US Navy programme in small cryocoolers

If superconducting and cryogenic electronic instrumentation are to be deployed in future US Naval operational systems, there is a strong need for compact, highly reliable cryogenic refrigerators. Accordingly, several years ago, a programme was initiated to develop fractional-watt cryocoolers capable of operating below 10 K. Several varieties of Stirling coolers have been built and are under evaluation. In addition, helium gas compressors designed for use with small, closed cycle Joule- Thomson coolers are under development. An overview of the technical aspects of the programme are presented.     

Superconducting electrical motorsMoteurs électriques supraconducteurs

Superconductors have always been very promising materials because they offer the possibility of building lighter and more efficient electrical machines than by any other conventional solution. These characteristics make superconducting motors very attractive drives for embarked equipment with low weight requirements. The historical development of superconducting machines is quickly reviewed. The high critical temperature superconductors have renewed the works about superconducting machines. Different motor options are presented (fully superconducting machine and permanent magnet superconducting motor). For each, the choice of the superconductor (low or high critical temperature) is discussed, according to their performance and technological problems, especially about cryogenics. The different solutions are compared through a preliminary electromagnetic design for a 10 MW–100 rpm torque motor. We carry out a research and development program on the permanent magnet superconducting motors. After a first 15 kW–750 rpm successfully tested model a second 150 kW–400 rpm demonstrator is under development.     

Cryogen-Free Superconducting and Hybrid Magnets

The first practical cryogen-free superconducting magnets using a GM-cryocooler and high temperature superconducting current leads have been demonstrated successfully at the High Field Laboratory for Superconducting Materials (HFLSM). Easy-to-operate cryogen-free 10–15 T superconducting magnets have been used to provide access for new research areas in fields of magneto-science. The HFLSM has started construction projects for new high field cryogen-free superconducting and hybrid magnets.     

Superconducting Applications: Present and Future

I examine present and future applications of superconductors. The host of requirements that must be satisfied for a successful commercial application are described and discussed briefly. The substantial role of materials in applications, the large number of requirements on successful commercial superconducting wire, and the trends in superconducting material development are discussed.     

组成对Bi系微晶玻璃超导纤维性能的影响

用熔体快速淬冷法制备了数种Ｂｉ（Ｐｂ）ＳｒＣａＣｕＯ玻璃，进而用动态加热荷重法将这些玻璃拉成纤维。用Ｘ射线衍射、差热分析、电子探针和能谱及电流测量、拉丝试验等手段研究了玻璃成分变化对成丝能力和晶化后超导性能的影响。结果表明，Ｓｒ、Ｃａ含量的变化不仅对超导性能，而且对玻璃成丝能力有很大影响。获得的超导纤维的最大长度为５３ｃｍ，在７７Ｋ和零磁场下超导短纤维的最高电流密度Ｊｃ＝１５Ａ／ｃｍ＾２。     

Electronic Structure of New Superconducting Perovskite MgCNi3

The electronic structures of new superconducting perovskite MgCNi3 and related compounds MgCNi2T (T=Co, Fe, and Cu) have been studied using MS-Xa method. In MgCNi3, the main peak of density of states is located below the Fermi level and dominated by Ni d. From the results of total energy calculations, it was found that the number of Ni valence electron decreases faster for the Fe-doped case than that for the Co-doped case. The valence state of Ni changes from +1.43 in MgCNi2Co to +3.02 in MgCNi2Fe. It was confirmed that Co and Fe dopants in MgCNi3 behave as a source of d-band holes and the suppression of superconductivity occurs faster for the Fe-doped case than that for the Co-doped case. In order to explain the fact that Co and Fe dopants in MgCNi3 behave as a source of d-band holes rather than magnetic scattering centers that quench superconductivity, we have also investigated the effects of electron (Cu) doping on the superconductivity and found that both electron (Cu) doping and hole (Co, Fe) dopin     

Polaron Coherence as Origin of the Pseudogap Phase in High Temperature Superconducting Cuprates

Within a two-component approach to high T _c copper oxides including polaronic couplings, we identify the pseudogap phase as the onset of polaron ordering. This ordering persists in the superconducting phase. A huge isotope effect on the pseudogap onset temperature T ^* is predicted and in agreement with experimental data. The anomalous temperature dependence of the mean square copper–oxygen ion displacement observed above, at and below T _c , stems from an s-wave superconducting component of the order parameter, whereas a pure d-wave order parameter alone can be excluded.     

Superconducting state in M3C60: Strong vs. weak coupling

The superconducting state in the doped fullerenes is due to strong coupling (e.g.,2.1 for Rb₃C₆₀) to low-frequency intramolecular modes _L 250 cm^–1 (^21/2). The analysis is based on an equation describingT _c for any strength of the coupling and on recent isotope effect and NMR data.     

Preparation and Superconducting Properties of F-doped SmO_(1-x)F_xFeAs

Here we report the fabrication and superconductivity of the iron-based arsenic oxide SmO1-xFxFeAs compound.X-ray diffraction(XRD) results prove that the lattice parameters a and c decrease systematically with increasing x in between 00.35 the a and c increase with the decrease of x in the SmO1-xFxFeAs.The critical temperature(Tc) increases with increasing x in between 0.15≤x≤0.3,while x>0.3 the Tc decreases with the increase of x.It is found that at x=0.3 SmO0.7F0.3FeAs has the highest onset resistivity transition temperature of 55.5 K.The critical current density(Jc) value at 10 K for the obtained SmO0.7F0.3FeAs is 1.3×10 5 A/cm2(0T).Meanwhile one can estimates Hc2(0) from the slope of the Hc2(T) curve at T =Tc(HC2 is the upper critical field),and for the 90% normal-state resistivity(ρn) criterion(Tc=55 K),Hc2(0) is determined to be ～253 T.     

二硼化镁超导线带材及磁体应用研究进展

由于具有超导转变温度（39K）较高,晶体结构简单,原材料成本低廉以及长线制备容易等一系列特点,金属间化合物二硼化镁（ MgB2）超导体自2001年被日本科学家发现以来,引起人们广泛的关注,被认为是目前最有可能首先实现大规模工业应用的超导材料。尤其在制冷机工作温度（15～20 K）、较低磁场（1～2 T）条件下的医疗核磁共振成像仪（ MRI）超导磁体应用上有着广泛的前景。本文主要围绕实用化 MgB2超导长线（带）制备研究而展开,重点回顾了近年来粉末套管法、连续粉末装管成型法及中心镁扩散法等MgB2超导线（带）材制备及加工方面的最新研究进展;同时综述了在 MgB2超导线带材工程临界电流密度性能改进方面的最新研究工作;最后,对近几年来 MgB2超导磁体及线圈等应用研究进展进行了回顾。     

Cryogenic magnetometer research at Twente University of Technology

In 1982 we started the project ‘Cryogenic Magnetometers’ with the aim to develop SQUID-magnetometers appropriate to a large variety of applications. The first system we developed is a SQUID-magnetometer with an open-ended horizontal access at room temperature. The measuring space inside the pick-up coils is easy accessible and the magnetization (remanent or induced) can be measured of materials in a static position or transported through the access.Further, systems have been developed with the pick-up coil set outside the cryostat, in order to arrive at a flexible system with which the object under investigation can be approached as close as possible. Another part of the project is the optimization of magnetometers with respect to the cryogenic system in order to develop cryogenic magnetometer systems with a very long time between helium refills. The present status of these three research subjects is briefly described.     

Cryogenic heat pipe for cooling high temperature superconductors

The research in this paper investigates a consumable-free method of operating a high temperature superconducting (HTS) coil in space. The HTS wire resides inside a cryogenic heat pipe which is used for isothermalization. This paper presents the design, implementation, and testing of a cryogenic heat pipe for cooling high temperature superconductors. As a proof-of-concept, an 86 cm long straight heat pipe was constructed and enclosed two straight lengths of HTS wire. The working fluid, at saturation condition, maintains a constant temperature below the HTS wire critical temperature. Testing of the heat pipe in a vacuum chamber was conducted to verify the drop in HTS resistance correlating to the wire operating in a superconducting state.     

Worldwide cryogenics — Kernforschungszentrum karlsruhe

The Institute for Technical Physics of the Nuclear Research Centre Karlsruhe has devoted its main activity to applications of superconducting magnets. In this article, results of its low temperature research and technical developments are presented.     

Superconducting toroidal combined-function magnet for a compact ion beam cancer therapy gantry

A superconducting, combined-function, 5 T, 90°, toroidal magnet with a large bore is described in this paper. This magnet is designed to be the last and most difficult part of a compact superconducting magnet-based carbon gantry optics for ion beam cancer therapy. The relatively small size of this toroidal magnet allows for a gantry the size of which is smaller or at least comparable to that of a proton gantry. The gantry design places the toroidal magnet between the scanning magnets and the patient, that is the scanning magnets are placed midway through the gantry. By optimizing the coil winding configuration of this magnet, near point-to-parallel optics is achieved between the scanning magnets and the patient; while at the same time there is only a small distortion of the beam-shape when scanning. We show that the origin of the beam-shape distortion is the strong sextupole components, whose effects are greatly pronounced when the beam is widely steered in the magnet. A method to correct such an undesirable effect is suggested and demonstrated by a numerical particle tracking through the calculated three-dimensional magnetic field.