Design of TE_(01δ) Test Probe for Measuring the Microwave Surface Resistance of HTS Thin Film

A new TEo1δ test probe with proper transmission factor is fabricated for the measurement of surface resistance of high temperature superconductor （HTS） thin film. Coupling holes instead of coupling loops are used in the probe for its easier machining and relatively low loss. Two 6 mm × 3 mm × 8 mm dielectric waveguides, one side of them is coated by silver, are used for coupling. The measurement result of S21 agrees well with the simulation because the size of the probe can be rigidly controlled by machine. The microwave surface resistance of four YBCO/MgO films are measured at 77 K and 12 GHz and scaled to 10 GHz according to thef2 rule. The average surface resistance of four HTS thin fdms is 0.38 mΩ, the standard deviation and relative standard deviation of one single HTS thin film are 0.009 mΩ and 2.4%, respectively.     

Superconducting Electronics Research at CSIRO Australia ——20 Years after Discovery of HTS

CSIRO has had a long-term research effort in superconductivity, in particular, since the discovery of HTS which promised big prospects. Significant progress has been made in research and development of HTS electronic devices and systems for practical applications such as mineral and exploration as well as some niche applications in emerging science and technology areas. This article presents an overview of the CSIRO research activities in HTS supercon- ducting electronics since 1987, outlining the HTS junction and device technology as well as various application systems developed by the group.     

Superconducting Electronics Research at CSIRO Australia-20 Years after Discovery of HTS

CSIRO has had a long-term research effort in superconductivity, in particular, since the discovery of HTS which promised big prospects. Significant progress has been made in research and development of HTS electronic devices and systems for practical applications such as mineral and exploration as well as some niche applications in emerging science and technology areas. This article presents an overview of the CSIRO research activities in HTS superconducting electronics since 1987, outlining the HTS junction and device technology as well as various application systems develop by the group.     

Improvement in Superconducting Properties of MgB2 Superconductors by Nanoscale Carbon-Based Compound Doping

MgB2 is a relatively new superconductor; it has attracted great interest from superconductor researchers all over the world. Thorough investigations have been carried out to study the material fabrication, as well as to study the material and superconducting properties from a fundamental physics point of view. The University of Wollongong has played a very active role in this research and a leading role in the research on high critical current density and high critical magnetic fields. Our recent research on the improvement of critical current density and the upper critical magnetic field by carbon-based compound doping is reviewed in this paper.     

Thermal anchoring of conduction-cooled current leads for superconductivity applications near liquid nitrogen temperature

As the YBa₂Cu₃O_7-δ, or YBCO, superconductor is commercially developed and utilized for various HTS (high temperature superconductor) applications such as motor, generator, and fault current limiter, the cryocooling for 50 or 60 K range is more demanded than ever. In this case, non-superconducting current leads instead of HTS ones need to be used for energization from room temperature all the way to the cryogenic operating temperature. This technical note describes a simple method of reducing cooling load requirement for those HTS applications. Non-superconducting current leads are to be thermally anchored at an appropriate intermediate cryogenic temperature before they are connected to the application target temperature. The optimum thermal-anchoring temperature and its configuration have been obtained to minimize the required cryocooler’s cooling capacity for practical as well as ideal cases.     

不同热处理制度对NbTiTa超导线材性能的影响

通过调整超导线材的最终附加应变、时效热处理时间和时效热处理温度3个参数来提高NbTiTa超导线材的J_c性能.在法国国家高场实验室通过标准四引线法,在4.2K、0～11T的磁场中测量了线材的临界电流.结果表明,适度升高时效热处理温度、延长时效热处理时间、增加最终附加应变,有益于提高NbTiTa超导线材的临界电流密度.经4次时效热处理385~C×(40～70)h,最终附加应变从2.5增加到3.5,Φ1.25mm超导线材的J_c在4.2K、8T下达到777A/nm~2,与国外文献报道的J_c值相当.     

CFD investigating the effects of different operating conditions on the performance and the characteristics of a high-temperature PEMFC

The effects of different operating conditions on the performance and the characteristics of a high-temperature proton exchange membrane fuel cell (PEMFC) are investigated using a three-dimensional (3-D) computational fluid dynamics (CFD) fuel-cell model. This model consists of the thermal-hydraulic equations and the electrochemical equations. Different operating conditions studied in this paper include the inlet gas temperature, system pressure, and inlet gas flow rate, respectively. Corresponding experiments are also carried out to assess the accuracy of this CFD model. Under the different operating conditions, the PEMFC performance curves predicted by the model correspond well with the experimentally measured ones. The performance of PEMFC is improved as the increase in the inlet temperature, system pressure or flow rate, which is precisely captured by the CFD fuel cell model. In addition, the concentration polarization caused by the insufficient supply of fuel gas can be also simulated as the high-temperature PEMFC is operated at the higher current density. Based on the calculation results, the localized thermal-hydraulic characteristics within a PEMFC can be reasonably captured. These characteristics include the fuel gas distribution, temperature variation, liquid water saturation distribution, and membrane conductivity, etc.     

Effects of Sr/Ca ratio and CuO content of the superconducting phases in the Bi-Pb-Sr-Ca-Cu-O system

The Bi-Pb-Sr-Ca-Cu-O superconductor was prepared by the three-step reaction process; the effects of Sr/Ca ratio and CuO content on the formation of the superconducting phases were studied. The Sr-short and Cu-rich nominal compositions are not advantageous for the formation of the 2223 phase but we are favored for the formation of the 2201 phase. The differences among the previous reports on the effect of composition on the formation of the superconducting phase is discussed. The best J _c value of the Ag-sheathed tape filled with the kind of powder is 13,000 A/cm² (77 K, OT).     

新型镍基抗热腐蚀长寿命定向凝固高温合金的显微组织

本文对一种新型镍基抗热腐蚀长寿命定向凝固合金的显微组织进行了研究，对铸态及热处理态各组成相的分布和形态作了分析说明．     

Current distribution in parallel-connected YBCO high-temperature superconducting elements with different critical currents

A high-temperature superconductor is investigated for application to a fault-current limiter. However, the current-carrying capacity of a single element is too low for practical use. This parallel connection of superconducting elements is required to increase the current capacity. This paper discusses an ac current distribution between two YBa₂Cu₃O_7-x superconducting elements connected in parallel that differ in electrical aspects such as a critical current level and voltage-current characteristic. As the instantaneous value of the current rises from zero to peak, the following processes are observed: (1) the transition from superconducting to normal conducting state is initiated in the element with the smaller critical current; (2) the current value in the element is kept constant until the other element with the larger critical current level becomes normal conducting state; and (3) only when the instantaneous value of the ac current exceeds the summation of the individual critical current values of each element does the voltage across parallel-connected elements appear. These results are caused by the quick recovery characteristic of YBCO superconductors from the normal conducting state to the superconducting state.