高温超导带材临界电流角度依赖性测量分析

第二代高温超导带材与第一代相比,有着载流能力强、交流损耗低、无需贵金属等优点,在超导电力应用中有广阔前景。高温超导带材临界电流在外磁场的影响下会发生衰减,超导带材临界电流的角度依赖性是超导电力装备设计必不可少的参数。实验选取温度50～77 K、磁场0～3.5 T、磁场角度0～360°区间,分别测量了上海超导、苏州新材料等厂家生产的市面主流第二代高温超导带材的临界电流,分析了不同背景磁场大小及角度下超导带材的各向异性。结果表明,各厂家生产的超导带材具有明显的各向异性。     

电镀铜对YBCO超导带材临界电流影响的研究

钇系超导带材(YBCO)由于载流能力强、不可逆场高,是近年来高温超导材料领域的研究热点,并在电力行业实现示范应用。YBCO超导带材由基底、缓冲层、超导层和保护层组成,可通过电镀铜工艺实现保护层的制备。目前,有关电镀铜对YBCO超导带材临界电流的影响还鲜有报道。因此,本研究对比了镀铜前后YBCO超导带材的表面形貌和临界电流。实验结果表明:电镀铜在提高带材机械强度的同时,对其超导电性并无明显影响。     

临界电流密度对场冷超导磁悬浮力的影响研究

基于Kim临界态模型,通过考虑超导块材内部屏蔽电流的穿透历史过程,讨论了场冷条件下临界电流密度对高温超导悬浮系统磁悬浮排斥力和吸引力的影响.结果显示:最大超导磁悬浮排斥力和吸引力均随临界电流密度的增加呈指数关系增加,并趋于饱和;场冷条件下的磁悬浮力回滞能量损耗远高于零场冷情况;存在一个磁悬浮力比率κ,κ值对于评价大电流...     

Processing of thallium-based superconducting tapes for high current density

Optimum thermomechanical processing conditions have been developed to achieve a high current density in powder-in-tube (PIT) thallium-based (Tl,Pb)-1223 and (Tl,Bi)-1223 tapes. Critical currents in excess of 25 A corresponding to a current density of 20 000 A/cm² have been achieved in these tapes at 77 K. Heat treatment and intermediate deformation sequences, heating rates, and starting precursor phase assemblages have been examined to optimize the current density. A combination of processing conditions that result in incremental densification, less microcracking and liquid formation in the early and final stages of thermomechanical treatment is found to result in the highest current densities.     

YBCO高温超导带材大电流冲击特性实验研究

随着第二代高温超导带材的性能不断提高和商业化供应,基于YBCO材料的超导电力技术应用研究也在逐步向多领域深入进行。超导带材的大电流冲击性能对于超导电缆的短路电流冲击耐受能力、电阻型限流器的限流性能等有着直接的影响。以不锈钢加强型超导带材样品为研究对象进行了实验研究,并对常压液氮浸没环境中,不同冲击时长、不同冲击电压条件大电流冲击过程中温升、冷却时长等特性开展了实验研究,总结了温升与冲击时长、冷却时间的关系和规律。实验是以超导限流器用超导带材为研究对象进行的。超导带材在故障电流下的发热量及其散热结构设计将成为超导电缆、超导限流器等超导电力装置设计成功与否的关键。     

Improvement of the critical current density of Ag-sheathed (Bi,Pb)2223 superconducting tapes by tension rolling

Monocore Ag-sheathed (Bi,Pb)₂Sr₂Ca₂Cu₃O_x tapes were prepared by the oxide-powder-in-tube method. The effects of tension during intermediate rolling between sinterings have been investigated. It has been revealed that the critical current density J_c is higher when the front and back tensions are applied simultaneously than when only one of them is applied. The excessive tension deteriorates the J_c. The optimum level of tension has been found to be ∼5 MPa. The application of tension suppresses the sausaging of silver/oxide core interface, improves the grain alignment of oxide core and results in higher J_c.     

Oscillations of the superconducting critical current in Nb-Cu-Ni-Cu-Nb junctions

We report on experimental studies of superconductor-ferromagnet layered structures. Strong oscillations of the critical supercurrent were observed with the thickness variation of the ferromagnet. Using known microscopic parameters of Ni, we found reasonable agreement between the period of oscillations and the decay of the measured critical current, and theoretical calculations.     

MgB2 coated superconducting tapes with high critical current densities fabricated by hybrid physical-chemical vapor deposition

The MgB₂ coated superconducting tapes have been fabricated on textured Cu (0 0 1) and polycrystalline Hastelloy tapes using coated conductor technique, which has been developed for the second generation high temperature superconducting wires. The MgB₂/Cu tapes were fabricated over a wide temperature range of 460-520 °C by using hybrid physical-chemical vapor deposition (HPCVD) technique. The tapes exhibited the critical temperatures (T_c) ranging between 36 and 38 K with superconducting transition width (ΔT_c) of about 0.3-0.6 K. The highest critical current density (J_c) of 1.34 × 10⁵ A/cm² at 5 K under 3 T is obtained for the MgB₂/Cu tape grown at 460 °C. To further improve the flux pinning property of MgB₂ tapes, SiC is coated as an impurity layer on the Cu tape. In contrast to pure MgB₂/Cu tapes, the MgB₂ on SiC-coated Cu tapes exhibited opposite trend in the dependence of J_c with growth temperature. The improved flux pinning by the additional defects created by SiC-impurity layer along with the MgB₂ grain boundaries lead to strong improvement in J_c for the MgB₂/SiC/Cu tapes. The MgB₂/Hastelloy superconducting tapes fabricated at a temperature of 520 °C showed the critical temperatures ranging between 38.5 and 39.6 K. We obtained much higher J_c values over the wide field range for MgB₂/Hastelloy tapes than the previously reported data on other metallic substrates, such as Cu, SS, and Nb. The J_c values of J_c(20 K, 0 T) ∼5.8 × 10⁶ A/cm² and J_c(20 K, 1.5 T) ∼2.4 × 10⁵ A/cm² is obtained for the 2-μm-thick MgB₂/Hastelloy tape. This paper will review the merits of coated conductor approach along with the HPCVD technique to fabricate MgB₂ conductors with high T_c and J_c values which are useful for large scale applications.     

Superconductivity in mesoscopic high-Tc superconducting particles

Based on the Hubbard model in the framework of non-phonon kinematical mechanism and taking into account the discreetness of an electronic energy spectrum, the superconducting critical temperature of a mesoscopic high-T_c sphere is analyzed as a function of doping and as a function of particle's radius. The critical temperature T_c is found to be an oscillating function of the radius of a particle. The size-dependent doping regime is revealed in high-T_c nanoparticles. Our analysis shows that each oscillation in T_c corresponds to the increase in a number of the energy levels in the sphere by 1. The amplitude of oscillations of T_c increases with decreasing R and can reach a value of 6 K for nanoparticles with sizes about 25 nm, in good agreement with experimental studies of YBa₂Cu₃O_7−δ nanoparticles.     

Bandwidth tunable high-Tc superconducting filter

We have developed a high-T_c superconducting band-pass filter, whose center frequency and bandwidth can be tuned independently, with steep attenuation at both lower and higher band edges. This tunable filter is composed of two different types of band-pass filters, one with steep attenuation at the lower band edge and the other with steep attenuation at the higher band edge. Two filters are connected in series and each filter is covered with additional dielectric plates, respectively. The tuning characteristics of the entire filter can be controlled by adjusting the distances between the dielectric plates and the substrate. The entire filter was fabricated monolithically on a 30-mm-wide and 60-mm-long LaAlO₃ substrate. A center frequency of 1.93 GHz, a 3 dB bandwidth of 20 MHz, and an attenuation of 30 dB, 1.0 MHz apart from both band edges, were obtained for the entire filter. Then, a sapphire plate was set above each of two filters, and a center frequency tuning of 10 MHz and a bandwidth tuning of 5 MHz were obtained by adjusting the distances between the substrate and the sapphire plates.     

Role of processing in improving the critical current of Ag/BPSCCO tapes

Silver-clad tapes of highT _c Bi-Pb-Sr-Ca-Cu-O superconductors have been fabricated through the powder-in-tube method. The critical current density, J _c , of a thick tape was 534 A.cm⁻² (77 K, 0 T). Subsequent rolling and sintering of the tapes led to a gradual decrease inJ _c, instead of the expected increase. This was caused by the microcracks developed in the core material by a rather drastic reduction during the rolling of the tapes. A modified and well controlled rolling technique, on the other hand, resulted in much improvedJ _c values. Repeated rolling and sintering resulted in a good grain alignment and no microcracks were observed. In the present studies, maximumJ _c of 1846 A.cm⁻² (77 K, 0 T) and 2.43 × 10⁴ A.cm⁻² (4.2 K, 0 T) have been obtained Optimization of the processing and sintering parameters are expected to lead to still higherJ _c values.     

Quantum oscillations of the critical current of asymmetric superconducting rings

The current-voltage characteristics and the magnetic field dependences of the critical current have been measured for symmetric and asymmetric superconducting rings and systems of such rings. The dependences obtained explain the periodic change in the rectified voltage observed on asymmetric rings as a result of a periodic change in the asymmetry of current-voltage characteristics.     

扭转应变与高温超导带材临界电流分布关系研究

为加工大电流导体和制备高温超导电缆,有必要掌握高温超导带材在扭转下性能。该文研究了扭转下高温超导一代铋锶钙铜氧(BSCCO)和二代钇钡铜氧(YBCO)带材临界电流的分布与扭转应变之间的关系,用四线法在液氮、自场环境下测量了不同扭距下带材临界电流,分析比较了三种不同带材(日本住友HT-CA;AMSC8501;Super Power SCS4050)临界电流随扭距变化规律的异同,建立了计算扭转下带材内部应变的模型,推导出了扭转下三种不同带材临界电流密度与应变之间的函数关系。此外,将实验测得的临界电流与通过模型理论计算得到的数值进行了比较和分析。     

超导变压器绕组带材抗短路冲击特性研究

为了研究超导变压器绕组带材的抗短路冲击的能力,制备了四组实验样品,用以模拟超导变压器原、副边绕组的运行环境,实验研究了超导带材并联不锈钢带材的抗短路冲击特性。实验结果表明,超导带材并联不锈钢带材后的抗短路冲击能力有明显的提升,这对超导变压器的研发与制作具有重要的应用参考价值。     

Spectroscopic studies of the high-Tc superconducting cuprate perovskites

We present XRD, ESR, IR, DR(UV, VIS) as well as resistivity and magnetic susceptibility data of single phase superconducting perovskites YBa₂Cu₃O_x and EuBa₂Cu₃O_x. A rich phonon structure for both oxide compounds has been observed with a peak at: 72, 108, 135, 148, 172, 570 and 620 cm^-1. The edge of the low energy side was observed at 55 cm^-1. The estimated carrier density for YBa₂Cu₃O_x is (1–2) × 10²¹ cm^-3. A weak ESR signal has also been observed for superconducting phases which is associated with the lattice defects.We also report ESR and optical measurements of constitutent materials as well as not superconducting phases Y₂Cu₂O₅ and BaCuO₂.