Analysis of the Self-Protection Characteristics of a 1.5T Bitter-Like HTS Magnet Operated at 65K

We present a conceptual configuration of a high-temperature superconducting(HTS)magnet made from REBCO(Re=Rare Earth,B=Barium,C=Copper,O=Oxide)annular plates,called a Bitter-like HTS magnet,which can operate in persistent current mode without joint resistance and can be excited by a flux pump and without current leads and a persistent power supply.An REBCO annular magnet which can generate 1.5 T corresponding to the operating current density 80%of critical current density of the magnet at an operating temperature of65 K is conceptually designed.Then the thermal stability of the magnet is numerically simulated by Comsol software.Whein a piece of RBCO annular plate quenches,the maximum released energy is its stored energy because each REBCO annular plate in the Bitter-like magnet is in parallel.To calculate the stored energy in the REBCO annular plate,the inductance of every annular plate,including self-inductance and mutual inductance,is calculated.Compared with the minimum quench energy(MQE)and stored energy in one REBCO annular plate,the stored energy in one REBCO annular plate is always smaller than the MQE,and the REBCO annular plate will not be damaged even though the stored energy in the REBCO annular plate is fully released,which indicates that this 1.5 T Bitter-like magnet has the property of self-protection.     

ELECTROCHEMICAL OXIDATION OF La2CuO4 SINGLE CRYSTALS

Bulk superconducting La₂CuO_4+δ single crystals are obtained by using electrochemical intercalation technique from the as-grown insulating samples. Oxidation is carried out by constant current I=10μA at temperature T=70℃ and room temperature, respectively. Structure and magnetic properties are studied by low-temperature X-ray diffraction and susceptibility measurements. A superconducting phase with T_c of 19K and δ-0.12 can be attributed to the formation of oxygen clusters. Room temperature oxidation is inhomogeneous: two superconducting phases with T_c1 of 24K and T_c2 of 8K and an antiferromagnetic phase are coexisting in the crystal. It is found that the appearance of T_c in this system has the "step" tendency.     

A Complete Frequency-Field Chart for the Antiferromagnetic Resonance in MnF2

Antiferromagnetic resonance (AFMR) measurements on a well characterized single crystal sample of MnF₂ have been performed using various kinds of millimeter and submillimeter sources up to 570 GHz and a superconducting magnet up to 20 T. All the AFMR modes predicted from the theory have been observed. We report a complete frequency-field chart for these AFMR modes.     

MgB_2超导储能磁体可行性研究及结构优化

MgB2作为超导材料中的一颗新星,可以很好的应用于超导磁体。文中对比分析了作为超导磁体应用材料MgB2的超导特性,之后进行了MgB2磁体电磁设计。并通过与已有的Bi系超导磁体的对比,论证了MgB2在超导储能磁体应用中的可行性。针对MgB2超导特性进行磁体结构优化设计,得到两种新思路的螺管型磁体模型,都能够达到更好的经济性。     

低温／高温复合超导体的热稳定性的数值模拟研究

本文提出了一种高温超导体与低温超导体直接复合成混杂结构的复合超导体的导体模型.针对NbTi/Bi2223复合超导体的热稳定性进行了初步的理论模拟研究,结果表明低温/高温复合超导体的最小失超能远大于低温超导体,失超传播速度介于纯低温超导体和高温超导体之间,对于超导磁体的热稳定和保护具有重要参考价值.     

SUPERCONDUCTING MICROSTRIP LINE MODEL STUDIES AT MILLIMETRE AND SUB-MILLIMETRE WAVES

This paper presents results of superconducting microstrip transmission line simulation for the frequency range 100–1100 GHz. The simulation is used to calculate the characteristic impedance and the wave propagation constant in a superconducting microstrip line having different geometry. Indeed, modelling provides the only tool for designing superconducting microstrip-based circuits at millimetre and sub-millimetre wavelengths because no direct measurements of such a line can be made at this wavelengths and at cryogenic temperature of 4 K with ultimate accuracy. Niobium, as the most commonly exploited superconducting material, was used for the modelling, though the same approach would work for any different BCS superconductor. In order to evaluate the model accuracy, we have made an extensive comparison study of the superconducting microstrip models known from earlier publications, performed numerical simulations using 3D EM — solver, HFSS, and used a new model introduced in this paper with all simulation result plotted in the paper.     

Magneto-optical measurements with a hybrid magnet

An FFT spectrometer has been constructed to measure magneto-optical spectra in the far-infrared region (3 to 40 cm^–1) with a hybrid magnet system. The magneto-absorption was studied in the spin-Peierls cuprate CuGeO₃ at various magnetic fields. Coil constants of superconducting magnet and resistive one, of which a hybrid magnet consists, were calibrated by ESR spectra at the constant field.     

用于分离重离子的紧凑型两维超导磁体

北京中科健超导有限责任公司与北京科技大学共同设计和制作了一种用于分离重离子的紧凑型两维超导磁体 ,目前磁体已经通过测试。该磁体中心场强为 2特斯拉。为了结构上的紧凑 ,外侧的螺线管线圈中间放置水平线圈 ,型状如热狗 ,它使磁体在水平和垂直两个方向上都产生了供离子偏转的磁场     

辅助永磁体厚度对单畴GdBCO超导体捕获磁场分布及其磁悬浮力的影响

研究了两种磁悬浮系统组态中圆台形辅助永磁体厚度对高温超导体捕获磁场和超导磁悬浮力的影响。结果表明,圆台形辅助永磁体的下表面和GdBCO超导体上表面同处在一个水平面上,磁化用圆台形辅助永磁体的厚度H从5 mm增加到45 mm时,超导体捕获磁场和磁悬浮力与圆台形辅助永磁体的厚度直接相关。（1）当圆台形辅助永磁体的北极垂直向上且用液氮冷却后移除辅助永磁体时,最大磁悬浮力从21.8 N增大到26.5 N,再减小到22.9 N;（2）当圆台形辅助永磁体的北极垂直向下且用液氮冷却后移除辅助永磁体时,最大磁悬浮力从20.5 N减小到11.9 N ,再增加到20.4 N;（3）两种磁悬浮系统组态中最大磁悬浮力不一致,与零场冷情况下的最大磁悬浮力14.6 N也不同。在超导磁悬浮应用系统设计中,只有科学选择辅助永磁体形状和尺寸,合理设计组合方式,才能获得较强的磁场强度,提高超导磁悬浮力特性,该结果对促进高温超导体的实际应用具有重要的指导作用。     

液氮流动沸腾换热研究综述

作为一种优良的低温冷却剂,液氮在航天、电子工业、超导磁体和超导电缆冷却及低温生物医疗等领域应用广泛。在这些应用中,准确预测液氮的流动沸腾换热特性对于系统设计和安全运行十分重要。该文主要介绍了液氮流动沸腾换热的特点,对已有的实验和数值模拟结果进行了归纳;并比较了四个液氮流动沸腾换热计算关联式的预测情况,以及关联式中干度、质量流量、热流密度和压力对换热系数的影响;指出了有待进一步研究的课题。     

Lambertson型切割磁铁漏场的3维模拟计算和优化设计

 Lambertson型切割磁铁的漏场对RCS中的束流运行有较大的影响，包括束流集体不稳定效应以及高阶共振效应，为了对该型磁铁进行优化，利用3维磁场模拟程序OPERA3D/TOSCA，对北京散裂中子源/快循环同步加速环（CSNS/RCS）引出Lambertson型切割磁铁进行了物理设计。通过对不同的磁铁设计方案进行3维模拟计算和优化发现，采用15 mm厚的切割板以及在屏蔽管出口处添加半径为200 mm、厚度为10 mm屏蔽帽的磁场屏蔽措施，将Lambertson型切割磁铁的横向漏场降低到主磁场的0.80‰（y方向）和0.36‰（x方向），可以满足CSNS/RCS环的束流动力学设计要求。     

Calculation of magnetic field in the region of the superconducting winding of window frame dipole for particle accelerators

The necessity of simulations in design of superconducting dipole magnets is due to the following circumstances. First, the critical current as a function of the magnetic field I _c(B) for the multicore superconducting cable which drops strongly requires the knowledge of the value of maximum magnetic field “felt” by its coils for estimation of the working current of the magnet. Second, for choosing the optimal number of coils of the winding (1 or 2) and the working current of the magnet, the ratio of B _max for the inner and outer layers of the dipole magnet winding should be known. Since usually the length of the dipole magnet exceeds many times its transverse size, in this work all calculations of B(x, y) are performed in the transverse plane crossing the center of the magnet. The field at the central point is chosen to be B(0, 0) = 2 T (this is the characteristic working value close to the maximum value in the dipole magnet of this type). In this work, the results of calculation of B(x, y) for single-and double-layered windings with 8 and 16 coils from circular hollow cable are presented.     

Microwave study of granular superconducting Al films

Microwave absorption and frequency shift measurements in the normal and in the superconducting state are presented for a metallic type AlAl₂O₃ film. The results are explained by simple models using an uniform conductivity for the normal state absorption and percolation ideas for the superconducting transition.     

在Tokamak装置中用中空超导环段冻结环向磁场的设想

本文提出一个设想:即将n个中空超导圆柱体放置于n饼纵场线圈之中,分段冻结环向磁场,则其所需要的电功率将比常规线圈降低到2/n倍。我们知道超导材料的冻结场可近似地写为。H_fj(r,T)=H_fj(r,0)[1-(T/(T_c))²。因此选定T=T₁,当轴向场H在大圆环的内壁达到H≥H_fj(r,T₁)时,中空体的内边缘达到临界场,则场进入中空区,再使H降到零,中     

Kosterlitz-Thouless vs. Ginzburg-Landau description of 2D superconducting fluctuations

We evaluate the charge and spin susceptibilities of the 2D attractive Hubbard model and we compare our results with Monte Carlo simulations on the same model. We discuss the possibility to include topological Kosterlitz-Thouless superconducting fluctuations in a standard perturbative approach substituting in the fluctuation propagator the Ginzburg-Landau correlation length with the Kosterlitz-Thouless correlation length. Received 30 June 1999     

Gradient-induced longitudinal relaxation of hyperpolarized noble gases in the fringe fields of superconducting magnets used for magnetic resonance

When hyperpolarized noble gases are brought into the bore of a superconducting magnet for magnetic resonance imaging (MRI) or spectroscopy studies, the gases must pass through substantial field gradients, which can cause rapid longitudinal relaxation. In this communication, we present a means of calculating this spatially dependent relaxation rate in the fringe field of typical magnets. We then compare these predictions to experimental measurements of (3)He relaxation at various positions near a medium-bore 2-T small animal MRI system. The calculated and measured relaxation rates on the central axis of the magnet agree well and show a maximum (3)He relaxation rate of 3.83×10(-3) s(-1) (T(1)=4.4 min) at a distance of 47 cm from the magnet isocenter. We also show that if this magnet were self-shielded, its minimum T(1) would drop to 1.2 min. In contrast, a typical self-shielded 1.5-T clinical MRI scanner will induce a minimum on-axis T(1) of 12 min. Additionally, we show that the cylindrically symmetric fields of these magnets enable gradient-induced relaxation to be calculated using only knowledge of the on-axis longitudinal field, which can either be measured directly or calculated from a simple field model. Thus, while most MRI magnets employ complex and proprietary current configurations, we show that their fringe fields and the resulting gradient-induced relaxation are well approximated by simple solenoid models. Finally, our modeling also demonstrates that relaxation rates can increase by nearly an order of magnitude at radial distances equivalent to the solenoid radius.     

The microwave response of MgB2 /Al2O3 superconducting thin films

Microwave characteristics of MgB2/Al2O3 superconducting thin films were investigated by coplanar resonator technique. The thin films studied have different grain sizes resulting from different growth techniques. The experimental results can be described very well by a grain-size model which combines coplanar resonator theory and Josephson junction network model. It was found that the penetration depth and surface resistance of thin films with smaller grain sizes are larger than those of thin films with larger grain sizes.     

A far-infrared laser magnetic resonance spectrometer for the investigation of radicals of atmospheric relevance

A far-infrared laser magnetic resonance spectrometer is described. A superconducting magnet is used for the tuning of the energy levels. Pressure broadening measurements of OH and NO have been performed. The measurements demonstrate that the laser magnetic resonance technique is well suited for this kind of measurements. Based on this results the design and expected performance of a compact laser magnetic resonance spectrometer is presented. The sensitivity as well as the mechanical ruggedness of this spectrometer is sufficient in order to be used aboard an aircraft for the in situ detection of OH and HO₂ in the lower stratosphere and upper troposphere.     

用于ITER的NbTi超导股线临界电流测试方法

介绍了一种用于ITER的NbTi超导股线在不同温度下临界电流测试的方法和装置。该装置包括一孔径为70mm、最高磁场高达16T的背景磁体以及变温杜瓦等系统。对NbTi超导线变温测试设计了二元电流引线。用该系统得到了其NbTi超导股线在不同磁场不同温度下的临界电流,用“Luca”定标律拟合了测试结果,并对测试结果进行了分析。