Abstract: A superconducting power cable having: a former including: an axially stretchable core, and a plurality of elongated outer elements wound helically around the core, wherein the core includes a first material and the elongated outer elements include a second material thermally contracting less than the first material at the operating temperature of the superconducting power cable; and a superconducting conductor layer arranged around the former.

Abstract: To provide a superconducting magnet apparatus with a structure which can prevent an increase in apparatus size even when a number of connection portions serving to connect superconducting wires is great. The superconducting magnet apparatus includes a first wiring-holding portion (tubular body (12)) extending from a bobbin (6) in an axial direction of a superconducting coil (1) and a second wiring-holding portion (joint plate (13)) which is provided on a same side in the axial direction as the tubular body (12), extends in a direction intersecting with the axial direction, and has a greater diameter than that of the bobbin (6) and the tubular body (12). Superconducting wires (7a to 11a) which extend from the superconducting coil (1) and connect to one another are spirally wound on the tubular body (12) and fastened to a groove (13a) formed on the joint plate (13).

Abstract: In the production of an internal-tin-processed Nb3Sn superconducting wire, the present invention provides a Nb3Sn superconducting wire that is abundant in functionality, such as, the promotion of formation of a Nb3Sn layer, the mechanical strength of the superconducting filament (and an increase in interface resistance), the higher critical temperature (magnetic field), and the grain size reduction, and a method for producing it. A method for producing a Nb3Sn superconducting wire according to an embodiment of the present invention includes a step of providing a bar 10 that has a Sn insertion hole 12 provided in a central portion of the bar 10 and a plurality of Nb insertion holes 14 provided discretely along an outer peripheral surface of the Sn insertion hole 12, and that has an alloy composition being Cu-xZn-yM (x: 0.

Abstract: The present invention is configured such that, in a low AC loss oxide superconductor constituted by providing an oxide superconducting layer 6 on a substrate 1, said oxide superconducting layer 6 is separated into a plurality of filament conductors 2 in parallel to the lengthwise direction of said substrate 1 by dividing grooves 3 plurally formed in the widthwise direction of said substrate, and a high-resistance oxide 8 is formed in said dividing grooves 3. Because of the invention, it is possible to increase the insulation properties of individually divided mated filament conductors, and to obtain an oxide superconductor that has low AC loss.

Abstract: An induction heating apparatus that can operate at current frequencies of greater than 60 Hz and at least 1 kW. The induction heating apparatus includes a high frequency power supply, a superconductive induction coil, and a fluid cooling system. A fluid cooling system is designed to cause a cooling fluid to flow at least partially about and/or through the superconductive induction coil.

Abstract: High-current, compact, flexible conductors containing high temperature superconducting (HTS) tapes and methods for making the same are described. The HTS tapes are arranged into a stack, a plurality of stacks are arranged to form a superstructure, and the superstructure is twisted about the cable axis to obtain a HTS cable. The HTS cables of the invention can be utilized in numerous applications such as cables employed to generate magnetic fields for degaussing and high current electric power transmission or distribution applications.

Abstract: A termination for a superconductive cable (1) is provided, consisting of a pressure-tight metal inner container (2) in which there is a liquid refrigerant and into which the cable protrudes, and a metal outer container (3) which is separated from the inner container by an intermediate space (4) in which vacuum insulation is applied. A first rupture diaphragm (6) is applied in the wall of the inner container (2) and a second rupture diaphragm (7) is applied in the wall of the outer container (3) level with the first rupture diaphragm (6). An evacuated relief space (8), which contains superinsulation and is sealed from the intermediate space (4) with the vacuum insulation by a pressure-tight wall (9), is provided between the two rupture diaphragms (6, 7).

Abstract: A precursor for fabricating a Nb3Sn superconducting wire by an internal Sn process includes one or a plurality of stabilizing copper portions collectively disposed in the center, each stabilizing copper portion being provided with a diffusion barrier layer in the periphery thereof, and a superconducting matrix portion disposed so as to surround the one or the plurality of stabilizing copper portions, the superconducting matrix portion including a Nb or Nb-based alloy core and a Sn or Sn-based alloy core embedded in a Cu or Cu-based alloy matrix.

Abstract: Tape-shaped superconducting wires, and a superconducting coil formed from said wires, wherein a plurality of electrically separated superconducting film parts, each having a rectangular cross section and arranged in parallel, form parallel conductors, providing superconducting wires capable of containing losses incurred in the presence of alternating current (A/C). A superconducting coil is made by winding the superconducting wires, wherein the coil structure contains at least a part wherein perpendicular interlinkage magnetic fluxes acting among conductor elements of the parallel conductors by the distribution of magnetic fields generated by the superconducting coils cancel mutually in order to contain circulating current within the wires and to make shunt current uniform, thereby providing a low-loss A/C superconducting coil.

Abstract: A precursor for manufacturing a Nb3Sn superconducting wire according to the present invention includes a mono-element wire including a Sn or Sn-based alloy core disposed at the, a Cu or Cu-based alloy matrix and a plurality of Nb or Nb-based alloy filaments surrounding the Sn or Sn-based alloy core, and a diffusion barrier layer and a stabilizing copper layer surrounding the Cu or Cu-based alloy matrix. In a final shape after a reduction process, the average diameter of the Nb or Nb-based alloy filaments is set to 5 ?m to 30 ?m, and the average distance between the Sn or Sn-based alloy core and the Nb or Nb-based alloy filaments nearest the Sn or Sn-based alloy core is set to 100 ?m or less.

Abstract: Tape-shaped superconducting wires, and a superconducting coil formed from said wires, wherein a plurality of electrically separated superconducting film parts, each having a rectangular cross section and arranged in parallel, form parallel conductors, providing superconducting wires capable of containing losses incurred in the presence of alternating current (A/C). A superconducting coil is made by winding the superconducting wires, wherein the coil structure contains at least a part wherein perpendicular interlinkage magnetic fluxes acting among conductor elements of the parallel conductors by the distribution of magnetic fields generated by the superconducting coils cancel mutually in order to contain circulating current within the wires and to make shunt current uniform, thereby providing a low-loss A/C superconducting coil.

Abstract: A method for forming improved superconducting composites having improved Jc values by assembling octagonal or curved octagonal elements which when assembled allow for formation of uniformly continuously spaced voids. The voids are then filled with a metal, alloy, intermetallic substance, or ceramic oxide. The assembly of the octagonal elements and the filling of the voids is performed in a metal can. Accordingly, the flexibility in design of the present invention allows control of the performance of the superconductor and is cost effective.

Abstract: A composite conductor suitable as a connecting conductor that includes a superconductor and is capable of reducing the generation of Joule heat in a joint part between the system side and power-supply sides of a superconductor apparatus. A composite conductor 10 includes a superconductor 12 provided continuously in the flowing direction of the electric current, and a metal conductor 11 joined with the superconductor 12 and provided at least at a joint part with mating conductors 50, 60 to be joined, wherein the electric current is fed and received between the metal conductor 11 and the mating conductors 50, 60 by joining the metal conductor 11 and the mating conductors 50, 60, and wherein the superconductor 12 is arranged in the metal conductor 11 so as to be approximately parallel to the joint surface (joint interface) between the metal conductor 11 and the mating conductors 50,60.

Abstract: The present invention provides a terminal structure of a superconducting cable including a cable core having a superconducting shield layer and an electrical insulation layer. The superconducting shield layer has a radially outer portion provided with by a connection electrode and the superconducting shield layer and the connection electrode are connected together with a low melting solder. The connection electrode has a ground wire connected thereto to ground the superconducting shield layer. For a multiphase cable including a plurality of cable cores, connection electrodes are linked by a conductive coupling member to short circuit superconducting shield layers. The superconducting shield layer can be grounded without impaired insulating property of the electrical insulation layer.

Abstract: Superconducting cable (1) comprising: a) a layer (20) of tapes comprising superconducting material, b) a tubular element (6) for supporting said layer (20) of tapes comprising superconducting material, c) a cooling circuit, adapted to cool the superconducting material to a working temperature not higher than its critical temperature, characterized in that said tubular element (6) is composite and comprises a predetermined amount of a first material having a first thermal expansion coefficient and a second material having a thermal expansion coefficient higher than that of said first material, said thermal expansion coefficients and said amounts of said first and second material being predetermined in such a way that said tubular element has an overall thermal shrinkage between the room temperature and said working temperature of the cable such as to cause a deformation of said tapes comprising superconducting material lower than the critical deformation of the same tapes.

Abstract: In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

Abstract: Superconducting cables, wires and methods of making the same are disclosed. The cables can offer improved flexibility while maintaining a high current carrying capacity. Advantageously, the superconducting filaments of the cables can be formed from relatively brittle materials having comparatively high critical temperatures and/or comparatively high critical magnetic fields. Magnet systems can be formed using these cables without using the conventional “react-then-wind” method.

Abstract: An aspected multifilamentary oxide article is provided having a plurality of aspected filaments including a metal oxide and extending continuously for the length of the article. A constraining member substantially surrounds each filament, wherein each of the filaments has an average transverse cross-sectional thickness less than about 35 &mgr;m and an average variation in cross-section along its length of less than about 10%. The article exhibits superior filament uniformity, hardness, and oxide density and texture.

Abstract: A low-aspect ratio multi-filament superconductor wire includes a plurality of oxide superconductor filaments arranged in an elongated wire structure. Each filament of the wire also has a low-aspect ratio. The filaments are textured such that a crystallographic c direction of each filament is aligned with a crystallographic c direction of all other filaments with the crystallographic c directions being perpendicular to the longitudinal axis of the wire structure. The invention also features a groove rolling machine for forming a low-aspect ratio multi-filament superconductor wire by texturing a precursor tape by deforming the tape to a low-aspect ratio wire by reducing a larger dimension of the tape in such a way as to prevent buckling of the tape. A superconducting cable can be formed by planetary winding a plurality of multi-filament superconductor wires.

Abstract: An oxide superconducting stranded wire having inter-strand insulation and high critical current is provided. A wire including an oxide superconducting material and a matrix covering the material and consisting essentially of silver or a silver alloy is coated with a paint containing, as a main component, an organometallic polymer such as a silicone polymer or aluminum primary phosphorus in a paint reservoir, and the paint is baked in a baking furnace via a drying furnace. A plurality of such wires with the baked paint are twined into a stranded wire, which is then heated up to a temperature necessary for sintering the oxide superconducting material. The stranded wire thus obtained through the step of sintering may have high critical current. A heat-resisting insulating coating layer may be formed by baking the paint.

Abstract: A tube made of oxygen free copper is filled with a plurality of copper matrix Nb—Ti superconducting lead wires to obtain a composite billet. The resulting billet is subjected to hydrostatic pressure extrusion. Further, ageing heat treatment and wire drawing process are repeated for the composite material three times to prepare a Cu/Nb—Ti superconducting single wire. Then, the resulting Cu/Nb—Ti superconducting single wires are stranded each other to produce a superconducting strand. The superconducting strand is coated with an aluminum alloy to which either a content of 20 to 100 ppm of Cu and Mg or Mg, or a content of 10 to 120 ppm of Si and Cu is added by means of hot extrusion, the strand thus extruded is reduced by 0 to 20% in accordance with cold working to produce an aluminum stabilized superconductor.

Abstract: Provided is an oxide superconducting conductor consisting of a plurality of metal-covered multifilamentary superconducting wires which are assembled with each other. Bending is applied to the superconducting conductor for improving its critical current density. It is possible to obtain a compact superconducting conductor having higher capacity, since its critical current density is increased by such application of bending.

Abstract: Structure for joining together metal-coated multi-core oxide superconductor wire material parts in a tape shape. The C axis of a oxide superconductor crystal is substantially oriented along the longitudinal (length) direction that the wire material extends. The end faces of the wire material parts contact each other at the joint part; and the C face of the oxide superconductor crystal is continuously oriented at the joint part.

Abstract: An a.c. cable has at least one cable core (15) with two concentric conductor arrangements (8, 9) used as forward and return conductors. At least one of the conductor arrangements (8, 9) contains a plurality of conductor layers (L.sub.j and L.sub.j ') made of stranded normally conducting or superconducting individual conductors (3). The individual conductors preferably feature high-T.sub.c superconducting materials. The wire angles (.alpha..sub.j, .alpha..sub.j ') in the individual conductor layers (L.sub.j and L.sub.j ') should be selected so as to minimize losses. A calculation formula for the wire angles (.alpha..sub.j, .alpha..sub.j ') is given for this purpose.

Abstract: An Nb.sub.3 Al multi-filamentary superconducting wire capable of realizing both stabilization of a superconducting state and increase in capacity is provided. The Nb.sub.3 Al multi-filamentary superconducting wire includes a core formed of copper or copper alloy and located at the center of the wire; a multi-filamentary superconductor layer located around the core and having filaments containing Nb and Al as constituent elements embedded in a matrix formed of copper or copper alloy; and a high resistance layer located around the multi-filamentary superconductor layer, and is characterized in that a sectional area of the core is at least 15% of the total sectional area of the core and the matrix and that the core and the matrix are formed of copper or copper alloy of at least 99.9% purity.

Abstract: In application to a superconducting magnet which is cooled by a cryogenic refrigerator, provided is a superconducting coil which can maintain a cooled state and enables a stable operation and continuous driving even if a ramping speed is increased. First and second superconducting conductors are connected with each other. Respective tape-like superconducting multifilamentary wires are electrically connected with each other through solder, to form joint bodies. The respective joint bodies are insulated from each other by interposition of an insulating material therebetween.

Abstract: A superconductor wire comprising a plurality of Nb--Ti superconductor filaments embedded in a copper matrix made of a copper alloy other than a two element copper alloy selected from the group consisting of a Cu--Ni alloy, a Cu--Sn alloy and a Cu--Mn alloy, wherein the resistivity (Z) at room temperature of the copper matrix is 2.times.10.sup.-8 .OMEGA.m to 65.times.10.sup.-8 .OMEGA.m, and the distance between superconductor filaments is not less than 0.0625.times.1/.sqroot.Z nm. The superconductor wire has a high critical current density, a small AC loss and improved workability.

Abstract: Carbonaceous materials based on the fullerene molecules have been developed which allow for superconductivity. The fullerene materials are soluble in common solvents.

Abstract: A superconducting wire saved in weight and enhanced in mechanical properties is provided without damaging electric and thermal characteristics as an Al stabilizer, and further a method for producing the same, a high strength Al sintered alloy and powders used for the process are provided. A superconducting wire comprising an Al alloy of a high purity Al in which a small amount of ceramic ultrafine particles are dispersed and superconducting filaments embedded in the Al alloy, in which a large number of the ceramic ultrafine particles are dispersed in the area of 1 .mu.m.sup.2, and the areas of 1 .mu.m.sup.2 in which a large number of the ceramic ultrafine particles are dispersed, are formed over nearly the whole of the alloy.

Abstract: A non-superconductive Ag-based sheath formed surrounding a superconducting tape or wire is stripped by placing a Bi- or Pb-based metal material on the Ag-based sheath to be removed; and then heating the Bi- or pb-based metal material to 250.degree. C.-450.degree. C. to dissolve the Ag-based sheath; and removing the dissolved Ag-based sheath.

Abstract: A superconductive conductor protected against partial transitions, the conductor comprising a superconductive region made up of superconductive filaments embedded in a non-superconductive metal matrix, and a non-superconductive metal region, wherein the cold resistivity of the non-superconductive metal region is less than half the overall cold resistivity of the superconductive region in the non-superconductive state, the superconductive region and the non-superconductive metal region being merely in mechanical contact, without cohesion.

Abstract: A superconducting magnet coil is produced by winding a superconducting wire to form a coil; impregnating the coil with a curable resin composition of low viscosity which contains for example at least one epoxy resin selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F and diglycidyl ether of bisphenol AF, all having a number-average molecular weight of 350-1,000, a flexibilizer and a curing catalyst, to obtain a curable-resin composition-impregnated coil; and heating the curable-resin-composition-impregnated coil to cure the composition.

Abstract: A housing is arranged outside a superconducting wire body to enclose it at a predetermined gap. A solder layer and/or a space are formed as a stress relaxation layer between the superconducting wire body and the housing. The gap between a surface of the superconducting wire body, to which a load acts in a direction perpendicular to the longitudinal direction of the superconducting wire body, and a housing material layer, is set to at least 0.25 mm at each side. Alternatively, a solder layer is formed to leave a space between a surface of the superconducting wire body, to which the above load mainly acts, and the housing material layer.

Abstract: An electrical lead having one end for connection to an apparatus in a cryogenic environment and the other end for connection to an apparatus outside the cryogenic environment. The electrical lead includes a high temperature superconductor wire and an electrically conductive material distributed therein, where the conductive material is present at the one end of the lead at a concentration in the range of from 0 to about 3% by volume, and at the other end of the lead at a concentration of less than about 20% by volume. Various embodiments are shown for groups of high temperature superconductor wires and sheaths.

Abstract: A superconducting magnet coil contains a coil of superconducting wire and a cured product of a curable resin composition with which the coil has been impregnated, the cured product having a thermal shrinkage factor of 1.5-0.3%, preferably 1.0-0.3%, when cooled from the glass transition temperature to 4.2K, a bend-breaking strain of 2.9-3.9%, preferably 3.2-3.9%, at 4.2K and a modulus of 500-1,000 kg/mm.sup.2 at 4.2K, or undergoing a thermal stress of 0-10 kg/mm.sup.2 when cooled from the glass transition temperature to 4.2K and resisting to quench during superconducting operation.

Abstract: A superconducting article has a matrix core containing a superconductor, a copper stabilizer layer disposed about the core, and an insulating layer surrounding the copper stabilizer layer. The insulating layer is a metallurgically bonded layer of a refractory metal selected from Nb, Ta, V, and Mo.

Abstract: A multifilamentary oxide superconducting wire includes a metal matrix and a plurality of flat oxide superconductor filaments arranged in the metal matrix such that wide directions thereof are radially arranged in a section of the metal matrix. A method of manufacturing a multifilamentary oxide superconducting wire includes the steps of filling a raw material of an oxide superconductor in a through hole of a metal member to form a composite billet, subjecting the composite billet to a diameter reduction process to form a composite wire having a fan-like section, arranging composite wires so that larger arcs of the composite wires are located on the outer side, thus forming form a composite wire arrangement, covering the composite wire arrangement with a metal member to form a metal-covered composite wire arrangement, and performing a predetermined heating process of the metal-covered composite wire arrangement, thus forming the raw material into an oxide superconductor.

Abstract: A strain tolerant multifilamentary wire capable of carrying superconducting currents is provided comprising a plurality of discontinuous filaments formed from a high temperature superconducting material. The discontinuous filaments have a length at least several orders of magnitude greater than the filament diameter and are sufficiently strong while in an amorphous state to withstand compaction. A normal metal is interposed between and binds the discontinuous filaments to form a normal metal matrix capable of withstanding heat treatment for converting the filaments to a superconducting state. The geometry of the filaments within the normal metal matrix provides substantial filament-to-filament overlap, and the normal metal is sufficiently thin to allow supercurrent transfer between the overlapped discontinuous filaments but is also sufficiently thick to provide strain relief to the filaments.

Abstract: Apparatus and method for forming long lengths of laminated superconducting tape by passing three foils over idler pulleys, through a solder bath and between pinch rollers having a portion which extend above the solder bath to enable cleaning of the pinch rollers during the formation of the superconducting tape with means to adjust the pressure applied by the pinch rollers, and to adjust the laminated tape takeup tension independently from the foil process tension.

Abstract: A vapor cooled current lead for a superconducting device located in a cryostat includes a normal conductor section extending from ambient conditions inward to an intermediate point, and a composite lead having a ceramic high temperature superconductor core with a metallic sheath extending between the normal conductor section and the superconducting device, preferably in a helical path to reduce heat leak by conduction. The metallic sheath is stripped away at spaced intervals, preferably adjacent the low temperature end of the composite lead, and the gaps are filled with a filler which provides mechanical strength for the core and reduces thermal conduction. A flow of cryogen vapor directed by a tubular housing maintains the high temperature superconducting material below its critical temperature, and cools the normal conductors.

Abstract: A superconducting conductor, having an excellent repeated temperature property with no reduction of critical current density against a temperature cycle, comprises an oxide superconductor and an fiber reinforced plastic ("FRP"), serving as a support member, which is composed with the oxide superconductor for integrally moving with the oxide superconductor in thermal expansion and thermal shrinkage. The oxide superconductor is bonded to the FRP with an adhesive agent, or wound on and fixed to the same with a Teflon tape or the like.

Abstract: A pseudo rod, fabricated from several plate sections joined together at their edges and having a cross-section resembling a polygon approximates a rod having a circular cross section. Using multiple plates joined at their edges permits growing a crystalline material on the planar faced substrates and if the plates are crystalline material, the crystalline material grown thereon can have improved current carrying capability.

Abstract: A superconducting wire is formed by twisting a bundle of a plurality of superconducting material filaments in which one material filament is arranged in a central portion of the filament bundle and a plurality of other material filaments arranged outside the central material filament so as to surround the central one. The filament bundle is twisted in that the central material filament is substituted with another one of outer material filaments one by one in order periodically during a twisting process along an axial direction of the filament bundle.

Abstract: A strain tolerant microfilamentary wire capable of carrying superconducting currents is provided comprising a plurality of discontinuous filaments formed from a high temperature superconducting material. The discontinuous filaments have a length at least several orders of magnitude greater than the filament diameter and are sufficiently strong while in an amorphous state to withstand compaction. A normal metal is interposed between and binds the discontinuous filaments to form a normal metal matrix capable of withstanding heat treatment for converting the filaments to a superconducting state. The geometry of the filaments within the normal metal matrix provides substantial filament-to-filament overlap, and the normal metal is sufficiently thin to allow supercurrent transfer between the overlapped discontinuous filaments but is also sufficiently thick to provide strain relief to the filaments.

Abstract: A superconductive transmission line is formed of mixed metallic oxide ceramic material, particularly Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-x drawn epitaxially upon a substrate. The superconductive material has basal crystallographic planes in alignment with copper oxide of the ceramic material. The planes are parallel to the substrate. The transmission line is constructed of a plurality of electrically conductive elements, each of which is formed of the superconductive material. The conductive elements are arranged with the crystalline planes parallel to an axis of the transmission line, along which axis power is to flow. Thereby, magnetic fields induced by currents flowing in the conductive elements intersect the conductive elements perpendicularly to the basal crystallographic planes to maximize the current which can flow while retaining linearity between magnetization and applied magnetic field.

Abstract: An electrical conductor particularly suited for use as a downlead to low temperature devices includes a ceramic honeycomb body having longitudinal channels wherein films of substantially single crystals of a ceramic superconductor are grown. The maximum current carrying capacity of the ceramic superconductor may be oriented parallel to the channels. Square channels arranged in alternating rows of oppositely directed current provide desirable magnetic field cancellations and permit high current flows. A method for making the electrical conductor and a method of extruding the ceramic honeycomb body are also disclosed.

Abstract: A process for producing a niobium-tin superconductor wire made from a multifilament composite via the internal tin approach is provided for. In particular, a process of preparing such a wire via an internal tin tube surrounded by a diffusion barrier and a stabilizer, this results in a drawn wire product have improved properties and lower cost.

Abstract: A superconductor protected against partial transition includes superconductor strands around at least one non-superconductor central strand or at least one non-superconductor central core electrically insulated from the superconductor strands. At least at both ends of the superconductor, the central strand or said central core is electrically connected to the superconductor strand. The central strand or the central core comprises at least one non-superconductor metal filament whose resistivity at 4.2.degree. K. is less than 10.sup.-9 .OMEGA..m embedded in a metal alloy matrix whose resistivity at that temperature is greater than 10.sup.-8 .OMEGA..m.

Abstract: A method of producing an oxide superconducting wire. A non-oxidizing metal layer is formed between an oxide superconducting material and an oxidizing metal support in order to prevent oxygen from being taken away from the oxide superconducting material by the oxidizing metal support during a subsequent heat treatment for producing an oxide superconductor to thereby obtaining a wire composite. The wire composite is then heated to produce the oxide superconductor.

Abstract: An improved transmission system for electrical energy comprising a plurality of ball members interspersed by mating members enclosed within at least one protective outer wrapping, with the ball members and the mating members being in contact with adjacent members and being formed of material which is electrically conductive at superconductor temperatures and each having an axial opening extending therethrough to permits passage of a suitable coolant fluid, such as liquid helium.