961results about "Superconductors/hyperconductors" patented technology

The invention discloses a method for improving deformation uniformity of a core wire of an NbTi superconducting wire, and belongs to the technical field of superconducting wire processing. The method comprises the following steps: performing deep hole drilling on an oxygen-free copper ingot rod, then assembling, welding and extruding the oxygen-free copper ingot rod and a single-core rod to obtain a composite rod, and performing multi-pass drawing on the composite rod to obtain the NbTi superconducting wire with high performance, low loss and high N value. The Jc of the prepared NbTi superconducting wire is 2880-3120 A / mm < 2 >, the loss is 450-550 mJ / cm < 3 >, the N value is 70-95, compared with a superconducting wire prepared through a conventional process, the N value is remarkably increased, the loss is remarkably reduced, the critical current density is increased, and the NbTi superconducting wire has wide application prospects in MRI magnets.

The invention discloses a self-adaptive anti-sticking cable and a preparation method and application thereof. The self-adaptive anti-sticking cable comprises a superconducting core wire, a self-adaptive anti-sticking layer, a self-repairing insulating layer and a multifunctional outer sheath which are sequentially arranged from inside to outside. According to the scheme, the problems of debonding, breakdown, energy consumption and failure of a traditional cable in an extreme environment are comprehensively solved through gradient piezoelectric-phase change synergistic dynamic stress compensation, vertical boron nitride insulation network directional blocking, thermoelectric-super-hydrophobic multifunctional outer sheath integration and an extreme environment adaptive self-repairing system.

The invention relates to a high-temperature superconducting cable and a manufacturing process thereof, and belongs to the technical field of electric wires and cables.The cable comprises a supporting framework, a buffer layer, a three-phase superconducting composite layer, a shielding layer, a heat insulation layer and a sheath layer which are sequentially arranged from inside to outside; the heat insulation layer comprises at least two layers of corrugated pipes formed by continuous rolling and welding, and the corrugated pipes are of periodic concave-convex structures obtained by conducting continuous rolling and side seam welding on metal strips to form closed pipe bodies and then conducting embossing treatment on the closed pipe bodies. A woven reinforcing layer wrapping the peripheries of the corrugated pipes is further arranged in the heat insulation layer, and the adjacent corrugated pipes are connected through supporting pieces to form a vacuum interlayer. According to the application, the corrugated pipe formed by continuous coiling and welding is combined with the combined structure of the braided reinforcing layer and the supporting piece, so that the continuous production of the large-length high-temperature superconducting cable can be conveniently realized, and the problems of axial stress concentration and seam accumulation defects existing in a heat insulating layer of a traditional prefabricated sleeve pipe can be eliminated; and the air tightness stability of the vacuum interlayer of the large-length high-temperature superconducting cable is ensured.

The invention belongs to the technical field of superconducting wires, and relates to a niobium-tin composite superconducting wire and a preparation method thereof. The invention provides a Nb3Sn composite superconducting wire. The Nb3Sn composite superconducting wire sequentially comprises an Nb3Sn superconducting wire core, a barrier layer, a stable layer, a transition layer, a substrate layer and a functional layer from inside to outside, the transition layer is formed by mixing copper and a dielectric polymer, and the copper content is continuously decreased in a gradient manner from inside to outside; the substrate layer is the dielectric polymer; the functional layer is a plurality of protruding metal microstructures. According to the invention, the functional layer with the broadband electromagnetic stealth function is integrated on the basis of the Nb3Sn superconducting wire rod, so that the radar cross section is obviously reduced while the Nb3Sn superconducting wire rod bears high-density superconducting current and generates a strong magnetic field, and the technical problem that a high-field superconducting magnet system is easy to detect in an electromagnetic environment is solved.

The invention belongs to the technical field of cable processing, and relates to a preparation method and application of a flexible superconducting coaxial cable outer conductor. The preparation method comprises the following steps: mixing Nb powder and Ti powder by adopting a vibrating ball mill to prepare NbTi composite powder; a substrate of laser powder bed melting equipment is preheated, the NbTi composite powder is spread on the substrate of the laser powder bed melting equipment, a melting powder layer is scanned through the laser powder bed melting technology, a three-dimensional communicated grid structure is formed through interlayer staggered scanning, finally, the NbTi net-shaped alloy pipe is placed in a strong acid solution to be soaked for a short time, redundant metal powder is removed, and the NbTi net-shaped alloy pipe is obtained. And finally, the preparation of the flexible superconducting coaxial cable outer conductor for the quantum computer is realized.

The invention relates to the technical field of electric wires and cables, and discloses an ultrahigh-conductivity electric wire and cable and a preparation method thereof. A graphene enhancement layer; a nano composite insulating material layer; an inner semi-conductive layer; a conductive copper strip shielding layer; a silver-plated copper wire woven mesh shielding layer; an intelligent monitoring and protection sheath; the method comprises the following steps: step S01, preparing a superconducting core wire strand; step S02, preparing a nano composite insulating material layer; s03, preparing a shielding layer; step S04, intelligent monitoring and protection sheath preparation; the superconducting core wire strand formed by twisting a plurality of YBCO superconducting material filaments forms a stable structure with excellent conductivity under the precise control of twisting process parameters, so that the resistance is effectively reduced, the loss in the electric energy transmission process is reduced, the electric energy transmission efficiency is improved, high-density current can be borne for stable transmission, and the service life of the cable is prolonged. And the requirement of the modern electrical engineering field on high conductivity of wires and cables is met.

The invention provides a method for preparing an iron-based superconducting material single crystal in a microgravity environment, and belongs to the field of superconducting materials. The method specifically comprises the following steps: carrying out a microgravity crystal growth experiment in a high-temperature experiment cabinet of a space station, putting a solid-phase sintered or pre-melted rod-like raw material into a furnace body, heating and melting, then slowly solidifying, and finally growing the iron-based superconducting material single crystal with large size and extremely low defect density.

Provided herein are methods and systems used with a repairable stellarator, including maintaining magnetic coils, such as HTS tape coils, and allowing for deconstruction and reconstruction of one or more components of the repairable stellarator. Further provided herein are methods and systems for a stellarator system which integrates a modular sacrificial coil set.

The invention discloses a dynamic load adjustment-liquid nitrogen cold storage integrated high-temperature superconducting power grid capacity expansion system and method. The system comprises a data preprocessing system, a dynamic load adjustment device, a liquid nitrogen cold storage device, a state monitoring device, a high-temperature superconducting cable capacity expansion device and a communication coordination system. The method comprises the steps of generating a standardized feature matrix through normalization processing; multi-time-scale load prediction is realized through an LSTM (Long Short-Term Memory) network, a collaborative instruction set is generated by adopting an optimal scheduling engine of mixed integer linear programming, and adaptive closed-loop control based on a fuzzy PID (Proportion Integration Differentiation) algorithm is realized; a multi-physics field coupling optimization model of a real-time cold energy distribution diagram is adopted to realize power grid capacity improvement; and the time sequence consistency of the whole system is coordinated and circulation is formed. Zero-resistance power transmission is realized in a liquid nitrogen temperature region by adopting the high-temperature superconducting cable, the loss is reduced to 0.5% or below, and the transmission capacity is improved by 3-5 times; the load demand is predicted in combination with the AI algorithm, and the renewable energy consumption rate is increased to 95%.

The present invention relates to the technical field of superconducting materials. Disclosed are a MgB2 superconducting wire and a preparation method therefor. The preparation method comprises: melting Mg, Cu and Ti to obtain a Mg alloy ingot, processing the Mg alloy ingot to obtain a Mg alloy rod, loading the Mg alloy rod and B powder into a Nb tube to obtain a composite rod, processing the composite rod to obtain a single-core wire, loading the single-core wire into an oxygen-free copper tube, then loading into a monel tube in a densely-packed manner, and performing cold-forming treatment to obtain a multi-core composite wire; and performing high-temperature phase-forming heat treatment on the multi-core composite wire to prepare the MgB2 superconducting wire. In the present application, the Mg alloy rod containing Cu and Ti metal elements is used as a Mg source for preparing a MgB2 multi-core wire, so as to improve the plastic deformation ability of the Mg alloy rod in the wire treatment processes, and improve the grain boundary coupling, thereby improving the current carrying performance of the MgB2 superconducting wire.

The invention relates to the field of superconducting wire forming methods, in particular to a Nb3Sn superconducting wire preparation method based on multi-core wire liquid nitrogen cold drawing, and the Nb3Sn superconducting wire preparation method based on multi-core wire liquid nitrogen cold drawing comprises the following steps: preparing ultrahigh-tin-content copper-tin alloy powder by adopting a gas atomization method; the oxygen-free copper pipe, the oxygen-free copper rod and the pure niobium rod are machined, and the oxygen-free copper pipe and an oxygen-free copper bolt plug are obtained; acid pickling, cleaning and drying are carried out; uniformly fixing the pure niobium rods in the oxygen-free copper pipe to form a combined blank; performing rotary swaging to a required size, and then continuously drawing to obtain a finished wire; carrying out pulse treatment, and then carrying out air cooling to room temperature; and finally obtaining the Nb3Sn superconducting wire. According to the method, the strength and plasticity of the oxygen-free copper pipe sheath are improved through a liquid nitrogen cold drawing method, the combined blank is subjected to subzero treatment in the rotary swaging and drawing process, the plasticity of the combined blank is improved, and the high-strength and high-plasticity Ni3Sn superconducting wire can be obtained.

The invention belongs to the technical field of superconducting cables, and discloses a superconducting cable, a preparation method and a preparation device.The preparation method of the superconducting cable comprises the steps that a core wire, X superconducting wires and Y carbon fibers are prepared, the X superconducting wires and the Y carbon fibers are used for being woven on the surface of the core wire, and Y is smaller than or equal to X; spirally winding a hot melt adhesive film on the surfaces of the Y carbon fibers; the core wire, the superconducting wires and the carbon fibers are woven in a heating environment, and the X superconducting wires and the Y carbon fibers wound with the hot melt adhesive films are woven on the surface of the core wire under the heating condition; cooling the heated and braided superconducting cable through conveying; and after cooling, wrapping an insulating layer outside the superconducting braid layer formed by the superconducting wires and the carbon fibers. In conclusion, the superconducting braid layer of the superconducting cable is formed by mixing and weaving the superconducting wires and the carbon fibers, and the hot melt adhesive film is spirally wound on the surfaces of the carbon fibers, so that the core wires, the superconducting wires and the carbon fibers are bonded with one another after weaving, and the structural strength of the whole cable is improved.

The present invention relates to a multi-objective optimization method for structure parameters of a superconducting cable, and a device and a medium. The method comprises the following steps: S1, acquiring structure parameters and performance parameters of a superconducting cable, setting constraint ranges of the structure parameters of the superconducting cable, constructing objective functions on the basis of the structure parameters and the performance parameters of the superconducting cable, and establishing a multi-objective optimization model of the structure parameters of the superconducting cable; and S2, iteratively solving the multi-objective optimization model of the structure parameters of the superconducting cable by means of an improved multi-objective grey wolf optimization algorithm to obtain optimal solutions of the structure parameters of the superconducting cable, wherein weight coefficients negatively correlated with the overall sensitivity indexes of the structure parameters of the superconducting cable are assigned to iteration coefficients in the multi-target grey wolf optimization algorithm so as to obtain the improved multi-target grey wolf optimization algorithm. Compared with the prior art, the present invention can further improve the optimization speed and optimization effect of structure parameters of superconducting cables.

The invention belongs to the technical field of superconducting material processing, and discloses a multi-barrier-layer MgB2 superconducting wire and a preparation method thereof. A plurality of groups of interlayers of the wire are composed of Cu / Ni / Nb, outer-layer copper serves as a stabilizer, Ni serves as a low-cost outer barrier layer, Ni and the outer-layer copper are mutually diffused in the hot extrusion process to form a stable Cu-Ni compound, and Nb foil is added into the Ni layer to serve as an inner barrier layer so as to restrain the diffusion problem of a small amount of Ni-Mg. According to the multi-barrier-layer MgB2 superconducting wire, Nb is greatly replaced by Cu / Ni, the raw material cost is remarkably reduced, the barrier layers are mutually diffused in the hot extrusion process to achieve metallurgical bonding, uniform deformation of the wire in the subsequent machining process is facilitated, the possibility of damage of the barrier layers is reduced, the current-carrying performance of the wire is improved, the Jc of the multi-barrier-layer MgB2 superconducting wire under 4.2 K and 3T is 5199-6271 A / mm < 2 >, and the service life of the multi-barrier-layer MgB2 superconducting wire is prolonged. And the current-carrying performance is obviously improved, and the application prospect is wide.

The invention relates to the technical field of superconducting material processing, in particular to a preparation method of an Nb3Sn superconducting wire. The method mainly comprises the steps that Nb-Zr alloy is loaded into the exterior and / or the center of a Sn-Cu single-core rod, oxide powder is filled between the Nb-Zr alloy and the Sn-Cu single-core rod, then the Sn-Cu single-core rod and the Nb-Zr alloy are loaded into a copper substrate, and Nb3Sn subcomponents are obtained after multi-pass stretching, forming and fixed-length cutting; and uniformly arranging the Nb3Sn sub-components in the copper pipe along the circumferential direction to form a bundle, and after multi-pass stretching, carrying out heat treatment and cutting to obtain the Nb3Sn superconducting wire. By introducing the artificial point pinning array in density gradient distribution, the critical current density of the Nb3Sn superconducting wire in a high magnetic field of 8T-16T is enhanced, the problems that an existing uniform artificial point pinning center scheme generates a matching effect and limits the actual application of the superconducting wire are solved, and the decline degree of the critical current density of the Nb3Sn superconducting wire in the high field is relieved.

A multi-objective optimization method for structural parameters of a superconducting cable, comprising steps of: S1, obtaining structural parameters and performance parameters of the superconducting cable, setting a constraint range of the structural parameters of the superconducting cable, based on the structural parameters and performance parameters of the superconducting cable, constructing an objective function, to establish a multi-objective optimization model of the structural parameters of the superconducting cable; and S2, through an improved multi-objective grey wolf optimization algorithm, iteratively solving the multi-objective optimization model of the structural parameters of the superconducting cable, to obtain an optimal solution for each of the structural parameters of the superconducting cable; where, to an iteration coefficient in a multi-objective grey wolf optimization algorithm, a weight coefficient negatively correlated with an overall sensitivity index of each of the structural parameters of the superconducting cable is given, to obtain the improved multi-objective grey wolf optimization algorithm.

Disclosed is a Josephson junction device including a first superconducting electrode and a second superconducting electrode spaced apart from the first superconducting electrode. Each of the first superconducting electrode and the second superconducting electrode includes CuxBi2Se3, and x is greater than or equal to 0.05 and less than or equal to 0.5.

The utility model provides a high-temperature superconducting cable and a high-temperature superconducting magnet. The high-temperature superconducting cable comprises a metal coating layer and a plurality of superconducting sub-cables arranged in an array. The superconducting sub-cable comprises a superconducting conductor extending in the cable extending direction and a heat conduction layer wrapping the periphery of the superconducting conductor, and the periphery of the superconducting conductor is tightly attached to the inner wall of the heat conduction layer. A first attaching part and a first gap part are arranged between the outer walls of the heat conduction layers of the adjacent parts of any two adjacent superconducting sub-cables, and a second attaching part and a second gap part are arranged between the inner wall of the metal coating layer and the outer wall of the heat conduction layer of the closest superconducting sub-cable. The first gap portion and the second gap portion each form at least one cooling channel. The current of the quenched superconducting sub-cable can be shunted to the heat conduction layer of the adjacent superconducting sub-cable through the heat conduction layer, and the heat conduction layer can exchange heat with the cooling liquid of the cooling channel, so that the temperature of the superconducting sub-cable can be quickly reduced to a superconducting interval, and the cable can be prevented from being burnt down due to quenching.

The invention relates to the technical field of cable preparation, in particular to a superconducting semi-rigid cable made of high-purity aluminum and a preparation method thereof.The method comprises the steps that the high-purity aluminum is adopted as an inner conductor, and the inner conductor is preprocessed; coating the surface of the pretreated inner conductor with a PTFE mixture by using a pushing machine at normal temperature to obtain a normal-temperature pushing core wire; the qualified normal-temperature pushing core wire is wound on a cable reel and then placed in a vacuum high-temperature furnace to be subjected to vacuum sintering so as to obtain an inner conductor wrapped with an insulating layer; and the inner conductor wrapped with the insulating layer penetrates into the processed pure aluminum outer conductor tube, and the outer conductor is wrapped with PTFE to form an outer protective sleeve. According to the invention, the performance stability of the superconducting semi-rigid cable preparation can be improved.

The invention relates to a storage cryostat (2) for liquid helium (7), suitable for transferring liquid helium (7) from the storage cryostat (2) into an application cryostat (3), wherein the storage cryostat (2) comprises: - a vacuum-insulated helium vessel (6) for liquid helium (7), the helium vessel (6) having a vertical height HHB that can be filled with liquid helium (7), - a transfer line (4) for liquid helium (7), having an inlet opening (20) which opens into a lower region of the helium vessel (6), in particular into a lower fifth of the helium vessel (6), and - a convection-suppression system (9) which is arranged within the helium vessel (6) and impedes vertical convection of liquid helium (7) in the helium vessel (6), characterised in that the convection-suppression system (9) is formed in the helium vessel (6) over a height interval (IKS) with a vertical height HKS, where HKS ≥ 0.50 × HHB, and in that the convection-suppression system (9) impedes the vertical convection of liquid helium (7) in the helium vessel (6) over the region of the height interval (IKS) of the convection-suppression system (9). The invention provides a storage cryostat that enables simple and rapid transfer of liquid helium from the storage cryostat into the application cryostat, with minimised helium losses.

An example method described herein includes operating a first component of a circuit. The method also includes, while operating the first component, supplying a current to a superconducting wire that is thermally-coupled to the first component, and determining whether the superconducting wire has transitioned between a superconducting state to a non-superconducting state in response to the current. The method further includes measuring a temperature of the first component based on whether the superconducting wire transitioned between the superconducting state to the non-superconducting state in response to the current, and adjusting operation of the first component in accordance with a determination that the temperature exceeds a predetermined threshold temperature.

A method for manufacturing a semiconductor structure and a semiconductor structure are provided. The manufacturing method includes the following operations. A substrate is provided, and a first groove and a second groove are formed in the substrate, each of the first groove and the second groove having a depth in a first direction. The first groove includes multiple first sub-grooves arranged in the first direction, the second groove includes multiple second sub-grooves arranged in the first direction, and sidewalls of the first sub-grooves and sidewalls of the second sub-grooves are convex outwards. Word lines protruding away from the first groove each are formed at an interface of adjacent first sub-grooves. First source-drain layers formed on the sidewalls of the first sub-grooves, and second source-drain layers protruding away from the second groove each are formed at an interface of adjacent second sub-grooves.

The utility model provides a superconducting cable assembly, a superconductor transmission line and a star simulator. The superconducting cable assembly comprises a superconducting cable and a connector, the superconducting cable comprises a cable body part and a cable connecting part, and the cable connecting part is arranged in the connector in a penetrating mode in the axial direction of the connector; the connector comprises a clamping assembly, the clamping assembly comprises a sleeve and a pressing block, the sleeve comprises a first clamping block and a second clamping block which are oppositely arranged in the circumferential direction of the sleeve and fixed to each other, a cavity is defined by the first clamping block and the second clamping block, the pressing block is arranged in the cavity in the axial direction of the sleeve, and a through hole for a cable connecting part to penetrate through is formed between the pressing block and the second clamping block; the axial direction of the sleeve is parallel to that of the joint; the first clamping block locks and fixes the pressing block through the locking structure so that the pressing block can be connected to the periphery of the cable connecting part in a pressed mode in the radial direction of the sleeve, the position, relative to the locking and fixing position of the first clamping block, of the pressing block in the radial direction of the sleeve can be adjusted, and the hole diameter of the through hole can be adjusted. The superconducting cable assembly has better adaptability and maintainability.

To provide a superconducting wire capable of realizing a high residual resistance ratio (RRR) and a high strength, and also a superconducting coil using the superconducting wire.SOLUTION: A superconducting wire 10 includes a superconductor 11 and a superconductivity stabilization material 20. The superconductivity stabilization material 20 includes an inner copper material 21 and an outer copper material 22 including a copper material with a Cu content of 99.9 mass% or more. One or more kinds of elements selected from Ca, Sr, Ba, and a rare-earth element are added to the inner copper material 21, and Mg is added to the outer copper material 22. A KAM value A of the inner copper material 21 is 1.0 or less. A ratio B / A is 1.5 or more with regard to the KAM value A of the inner copper material 21 and a KAM value B of the outer copper material 22.SELECTED DRAWING: Figure 1

A superconducting machine system includes a superconducting electrical machine and a cryogenic vessel encompassing the superconducting electrical machine. The superconducting machine system includes a ramp lead assembly disposed within a vacuum vessel wall and having a first end and a second end. The first end of the ramp lead assembly is coupled in a fixed manner to the vacuum vessel wall and the second end is coupled to a high temperature superconductor power lead coupled to the superconducting switch. The ramp lead assembly includes a non-conductive support and a metal rod. The ramp lead assembly includes a thermal storage device coupled to the metal rod. The thermal storage device is configured to store heat, to limit heat transfer along the metal rod, and to limit an increase in temperature along the ramp lead assembly during the energization of the superconducting electrical machine.

The invention discloses a preparation method of stable in-situ 14: 24 AEC second-phase Bi-2212 powder, which comprises the following steps: preparing powder with specific components by controlling the components of a Bi-2212 precursor solution, and then adjusting by a fine heat treatment process to obtain the stable in-situ 14: 24 AEC second-phase Bi-2212 powder. According to the method disclosed by the invention, components of a Bi-2212 precursor solution are controlled, the components of Bi-2212 precursor powder after heat treatment and the molar ratio of Sr to Ca are monitored to be within a specific range, and a heat treatment process is matched for adjustment, so that stable generation of a 14: 24 AEC second phase in the Bi-2212 precursor powder is ensured; the self-generated 14: 24 AEC second phase can improve the critical current density of the Bi-2212 superconducting material; the method is easy to operate, low in cost, high in controllability and operability and suitable for being rapidly applied to the field of Bi-2212 superconducting material preparation.

The invention discloses a high-strength metal composite strip and a preparation method thereof.The high-strength metal composite strip is composed of a first outer-layer alloy, a middle-layer alloy and a second outer-layer alloy which are sequentially stacked, the first outer-layer alloy and the second outer-layer alloy are Ni-9wt.% W alloy, the middle-layer alloy is Ni-12wt.% W-3% Mo alloy, and the second outer-layer alloy is Ni-12wt.% W-3% Mo alloy. Wherein the content of the cubic texture of the composite strip is not lower than 90%, and the yield strength of the composite strip is not lower than 480 MPa. According to the composite strip, a strong cubic texture is formed on the surface layer, and the whole strip is high in strength and free of ferromagnetism.

The invention discloses a superconducting cable bending correction device and correction method, and a nuclear fusion device, and belongs to the technical field of nuclear fusion. In the correcting device, a control processing module controls feeding of a straightening mechanism, rotation of a rotating mechanism and starting and stopping of a bending mechanism; the detection assembly is used for detecting a bending angle deviation value of the superconducting cable bent by the bending mechanism in real time and sending the bending angle deviation value to the control processing module, and is used for detecting a rotation angle deviation value of the superconducting cable rotated by the rotating mechanism in real time and sending the rotation angle deviation value to the control processing module; when the bending angle deviation value exceeds a preset bending tolerance value, bending correction is carried out; and when the rotation angle deviation value exceeds a preset rotation tolerance value, rotation correction is carried out. According to the invention, the preparation precision and consistency of the superconducting cable can be improved, and the high-precision requirement of nuclear fusion devices and other fields on superconducting cable laying can be met.

In a general aspect, a flexible cable communicates electromagnetic signals in a cryogenic system. In some aspects, the flexible cable includes a signal layer and a ground layer. The signal layer includes signal lines embedded in adhesive material. Each signal line includes a multilayer structure. The multilayer structure includes a layer of non-superconducting material and a layer of rhenium metal. The ground layer is laminated to the signal layer.

The present invention provides: a MgB2 superconducting wire that has a barrier layer of highly uniform thickness covering a MgB2 core and that reduces MgB2 filament defects and is suitable for thinning and lengthening; a MgB2 superconducting wire manufacturing method for manufacturing the same; a superconducting coil using the same; and a magnetic generator including the superconducting coil. A MgB2 superconducting wire (200) comprises: a core material (210); a MgB2 filament (220) in which a MgB2 core (221) is covered with a barrier layer (222); and a metal sheath (230). The MgB2 filament (220) has a barrier layer (222) thickness on the outer peripheral side of the wire not more than three times the barrier layer (222) thickness on the core side of the wire. The method for manufacturing the MgB2 superconducting wire includes a step for forming a single core wire, a step for forming an embedded material, a surface reduction processing step, and a heat treatment step. The embedded material is formed by arranging the single core wire in a recess formed in the outer surface of the core material or by incorporating a spacer in a gap.