数值模拟的方法,研究在Ｌｏｒｅｎｔｚ 驱动力作用下,随机钉扎环境中运动的二维磁通点阵的动力学行为．通过对不同随机分布点钉扎中心密度和不同磁通间相互作用强度的研究,发现磁通点阵存在从弹性区向塑性区的渡越（ｃｒｏｓｓｏｖｅｒ） , 并且这种渡越强烈依赖于磁通之间及磁通与钉扎之间的相互作用．随着钉扎中心密度的增加及磁通间相互作用强度的减弱,临界钉扎力增强．模拟结果与最近实验结果定性一致．部分结果偏离集体钉扎理论     

GdBCO超导体的顺磁性及低温下磁通分布的动态观测

本文研究了100～300K之间Gd1.8Ba2.4Cu3.4O7-δ(简写为GdBCO)超导体的顺磁性,对GdBCO的磁化强度随磁场和温度的变化分别在100K和0.1T进行了测试,GdBCO的顺磁性遵从朗之万顺磁性理论.在磁光显微镜下,低温12K场冷下,我们观察了从0mT～29mT磁通线进入GdBCO的超导体的过程,以及磁通线在GdBCO超导体中的分布.     

高T_c超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.     

第Ⅱ类超导体中磁通运动的低频电压噪声研究

用有限温度下的分子动力学方法模拟二维无序钉扎磁通系统的低频宽带电压噪声.计算了磁通运动的电压噪声谱密度，研究了宽带噪声（BBN）随驱动电流、钉扎强度和温度的变化规律.BBN随钉扎强度的增加而增大，反映了BBN是磁通运动受体钉扎阻碍而产生的内部耗散. BBN随温度的升高而减小，表明热运动部分抵消了体钉扎以及磁通之间相互作用，软化了磁通线格子，使磁通运动BBN减小.以上结论与实验相符，并能解释磁通运动的微观图像. 关键词： 第Ⅱ类超导体 电压噪声 动力学模拟     

Analysis of the magnetic field distribution and estimation of the critical current density based on a magnetooptical study of the superconducting strip composites

The results of magnetic flux penetration into high-temperature superconducting composites of the second generation have been analyzed and described. The distribution of magnetic flux was observed experimentally using the magnetooptical visualization technique at various temperatures of 4.2–80 K. The experimental data have been found to coincide with the results of analytical and semi-numeric calculations of magnetic field profiles carried out for regimes of full and partial field penetration into superconducting composites. The method of estimating the critical current density based on measurements of the topography of the transverse magnetic flux has been considered, and an approach to estimating the critical current density for strips from measurements of the tangential field component has been proposed.     

Estimating the absolute flux distribution for a synchrotron X‐ray beam using ionization‐chamber measurements with various filters

It is shown that an extensive set of accurate ionization‐chamber measurements with a primary polychromatic synchrotron X‐ray beam transmitted through various filter combinations/thicknesses can be used to quite effectively estimate the absolute flux distribution. The basic technique is simple but the `inversion' of the raw data to extract the flux distribution is a fundamentally ill‐posed problem. It is demonstrated, using data collected at the Imaging and Medical Beamline (IMBL) of the Australian Synchrotron, that the absolute flux can be quickly and reliably estimated if a suitable choice of filters is made. Results are presented as a function of the magnetic field (from 1.40 to 4.00 T) of the superconducting multi‐pole wiggler insertion device installed at IMBL. A non‐linear least‐squares refinement of the data is used to estimate the incident flux distribution and then comparison is made with calculations from the programs SPECTRA, XOP and spec.exe. The technique described is important not only in estimating flux itself but also for a variety of other, derived, X‐ray properties such as beam quality, power density and absorbed‐dose rate. The applicability of the technique with a monochromatic X‐ray beam for which there is significant harmonic contamination is also demonstrated. Whilst absolute results can also be derived in this monochromatic beam case, relative (integrated) flux values are sufficient for our primary aim of establishing reliable determinations of the percentages of the various harmonic components.     

磁场对水系统内能影响的MC计算机模拟方法研究

用Monte-Carlo计算机模拟方法,通过对一个含有64个水分子的三维体系在磁场作用时内能变化的计算,定量评估了磁场强度及温度对磁处理效应的影响。研究发现:水的内能与外加磁场强度的关系曲线是一条多极值曲线;水-水径向分布函数伴峰的高度与磁感应强度也具有多极值特征;计算机模拟结果与实验结果基本一致,计算机模拟确实是从分子水平研究磁处理机理的有效方法。     

Comparison of adjustable permanent magnetic field sources

A permanent magnet assembly in which the flux density can be altered by a mechanical operation is often significantly smaller than comparable electromagnets and also requires no electrical power to operate. In this paper five permanent magnet designs in which the magnetic flux density can be altered are analyzed using numerical simulations, and compared based on the generated magnetic flux density in a sample volume and the amount of magnet material used. The designs are the concentric Halbach cylinder, the two half Halbach cylinders, the two linear Halbach arrays and the four and six rod mangle. The concentric Halbach cylinder design is found to be the best performing design, i.e. the design that provides the most magnetic flux density using the least amount of magnet material. A concentric Halbach cylinder has been constructed and the magnetic flux density, the homogeneity and the direction of the magnetic field are measured and compared with numerical simulation and a good agrement is found.     

Fast imaging for magnetic resonance electrical impedance tomography

In magnetic resonance electrical impedance tomography (MREIT), currents are injected into an object, the resulting magnetic flux density is measured using MRI, and the conductivity distribution reconstructed using these MRI data. The relatively long acquisition times of conventional MREIT methods limit the signal averaging rate and are susceptible to motion artifacts. In this study, we reconstructed the conductivity distribution of an agarose gel phantom from data acquired in under a minute using a single-shot, spin echo, echo planar imaging (SS-SEPI) pulse sequence. The results demonstrate that SS-SEPI can be used for MREIT data acquisition.     

A measurement method of the magnetic properties of magnetic sheet by means of a single sheet tester at audio frequency

A single sheet tester (SST) for audio frequency of 400 Hz–10 kHz was made experimentally and the magnetizing winding can get the nearly uniform distribution of flux density of a specimen in the longitudinal direction at the frequency up to 10 kHz. The flux densities at various positions of strips measured by the Epstein method were detected by search coils wound on strips at 400 Hz and 1.0 T. They have large discrepancy. However, the magnetic properties obtained from both methods have a little discrepancy. Although the uniformity of flux distribution in the Epstein frame is not sufficient, the average is fairly effective because the magnetic properties can be assumed to be locally linear within the small deviation of flux density.     

利用Grad-Shafranov重构方法研究磁尾通量绳的特征参量和内部结构

2009年2月21日THEMIS-C卫星在磁尾X=-15.7R_E(R_E为地球半径,1R_E=6371 km)观测到典型的磁通量绳事件.采用Grad-Shafranov 重构技术研究该磁通量绳的特性、内部磁场和电流结构.研究表明,磁通量绳不变轴位于GSM(geocentric solar magnetospheric coordinates)坐标为(-0.3975,0.8905,0.221 关键词： 磁尾 磁通量绳 Grad-Shafranov重构 多X线重联     

Nb3Sn超导电磁铁

本文报导了关于筒形Nb₃Sn磁体的研究结果。观察到磁通跳跃现象。“冻结”场的分布和历史及激发场的分布紧密相关。“冻结”场可以不是中心对称的,这进一步证明了烧结的Nb₃Sn材料是非均匀介质。我们描述了新的磁体结构,避免了磁通跳跃。除利用铁心来捕获磁通外,在激发和测量磁场的方法上均具有一定的特点。利用圆筒状Nb₃Sn作为压挤磁通的活塞,在1.5°K时,曾获得的最高场强是28.5KG。     

Dependence of resonance condition on pressure in an RF resonancemethod

The plasma density is shown as functions of pressure and magnetic flux density in an RF resonance method using the XPDP1 simulation code. The RF resonance method has the unique feature that a strong electric field in bulk controls the plasma density. Owing to the balance between the electric field decrease and the collision rate increase, the plasma density in the RF resonance method has a peak with respect to pressure. The plasma density with respect to the magnetic flux density depends on the condition of the RF resonance method, and the dependence is strong at low pressure because of the strong resonance. Sheath thickness is the most important parameter that determines the strength of the resonance induced. It is shown that the sheath thickness s is related to the plasma density n as a function of ns, obtained from a dispersion relation at constant external parameters. The magnetic flux density which induces the strong resonance is determined from sheath thickness. The plasma density in the RF resonance method can be predicted from discharge parameters using the relation between plasma density and sheath thickness     

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.