The Magnetic Moment of a Superconducting Ball in a Axisymmetric Magnetic Field

Journal of Superconductivity and Novel Magnetism - The magnetic moment of a spherical superconductor that is located on the axis of the external axisymmetric magnetic field is found. It is proved...     

The Resistance of a Superconducting BSCCO-2223 Ag-Sheathed Tape as a Function of Temperature, Current, and Magnetic Field

The electrical transport of a superconducting BSCCO-2223 Ag-sheathed tape is studied as a function of temperature T, current I, and magnetic field H. In a range of current and field, covering two orders of magnitude, the resistance R(T) is described by R = R _o exp{–b[(T _m –T)/(T –T _o )]^0.5}, where T _o and T _m are the limits of the non-ohmic and field dependent behavior. The threshold T _o is a decreasing function of I and H, whereas T _m depends only on H. The isothermal R(I) and the R(H) trends confirm the previous function, suggesting that, within the examined ranges, the dissipation may be attributed to a process in which the temperature has a prevalent role, whereas I and H change the limits of the process. The experimental data are consistent with a process in which the dynamics of thermally generated vortices is current and field controlled.     

Steady States of Current Carrying Layered Superconducting Film

The model of heat production by the transport current flowing in a layered superconducting film with nonlinear resistivity is proposed. It reflects the main features of the quasi-two-dimensional behavior of the system. The steady states of the superconductor and stability of the superconducting state are investigated within the framework of the model. Diagrams of the steady states of a layered superconductor are presented. The velocity of the resistive zone motion as a fuction of the transport current is calculated for superconductors with different anisotropy.     

Fatigue of a Reinforced High Temperature Superconducting Tape

High‐cycle fatigue‐life behavior of commercial multifilamentary BSCCO 2223 powder‐in‐tube tape and reinforced tape was evaluated. Mechanical fatigue at room temperature and 77 K, and the onset of significant superconductivity degradation at 77 K were evaluated under tension perpendicular to the flat faces of the tapes. No fatigue behavior was observed in this transverse configuration for unreinforced tape, but fatigue–life behavior associated with delamination of the reinforcement was found for reinforced tape. Fatigue tolerance of the reinforced tape is very high, about 24 MPa, to at least 100.000 cycles.     

Non-linear Flux Flow Resistance of Type-II Superconducting Films

We analyze the flux-flow (FF) regime in type-II superconducting films exhibiting quite strong pinning. By driving the vortex lattice (VL) up to high dissipative states, the moving VL undergoes an instability, leading to an abrupt change from the FF to the normal state, which is displayed in the current-voltage characteristics as a voltage jump at a critical vortex velocity v ^?. The temperature and magnetic field dependence of v ^? is investigated in different materials, and an unpredicted low field behavior of v ^?(B) is found. Moreover, for velocities lower than v ^?, a non-linear FF resistance is observed, with a ??peak?? in the current dependence of the dynamic resistance. This is a remarkable feature of a dynamic transition from disordered to ordered VL occurring in the FF state. We suggest that both unusual effects observed in v ^?(B) and R _FF(I) can be accounted for intrinsic pinning.     

Microwave Transmission and Reflection for a Type-II Superconducting Superlattice in the Mixed State

The microwave reflection and transmission for a type-II superconducting superlattice in the mixed state are theoretically calculated based on the vortex dynamical model together with the transfer matrix method in a layered medium. The superlattice is made of alternating layers of high-temperature superconductors and dielectric materials. We analyze the microwave reflection and transmission as functions of the static magnetic field, the number of periods, and the thickness of the dielectric layer. It is shown that the reflection decreases as the static field increases. In addition, the reflection will be enhanced by increasing the number of periods.     

Driving Mechanism of a Superconducting Magnetic Bearing System

Driving the rotor of a superconducting magnetic bearing without mechanical contact in the optimum conditions is an important task for high operational speeds. For this reason, an alternative eddy current mechanism is proposed to drive the rotor by means of magnetism with a speed higher than that of the driver. The designed driving system provides strong and stable magnetic coupling between the relatively rotating parts. The drag and lift forces between the rotor and driver disc are discussed by considering various conditions, such as the rotor configurations and the saturation of the magnetic field within the conducting material. The overall results indicate that the designed electromechanical driving system has potential solutions for the various applications for magnetic bearings from the effective driving mechanism point of view.     

Thickness-Dependent Current Density and Flux Distribution in Thin Current-Carrying Superconducting Films Exposed to a Magnetic Field

With the rapid development of high-temperature superconductors, it is of great significance to get the precise current density and flux distribution within thin high-temperature superconducting films subjected to a transport current and an applied magnetic field. The transport current distribution and flux density in thin high-temperature superconducting films are calculated by a numerical method based on the Kim model and exponential model in this paper. The influences of transport current, applied magnetic field, width, and thickness of a superconducting film on the current distribution are discussed. The results reveal that the thickness has a significant effect on the critical current density of superconducting films.     

Testing of a 5.5 T High-Gradient Superconducting Magnetic Separator

A 5.5 T central field high-gradient superconducting magnetic separator (HGMS) has been designed, fabricated, and tested at the Institute of High Energy Physics, Chinese Academy of Sciences. It has been developed for processing kaolin, to increase the brightness or whiteness whether it is for paper or ceramic applications. The HGMS system mainly consists of an NbTi superconducting magnet, a double-canister system, and a PLC (Process Logic Controller) control system. The solenoid magnet, with operating current of 148 A, has a clear bore of 300 mm. By using a G-M cryocooler (35 W/50 K, 1.5 W/4.2 K), the results of the experiment show that the HGMS system can be run in zero boil-off regimes without any additional cooling. A pressure control system for the helium vessel can accurately respond to variations of pressure above the pressure outside the vessel. The system will process kaolin slurry at typically 0.6～2.5 cm/s, resulting in a production rate of approximately 80～120 tones per day (dry basis). The operation is fully automatic, with a simple system for adjusting the process parameters. The HGMS magnet suffered no quench and operated stably during many experiments since January 2012. The details of the design, fabrication, and performance results of the HGMS are presented in this paper.     

A New Technique for the Determination of the Critical Current Density in Superconducting Films and Flat Samples

The determination of their critical current density in the whole range of the temperature below T _c is of first importance to understand the physical processes occurring in superconducting films. We describe here a technique suitable for square films based on the measurement of the magnetic moment due to the currents persisting in the superconductor after the application of a perpendicular high magnetic field. Typically, with a SQUID magnetometer, the measurement time in the whole range of temperature with a 1 K interval is of 2 hours only by this technique. An intriguing aspect of the obtained results is that they are much more accurate if the current lines are supposed to be circular than if we suppose, as suggested by theoretical considerations and magnetooptical observations that they have the sample symmetry.     

A New Technique for the Determination of the Critical Current Density in Superconducting Films and Flat Samples

The determination of their critical current density in the whole range of the temperature below T _c is of first importance to understand the physical processes occurring in superconducting films. We describe here a technique suitable for square films based on the measurement of the magnetic moment due to the currents persisting in the superconductor after the application of a perpendicular high magnetic field. Typically, with a 1 K interval between two measurements, using a SQUID magnetometer the measurement time is of 2 hours only by this technique. An intriguing aspect of the obtained results is that they are much more accurate if the current lines are supposed to be circular than if we suppose, as suggested by theoretical considerations and magnetooptical observations that they have the sample symmetry.     

Influence of Critical Current Density Distribution on Transport AC Losses in Superconducting Wire in a DC Magnetic Field

In typical application-like conditions, the inhomogeneous distribution and anisotropy of critical current density must be considered simultaneously in transport AC loss calculation. In this paper, we derive the analytical formulas of transport AC losses for high-temperature superconductors (HTSs) with linear and quadratic distribution of critical current density under applied DC magnetic field. The influence of the inhomogeneous distribution and anisotropy of critical current density has been analyzed. The results show that the impact of the distribution form on transport AC loss is more obvious under applied DC magnetic field. And the influence of applied DC magnetic field will increase as the distribution form becomes steeper.     

Development of a Thin Film Magnetic Moment Reference Material

In this paper we present the development of a magnetic moment reference material for low moment magnetic samples. We first conducted an inter-laboratory comparison to determine the most useful sample dimensions and magnetic properties for common instruments such as vibrating sample magnetometers (VSM), SQUIDs, and alternating gradient field magnetometers. The samples were fabricated and then measured using a vibrating sample magnetometer. Their magnetic moments were calibrated by tracing back to the NIST YIG sphere, SRM 2853.     

基于超导磁场环境真空测量电离规磁屏蔽结构仿真研究

聚变装置超导磁场环境下真空测量电离规因灯丝变形、带电粒子轨迹变化等物理机制导致真空测量精度不高,不能满足工程精确测量的需求。基于磁屏蔽的理论,构建了半封闭式和开放式的两种多层磁屏蔽结构模型,利用Maxwell有限元软件,仿真研究了结构材料层不同厚度和不同磁场方向等条件下磁屏蔽效能的变化规律。结果表明,屏蔽效能随铁层材料径向厚度的增加而增大,铁层材料端部厚度对其影响较小;超导材料层厚度对屏蔽效能影响较小;磁场方向角在0°~90°范围内,屏蔽效能先减后增,并在90°(屏蔽结构轴向与磁场方向平行)时达到最大值。为电离规在复杂磁场应用条件下的屏蔽结构工程设计提供了依据。     

利用废旧PET生产扁丝的设备设计

目的设计利用废旧PET生产扁丝的专用设备,以解决PET扁丝生产过程中断丝情况严重,无法正常连续生产的难题。方法通过分析扁丝生产的工艺过程,合理划分生产线工位,并对其设备进行机械结构设计,验证其合理性。结果制得的PET扁丝有较好的韧性、拉伸性能,断裂强度达50 MPa以上,可应用于生产高性能的编织袋和集装袋。结论其专用设备组成的生产线可实现PET扁丝的连续化生产。废旧PET的利用既降低了生产成本,提高了经济效益,又充分利用了资源,同时也有利于环境保护。     

Angular Dependence of Transport AC Losses in Superconducting Wire with Position-Dependent Critical Current Density in a DC Magnetic Field

Transport AC losses play a very important role in high temperature superconductors (HTSs), which usually carry AC transport current under applied magnetic field in typical application-like conditions. In this paper, we propose the analytical formula for transport AC losses in HTS wire by considering critical current density of both inhomogeneous and anisotropic field dependent. The angular dependence of critical current density is described by effective mass theory, and the HTS wire has inhomogeneous distribution cross-section of critical current density. We calculate the angular dependence of normalized AC losses under different DC applied magnetic fields. The numerical results of this formula agree well with the experiment data and are better than the results of Norris formula. This analytical formula can explain the deviation of experimental transport current losses from the Norris formula and apply to calculate transport AC losses in realistic practical condition.     

Thermal Release of Hidden Magnetic Moments in High T c Bi:2223/Ag Superconducting Tape During Warming to T c

We report on measurements of the evolution of the magnetization ??M??, upon warming from T ₀ (77?K) to T _c , for Bi:2223/Ag tape prepared by the continuous filling and forming (CTFF) with the locus of ??M?? initially situated along bridges between the envelopes of the major hysteresis curves. Concentric, oppositely directed magnetic moments coexist in the specimens when ??M?? lies along the bridges. We focused on the cases where ??M??=0, hence before warming, the constituent moments cancel each other exactly. Since they diminish in magnitude at different rates as T is increased to T _c , their sequential ??release?? leads to a rich variety of phenomena. A comparison of experimental and theoretical results shows that our simple model semiquantitatively reproduces the major features of the observations on the specimen of Bi:2223/Ag tape.     

Levitation Force Between a Point Magnetic Dipole and Superconducting Sphere

The magnetic interaction between a point dipole and a superconducting sphere in the Meissner state is investigated in detail. It is demonstrated that the special case of perfect flux exclusion can be solved by the method of images when the dipole is vertically magnetized. The incorporation of a nonzero penetration depth is then made by developing the solution within London theory. The analytic solution, given in terms of an infinite series representation, is refined by exactly summing the perfectly diamagnetic response. Throughout, special cases of physical interest are discussed and applications to magnetic force microscopy and levitation are described.