50 kA超导变压器的设计及研制

针对管内铠甲超导导体测试装置的需要,设计并研制了50 kA超导变压器,详细介绍了超导变压器的主要设计参数和主要部件的研制加工.变压器初级线圈及次级线圈均采用NbTi超导股线.初级线圈由单根NbTi股线绕制而成,次级线圈由441根NbTi股线经过多级绞缆而成.为了便于安装和拆卸,接头采用单室低电阻接头方式;为了有效减小接头电阻,采用预压灌锡的方法来制备接头.变压器初级线圈采用LHe浸泡冷却方式,次级线圈及接头采用超临界He迫流冷却方式.整个低温环境由500 W@4.5 K制冷机提供.     

大电流Bi系超导电缆的研制

Bi-Sr-Ca-Cu-O(BSCCO)高温超导体(HTS)很有可能成为一种实际应用的材料.特别是Bi2Sr2CaCu2Oy(Bi-2212)超导线材,除了其T.比Bi2Sr2Ca2Cu3Oy(Bi-2223)以外,很有希望在诸如变压器、超导磁储能(SMES)和粒子加速器等大型功率的应用项目中使用,因为这种材料在低于30K以下的温度有高的钉扎势,并且线材加工容易.在Bi-2212导体的制造过程中,通常采用部分熔融和固化工艺.由于单根Bi-2212线材无论是电流载运能力,还是机械强度,均不能满足大型应用的要求,因此,在Bi-2212线材的大型应用中,线材必须绞缆.     

强磁场(40T)混合磁体中超导线圈的气密性检测

超导线圈作为强磁场混合磁体中,核心部件,其制造过程关系到产品最终的质量和性能。超导线圈的导体在生产制造过程中,以及在最后绕制成形后,经过了多个工艺环节,导体以及导体上氦管的材料、焊缝、形状都相应的产生了变化,基于超导线圈的使用环境以及对线圈中各个焊缝和整体结构的密封性要求,设计适用于大型超导线圈的气密性检测平台。为了达到检测密封性的要求,在对线圈检漏时,使用正压法检漏,通过对系统的标定,最终完成大型线圈的整体密封性检测。     

日本开发出在Nb3Al超导线上快速镀厚铜工艺

日本物质及材料研究机构超导材料研究中心与Hikifune公司共同开发出在km级Nb3Al超导线上快速镀厚铜工艺。与以前包覆轧制的线材相比，在极低温度下电阻可减少4～5倍，作为超导稳定化导体，可耐1000A级的运转电流，且断面可制成圆形，因此有望用于具有大型强磁场超导磁体的加速器和热核炉等多种用途。另外，该技术还可用于超导线以外的领域，如机械复合加工较困难的高强度钢琴线、光纤等需要高效、大量复合高质量铜的产品。[第一段]     

ITER CC导体接头测试装置设计与研制

根据国际热核实验反应堆(ITER)校正场线圈(CC)导体接头低温电阻的测试要求,设计并研制了一套用于超导导体接头的低温测试装置。该装置主要包括10 kA超导变压器、低温测试杜瓦、磁体失超保护系统和数据采集系统等。超导变压器的初级线圈及次级线圈采用LHe浸泡的方式进行冷却。超导变压器初级线圈电流引线采用常规铜电流引线,为增加铜的传热面积,采用编织铜引线代替铜棒引线。初级线圈外接磁体电源,利用电磁感应原理,在次级回路感应出超导导体接头测试所需的电流。已经成功进行了一次CC导体接头的低温实验,接头电阻的测试结果分别为8.4纳欧姆和9.3纳欧姆。     

高温超导薄膜YBa2Cu3O6.5正常态电荷传输特性研究

介绍了50T左右脉冲强磁场的实验技术,诸如脉冲磁体设计、实验探针设计及测量线路设计等.随后,对高温超导薄膜YBa2Cu3O6.5在强磁场中的磁阻进行了实验研究.进而揭示正常态时超导薄膜YBa2Cu3O6.5随温度降低展现由导体向绝缘体的过渡过程.     

强电用超导材料的发展现状与展望

超导材料具有常规材料不具备的零电阻、完全抗磁性等宏观量子现象，是典型的量子材料。在强电应用领域，使用超导材料可以实现常规技术无法实现的超强磁场、大容量储能等诸多颠覆性技术，因此，强电用超导材料制备技术一直是国际高技术竞争前沿。本文通过梳理国内外强电用超导材料及其制备技术的发展现状，系统分析和阐明了包括低温超导材料NbTi、Nb3Sn和高温超导材料YBCO涂层导体、Bi-2223带材、Bi-2212线材以及MgB2线材等实用化超导材料在强电应用领域的发展趋势。分析我国强电用超导材料发展存在的问题，我国需要以开发出面向不同强电应用需求的高性能超导材料体系为基础，实现超导材料和强电应用产品的协同发展，推动强电用超导材料制备技术和应用技术的创新水平提升和产业化规模。研究建议，通过国家层面组织“产学研用”联合攻关，实现低温超导材料产业升级，突破高温超导材料批量化制备关键技术的发展思路，实现强电用超导材料的快速发展和应用。     

金属与粉末冶金

<正>欧盟研制超导铜材料近日,欧洲铜研究所(European Copper Institute)宣布,来自17个公司和大学的代表签署了330万欧元的资金合同,将通过欧盟的第7科技框架计划(FP7)开发超导铜材料。上述联盟成员将为该项目研究另外提供170万欧元的赞助。超导铜材料由含量超过99%的铜和不超过1%的纳米碳组成,在室温下,其导电性是纯铜的2倍。科学家们认为,把铜与高性能的纳米材料结合可以显着提高能源输送系统的性能。铜纳米碳复合材料可能成为下一代导体,其中铜提供导     

40-T混合磁体外超导线圈迫流氦流动摩擦系数分析

40-T混合磁体外超导磁体使用4.5 K超临界氦进行迫流冷却。迫流氦在管内电缆导体(CICC)内的流动过程受到摩擦阻力的影响会造成一定的压降和热量产生,同时由外界带来的热量也会由迫流氦带走来让磁体保持在超导温区。使用了超导磁体实际运行过程中的实验数据计算不同导体结构下雷诺数与摩擦系数的变化关系,利用Katheder经验公式对实验的摩擦系数进行了重新拟合,给出了适用于该导体摩擦系数的经验公式。     

新一代有线电视CATV电缆用材料的发展动向

认为有线电视ＣＡＴＶ电缆的发展正向第四代物理高发泡ＰＥ绝缘材料过渡。介绍了包ＣＡＴＶ电缆参数的计算公式。指出导电材料开始从纯铜线向铜包钢线，铝镁合金线的发展，是新一代ＣＡＴＶ电缆的革命性转变。     

Test results and analyses of conductor short samples for HT-7U

The experiments of Cable-in conduit conductor (CICC) short samples with high proportion of segregated copper strands have been carried out in SULTAN facility last September. These experiments aimed to investigate transient stability and AC losses of CICC conductor coated with different resistive barriers (Pb–30Sn–2Sb or Ni plating on strands) and to check the design of PF and TF CICC for HT-7U magnets. The resistive barriers’ influences on the stability and AC losses of CICC are evaluated. These experimental results are used for the choice of HT-7U TF and PF CICC design.     

HT-7U超导磁体导体摩擦系数的测定

HT－7U超导托卡马克的纵场磁体（TF）和极向场磁体（PF）都将采用3.8K超临界氦迫流冷却的CICC（Cable in Conduit Conductor）。描述了HT－7U超导托卡马克CICC的摩擦阻力实验。实验采用常温的氮气作工质，雷诺数Re范围达到300－6000。利用Katheder经验公式对实验的摩擦阻力系数进行了重新拟合，它与经验公式的计算结果存在一定的误差。给出了适于测试导体摩擦阻力系数的经验公式，以及导体在工作状态下的摩擦阻力损失。     

Simulation of quench for the cable-in-conduit-conductor in HT-7U superconducting Tokamak magnets using porous medium model

A cable-in-conduit-conductor (CICC) consists of superconducting cable, copper, supercritical helium and conduit. To keep the operating temperature of superconducting cable lower than its current sharing temperature, the supercritical helium is forced flow through the CICC. The supercritical helium through the cable bundle has the complex directional changes due to the interaction between the supercritical helium and strands. The structure of CICC is characterized with the porous medium. The quench characteristics of CICC are analyzed by the model which the temperature difference between the strands and helium is assumed to be very small due to the heating induced flow to generate high heat transfer coefficient of supercritical helium. A moving mesh method is developed for the numerical solution of the problem with the steep drop for temperature and density of supercritical helium in the short front region of the normal zone. The computational mesh is obtained by equidistribution of a monitor function tailored for the functional variation of the arguments for density, temperature and velocity of supercritical helium. Existence and uniqueness of the discretised equations using a moving mesh are also established. The coupled equation for porous medium is solved using the finite element method with the artificial viscosity term. The validation of the code is tested by comparing it with the other codes with good accuracy. The converged properties of numerical solution due to quench in CICC are studied. We present preliminary estimates of the maximum conductor temperature rise and helium pressure during a quench in the inner layer of toroidal field (TF) magnet for HT-7U. The quench scenarios with different dump time constants of 6.25, 12, and 21.1 s are considered. The goal of such work is to guide the protection scheme and a detailed prediction of the quench evolution of magnet.     

氦制冷机的效率

随着超导技术发展和广泛应用,它对低温系统的容量要求也越来越庞大。对于大型超导磁体系统的氦制冷系统,其效率直接影响大型超导装置的运行费用。论述了影响氦制冷机效率的各种因素,并指出了提高制冷机效率的各种基本途径。     

Effect of Temperature on Hydraulic Parameters of Cable-In-Conduit-Conductor of SST-1

Stable operation of superconducting magnets depend critically on the balance of heat deposition rate versus heat extraction rate by the cryo-coolant. Thus, the mass flow rate of the coolant in case of force-flow cooled superconducting magnet with Cable-In-Co-nduit-Conductor (CICC) construction becomes an important factor for optimum stability of magnets. The Toroidal and Poloidal Field magnets of Steady-state Superconducting Tokamak-1 (SST-1) is made of superconducting CICC with a void fraction of 40 %±2 %. For adequate cooling of magnets, supercritical helium at 4 bar and 4.5 K is forced-flown through the voids. Effect of temperature on mass flow rate and pressure drop in SST-1 CICC is studied in a 7 m long piece wound helically. The experimental friction factor of the CICC is also measured at different temperatures and flow rates and is compared with the standard Katheder equation and Tada equation. Also, based on the new findings obtained from the experimental results, the dimensionless Reynolds number has been slightly modified. This new number is used to propose a modified Katheder correlation for the friction factor in CICCs similar to that of SST-1.     

Flux linkage areas of coupling current loops for different shape cable-in-conduit conductor

For large scale application such as fusion magnets, the cable-in-conduit conductor (CICC) is the most promising conductor because of its high mechanical strength under large electromagnetic force. However, there are still remained issues about degradation of critical current of Nb₃Sn conductor and unpredictable AC loss. With regard to the second item, inter-strand coupling current loss is dominant among the AC losses and unpredictable before fabricating large scale conductor. The strand displacements which are caused by the compaction of the conductor in order to increase its current density would cause the loss. In order to do quantitative investigation of the relation between the loss and the strand displacements, we measured strand traces for circular conductor and rectangular conductor. The evaluation of the flux linkage areas which are driving forces of the coupling current indicated that the flux linkage areas have strong dependence on the changing magnetic field only for the rectangular one. It also indicated that the loss should be large when the field is applied from the direction which is perpendicular to the wide surface of the conduit.     

Design,development and fabrication of indigenous 30 kA NbTi CICC for fusion relevant superconducting magnet

The fusion relevant superconducting magnet is under development in India using a cable-in-conduit-conductor (CICC) with operating current of 30 kA at 5.5 T and 4.5 K. The 30 kA NbTi based CICC is designed on the basis of desired critical design parameters as well as mechanical fabrication considerations. The 30 kA CICC has been designed having square cross-section (30 mm × 30 mm) consisting NbTi as superconducting cable, SS316LN as jacket material and SS304 foil as wrapping around the cabled strands. The design configuration of 30 kA NbTi CICC has been discussed in this paper. The NbTi base high current carrying strands have been fabricated indigenously using direct extrusion and cold drawing process. The 100 m long NbTi–Cu strands twisting, insertion of cabled strands into a circular conduit has been developed with pull through technology. The welding process qualification and effects of cold work on jacket material at room temperature have been elaborated in this paper. The manufacturing parameters and quality procedures for development of CICC have been successfully established and demonstrated with fabrication of 100 m NbTi based CICC without any technical difficulties.     

A review of thermal-hydraulic issues in ITER cable-in-conduit conductors

Problems related to cable-in-conduit conductors (CICC) are intrinsically multi-physics involving coupled electro-magnetic/mechanical/thermal-hydraulic fields. Here we concentrate on the thermal-hydraulic issues because, although the CICC was first proposed for the low-T_C superconducting coils of the International Thermonuclear Experimental Reactor (ITER) many years ago, CICC thermal-hydraulics alone is less understood than could be expected. Some of the difficulties are due to the multi-channel nature of the ITER CICC, where strands containing the superconducting filaments are twisted in multi-stage sub-bundles (petals) delimited by wrappings and concentrated in an annular (porous-medium like) region, while a central channel, delimited by a spiral, provides lower hydraulic impedance and pressure relief to the flow of the supercritical helium coolant. Other difficulties are related to the multi-scale nature of this problem, with length scales relevant for thermal-hydraulics ranging from the strand diameter (<∼10⁻³ m), to the CICC length in a coil (up to several 10² m). On the other hand, taking advantage of this length-scale separation, the models presently used for CICC simulations are typically 1D (along the conductor) but they need constitutive relations (like friction and heat transfer coefficients) for the transverse mass, momentum and energy transport processes occurring between different conductor elements. The database for the transverse transport coefficients, unfortunately, does not appear complete, or free of internal contradictions, often because the smallness of the transverse scales makes even an experimental assessment of these processes difficult. Here we discuss these issues and possible strategies for overcoming some of the difficulties are proposed.     

Electro-mechanical modeling of Nb3Sn CICC performance degradation due to strand bending and inter-filament current transfer

Performance degradation of Nb₃Sn cable-in-conduit conductors (CICCs) is a critical issue in large-scale magnet design such as the International Thermonuclear Experimental Reactor (ITER) and the series-connected hybrid (SCH) magnets currently under development at the National High Magnetic Field Laboratory (NHMFL). Not only the critical current is significantly lower than expectations but also the voltage-current characteristic is observed to have a much broader transition from a single strand to a CICC cable. The variation of conductor voltage-current characteristic as a result of cable electromagnetic, mechanical and thermal interactions is challenging to model. In this paper, we use a new numerical model, called the Florida electro-mechanical cable model (FEMCAM) benchmarked against 40 different conductor tests, to study the influence of bending strain and current non-uniformity on the critical current and n-value of Nb₃Sn strands and CICC cables. The new model combines thermal bending effects during cool-down, electromagnetic bending effects during magnet operation and current transfer in strands with filament fracture. The n-value of a strand under bending is derived from integration of filament critical current over strand cross-section for full and no current transfer. The cable n-value is obtained from the power law relation of cable electric field and critical current curve. By comparing numerical results with measurements of advanced Nb₃Sn strands and various CICC cables, we demonstrate that FEMCAM is self-consistent in modeling inter-filament current transfer. The new model predicts that I_c degradation of bent strands initially follows closely full current transfer but starts deviating and falls between full and no current transfer with an increasing bending strain. The results agree with recent TARSIS measurements for less than 1% bending strain mostly interested in practice. The strand n-value degradation from FEMCAM with no filament current transfer agrees better with measurements than that from full current transfer. Finally, FEMCAM simulated cable n-values are compared with various CICC measurements. The results imply that FEMCAM is a useful tool for the design of Nb₃Sn-based CICCs and both thermal bending and electromagnetic bending play important roles in CICC performance.