Critical-Current Degeneration Dependence on Axial Strain of Bi-based Superconducting Multi-filamentary Composite Tapes

Superconducting materials are always severely restricted in practical engineering applications due to their carrying- current degradation under mechanical loads. Based on Ekin＇s exponential model and Weibull＇s distribution func- tion, we propose an empirical degradation model for describing the mechanical deformation influence on the critical-current of Bi-based superconducting multi-filamentary composite tapes under axial loading. The critical currents of superconducting tapes depending on the axial strain are investigated analytically. It is shown that the predictions by the developed degradation model agree with the experimental data, in the processes of axial mechanical loading and unloading on the samples. The effect of the critical tension and compression damage strains on the normalized critical currents is also discussed.     

Josephson Effect in Graphene： Comparison of Real and Pseudo Vector Potential Barriers

The Josephson currents through real vector potential （RVP） and pseudo vector potential （PVP） barriers in graphene are investigated. In graphene, the pseudo vector potential may be caused by a local strain. The comparison of supercurrents induced by the two type-barriers is focused. As a result, we find that not only will the RVP induce a transition Josephson current from the 0→π state but also causes the difference in the phases of the order parameters of the two superconducting graphene layers to shift from φ→2φ. The critical current is PVP-independent around the neutrality point while it strongly depends on the RVP. The vector potential dependence of critical current is found to be perfectly linear for both PVP and RVP barriers.     

AC Alternating-Current Loss Analyses of a Thin High-Temperature Superconducting Tube Carrying AC Transport Current in AC External Magnetic Field

Numerical simulations on the AC loss characteristics in a thin high-temperature superconducting （HTS） tube are presented. Geometry of the HTS conductor is modeled as a tube with negligible thickness, and assumed to carry a transport current with the same phase as an AC externally applied magnetic field perpendicular to the axis. Based on the classical theory of AC loss with the Bean critical current model, the distribution of critical current density jc and AC loss Q are obtained by means of numerical analysis. The results are in very good agreement with experiments. A double-peak profile is observed in the curve of the critical current density distribution along the azimuth angle. This numerical simulation method is suitable for a thin HTS tube, which may be applicable on a thin tube configuration consisting of coated superconductors.     

Mechanical Analysis and Measurements of a Multicomponent NbTi/Cu Superconducting Magnets Structure for the Fully Superconducting Electron Cyclotron Resonance Ion Source

A fully superconducting electron cyclotron resonance(ECR) ion source(SECRAL Ⅱ) is currently being built in the Institute of Modern Physics,Chinese Academy of Sciences.Its key components are three superconducting solenoids(Nb-Ti/Cu) and six superconducting sextupoles(Nb-Ti/Cu).Different from the conventional superconducting ECR magnetic structure,the SECRAL Ⅱ includes three superconducting solenoid coils that are located inside the superconducting sextupoles.The SECRAL Ⅱ can significantly reduce the interaction forces between the sextupole and the solenoids,and the magnets can also be more compact in size.For this multi-component SECRAL Ⅱ generating its self Held of ~8T and being often exposed to the high self Geld,the mechanical analysis has become the main issue to keep their stress at 200 MPa on coils.The analytical and experimental results in mechanics are presented in the SECRAL Ⅱ structure.To improve the accuracy and efficiency of analysis,according to the composite rule of micromechanics,the equivalent uniform windings are used to simuiate the epoxy-impregnated Nb-Ti/Cu coils.In addition,using low temperature strain gauges and a wireless fast strain acquisition system,a fundamentai experiment on the strains developments of a sextupole is reported.Finally,based on our analysis,the stresses and deformations for its assembly of each SECRAL Ⅱ coil will be further optimized.     

DEMAGNETIZATION EFFECT IN CRITICAL STATE IN CYLINDRICAL SUPERCONDUCTORS

This paper presents the results of field and current distribution in the critical state in a superconducting cylinder using Bean critical state model and isotropic critical current density Jc. We introduced an equivalent effective field and demagnetization factor Dc, and showed that Dc, from extremely long cylinder to very thin disks, is equal to Meissner demagnetization factor of the inscribed spheroid of the cylinder. The application of these parameters is discussed at the end of paper.     

Transport properties of Tl_2Ba_2CaCu_2O_8 microbridges on a low-angle step substrate

Tl-based superconducting devices have been drawn much attention for their high transition temperature(T_c), which allow the high temperature superconductors(HTS) devices to operate at temperature near 100 K. The realization of Tlbased devices will promote the research and application of HTS devices. In this work, we present transport properties of Tl_2 Ba_2 CaCu_2 O_8(Tl-2212) microbridges across a low-angle step on LaAlO_3(LAO) substrate. We experimentally demonstrate intrinsic Josephson effects(IJEs) in Tl-2212 films by tailoring the geometry, i.e., reducing the width of the microbridges. In the case of a 1 μm width microbridge, in addition to the observation of voltage branches and remarkable hysteresis on the current–voltage(I–V) characteristics, the temperature dependence of differential resistance shows a finite resistance above 60 K when the bias current is below the critical current. For comparison, the wider microbridges are also investigated, exhibiting a highly critical current but do not showing obvious IJEs.     

Fabrication and Properties of Double-Side Tl2Ba2CaCu2O8 Thin Film on CeO2 Buffered Sapphire Substrate

The double-side Tl2Ba2 CaCu2O8 （Tl-2212） superconducting thin films were fabricated on CeO2 buffered sapphire substrates. The reactive magnetron sputtering technique was used to grow CeO2 buffer thin films on sapphire substrates. Making use of the metal cerium as a sputtering source, the depositing rate is much higher compared with the CeO2 target. The Ti-2212 thin films on CeO2 buffered sapphire substrates were fabricated by adc magnetron sputtering and post-annealing process. The x-ray diffraction indicates that the thin film is pure Tl-2212 phase with the e-axis perpendicular to the substrate surfaces, and epitaxially grown on the CeO2 buffered sapphire. The critical transition temperature Tc is around 106K, the critical current density Jc is around 3.5 MA/cm^2 at 77K, and the microwave surface resistance R8 at 77K and 10 CHz of the film is as low as 390μ Ω.     

Superconducting(Li,Fe)OHFeSe Film of High Quality and High Critical Parameters

A superconducting film of(Li_(1-x)Fe_x)OHFeSe is reported for the first time. The thin film exhibits a small in-plane crystal mosaic of 0.22°,in terms of the full width at half maximum of the x-ray rocking curve,and an excellent outof-plane orientation by x-ray φ-scan. Its bulk superconducting transition temperature T_c of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field H_(c2) is estimated to be 79.5 T and 443 T for the magnetic field perpendicular and parallel to the ab plane, respectively.Moreover, a large critical current density J_c of a value over 0.5 MA/cm~2 is achieved at ~20 K. Such a(Li_(1-x)Fe_x) OHFeSe film is therefore not only important to the fundamental research for understanding the high-T_c mechanism, but also promising in the field of high-T_c superconductivity application, especially in high-performance electronic devices and large scientific facilities such as superconducting accelerator.     

Deposition of MgB2 Superconducting Films on Different Metal Substrates

By a method of hybrid physical-chemical vapour deposition （HPCVD） on three metal substrates of stainless steel, copper and niobium, we deposit MgB2 superconducting films over 1 μm thickness. All of them have zero resistance temperatures To（O） 〉 36 K and critical current densities Jc （IOK, OT） 〉106 A/cm^2. Meanwhile, in the bending test, all the MgB2 superconducting films adhere strongly to the metal substrates without peeling off. Therefore, the MgB2 superconducting films supplied by the HPCVD method exhibit preferable electrical, magnetic and mechanical properties, and have potential applications in future.     

First-principles study on superconductive properties of compressive strain-engineered cryogenic superconducting heavy metal lead(Pb)

As one of the main materials in the practical application.of superconductor,lead(Pb)has been used to manufacture superconducting AC power cable,and some weak current fields.With the development of manufacturing,technology,more and more researchers focus on exploring the physical and chemical properties of cryogenic superconducting materials,instead of blindly pursuing the improvement of the superconducting transition temperature(T_c).In this paper,the structural properties and superconducting transition temperature under high pressure of Pb have been studied by first-principles calculations.It has shown that Pb can withstand the compressive strain up to 10%while the lattice structure remains stable,indicated by the calculations of phonon band structures.From 0%to 10%compressive strain,there is neither a band-gap nor changing of the band structure.The.changing of electronic DOS.at the Fermi level leads to a decreasing of T_c.Our calculations show that Pb is a stable elemental metallic superconductor even under high pressure,which explains the reason why it has been used in practical productions.     

超导限流器限流性能的检测

在电网中加入超导限流器是限制电网短路电流的一种新技术。超导限流器的形式很多,不同工作原理的限流器其限漉特性也会有所差异,因此准确测量超导限流器的限流性能对研制超导限流器具有十分重要的意义。文中根据超导限流器的主要性能参数,设计了一套限流性能检测实验装置,该系统设计为三相380V/500A,可以模拟任意一相对地短路故障,能够检测出限流器正常阻抗、故障阻抗、响应时间和恢复时间等限流特性参数。     

The contribution of color-octet current color-octet current toD decays

Bauer and Stech pointed out that inD decaysa ₁ anda ₂ are approximately equal toc ₁ andc ₂ obtained from the renormalization group equation. This means that the non-leading 1/N _c term in the formulation vanishes. Many authors conjecture that there is a cancellation between the 1/N _c term and an extra <λ ^a λ λ ^a > term emerging from the analysis of non-factorizable matrix elements. We employ the hybrid MIT bag model to estimate the cancellation effects and find that the ratio of <λ ^a λ λ ^a > over the 1/N _c term is about ?0.16～?0.24 which is 2～3 times smaller than the value from data fitting.     

光导开关中的感生电流与传导电流

利用数值方法对线性条件下横向光电导开关的感生电流和传导电流进行了计算和比较.结果表明在特定的实验条件下，感生电流才会对输出电脉冲产生较大的影响.分析了超快光电导开关在不同实验条件下传导电流与位移电流对输出电脉冲的影响.根据该结论，给出非线性模式下，光电导开关电脉冲超快上升沿小于载流子以饱和速度在电极间渡越所需时间的现象. 关键词： 光电导开关 传导电流 位移电流     

直流和交流Josephson效应的研究

基于Feynman模型得到的Josephson方程,在求解过程中采取了ρ1=ρ2的假设,但这个假设在数学处理上并不严格。为了得到严格的结果,未进行上述假设,通过解微分方程得到了严格的Josephson方程,结果显示在一定条件下才能得到通常所说的Josephson方程。     

等离子体在任意强度的直流电场中产生电流的过程

通过Fokker-Planck模拟,研究了等离子体在任意强度的直流电场中产生电流的过程以及电子分布函数的演变过程.研究发现,不同强度的电场中等离子体的行为存在着明显的差别.在弱电场中,电流与电场满足Spitzer公式,且电流产生的响应时间约等于撤销电场后电流衰减的弛豫时间;在中等强度的电场中,电子分布函数呈现为静止Maxwell分布和漂移Maxwell分布之和,而且在中等强度或者强直流电场中弛豫时间也将远远大于响应时间.根据电子分布函数的演变规律,推导了一组类似于流体力学方程的公式,这组方程像Spitzer公式一样简便地描述了等离子体中电流与电场的关系,并且对电场强度没有限制.数值模拟显示这组方程比Spitzer公式更适用于等离子体的混合粒子模拟中. 关键词： 等离子体电流 电子分布函数 Fokker-Planck模拟 Spitzer公式     

Railgun current guard plates: active current management andaugmentation

A system of auxiliary conductors designed to reduce current density peaks in railgun rails is described, and the effects on rail current density and projectile force are discussed. Performance comparisons with simple railguns and typical augmented railguns are made. It is shown that the wrap-around design of the guard plates can produce four to eight times the force produced by the usual augmented railgun design, without increasing local peak current densities. The range of performance contained in the factors between four and eight is primarily a function of the complexity of design. The more complex designs involve allowing the guard plates to overhang the rail slightly (intruding into the bore space, similar to rifling in a conventional gun barrel), and the use of separate power supplies for the rail and guard-plate conductors. These added complexities represent unacceptable complications for many applications, but may be justifiable for others     

电压补偿型超导限流器对电流保护的影响

基于电压补偿型超导故障限流器(SFCL)的工作原理,分析了电网故障时由于限流器限流阻抗串入对电流保护的影响.通过重新整定电流保护的动作值,得到了限流器与电流保护配合的解决方法.以一个10kV中性点不接地配电网为例,分别对引入SFCL前后系统三相短路的电流保护进行仿真,验证了该方法的有效性.     

HL80型低纹波系数大电流程控恒流源研制

HL80型大功率恒流源采用闭环实时串联线性调整技术实现输出电流的恒流控制,应用三相交流调压模块调控电源变压器的初级电压,以可编程控制器与触摸屏配合实现图形化的交互式操作界面,采用以太网构成通讯控制网络。当负载在2.0~3.0Ω之间变化且输出电流在20~80 A之间变化时,HL80型恒流源的调整管压降可控制在(8±2)V范围内,输出电流稳定度优于0.12%,纹波系数优于0.11%。样机实现万次拷机实验无故障。     

Application of current algebra and partial conservation of axialvector current to kaon-proton interactions

A soft-pion study using current algebra and the partially conserved axial vector current (PCAC) hypothesis is made of the kaon-proton interaction processKp →Kp2π ⁰. Considering both pions to be soft, the differential rate for the process is normalized to the differential rate of the corresponding process without the pions. Theoretical predictions for the ratio of cross-sections at various kaon momenta are compared with experimental results.