Magnet structure with high temperature superconductor (HTS) cables in grooves

Abstract

The method includes inserting a high temperature superconductor (HTS) cable into a groove in a support structure and pouring molten metal into the HTS cable while the HTS cable is in the groove. The magnet structure includes a support structure having a groove and a high temperature superconductor (HTS) cable, the high temperature superconductor (HTS) cable including a metal that at least partially fills the HTS cable and is disposed in the groove.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of Provisional Application No. 63 / 044,574, filed June 26, 2020, which is incorporated herein by reference in its entirety.

[0002] The concepts described herein relate generally to superconducting electromagnets (magnets), and more particularly to superconducting magnets that include cables containing high temperature superconductors. [Background technology]

[0003] Superconducting magnets can be used in a variety of applications to generate high magnetic fields. Some example applications include thermonuclear fusion reactors, motors and generators, and magnetic resonance imaging (MRI) machines, among others. To generate high magnetic fields, superconducting magnets can be in the form of many windings of electrical conductors. When an electric current flows through a conductor, a magnetic field is generated according to Maxwell's equations. Conductors that are not superconducting have non-zero electrical resistance, which results in power losses within the conductor. In contrast, an ideal superconductor has exactly zero electrical resistance. Using superconductors as conductors in magnets improves the efficiency of the magnet, allowing for higher magnetic fields and reducing heating. Summary of the Invention

[0004] Some embodiments relate to a method that includes inserting a high temperature superconductor (HTS) cable into a groove in a support structure and pouring molten metal into the HTS cable while the HTS cable is in the groove.

[0005] The molten metal may be molten solder, and the step of flowing the molten metal into the HTS cable includes flowing the molten solder into the cable.

[0006] The step of inserting the HTS cable into the groove may include inserting and spiraling the HTS cable into the groove.

[0007] The method may further include cooling the molten metal to solidify the molten metal.

[0008] The method may further include inserting a second HTS cable into a second groove in the second support structure and pouring a second molten metal into the second HTS cable while the second HTS cable is in the groove.

[0009] The method may further include attaching the first support structure to a second support structure.

[0010] The method may further include electrically connecting the HTS cable with a second HTS cable.

[0011] Some embodiments relate to a magnet structure comprising a support structure having a groove and an HTS cable, the HTS cable including a metal that at least partially fills the HTS cable, disposed within the groove.

[0012] The metal may include solder.

[0013] The shape of the HTS cable can conform to the shape of the groove.

[0014] An HTS cable may comprise at least one HTS tape stack.

[0015] The HTS cable may include a plurality of flow paths and a plurality of HTS tape stacks disposed in each of the plurality of flow paths.

[0016] The HTS cable may include a former that separates at least first and second HTS tape stacks of the plurality of HTS tape stacks.

[0017] The former may comprise a conductive metal.

[0018] The magnet structure may further comprise an electrical insulator that insulates the sections of the former from one another.

[0019] The conductive metal may include copper or steel.

[0020] The HTS cable includes cooling channels.

[0021] At least one HTS tape stack may be twisted along the length of the HTS cable.

[0022] The support structure may include an electrically conductive material.

[0023] The HTS cable may have a helical shape within the groove.

[0024] The HTS cable may have multiple turns, and each turn of the multiple turns may be electrically coupled to one another via a support structure.

[0025] The magnet structure can include a second support structure having a second groove and a second HTS cable, the second HTS cable including a second metal at least partially filling the second HTS cable and disposed within the second groove, and the HTS cable is electrically connected to the second HTS cable.

[0026] An HTS cable may include an outer sheath and an HTS tape within the outer sheath.

[0027] The sheath and HTS tape may extend along the length of the HTS cable.

[0028] The support structure may comprise a plate.

[0029] The HTS cable may include an HTS tape stack that can slide along the length of the HTS cable when the HTS cable is inserted into the groove.

[0030] The step of pouring the molten metal into the HTS cable may include pouring the molten metal into a channel in the HTS cable.

[0031] Non-limiting embodiments illustrating the concepts will be described by way of example with reference to the accompanying drawings, which are schematic and not intended to be drawn to scale. In the figures, each identical or nearly identical component shown is typically represented by a single numeral. For purposes of clarity, not every component will be labeled in every drawing, and not every component of each embodiment will be shown unless illustration is necessary to enable those skilled in the art to understand the concepts and embodiments being described. [Brief explanation of the drawings]

[0032] [Figure 1] 1A-1D illustrate a method of forming a high temperature superconductor (HTS) magnet. [Figure 2A] FIG. 10 is a diagram showing an example of a cross section of a support structure. [Figure 2B] FIG. 2 is a top view of the support structure. [Figure 2C] FIG. 2 shows that the HTS cable can be placed in the groove 220. [Figure 2D] FIG. 1 illustrates filling of an HTS cable with molten metal. [Figure 3A] 10A-10C show an example in which a cap is disposed over an HTS cable in a groove in a support structure. [Figure 3B1] FIG. 10 illustrates that the support structure can have a cylindrical layered winding scheme, with the top of the support structure having outward facing grooves. [Figure 3B2] FIG. 10 illustrates that the support structure can have a cylindrical layered winding scheme, and the top of the support structure has inward-facing grooves. [Figure 3B3] FIG. 1 shows an example of a coke screw-shaped HTS cable. [Figure 3C] FIG. 1 illustrates a support structure with a pancake winding scheme. [Figure 3D] FIG. 10 illustrates configuring the shape of the non-insulating shell to be parallel to the magnetic flux lines of a varying external magnetic field. [Figure 3E] FIG. 1 illustrates an example of a segmented HTS cable. [Figure 3F] FIG. 1 illustrates an example of a non-segmented HTS cable. [Figure 3G] FIG. 10 shows plots of loss versus frequency for various different formers. [Figure 3H] FIG. 10 shows an example of an HTS cable in which the cooling channels are removed and replaced by an extension of the segmented former. [Figure 3I] FIG. 1 is a diagram showing a TSTC cable as an example of an HTS cable. [Figure 3J] FIG. 1 is a diagram showing a CROCO cable as an example of an HTS cable. [Figure 3K] FIG. 1 illustrates an example of a filamented table that can be used for HTS tape stacking. [Figure 4] FIG. 1 illustrates an example of an HTS cable with a single HTS tape stack. [Figure 5] FIG. 1 illustrates an example of an HTS cable having multiple HTS tape stacks disposed within respective channels of a former. [Figure 6] FIG. 6A shows a cable with a former having multiple flow channels provided therein, and FIG. 6B shows a cable with a former having multiple flow channels provided therein. [Figure 7A] 1 is a flowchart comprising a sequence of processing elements forming an exemplary embodiment of a metal filling process in accordance with the concepts described herein. [Figure 7B] 1 is a flowchart comprising a sequence of processing elements forming an exemplary embodiment of a metal filling process in accordance with the concepts described herein. [Figure 8] FIG. 1 shows an apparatus for filling a cable with solder using vacuum pressure techniques. [Figure 9]It is a diagram showing an example of a structure inside an HTS cable. [Figure 10] It is a diagram showing an example of an HTS tape.

Embodiments for Carrying Out the Invention

[0033] High temperature superconductors (HTS) can be advantageous for superconducting magnets because they maintain superconductivity at higher temperatures than low temperature superconductors and thus do not need to be cooled to low temperatures to maintain superconductivity. As used herein, the phrases "HTS material" or "HTS superconductor" and the like refer to superconducting materials having a critical temperature above 30°K in a self-field. An example of a ceramic HTS is rare-earth barium copper oxide (REBCO). HTS superconductors can be formed within a tape or tape stack that includes several layers of various materials. An HTS magnet is a magnet that includes an HTS material to conduct at least a portion of an electric current.

[0034] <HTS Materials and Magnet Design Considerations> High temperature superconductors (HTS) open up new opportunities for constructing high magnetic field magnets for a variety of applications.

[0035] Some characteristics of HTS and HTS-REBCO tapes are specifically as follows. - A small critical current sensitivity with respect to the operating temperature (compared to low temperature superconductors (LTS)), which enables a larger operating temperature margin. - An operating temperature higher than that of LTS, at which temperature, if there is sufficient cooling to limit the associated temperature rise, the heat capacity of the material including the cold mass of the magnet is significantly higher than that at the LTS-corresponding temperature, and as a result, the sensitivity to local heating is lower. - Compatible with No-Insulation (NI) design principles due to good current sharing between bundled HTS-REBCO tapes and between them and the surrounding conductive media, including cold mass structures and co-wound stabilizers. - The possibility of solder impregnation, which significantly enhances current sharing and leads to much better resistance and stability to quenching, as well as guaranteed recovery from quenching under certain circumstances. - Allows for larger inherent strains compared to LTS. - During typical operating modes as well as during quenches, small (<approximately 1V) voltages inherent in the NI windings occur within the magnet, which, as for LTS magnets, do not require high-voltage electrical isolation.

[0036] This disclosure describes a class of innovative magnet designs that can use HTS materials technology and provides examples of applications that can benefit from the use of this class of magnet designs.

[0037] A simplified classification of superconducting magnets, relevant to the selection of winding schemes of the type considered here, can be presented in the following form: Magnets can be subdivided into two main groups: - Constant current magnets, usually referred to as direct current (DC) magnets. - Variable current magnets, usually referred to as alternating current (AC) magnets.

[0038] The techniques and apparatus described herein apply particularly to DC magnets, but are not limited to DC magnets, and also apply to AC magnets.

[0039] In this regard, magnets can be subdivided into the following subgroups: - Group 1: DC magnets operating in a constant external field environment. - Group 2: DC magnets in an environment where a weak fluctuating external magnetic field is superimposed on the constant self-field of the DC magnet. - Group 3: DC magnets operating in an environment with a fluctuating external magnetic field of the same order of magnitude as the DC magnet's self-field.

[0040] Typical representatives of magnets belonging to these groups include, but are not limited to: Group 1: MRI and NMR magnets, multipole focusing magnets in linear accelerators (Linacs), magnets of synchrocyclotrons, magnetic field coils in induction motors and generators, widely used in wind power systems. Group 2: Toroidal field (TF) magnets in tokamak reactors (tokamaks). Group 3: Background field coils for various test facilities and high-energy physics experiments.

[0041] All three groups can benefit from the concepts, structures, and techniques described herein. The applicability of these engineering solutions may be limited by the balance between AC losses within the magnet and its cooling power, but these limitations are more discriminatory for Group 3 magnets.

[0042] There are four types of AC (power) losses that can be considered for magnets comprising one or more HTS tape stacks: ferromagnetic, hysteretic, coupling, and eddy current induced.

[0043] 1. Ferromagnetic losses are associated with the heat generated by the magnetization or demagnetization of ferromagnetic elements such as iron. If the materials in the cable are not ferromagnetic, these losses can be neglected.

[0044] 2. Hysteresis losses are similar to ferromagnetic losses, but are only relevant to type-II superconductors. Unlike type-I superconductors, type-II superconductors can be penetrated by magnetic field lines. When an applied magnetic field changes within the material, losses occur that are proportional to the frequency and magnitude of that change, as well as the critical current density (Jc) of the tape and the width of the tape. Typically, capacitive hysteresis power losses are evaluated using the Bean model, although the concepts described herein are not limited in this regard.

[0045] 3. Coupling losses are generated by currents flowing between tapes and the tape stack. Coupling losses between tapes in a stack can occur for many reasons. For example, the critical current (Ic) of each tape varies along its length, so if a high-average Ic tape has a relatively low Ic spot, some current can leak into other tapes in the stack. In single-stack cables, current sharing between stacks is not an issue; in multi-stack cables, sharing between stacks can be blocked by insulation. In that case, tapes parallel to the magnetic field will generally have a much higher Ic than tapes more perpendicular, and twisted cables cause each stack to have a constantly changing orientation relative to the magnetic field.

[0046] 4. As explained by Faraday's Law, voltages are induced in cables (among other structures) by changing the magnetic field environment. The voltages create eddy currents inversely proportional to the resistance of the current path, so that currents are developed almost entirely through the copper and HTS.

[0047] Although little can be done to mitigate ferromagnetic and hysteresis losses, they are expected to be small in magnets comprising one or more HTS tape stacks. Coupling losses in HTS tape stacks can be reduced by reducing the width of the superconducting tapes in the stack and the overall cross-sectional dimensions of the tape stack.

[0048] In some embodiments, the techniques and apparatus described herein may reduce eddy current AC losses in viable superconducting magnets, thereby helping to meet practical and engineering requirements.

[0049] In some applications, the magnet may need to meet the following requirements: - The magnet is capable of operating at a constant operating current in a high self-field of up to 20 T and is capable of sustaining eddy current heating caused by ramping or vibration limited by an external magnetic field of that magnitude and frequency range. - The magnets are capable of operating at cryogenic temperatures raised above 10 K and are capable of sustaining magnetic quenching, optionally in passive mode, i.e. without interference by any kind of quench protection system.

[0050] Two common methods of reducing eddy current losses in magnets are: - Segmentation of components with magnets to reduce trapped magnetic flux current loops, as may be done (for example) in transformers with laminated iron sheets. - Reduction or complete removal of copper or other highly conductive materials.

[0051] One approach to magnet design is through the use of a so-called non-insulated (NI) winding scheme. In this case, the magnet consists of cables installed with no continuous inter-winding insulation, which allows for limited inter-winding current sharing. A simplified representation of the non-insulated scheme is by representing it as a set of parallel superconducting cables placed within a thin, highly electrically resistive matrix. Good electrical conductivity is established between each winding of the magnet. One advantage of HTS non-insulated magnets is that they are passively resilient to quenches (where regions of the HTS superconductor become resistive). Another advantage is that NI magnets with one or more superconducting cables may require little or no copper stabilizers. These features make the NI winding scheme attractive for applications requiring DC superconducting magnets operating in the presence of a fluctuating external magnetic field.

[0052] <HTS cable in a groove in a support structure> There are several ways in which HTS tapes can be formed into magnets. In some embodiments, HTS superconductors can be disposed in cables. Under certain conditions, HTS cables can be bent into various shapes. HTS cables are cables that have HTS superconductors to conduct current along the length of the HTS cable. HTS cables can be insulated or non-insulated. Non-insulated HTS cables can allow for the formation of NI magnets.

[0053] One consequence of generating a high magnetic field is that large forces (Lorentz forces) are exerted on conductors that carry electrical current. It is therefore desirable to provide magnets with structures that are structurally robust enough to withstand such forces.

[0054] In some embodiments, HTS magnets can be formed by placing an HTS cable in a groove within a support structure that defines the desired shape for the HTS cable. At this stage, the HTS cable can be bent into the desired shape without damaging the HTS tape stack because the position of the HTS tape stack is not fixed and the HTS tape stack can slide along the length of the HTS cable as the HTS cable bends. The HTS cable includes an exterior that surrounds the HTS tape and a flow path (channel) for receiving molten metal. Once the HTS cable is bent into the desired shape, molten metal (e.g., solder) can then be poured into the cable while the cable is still in the groove of the support structure. Once the molten metal cools, it "freezes" the HTS cable into its final shape within the groove of the support structure, and the HTS tape stack can no longer move significantly within the HTS cable. Advantageously, the support structure can provide mechanical support for the HTS magnets, allowing them to withstand forces generated during operation of the magnets.

[0055] It should be understood that to promote clarity in drawings and text of the concepts, structures, and techniques described herein, exemplary embodiments of cables helically bent in a single plane are described herein. However, after reading the description provided herein, one skilled in the art will understand that the cable may be bent into any desired shape, including shapes defined by curved surfaces (e.g., as may be required to form complex, multi-dimensionally curved structures). Some non-limiting examples of curved surfaces are described herein below.

[0056] It should also be understood that high-field superconducting magnets often comprise multiple cable windings grouped in a layered arrangement (i.e., the magnet consists of multiple layers). The multiple windings may be closely packed. In embodiments where a high-field superconducting magnet is formed by windings of HTS, HTS tape, or HTS tape stacks arranged in flat layers (e.g., formed so that the interface of the layers is perpendicular to the central longitudinal axis of the magnet around which the layers are arranged), such an arrangement may be referred to as a "pancake winding," or even more simply as a "pancake." Thus, the pancake includes both the HTS elements and the structural elements for housing the HTS. When a magnet is formed by layers having multiple windings (e.g., so that the interface of the layers is parallel to the central longitudinal axis of the magnet around which the layers are arranged), such an arrangement may be referred to as a "layered winding scheme," or simply a "layered configuration," or even more simply as "layering."

[0057] FIG. 1 illustrates a method 100 for forming an HTS magnet, according to some embodiments. In step S5, an HTS cable may be constructed. The HTS cable may be constructed using any suitable manufacturing technique and having any suitable structure, examples of which are described herein. The channels within the HTS cable may not be filled with molten metal (e.g., solder) in this step. For example, the channels may be left empty to accommodate filling with molten metal in a later step. In step S10, the support structure may be formed with a groove. In some embodiments, the support structure may be a plate. However, the apparatus and techniques described herein are not limited in this respect, as the support structure may have a shape other than that of a plate. The support structure may be formed of a mechanically rigid material. In some embodiments, the support structure may be formed of a conductive material. A support structure including a conductive material between turns of the HTS cable may facilitate the formation of a non-insulated (NI) magnet. In some embodiments, the support structure may be formed of a metal. An example of a metal that provides mechanical rigidity and is conductive is steel. Suitable types of steel include, for example, NITRONIC 40 and NITRONIC 50. However, the apparatus and techniques described herein are not limited in this regard, as the support structure may be formed of other metals or non-metals, or various combinations of materials in the various layers may be used. The support structure may have a groove formed therein to receive the HTS cable. For example, if the support structure is a plate, the first surface of the plate may have a groove formed therein. In some embodiments, the groove may have a helical shape and / or may be shaped to receive the HTS cable in a helical manner.

[0058] In step S20, the HTS cable may be inserted into a groove in the support structure. If the groove has a helical shape, the HTS cable may be wound helically and pressed into the groove. Before placing the cable into the groove in the support structure, a conductive material may be disposed in the groove or on the outside of the HTS cable, which may reduce the contact resistance between the HTS cable and the support structure. For example, the conductive material may be a malleable material such as indium, or a material that flows when heat is applied, such as solder. The solder may be heated, poured into the groove, and then solidified. In some embodiments, a non-conductive material may be present between the support structure and the outside of the HTS cable (e.g., any space between the support structure and the HTS cable may be left empty). In the latter case, current sharing between the HTS cable and the support structure will be relied upon via these contact resistances.

[0059] In step S30, molten metal, such as solder, may be poured into the HTS cable while the HTS cable is in the channel. For example, as described in further detail herein, an apparatus may be connected to the HTS cable to heat the molten metal and pour the molten metal into one or more channels in the HTS cable.

[0060] In some embodiments, the HTS cable may be placed into a groove in the support structure without any additional material between them. In step 30, molten material flows into this space, forming a conductive layer between the HTS cable and the support structure.

[0061] In step S40, the molten metal is allowed to cool and solidify, which can be done by removing the heat source or by cooling the HTS cable.

[0062] Once the molten metal solidifies, the HTS cable is "frozen" or "set" into its final shape. The HTS cable cannot be bent significantly thereafter without breaking. The resulting structure can therefore be an HTS magnet with the HTS cable having solder in grooves in the support structure. Such a structure can be used as an HTS magnet, or multiple such structures can be joined together (e.g., stacked) to form an HTS magnet with an even greater number of turns, with suitable electrical interconnections between each structure.

[0063] FIG. 2A shows an example cross-section of a support structure 210 according to some embodiments. In this example, support structure 210 has a groove 220 on its top surface. Groove 220 may have a spiral shape as illustrated in FIG. 2B, which depicts a top view of support structure 210. It should be understood that groove 220 may have any suitable number of turns, and the term "turn" refers to one rotation around a center point. FIGS. 2A and 2B show the results of step S10 of FIG. 1 according to some embodiments.

[0064] FIG. 2C illustrates that HTS cable 230 may be placed within groove 220. FIG. 2C illustrates the results of step S20 of FIG. 1, according to some embodiments. As shown in FIG. 2C, the shape of groove 220 may be formed to match the shape of HTS cable 230. For example, if HTS cable 230 has a circular cross-section, as shown in FIG. 2C, the groove may have a semicircular cross-section with a radius that closely matches the radius of HTS cable 230. In embodiments, the cable and groove radii (or more broadly, the cable and groove dimensions when either the cable or groove are not provided with a circular or semicircular cross-sectional shape) may be selected to provide a pressure fit. In other embodiments, the cable and groove radii (or the cable and groove dimensions) may be selected to provide an interference fit. In other embodiments, the cable and groove radii (or the cable and groove dimensions) are selected to provide a movement fit. In still other embodiments, the cable and groove radii (or the cable and groove dimensions) are selected to provide a transition fit. However, the techniques and apparatus described herein are not limited in this regard, as the cross-sections of the HTS cables and grooves can have any regular or irregular shape, such as square, rectangular, oval, triangular, etc.

[0065] FIG. 2D illustrates filling the HTS cable 230 with molten metal in step S30 of FIG. 1 according to some embodiments. While filling the HTS cable 230 with molten metal is illustrated schematically in FIG. 2D by hashing, it should be understood that only a portion of the HTS cable 230 may be filled with molten metal. For example, as described in further detail below, one or more flow paths (channels) within the HTS cable 230 may be filled with molten metal. The molten metal may then solidify as described above. A structure such as that shown in FIG. 2D may then be used as an HTS magnet or may be connected to other structures, such as that shown in FIG. 2D, to form a composite or stacked HTS magnet.

[0066] FIG. 3A shows an example in which a cap 240 is disposed over an HTS cable 230 in a groove 220 of a support structure 210. The cap 240 may hold or secure the HTS cable 230 in place within the groove 220. The cap 240 may be formed of any conductive or non-conductive material. In some embodiments, the cap 240 may be formed of the same material as the support structure (e.g., steel). The cap 240 may be secured to the support structure in any suitable manner. In some embodiments, the cap 240 may be welded at its end to the end of the groove 220 in the support structure, as shown in FIG. 3A. Placing solder or other molten metal between the outside of the HTS cable and the support structure may occur before or after installing and securing the cap.

[0067] As described above, multiple pancakes can be joined together (e.g., stacked) to form an HTS magnet. They can be arranged in a layered arrangement using a layered winding (FIGS. 3B1, 3B2) or pancake winding (FIG. 3C) scheme, respectively. As shown in FIGS. 3B1 and 3B2, the support structures can each have a cylindrical shape with a groove facing either outward (FIG. 3B1) or inward (FIG. 3B2) on the top of the support structure. As shown in FIGS. 3B1 and 3B2, these support structures can also be nested within each other. The surface of each cylindrical support structure can have a groove extending along the surface of the coke screw to receive a coke screw-shaped HTS cable. An example of a coke screw-shaped HTS cable is shown in FIG. 3B3. The cylindrical structures with the cylindrical support structures and the HTS cables in the support structure grooves can be formed separately and then nested inside or outside each other to form the nested cylindrical structures shown. The nesting of the cylindrical layers can be performed by a "shrink-fit" process, e.g., by heating and cooling the layers, to reduce or eliminate voids between the layers. Alternatively, they can be nested differently to reduce voids, or with small voids. The voids can be filled with fiberglass cloth or other suitable material, and the entire assembly can then be filled (e.g., vacuum-impregnated) with epoxy to form interlayer insulation between adjacent cylinders. Alternatively, the interlayer insulation can be formed by pre-fabricated solid sheets of Kapton-G10 or G11. The HTS cables within adjacent cylinders can be connected to each other by suitable electrical joints. When multiple pancakes are stacked, as shown in Figure 3C, connections can be made between the pancakes by conductive joint structures. Such joint structures can be superconducting or non-superconducting. Apart from the joining structure, the interface between each pancake (eg, flat support structure) or between multiple layers (eg, cylindrical support structure) can be an insulating material.

[0068] In non-insulated magnets, there are two main mechanisms of eddy current superconducting cable loss: - Eddy currents generated by loops formed by superconducting cables and shunted through a highly electrically resistive matrix at their ends. - Eddy currents in the superconducting cable. Reducing these losses is specific to the design of the cable as explained below.

[0069] Eddy currents in the matrix are mainly caused by a varying external magnetic field perpendicular to the thin non-insulating shell (layer, pancake, etc.).

[0070] In the case of a clearly shaped varying external magnetic field, those losses can be reduced by adjusting the shape of the non-insulating shell so that it is parallel to the magnetic flux lines of the varying external magnetic field (Figure 3D).

[0071] <Example of HTS cable> The HTS cable 230 can be structured according to several different designs. Several HTS-REBCO-based cable designs have been proposed and developed. Many of them are designed to reduce AC coupling losses. This can be achieved by so-called transposition of the tapes in the cable. This transposition is done in many different ways.

[0072] One example of an HTS cable 230 is the so-called PIT-VIPER cable (FIG. 3E). It is a multi-stack cable (in this example, there are four HTS tape stacks, but other designs may have a different number of channels / tape stacks). The tape stacks may be helically twisted along their length, as shown in FIG. 6B. Optionally, each tape stack may be surrounded by a conductive (e.g., copper) former, which may act as a stabilizer to stabilize the tape stacks within the HTS cable. Reduced eddy current losses may be achieved by dividing or segmenting the former and placing dielectric insulation between the segments. In embodiments, such an approach may result in a more than 20-fold reduction in eddy current heating compared to another example of an HTS cable 230, the non-segmented VIPER cable (FIG. 3F). The VIPER cable of FIG. 3F is similar to the VIPER cable of FIG. 3E, but without the insulation that segments the former.

[0073] In some embodiments, AC losses can be reduced by using a material with higher electrical resistivity for the former. For example, steel can be used for the former instead of copper. Numerical models (confirmed by experiment) show that sectioning the VIPER cable reduces AC losses in the former due to the oscillating external transverse magnetic field by a factor of 1.7. Replacing the copper former with steel further reduces losses by a factor of 2.7. These results are shown in Figure 3G.

[0074] One advantage of the VIPER and PIT-VIPER configurations is that this topology lends itself to the presence of a central cooling channel, as shown in Figure 3E, which allows for efficient cooling of the HTS material by the flow of liquid cryogenic fluid.

[0075] For relatively small AC losses, when technological conditions allow for conduction cooling, the cooling channels can be removed and replaced by segmented former extensions (Figure 3H). Alternatively, the channels can be left empty or filled at room temperature with a liquid or high-pressure gas that is in a liquid or solid state at cryogenic operating temperatures, providing additional thermal stability for the superconductor.

[0076] In a conduction-cooled arrangement, there is no coolant to remove heat from inside the windings. Instead, heat is removed from the body of the magnet by conduction through high thermal conductivity components to thermal cross points on the outside of the windings. These can be along the lines of insulated copper wire or insulated copper strips with inter-layer (inter-pancake) insulation.

[0077] Other cables without cooling channels can be used if a conduction cooling scheme is sufficient. TSTC cables (FIG. 3I), CROCO cables (FIG. 3J), and CORC cables (not shown) are other examples of HTS cables 230 suitable for use in non-insulated configurations. In both cases, the twisted tape stack can be vacuum-pressured into a round (e.g., steel) tube using solder for better lateral thermal and electrical conduction. The advantage of these cables is their high packing factor, i.e., the ratio of the superconductor area to the winding area, resulting in high engineering current densities, which can be significant in some applications. To further reduce AC losses from intra-stack coupling between tapes, the tape stack can be reduced in size by using narrower tapes, reducing the number of tapes in the stack, or both. The use of advanced tapes, such as the filamentized tape from Subra (www.subra.dk) shown in FIG. 3K, can significantly reduce AC losses. Another advantage of these cables is that they are formed by twisted tape stacks. Twisting the tape stack along the length of the cable allows for limited bending of the cable with little or no strain along the tapes in the stack. Bending the cable can be done before soldering the tapes into the cable. In the process of bending the cable to assume the desired shape, this allows the tapes in the twisted stack to slide over each other, significantly reducing or completely eliminating undesirable intrinsic axial strain that could otherwise cause significant degradation of the superconductor and a reduction in its critical current. Soldering the tapes in the cable can be done in place after bending the cable and inserting it into the grooves in the structural matrix.

[0078] In some embodiments, HTS magnets formed according to the techniques described herein may have several advantageous properties. For example, the use of a support structure may result in high structural integrity. When the HTS magnet is formed as a NI magnet that provides a conduction path between each winding of the HTS material, several advantages may exist. For example, omitting insulation may avoid problems with radiation damage. The NI magnet may have high quench resistance. Cooling of the HTS material may be provided by the flow of a coolant within a flow path of an HTS cable that is in contact with a highly conductive material (e.g., copper) that can be in close proximity to the HTS material. Such magnets may also be less exposed to AC (alternating current) losses, shielding, and eddy currents. The soldering quality of the HTS material may be high due to the flow of molten metal into the cable.

[0079] <Further Examples of HTS Cable and Molten Metal Filling> A process, system, device, and technique for filling a high temperature superconducting (HTS) cable with molten metal are described.

[0080] FIG. 4 shows an example of an HTS cable having a single HTS tape stack. The HTS cable includes an outer jacket within which the HTS material is disposed. The outer jacket may be in the shape of a tube. The HTS tape stack is shown as having a plurality of tape layers of the HTS material. Each layer may include a single HTS material or multiple different HTS materials.

[0081] In this example, the sheath (and therefore the cable) is shown as having a circular cross-sectional shape. Of course, it should be understood that the sheath or cable may be provided with any regular (e.g., rectangular, square, triangular) or irregular cross-sectional shape. Furthermore, depending on the application, different sheaths / cables may not have the same cross-sectional shape. The particular cross-sectional shape of the sheath / cable may be selected to meet the needs of the particular application in which the sheath / cable will be used. In some embodiments, the processes described herein for filling an HTS cable with molten metal may result in the molten metal being disposed around and / or in contact with the surface of the HTS material. In some embodiments, the molten metal may be filled into the interstitial spaces between multiple layers of HTS tape.

[0082] Figure 5 shows an embodiment of an HTS cable having multiple HTS tape stacks disposed within respective channels of a former. In this example, the cable is formed or provided with a former having multiple channels (here, four channels) with a multi-stack HTS tape disposed within each channel. An armor is disposed around the former. Any number of channels may be used. The number of channels may be selected to meet the needs of the particular application in which the cable will be used.

[0083] In this exemplary embodiment, each channel may have a generally square cross-sectional shape. However, the channels may have any regular (e.g., rectangular, circular, triangular) or irregular cross-sectional shape. Furthermore, depending on the application, each channel may not have the same cross-sectional shape; i.e., different channels may have different shapes. The particular cross-sectional shapes of the channels may be selected to meet the needs of the particular application in which the cable will be used. The metal filling process described herein may be used to fill the cable, and in particular, any channels provided in the former, with molten metal (e.g., solder). The described metal filling process may fill around each HTS tape stack, spaces between HTS tape layers comprising the stack HTS tape, and spaces that may exist between the surface of the former and the surface of the sheath.

[0084] The metal filling process described herein can be applied to any cable that has an armor but no former (e.g., as shown in FIG. 4) and / or has both an armor and a former (e.g., as shown in FIG. 5). Moreover, the metal filling process described herein can be readily used to fill tubes or channels having any or complex cross-sectional shape and any or complex pattern with molten metal. Furthermore, the metal filling process described herein can be used for cables of any length.

[0085] Referring now to FIGS. 6A and 6B, a cable includes a former having multiple channels provided therein. In this exemplary embodiment, the former has one channel corresponding to the cooling channel provided along the central longitudinal axis of the former. In embodiments, the former may have multiple cooling channels therein. The former has multiple channels, which are formed or provided within the former with HTS material provided therein. In the exemplary embodiment of FIG. 6A, the HTS material is shown as a multi-stack HTS tape disposed within each channel. Of course, other configurations of HTS material may also be used. An outer sheath is disposed around the former. In this exemplary embodiment (and as can be more clearly seen in FIG. 6B), the channels may have a twisted or helical pattern along the surface of the former along its length, with each channel having a generally square cross-sectional shape, meaning that the HTS tape twists along the length of the HTS cable. Twisting the HTS tape along the length of the HTS cable allows for redistribution of forces within the tape when the cable is bent.

[0086] 7A and 7B are flowcharts made up of a sequence of processing elements that form an exemplary embodiment of a metal filling process in accordance with the concepts described herein. Unless expressly stated, the processing elements in the flowcharts are understood to be unordered, meaning that the process elements listed in the flowcharts can be performed in any suitable order.

[0087] 7A and 7B, an exemplary process for solder-filling an HTS cable begins by cleaning the elements (e.g., tubing, formers, HTS materials, sheaths, fittings, etc.) that will be used in the cable that has undergone the solder-filling process (62). In an embodiment, the cable elements may be cleaned using a process involving rinsing with an acidic solution followed by a water rinse. Details of such a process related to one particular embodiment are described below.

[0088] As one non-limiting example, a reservoir containing a mixture of water and cleaning solution (e.g., Citronox acid cleaner) can be coupled to the cable former, and the mixture can be pumped from the reservoir through the cable former. Cleaning water can then be pumped through the cable former to rinse the cleaning solution out of the cable former. In some cases, the mixture and / or cleaning water can be heated to above room temperature (e.g., 60°C (140°F)) during rinsing.

[0089] Once the elements are cleaned, the HTS material is disposed within the sheath or within the channels of a channeled former (64). In embodiments, the HTS material may be provided as an HTS tape stack. In embodiments, the HTS tape stack may be pre-tinned to ensure good adhesion between the tapes in a tight stack (e.g., adhesion that securely bonds the tapes to one another). In one embodiment, the HTS tape stack may be pre-tinned with the metal to be used to fill the cable. In one embodiment, the HTS tape is pre-plated with PbSn solder.

[0090] A "loose HTS cable assembly" (or more simply, "HTS cable assembly") is then formed (65). HTS cable assemblies are sometimes referred to as "loose cable assemblies" because at least the HTS material (and possibly other elements) is not structurally fixed to a tube or channeled former or other structure that forms part of the HTS cable. As used herein, "HTS cable assembly" or "loose HTS cable assembly" may refer to any container comprising HTS (e.g., HTS tape), examples of which are provided herein. For example, one type of HTS cable assembly may be formed by disposing HTS material within a tube, optionally adding fittings, etc., as needed. As another example, an HTS cable assembly may comprise a channeled former in which the HTS material is disposed within appropriate ones of the channels, optionally adding fittings, etc., as needed. Other types of HTS cable assemblies may be envisioned, and techniques for filling HTS cable assemblies with metal may be applied thereto.

[0091] Referring now to FIG. 7A, the HTS cable assembly is then evacuated (e.g., through a vacuum process) and purged with an inert gas (66) to eliminate any oxidation, and a flux is applied to the HTS materials and cable elements that form the HTS cable. In embodiments, the liquid flux may be applied just prior to soldering. This may penetrate all surfaces in a manner similar to the subsequent flow of molten metal to be described. In embodiments, the application of the liquid flux has been found to allow good wetting of the solder to the tape and cable. In embodiments, RMA-5 liquid flux was used, but other liquid fluxes with the same or similar properties may also be used.

[0092] Excess flux is evacuated from the assembly (68). Any remaining flux has been found to be effectively washed away by the heavier flow of molten metal solder (to be described in conjunction with 78). As such, an explicit step of evacuating excess flux may not be required, depending on how much flux remains in the assembly. In embodiments having long and complex cable geometries, pressure may be effectively used to evacuate excess flux.

[0093] The HTS cable assembly is heated to a temperature below that which would melt the metal (e.g., solder) (74). In embodiments, a convection oven may be used to control the temperature of all of the cable and fittings and tubing during the metal filling process. This provides a degree of uniformity with minimal external control required, and importantly, avoids any risk of the HTS tape exceeding the oven setpoint and causing degradation in that portion of the cable.

[0094] Before, after, or simultaneously with heating the cable assembly (74), the metal to be loaded into the HTS cable is melted to a liquid state (75). The metal may be melted, for example, using a temperature-controlled heater in a can or crucible. Thermocouples inside and outside the can may be used to determine when melting is complete and the temperature of the molten metal before it flows. In some embodiments, the metal may be melted inside the oven in which the cable is located, while in other embodiments, the metal may be melted separately (i.e., outside the oven). The HTS cable assembly is then heated (76) to a temperature at which the metal will flow.

[0095] One aspect of the metal loading process that has proven important is obtaining a desired time-temperature profile: the temperature must be high enough to make the metal a low viscosity fluid, but with a low enough exposure to avoid thermal degradation and degradation due to the chemical effects of the metal on the HTS material (e.g., REBCO tape stack).

[0096] In one embodiment of solder filling an HTS cable comprising an HTS tape stack with layers of REBCO tape and using PbSn solder, two steps can be used. First, an oven can be set to a temperature that heats the HTS cable assembly but does not degrade the HTS tape. In an embodiment, the oven is set to a temperature below the melting point of the solder on the HTS tape (e.g., 185°C for PbSn solder), which greatly reduces and ideally can avoid degradation of the HTS tape stack, and allows the temperature throughout the cable (or more appropriately, the cable assembly) to equilibrate. The cable assembly is held at this temperature until the solder supply is fully melted and equilibrates to the process temperature of 200°C. Next, the oven temperature can then be set to a temperature that achieves the desired flow temperature. In embodiments utilizing PbSn solder, the oven temperature may be set to a temperature of approximately 205° C., a waiting period may occur until all points on the cable and solder station piping achieve the desired flow temperature (e.g., a flow temperature of 200° C. for PbSn solder), and temperature monitoring is performed to ensure that no points exceed a temperature of 202° C. (to reduce, and ideally avoid, any degradation of the HTS tape stack). Once these conditions are met, solder flow step 78 may begin (and preferably begins immediately, to reduce, and ideally minimize, heat exposure of the HTS tape stack).

[0097] The application and monitoring of multiple temperature monitoring devices (e.g., thermocouples) within the processing station (an example of which is described below in conjunction with FIG. 8) and at multiple points on the cable can be important to this process because REBCO degradation increases exponentially at temperatures above 200°C. The location of the temperature monitoring devices is selected for each cable geometry. Considerations include the size and expected thermal uniformity of the cable, as well as the power input required to guide the planned cooling process. Temperatures can be adjusted for different solder or HTS tape types. Such an optimized time-temperature profile for solder filling of HTS cables is a critical aspect in the success of the described technology.

[0098] The processing elements 78, 80 implement a loop to ensure that the molten metal flows throughout the cable assembly. In embodiments, the flow of the molten metal through the cable assembly may be achieved at least in part by gravity (e.g., at atmospheric pressure), by a positive displacement pump, or using vacuum pressure techniques. An example of a vacuum pressure technique is described below in conjunction with FIG. 8.

[0099] Once a determination is made at decision block 80 that the molten metal has flowed through the portion of the cable assembly within which the HTS material is disposed, the flow of molten metal is stopped (82) and the molten metal and HTS cable assembly are allowed to cool (84), resulting in a solder-filled HTS cable after cooling is complete.

[0100] In the exemplary method shown in FIGS. 7A and 7B, it should be understood that the method may be practiced without necessarily always performing all of the steps shown in the flowchart, and in the specified order presented. Furthermore, in at least some cases, some steps of the method may be performed simultaneously. As one non-limiting example, in some cases, the application of flux at (68) may be performed before the evacuation of the HTS cable assembly at (66). As another non-limiting example, in some cases, the HTS cable assembly (74) and the melting of the metal (75) may be performed simultaneously, or either step may be initiated or even completed before the other. In some cases, steps (and / or portions of steps) of the exemplary method shown in FIGS. 7A and 7B may be omitted entirely. For example, in some embodiments, step (68), in which flux is applied to the HTS material and discharged, may be omitted. In some embodiments, the purging aspect of step (66) may be omitted, but the vacuum aspect of step (66) may be performed.

[0101] 8, a processing station 90 that may be used to perform a metal filling process, which may be the same as or similar to the process described in conjunction with Figures 7A and 7B, includes an oven sized to accept an HTS cable assembly 94, the resulting HTS cable (not shown in Figure 8), and, optionally, a container 96 (e.g., a crucible) for holding the molten metal, and associated inlet and outlet piping generally indicated at 97. A gas source 95 is coupled to an input 96a of the container 96 through one or more valves V4, V5, and to a flow controller 99 that limits the gas flow rate and therefore the initial viscosity of the solder flow.

[0102] Container 96 (sometimes referred to herein as a "can") is arranged to hold a quantity of metal (e.g., solder) sufficient to fill cable assembly 94 and may be located inside or outside oven 92. In embodiments, the container may be provided having a cylindrical shape of sufficient length and dimensions to hold the metal (e.g., solder). In embodiments, the container may comprise a cylindrical stainless steel (SS) tube of approximately 3.5 inches (8.89 cm) outer diameter configured to hold up to 30 lbs (13.61 kg) of metal (e.g., up to 30 lbs (13.61 kg) of solder bar). Of course, other shapes may be used. In general, however, container 90 should be sized to hold at least a quantity of molten metal sufficient to fill an HTS cable of known size in accordance with the concepts and processes described herein, and ideally with some additional metal flowing through the cable to fill all interstices and flush out any impurities. After reading the description provided herein, one skilled in the art will understand how to select the appropriate amount of metal and therefore the container shape and size (e.g., volume) for a particular application.

[0103] Multiple heaters 98 are disposed around the vessel 96 (e.g., on the interior or exterior surfaces of the vessel 96) and configured to heat the vessel in a desired manner. The heaters may be coupled to one or more controllers 100 that control the heaters. In one embodiment, three 650 W, 120 VAC heaters are thermally coupled to the vessel and controlled by one or more proportional-integral-derivative (PID) processors (not shown in FIG. 8 ). In an embodiment, the controllers may be provided as Solo SL4848-VV series controllers from Automation Direct. In this embodiment, the output of the controller 100 is a voltage pulse that operates relays that gate duty-cycle controlled 120 VAC power to the heaters. Other means for heating the vessel 90 (or for melting the metal inside the vessel) may, of course, be used.

[0104] Multiple thermocouples 102 outside the vessel 96 and two thermocouples 103 at different levels inside the vessel 96 (e.g., disposed in piping such as stainless steel piping of known thickness selected so as not to interfere with the operation of the thermocouples) can be used to control the melting process and establish when melting of the metal inside the vessel is complete. Multiple heaters 99 (two heaters 99 are shown in FIG. 8) proximate the outlet of the vessel 90 are controlled together using a single external thermocouple (TC) 101, and an upper heater 98 (650 W max) is controlled separately from heater 99. The details of the thermocouples and other instrumentation can vary depending on the size and shape of the cable being processed (i.e., the cable to be filled).

[0105] After reading the description provided herein, one skilled in the art will understand how to select the appropriate number, size (in watts), and placement (i.e., physical location) of heaters, as well as the number, characteristics, and placement (i.e., physical location) of thermocouples to suit the needs of a particular application.

[0106] Siphon 104 has a first end coupled to output 96b of vessel 96. The siphon is provided to have a height greater than the height of the molten metal in the vessel so that flow cannot occur without pressurization. In an embodiment, siphon 104 may comprise tubing having a 0.5 inch inner diameter.

[0107] Multiple contact sensors 108 are disposed at various points within the processing station 90 to monitor both the melting and flow of the metal. In an embodiment, the contact sensors may be provided as commercially available single-conductor vacuum feedthrough sensors. In an embodiment, the contact sensors have pins. In an embodiment, the pins may be part of a coaxial structure having a center pin, a ceramic insulator, and a stainless steel outer housing. In one embodiment, the feedthroughs are brazed or otherwise secured to fittings (e.g., threaded end caps) that can be connected to mating fittings on various devices (e.g., siphons, connecting piping, and dump tanks) that are part of the processing station. Some sensors 108 may be disposed near the expected level of liquid solder in the vessel, while sensors 109 may be disposed at different levels or heights within or above the dump tank 110 (either internally or externally). In the exemplary embodiment of FIG. 8, a set of three sensors is disposed at different heights within the dump tank. Such sensor placement may be useful for monitoring the metal filling process and stopping at a desired amount of solder or other metal.

[0108] In one embodiment, to detect the presence of solder, the center pin of the sensor is connected to a DC power source (e.g., 5-24 volts DC) through a light-emitting diode (LED) lamp and a current-limiting resistor. The tank and piping are connected to a reference potential (e.g., electrical ground or 0 VDC) and the voltage on the center pin is recorded.

[0109] In this embodiment, when there is no solder, there is no connection between the center pin of the sensor and a reference potential (e.g., there is no connection between the center pin of the sensor and ground). The LED is off and the recorded voltage is HIGH (e.g., a voltage level corresponding to a logic HIGH value). In the presence of solder, the center pin is grounded. The LED is energized and the recorded voltage is LOW (e.g., a voltage level corresponding to a logic LOW value). Such electronics provide both a visual indication of solder flow that is very useful for rapid manual operation of the process, as well as an electronic record and inlet that is useful for downstream interpretation and can be used for process automation (e.g., using a programmable logic controller).

[0110] In embodiments in which the HTS cable assembly 94 includes a former and an armor disposed about the former, the armor extends beyond the end of the HTS cable assembly 94, as indicated by reference numerals 112a, 112b in FIG. 8. The extensions 112a, 112b allow for a smooth transition of the metal flow (e.g., solder flow) from the fill tube 114 to the cable assembly (e.g., the former and armor) and in the discharge tube 115 leading to the dump tank 110. If it is desired or required that the extension bend, the extension is preferably provided to have a smooth bend.

[0111] Heaters 116a, 116b are disposed adjacent to or coupled to extensions 112a, 112b and heat the extensions to maintain liquid solder in those extensions until the solder in cable assembly 94 solidifies. In embodiments, heaters may be located on either side of each bend in the inlet and outlet tubes 114, 115 or even at each end of the cable assembly. As explained below, the heaters serve to prevent gaps from forming, which may otherwise occur as a result of cooling of the molten metal in the cable assembly.

[0112] The tube 115 at the inlet 110a of the dump tank 110 is provided with a second "U-bend" 140. This prevents the initial solder and flux that flows into the dump tank through the cable to be filled from flowing back into the cable assembly.

[0113] The dump tank holds excess molten metal after it has flowed through the cable assembly. As noted, contact sensors 109 at various heights indicate how much molten metal has reached the dump tank. A variable flow valve (99) adjusts the amount of gas flow (e.g., inert gas flow) and pressure buildup. In an embodiment, an inert gas such as argon may be used, although other inert gases may also be used. In an embodiment, the dump tank may comprise stainless steel having a diameter of approximately 4 inches with an inlet from the top and may be sized to hold up to approximately 10 lbs of excess molten metal (e.g., excess solder). Those skilled in the art will understand how to size a dump tank to meet the needs of a particular application.

[0114] The vessel and dump tank are coupled to (i.e., in fluid communication with) a vacuum system 122 and a gas system 124 that allow them to be either evacuated (typically to 250 mTorr) or pressurized with an inert gas such as argon. Variable flow valve 99 can be used to regulate gas flow and pressure buildup. Valve V4 is an open / close valve, and valve 99 is a flow regulator / valve.

[0115] Thermocouples may be disposed at various points within the system (e.g., on cans, pipes, ovens) and monitored in real time (e.g., via monitors), including thermocouple 130a along the cable 94 to be filled. In an embodiment, for a cable assembly having a length of approximately 10 meters, up to 18 thermocouples may be monitored in real time via two 16-channel Agilent 34972A scanners at a typical rate of 1 second. Such a monitor may also store and display contact sensor status, converted to DC voltage as described above, and pressure gauge analog output. Thermocouple spacing depends on the cable length, geometry, expected thermal uniformity, and planned cooling method.

[0116] The processing station also includes a vacuum and pressurization system 131 comprising a vacuum pump 133 and a plurality of valves 134, and piping 136 that allows the inlet area of the cable assembly and solder can, and the outlet area of the cable assembly 94 and solder dump 110, to be independently evacuated, pumped, or pressurized. It should thus be understood that the cable assembly 94 is coupled to associated piping, fittings, sensors, heaters, thermocouples in a manner that forms a closed system, thereby allowing the various elements (including the cable assembly) to be evacuated and / or pressurized.

[0117] Prior to filling the HTS cable with metal, bypass valve V2 remains open to allow pressure to equalize at each end of cable assembly 94. This siphon area 104 between container 104 and cable assembly 94 prevents premature solder flow before all elements are at the target temperature. Once both the metal in the container and the cable are at their respective target temperatures, metal flow is initiated. In an embodiment, metal flow may be initiated by setting the gas pressure for gas source 95 to the target pressure.

[0118] To allow the metal to flow, bypass valve V2 is closed, allowing a pressure differential between cable assembly ends 94a, 94b. At this point, outlet 96b of vessel 96 is blocked by the molten metal, and pressure from gas source 95 forces the metal from vessel 96, through piping and siphon 104, and into cable assembly 94 via extension 112a.

[0119] In an embodiment, pressurized inert gas from source 95 is applied to the vessel (e.g., by opening valves V4 and V5), thereby forcing the molten metal down through the injection siphon 104 and into the cable assembly. The flow of molten metal continues through the cable assembly, penetrating all vacuum gaps, including any space between and around the HTS materials. Because the molten metal is heavier than the flux, it pushes out any remaining lighter flux in front of it. In this manner, a vacuum-pressure impregnation (VPI) process is provided for filling a cable assembly (e.g., one comprising a tube or armored former) comprising high temperature superconductor material with molten metal.

[0120] A second inverted pipe ("siphon") 139 is used between the cable assembly outlet 94b and the dump tank inlet 110a at a similar height as the inlet siphon 104. This prevents the molten metal from flowing out under gravity. The molten metal remaining in each vertical section 104a, 104b, 139a provides pressure against the metal-filled cable assembly after flowing.

[0121] In embodiments, contact sensors 108, 109 may be used at multiple points in the system to help monitor and control the flow of molten metal. For example, contact sensors may be located internal and / or external to the can, at the container outlet, in the fill siphon, at the cable inlet and / or outlet, and at multiple levels within the dump tank. In embodiments, the contact sensor includes a pin that must be internal to the can and contact the solder. In embodiments, one or more sensors may be disposed in the wall of the can using a through-wall fitting, with the sensor pin positioned so that it can contact the solder when the solder (or other molten metal) reaches the level of the sensor pin. In embodiments, one or more sensors may be disposed in a tube that is internal to the can. Contact sensors at the cable outlet and inside the dump may be used to monitor the flow of molten metal. The use of sensors inside the dump tank at multiple levels allows for the setting of a predetermined amount of molten metal that flows through the cable to flush out flux for optimal filling.

[0122] In an embodiment, typically 2.27 to 4.54 kg (5 to 10 lbs) of molten metal is present in the outlet piping and dump tank, which is sufficient for a cable having a length of approximately 3 meters. Once the target level is reached, bypass valve V2 is opened, thereby re-equilibrating the pressure between the first and second ends of the cable assembly, thereby stopping the flow and ensuring that the inlet piping of the cable assembly is not emptied.

[0123] In an embodiment, the contact sensors 108, 109 may be provided as commercially available single-conductor vacuum feedthroughs having a coaxial structure with a center pin, ceramic insulator, and stainless steel outer housing. For this application, the feedthroughs may be brazed to threaded end caps that may be coupled to mating fixtures on the equipment.

[0124] In embodiments, all tanks, piping, and fixtures may include or consist of conductive copper or stainless steel and may be disposed within an oven to ensure uniform temperature. In embodiments, a vacuum level of several hundred millitorr is typically achieved before flux application, and typically one to several torr after flux application. After reading the disclosure provided herein, one skilled in the art will understand how to select a vacuum level for a particular application. The vacuum ensures an oxygen-free environment before heating and good impregnation of the metal (e.g., solder) into all parts of the cable, around and between the tapes, and even in gaps between the former and sheath surfaces.

[0125] After solder flow, one or more air movers (e.g., blowers) can be used to preferentially direct air to selected zones on the cable to control the cooling profile of the cable. The specific technique for cooling a metal-filled cable is selected according to the cable's geometry. For HTS cables bent into a generally circular or looped shape, movable baffles can be utilized to localize cooling to designated portions of the loop.

[0126] Exemplary Solder Materials and Tape / Cable Structures and Methods of Forming the Same Some aspects of the concepts described herein relate to solders and other liquid metals, and in particular solders or other liquid metals used for superconducting materials or other applications. Particular aspects relate, for example, to structures, such as wires or tapes, that generally include a superconducting material and a portion that includes copper or silver. The structure may be in contact with a metal, such as solder, that is in contact with the copper or silver portion; for example, the metal may be used to form the structure into a cable or other article. While some types of solder may "extract" or remove copper or silver from the structure when in contact with the solder, for example, due to diffusion or dissolution of the metal into the solder, the metals described herein that may be used with the structure may exhibit little or no extraction from the structure. Thus, such metals may help prevent degradation of the structure. Other aspects include methods of making or using such solders and other liquid metals, kits therewith, or the like.

[0127] Certain embodiments relate to solder or other metals being added to superconducting materials, for example, to form cables or other articles. For example, the superconducting material may be present in wires or other structures, and multiple such wires and / or structures may be formed into a cable. The wires may be held or secured in place within the cable using solder or other metal, which may be present in gaps or interstitial spaces created between the wires, for example.

[0128] Examples of superconducting materials that can be used include cuprate superconductors, e.g., rare-earth barium copper oxides (REBCOs), such as yttrium barium copper oxide (YBCO). Such superconductors typically contain oxygen atoms in their atomic structure, which helps such materials exhibit superconductivity when exposed to suitably low temperatures. However, in some cases, some of the oxygen atoms can migrate away, which limits or prevents such materials from becoming superconducting.

[0129] To prevent this from occurring, in some cases, the wire or other structure may include a portion or layer of a material surrounding the superconducting material that prevents or inhibits oxygen migration therethrough. One example of such a material is silver. Thus, in some embodiments, the superconducting material may be partially or completely surrounded by a layer that includes silver, which may prevent oxygen migration away from the superconducting material.

[0130] However, solder in contact with silver or other materials may be able to remove or extract some of the silver (e.g., as silver ions) out of the silver layer, for example, due to diffusion or dissolution of silver into the solder. This process may be exacerbated by higher temperatures, which may increase the rate at which diffusion or dissolution occurs. Thus, for example, solder may be applied in liquid form at relatively high temperatures and may remain at such temperatures for relatively long periods of time (e.g., several hours) during the manufacturing process of a cable or other article. During that time, a surprisingly large amount of silver may be extracted by the solder, resulting in a significantly degraded silver layer and poor performance of the resulting article.

[0131] One way to reduce this effect is to add an intervening layer of another material to the wire or other structure, such as a copper layer around the silver layer. Copper may also provide other benefits, such as electrical or thermal stabilization. For example, if the superconducting material loses its superconducting properties, copper may help absorb heat and / or bypass current around the superconducting material. However, some solders can also extract copper from the copper layer. Thus, solder in contact with the copper layer may initially extract copper from the copper layer, and in such cases, extract so much copper that the solder also comes into contact with the silver layer, resulting in the degradation described above. In some cases, further degradation can occur through intermetallic compound formation with the outer copper layer, such as scalloped intermetallic compound formation. Intermetallic compound formation can reduce the n-value (a measure of performance) of the superconductor and / or allow delamination of the copper and / or silver layers. Thus, various metal layers around the structure can deteriorate.

[0132] Thus, certain embodiments as discussed herein relate to solders and other metals that are unable to extract significant amounts of copper and / or silver from wires or other structures. In some cases, the solder or other metal may contain some amounts of copper and / or silver, e.g., such that the solder or other metal has reduced or no ability to contain additional amounts of copper and / or silver (e.g., to be removed from the wire). For example, the solder may contain a saturation concentration of copper and / or silver and / or a concentration that is greater than the saturation concentration (e.g., at least 50%, at least 75%, at least 90%, at least 95%, etc.).

[0133] A wide variety of solders and other metals may be used, including lead-tin (PbSn) or indium-tin (InSn) solder. Other solders are described in more detail below. Such solders may contain varying amounts of copper and / or silver.

[0134] One non-limiting example of such a structure can be seen in Figure 9. In this figure, an article 10, such as a cable, can include one or more structures 20. The structures 20 can be wires or other structures such as those described herein, and when more than one structure is present in the article 10, they can be the same or different. Only one such structure is provided in detail in this figure for purposes of clarity.

[0135] Such articles may be partially assembled by applying liquid metal around at least a portion of the structure, for example, into gaps or interstitial spaces around the structure, and allowing the liquid metal to cool to form a solid 30 within the article. As noted, the liquid metal may be introduced using a variety of techniques. The metal may also be introduced or used in other applications in other embodiments, not just VPI techniques. Other elements 40 may also be present within the article, for example, to define channels, slots, etc., including the structure 20, while the metal 30 may be used within the article to facilitate thermal and / or electrical contact.

[0136] Structure 20, in this illustration, includes a first region 21, a second region 22 at least partially surrounding the first region, and a third region 23 at least partially surrounding the second region. While only three such regions are shown here for purposes of clarity, fewer or more regions may be present in other embodiments and may be located between any two of these regions or in other suitable configurations. In addition, while they are shown here as having a rectangular cross-section, other shapes (e.g., flat or layered such as that shown in FIG. 1, circular, etc.) are possible in other embodiments. Non-limiting examples include regular (e.g., rectangular, circular, triangular) or irregular cross-sectional shapes.

[0137] In this example, for example, first region 21 may include a superconducting material, such as REBCO or another copper superconductor. Second region 22 may include silver. This region may be used to prevent or inhibit oxygen migration out of first region 21. Third region 23 may include copper. This may be used to at least partially prevent metal 30 from coming into contact with second region 22. As discussed above, in some cases, metal 30 may include copper, e.g., in an amount that can prevent or inhibit copper migration out of third region 33. For example, metal 30 may include a solder, such as PbSn solder, with some copper present. One non-existent example of such a solder is Sn. 62 Pb36 Cu2 (i.e., 62% Sn, 36% Pb, 2% Cu; it should be understood that subscripts within such formulas represent weight percentages rather than stoichiometric ratios).

[0138] Other embodiments are possible in addition to those described above and with reference to Figure 9. Thus, more generally, various aspects of the described concepts relate to various systems and methods for solder or other metals used for superconducting materials or other applications.

[0139] For example, certain embodiments generally relate to cables or other articles that include one or more structures, including wires such as those discussed herein. Non-limiting examples of other articles include superconducting joints or magnets, such as cable structures, pancake-like "wrapped" structures, or the like. Any number of structures may be present in the article, e.g., 1, 2, 3, 4, 5, 6, 7, 8, or more wires or other structures. If more than one is present, the structures may be the same or different. Examples of such structures are provided in more detail herein.

[0140] As mentioned, such articles can be partially assembled by applying solder or other metal in liquid form around at least a portion of a structure, e.g., into the space around the structure, and solidifying the solder or other metal to form a solid, e.g., by cooling. The solder or other metal can fill all or only a portion of the space around the structure. For example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or substantially all of the volume of the article can be filled, e.g., with solder or other metal and / or with structures, wires, or other elements.

[0141] In some cases, the solder or other metal may form a significant portion of the article. For example, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, etc., of the volume of the article may be solder or other metal. However, in some cases, no more than 50%, no more than 45%, no more than 40%, no more than 35%, no more than 30%, no more than 25%, no more than 20%, no more than 15%, no more than 10%, or no more than 5% of the volume of the article may be solder or other metal. Combinations of these ranges are also possible in various embodiments; for example, the solder or other metal may form 5% to 10% of the volume of a cable or other article as discussed herein.

[0142] Any of a wide variety of solders may be used. The solder may be a metal with a relatively low melting point, for example, less than about 250°C or less than 225°C. In another embodiment, the melting point is less than about 200°C. In some cases, the melting point of the solder is at least 100°C, at least 150°C, at least 160°C, at least 170°C, or at least 180°C. Additionally, in certain embodiments, the melting point may fall within any of these ranges. For example, the melting point may be between 180°C and 200°C.

[0143] One, two, three, or more metal elements may be present in the solder or other metals. Non-limiting examples of metal elements include Ag, Pb, Sn, In, Bi, Hg, Zn, or the like. Additionally, in some cases, noble metals, such as those discussed herein, may be present.

[0144] Any of these elements may be present in any suitable combination. For example, the elements may be present in the solder or other metal in a concentration of at least 5 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, at least 70 wt%, at least 75 wt%, at least 80 wt%, etc., and / or 75 wt% or less, 70 wt% or less, 65 wt% or less, 60 wt% or less, 55 wt% or less, 50 wt% or less, 45 wt% or less, 40 wt% or less, 35 wt% or less, 30 wt% or less, or 25 wt% or less. Other percentage ranges are possible for each of the elements in other embodiments.

[0145] As a non-limiting example, the solder or other metal may include at least 10% by weight, at least 20% by weight, at least 30% by weight, at least 40% by weight, at least 50% by weight, at least 60% by weight, at least 70% by weight, etc. (or other percentages as described above) Sn, e.g., in a metal such as PbSn or InSn. As another example, the solder or other metal may include at least 10% by weight, at least 20% by weight, at least 30% by weight, at least 40% by weight, at least 50% by weight, at least 60% by weight, at least 70% by weight, etc. (or other percentages as described above) Pb. As yet another example, the solder or other metal may include at least 10% by weight, at least 20% by weight, at least 30% by weight, at least 40% by weight, at least 50% by weight, at least 60% by weight, at least 70% by weight, etc. (or other percentages as described above) In.

[0146] In some cases, one or two elements may form the majority of the solder or other metal. For example, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, at least 70 wt%, at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt%, or at least 95 wt% of the solder or other metal may be formed by two or three metal elements. As a non-limiting example, a solder may be formed from Pb and Sn, and these two elements may together form at least 50 wt%, at least 55 wt%, etc., of the solder's composition.

[0147] Non-limiting examples of tin-lead solders include Sn 60 Pb 40 , Sn 63 Pb 37 , or various tin-lead solders containing Ag and / or Cu, such as SnPbCu, SnPbAg, or SnPbCuAg (Sn 61 Pb 35 Examples of suitable solders include AgCu and others as discussed herein, each having various compositions, and the like. In addition to tin-lead (SnPb), other non-limiting examples of suitable solders include tin-indium (SnIn) solder. As noted, it should be understood that subscripts within such formulas represent weight percentages rather than stoichiometric ratios.

[0148] As noted, according to certain embodiments, such solder or other metals may include precious metals such as copper (Cu) and / or silver (Ag). Other examples of precious metals include ruthenium (Ru), rhodium (rh), palladium (pd), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au). One, two, three, or more precious metals may be present in various embodiments.

[0149] The noble metal, such as copper or silver, can be present in any suitable amount or concentration. For example, the noble metal can be present in the solder or other metal at at least 0.01 wt%, at least 0.02 wt%, at least 0.3 wt%, at least 0.05 wt%, at least 0.07 wt%, at least 0.1 wt%, at least 0.2 wt%, at least 0.3 wt%, at least 0.5 wt%, at least 0.7 wt%, at least 1 wt%, at least 1.1 wt%, at least 1.2 wt%, at least 1.3 wt%, at least 1.5 wt%, at least 1.7 wt%, at least 2 wt%, at least 2.5 wt%, at least 3 wt%, at least 4 wt%, at least 5 wt%, at least 7 wt%, at least 10 wt%, etc.

[0150] In one set of embodiments, the noble metal is present in the solder or other metal at or near its saturation concentration (however, in some cases this may be exceeded, for example, by creating a supersaturated solution, alloying, or other techniques). Thus, as a non-limiting example, Cu may be present at or near its saturation concentration. Additionally, it should be understood that the saturation concentration may depend on various factors, for example, the saturation concentration may change as a function of temperature. Thus, as a non-limiting example, the saturation concentration may increase or decrease at higher temperatures for some noble metals.

[0151] By way of example, and not wishing to be bound by any theory, it is believed that Cu has a saturation concentration in 65 / 35 Sn-Pb solder of about 0.1 wt. % at approximately 200° C. When this solder is exposed to a copper source (e.g., as discussed herein), the solder can dissolve or extract enough copper to form a Sn-Pb solder having Cu at its saturation concentration. As another non-limiting example, Ag has a saturation concentration of about 2 wt. % in 63 / 37 Sn-Pb solder at approximately 200° C., and when this solder is exposed to a silver source (e.g., as discussed herein), the solder dissolves or extracts enough copper to form a Sn-Pb solder having Cu at its saturation concentration. 62 Pb 36Enough silver can be removed or extracted to form Ag2 (62% Sn, 36% Pb, 2% Ag) or other Sn / Pb solders containing Ag at its saturation concentration.

[0152] Other non-limiting examples include Sn 59 Pb 39 Cu2, Sn 59 Pb 39 Ag2, Sn 58 Pb 38 Cu2Ag2, Sn 96.5 Ag3Cu 0.5 or the like. Solders such as these, and / or solders with different ratios of Sn and / or Pb (and / or other elements) are often commercially available and / or can be produced by passing the solder or other metal, for example, in a liquid state, to a source of precious metal (e.g., Cu, Ag, etc.) to produce a composition including the precious metal.

[0153] Additionally, it should be understood that the noble metal need not be present in the solder or other metal at its saturation concentration in other embodiments. For example, the solder or other metal may include a noble metal, but at a concentration lower (or higher) than its saturation concentration. For example, in certain embodiments, the noble metal may be present in the solder or other metal at a concentration of at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of its saturation concentration.

[0154] In some (but not all) embodiments, the solder or other metal may comprise or consist essentially of any combination of the elements described herein. For example, the solder or other metal may consist essentially of Pb, Sn, and Cu; Pb, Sn, and Ag; Pb, Sn, Ag, and Cu; In, Sn, and Cu; In, Sn, and Ag; In, Sn, Ag, and Cu, or the like. It should be understood that absolute purity is often nearly impossible to obtain as a practical matter. However, in certain embodiments, if other elements are present, they may be present in amounts less than 5 wt. %, less than 1 wt. %, less than 0.1 wt. %, less than 0.01 wt. %, or in amounts too small to substantially alter the melting point of the solder or other metal.

[0155] In certain aspects, as noted, the solder or other metal may be disposed within a cable or other article. For example, the article may be a superconducting article, i.e., an article that exhibits superconducting properties when cooled to a sufficiently low temperature.

[0156] In some cases, the article may be formed as a cable or the like. For example, in some cases, multiple wires or other structures may be included within the cable, e.g., in a twisted or untwisted configuration, and the wires or other structures may have substantially the same or different structures. Solder or other metal may be present between some or all of these. In some cases, the cable may be bent, coiled, molded, formed, or otherwise fabricated into a desired shape (e.g., the final shape of a magnet, current lead, or other structure) prior to or simultaneously with adding the solder or other metal to the cable. In some embodiments, the cable may be provided as a tape-in-conduit cable.

[0157] The cable or other article can have any suitable length, for example, at least 1 m, at least 3 m, at least 10 m, at least 11 m, at least 25 m, at least 50 m, at least 75 m, at least 100 m, or in some cases longer.

[0158] As explained above, the HTS cable may first be placed into a groove in the support structure and then filled with molten metal (e.g., solder), which is then cooled to freeze the HTS cable in place within the groove in the support structure.

[0159] In some cases, for example, the cable may be coiled so that the cable can generate a relatively large magnetic field when a suitable current is passed through the cable. For example, if the cable is cooled so that at least a portion of the wire or other structure becomes superconducting, the coil may be capable of generating a magnetic field of at least 0.01 T, at least 0.1 T, at least 0.3 T, at least 0.5 T, at least 1 T, at least 3 T, at least 5 T, at least 10 T, etc. For example, the cable may be used in a magnetic field magnet (e.g., a toroidal field magnet). In some cases, such a cable may be used in fusion applications, such as, for example, in an affordable, robust, and compact (ARC) fusion reactor, in MRI applications, or the like. In one embodiment, the coil is a non-insulating non-twisted (NINT) coil.

[0160] However, it should be understood that cables such as those described herein (e.g., including solder and / or liquid metal as discussed herein) can be used not only in fusion applications but also in a variety of other applications as well, including, but not limited to, nuclear magnetic resonance, magnetic resonance imaging, magnetic material separation, accelerator / HEP magnets, disposable mixing systems, generators and motors, fault current limiters, RF filtering, SQUID (Superconducting Quantum Interference Device) circuits, transmission lines, magnetic energy storage, transformers, and current leads for low-temperature superconducting cables.

[0161] Various methods can be used to cool an article so that it becomes superconducting. For example, the article can be cooled by exposure to liquid nitrogen (which has a boiling point of 77 K), liquid neon (which has a boiling point of 25 K), liquid hydrogen (which has a boiling point of 20 K), or liquid helium (which has a boiling point of 4 K). Other cooling techniques can also be used in other embodiments to cause an article to become superconducting. Thus, during use of a cable or other article, it can be at least partially exposed to a cryogenic fluid (e.g., liquid nitrogen, liquid hydrogen, liquid helium, etc.) and / or low temperatures (e.g., temperatures below 180 K, below 140 K, below 100 K, below 77 K, below 50 K, below 20 K, below 10 K, below 4 K, below 2 K, etc.). As a further example, the article can be cooled by exposure to gaseous hydrogen, gaseous or supercritical helium (e.g., at cryogenic temperatures such as those described herein), conduction cooling using a cryocooler, or the like.

[0162] In some embodiments, the cable or other article comprises a superconducting material. As discussed, a superconducting material can exhibit superconductivity when cooled to a sufficiently low temperature.

[0163] A variety of superconducting materials can be used. For example, the superconducting material can be a low-temperature superconducting material (which exhibits superconductivity at temperatures below about 30 K in a self-field or zero external field) or a high-temperature superconducting material (which exhibits superconductivity at temperatures above about 30 K in a self-field or zero external field). For example, a high-temperature superconducting material can exhibit superconductivity when cooled using liquid nitrogen or liquid hydrogen. In some cases, a high-temperature superconducting material can exhibit superconductivity at temperatures below 140 K, below 77 K, or below 20 K.

[0164] Non-limiting examples of high-temperature superconducting materials include cuprate superconductors. An example of a cuprate superconductor is a rare-earth barium copper oxide (REBCO) material. Specific, non-limiting examples include yttrium barium copper oxide (YBCO) or bismuth strontium calcium copper oxide (BSCCO). Other examples include, but are not limited to, MgB2, lanthanum barium copper oxide (LBCO), thallium barium calcium copper oxide (TBCCO), mercury barium calcium copper oxide (HBCCO), or the like. As noted, such superconductors typically contain oxygen atoms within their atomic structure. However, some of the oxygen atoms can migrate away, which can limit or prevent such materials from becoming superconducting.

[0165] Thus, in some cases, the superconducting material may be contained within a first region within a cable or other article and partially or completely surrounded by a second region. Thus, the second region may substantially separate the first region from a third region or element (such as solder or other metal) outside the wire, tape, or other structure. The second region may be partially or completely impermeable or impermeable to oxygen, for example, to prevent oxygen from migrating away from the superconducting material.

[0166] By way of example, in one set of embodiments, the second region can comprise silver. In one embodiment, the second region consists essentially of silver. In certain cases, at least 50%, at least 75%, at least 90%, at least 95%, at least 99%, or substantially all of the second region can comprise silver.

[0167] The second region can be positioned directly adjacent to the first region, or one or more intervening regions can exist between the first and second regions. In addition, the second region can have any suitable thickness. For example, the second region can have an average cross-sectional thickness that is less than 10 micrometers, less than 8 micrometers, less than 7 micrometers, less than 6 micrometers, less than 5 micrometers, less than 4 micrometers, less than 3 micrometers, less than 2 micrometers, less than 1 micrometer, etc. In some cases, the second region can have a substantially uniform thickness, while in other cases, the second region may not have a substantially uniform thickness.

[0168] Additionally, in certain embodiments, the second region may be partially or completely surrounded by a third region (which in some embodiments, as described above, may partially or completely surround the first region; thus, the third region may be an outer region that further surrounds the interior or first region). In some embodiments, the third region may prevent the second region from contacting and integrating with elements (such as solder or other metal) outside the wire, tape, or other structure. The third region of the wire or other structure may be in contact with the solder or other metal, or there may be an additional region between the third region and the solder or other metal.

[0169] By way of example, in one set of embodiments, the third region may include copper. In one embodiment, the third region consists essentially of copper. In certain cases, at least 50%, at least 75%, at least 90%, at least 95%, at least 99%, or substantially all of the third region may include copper.

[0170] The third region can be positioned directly adjacent to the second region, or one or more intervening regions can exist between the second and third regions. In addition, the third region can have any suitable thickness. For example, the third region can have an average cross-sectional thickness that is less than 10 micrometers, less than 8 micrometers, less than 7 micrometers, less than 6 micrometers, less than 5 micrometers, less than 4 micrometers, less than 3 micrometers, less than 2 micrometers, less than 1 micrometer, etc. The thickness of the third region can be the same as or different from that of the second region. In some cases, the third region can have a substantially uniform thickness, while in other cases, the third region may not have a substantially uniform thickness.

[0171] As noted above, even if an outer region of a wire or other structure includes copper (or another noble metal, such as silver) and is in contact with solder or other metal, in certain embodiments, the solder or other metal cannot significantly remove or extract the copper or other metal from a third region of the wire or other structure. Thus, the concentration of copper or other metal in the third region can remain substantially homogeneous.

[0172] As mentioned, according to certain aspects, solder or other metals may be introduced into cables or other articles using a variety of techniques, such as those described herein.

[0173] In some cases, the article and / or structures contained within the article may serve to define spaces that can be filled with solder or other metals. For example, the article and / or portions of the structures contained within the article may define gaps, channels, slots, grooves, or the like. Of course, it should be understood that any number of these may be present, and that the particular number may be selected to meet the needs of the particular application in which the cable or other article will be used. The gaps, channels, slots, grooves, or the like may have any regular (e.g., rectangular, circular, triangular, square, etc.) or irregular cross-sectional shape. Furthermore, depending on the application, each of these may or may not have the same cross-sectional shape.

[0174] In some cases, some or all of these may include solder or other metal. For example, in some embodiments, some of the channels may have a spiral shape. As mentioned, the solder or other metal may partially or completely fill them, such that, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or substantially all of the volume comprises metal.

[0175] The solder or other metal may be solid at room temperature and may be heated to liquefy it. Various methods may be used to heat the solder or other metal, including resistance heating, placing the solder or other metal in a heated crucible, hot air heating, exposure to a flame, a torch, or another heating source such as a soldering gun or ionizer. The solder or other metal may be heated to a temperature at least sufficient to melt, e.g., 180°C to 200°C, or other temperature ranges for melting points as discussed herein. For example, the solder or other metal may be heated to a temperature of at least 150°C, at least 180°C, at least 190°C, etc.

[0176] In some cases, the temperature of the solder or other metal may be maintained at a temperature sufficient to keep the solder or other metal liquid for a relatively long period of time, e.g., at least 5 minutes, at least 10 minutes, at least 15 minutes, at least 30 minutes, at least 1 hour, at least 2 hours, at least 3 hours, at least 4 hours, at least 5 hours, etc. For example, if the cable is relatively long, it may take a relatively long time to produce such a long cable, during which time the temperature of the solder or other metal is maintained high enough to keep it liquid.

[0177] Additionally, once installed, any technique can be used for cooling, including passive cooling (exposure to ambient temperature) or active cooling techniques such as increased airflow, refrigeration, or the like.

[0178] The following examples are intended to illustrate certain embodiments, but do not exemplify the full scope of the concepts described. [Example]

[0179] In this embodiment, solder is added to a cable that has slots or channels to hold stacks of superconducting wires or "tapes."

[0180] Conventional Pb 40 Sn 60 Solder (40% Pb, 60% Sn) is one of the cheapest choices for solder, but Pb 40 Sn 60Solder has solubility issues with both copper and silver (which may be present in the tape). For example, a single HTS tape may be confined within a layer of silver and / or a layer of copper to protect and maintain the tape's superconducting properties. The silver layer may prevent oxygen from diffusing out of the tape's superconducting layer (labeled "REBCO" in Figure 10) to prevent degradation of tape performance. Similarly, the outer copper layer of the tape may function as an electrical and / or thermal "stabilizer." This may allow a finite amount of current sharing within the copper when the superconducting layer becomes resistive. However, studies have shown that when the tape is immersed in a PbSn solder bath above 200°C, a large portion of the silver or copper may be removed or "extracted" from the tape, causing degradation of the tape or its performance.

[0181] Thus, this example demonstrates that saturating PbSn solder with copper (Cu) can prevent solubility and / or diffusion problems with the copper layer of the tape. This may be due, for example, to a reduced concentration gradient between the tape and the solder mixture. In addition to protecting the copper layer, the solder may prevent tin exposure to the silver layer. This may be useful in preserving the superconducting performance of the tape when exposed to the solder. Such a technique may be used, for example, to allow sufficient time to successfully solder long lengths of cable without degradation of superconducting performance, or for other applications such as those discussed herein. One example of such a solder is a Sn 62 Pb 36 Cu2 (62% Sn, 36% Pb, 2% Cu), which was used in this example in a mixture for up to 3 hours at elevated temperature, however, longer times and / or other types of solder may also be used in other embodiments.

[0182] This example uses solder to solder long lengths (hundreds of meters) of multiple PbSn-coated tapes layered in a multi-tape stack. The solder is injected along square channels inside the copper structure carrying the multi-stack of tapes. The solder fills the gaps in the slots to ensure thermal and electrical contact of the tapes to the copper structure. This can help optimize cable performance by allowing better current sharing, heat removal, and / or structural support.

[0183] Because this solder is used in long lengths of cable, the tape and cable may likely experience elevated solder temperatures for extended periods of time (e.g., 1-3 hours). 62 Pb 36 Experiments using the Cu2 composition, as discussed herein, successfully soldered REBCO tape for 3 hours without any significant performance degradation being observed.

[0184] Sn 62 Pb 36 Cu2 solder can be supplied in many forms (solder bars or solder wire) and is commercially available, however, it has not previously been applied to soldering tapes (in a solder bath or solder impregnation process) at elevated temperatures for extended periods of time to mitigate performance degradation, as previously mentioned.

[0185] In some experiments, solder was used during solder bath experiments with PbSn-plated REBCO tape. The tape was exposed to Sn for different exposure times (e.g., 60 min to 210 min) at 193 °C. 62 Pb 36 The tapes were exposed to a Cu2 bath. The critical current was tested for all tapes before and after each exposure time to determine superconducting degradation.

[0186] Sn 62 Pb 36 Cu2 can be applied to the tape stack in many ways. 62 Pb36 The Cu solder bar can be purchased commercially. The bar is then placed inside a holding pot and heated to a temperature above the liquidus point. Once in liquid form, the solder is injected into the copper cable channels containing the HTS tape using a pressure impregnation process.

[0187] Solder mixtures can also be used in wire form. The solder can be applied to the tape, for example, using a soldering iron technique or a hot plate. As another example, thin strips of flattened solder wire can be pancaked between or on top of the stack. When the tape stack is heated above its melting point, the solder can adhere all the tapes to each other and fill any gaps.

[0188] Different compositions are possible, for example, Sn 62 Pb 36 In addition to Cu2, Pb, Sn, and Cu may be used in the solder mixture. The solder may have a relatively low melting point (e.g., below 200°C). In some cases, the solder composition may prevent, avoid, or at least minimize scavenging of protective layers, such as silver and / or copper layers, around the superconductor. This can be generalized to a variety of different superconducting protective layers and non-scavenging solder combinations. For example, having a low melting point and non-scavenging properties allows the superconductor to be held at the elevated temperatures and times required to solder it over long lengths without substantial degradation of its superconducting performance.

[0189] While several embodiments of the concepts described herein have been described and illustrated herein, those skilled in the art will readily envision various other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each such variation and / or modification is deemed to be within the scope of the concepts described herein. More generally, those skilled in the art will understand that all parameters, dimensions, materials, and configurations described herein are intended to be exemplary, and that the actual parameters, dimensions, materials, and configurations will depend on the particular application or applications for which the teachings of the concepts described herein are used. Those skilled in the art will recognize or be able to ascertain, using no more than routine experimentation, many equivalents to the specific embodiments of the concepts used herein. Accordingly, it should be understood that the foregoing embodiments are presented merely by way of example, and that, within the scope of the appended claims and their equivalents, the described concepts may be practiced differently from what is specifically described and claimed. The concepts described herein relate to each individual feature, system, article, material, kit, and / or method described herein. Additionally, any combination of two or more such features, systems, articles, materials, kits, and / or methods is included within the scope of the concepts described herein, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent.

[0190] In the event that the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and / or inconsistent disclosure with respect to each other, the document having the later effective date shall control.

[0191] All definitions as defined and used herein shall be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0192] The indefinite articles "a" and "an," as used in the specification and claims, unless expressly indicated to the contrary, shall be understood to mean "at least one."

[0193] The term "and / or," as used in the specification and claims, shall be understood to mean "either or both" of the elements so coordinated, i.e., elements that are present conjunctively in some cases and disjunctively in other cases. Multiple elements listed with "and / or" shall be construed in the same manner, i.e., "one or more" of the elements so coordinated. Other elements, whether related or not to those elements specifically identified, may optionally be present beyond the elements specifically identified by the "and / or" clause. Thus, as a non-limiting example, a reference to "A and / or B," when used in conjunction with open-ended language such as "comprising," may refer in one embodiment to A only (optionally including elements other than B); in another embodiment to B only (optionally including elements other than A); in yet another embodiment to both A and B (optionally including other elements), etc.

[0194] As used in this specification and claims, "or" shall be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including two or more of several elements or lists of elements, and optionally, additional unlisted items. Only terms expressly indicated to the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," shall refer to the inclusion of exactly one element of several elements or lists of elements. In general, as used herein, the term "or" shall only be interpreted as indicating exclusive alternatives (i.e., "one or the other, but not both") when followed by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of."

[0195] As used in this specification and claims, the phrase "at least one" in connection with a list of one or more elements should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but does not necessarily include at least one of each and every element specifically listed in the list of elements, nor does it exclude any combinations of elements in the list of elements. This definition also allows for elements to optionally be present other than those specifically identified in the list of elements to which the phrase "at least one" refers, whether related or not to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B" or, equivalently, "at least one of A and / or B") can refer in one embodiment to at least one A (and optionally including more than one) with no B present, in another embodiment to at least one B (and optionally including more than one) with no A present, in yet another embodiment to at least one A, optionally including more than one, and at least one B (and optionally including other elements), optionally including more than one, etc.

[0196] When the word "about" is used herein in connection with a number, it is to be understood that yet another embodiment may include the number unmodified by the presence of the word "about."

[0197] It is also to be understood that, unless expressly stated to the contrary, in any method claimed herein including two or more steps or actions, the order of the method steps or actions is not necessarily limited to the order in which the method steps or actions are recited.

[0198] In the claims, as well as in the above specification, all transitional phrases such as "comprise," "include," "hold," "have," "contain," "involve," "hold," "consist of," and the like, shall be understood to be open-ended, i.e., to mean an inclusion without limitation. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

1. A method of manufacturing a cable, comprising: inserting an HTS cable having first and second high temperature superconductor (HTS) tape stacks and a former separating the first and second HTS tape stacks into a groove in a support structure; and pouring molten metal into the HTS cable while the HTS cable is placed in the channel.

2. 2. The method of claim 1, wherein the molten metal is molten solder, and wherein the step of flowing the molten metal into the HTS cable comprises flowing the molten solder into the HTS cable.

3. 3. The method of claim 1, wherein the step of inserting the HTS cable into the groove comprises inserting and spiraling the HTS cable into the groove.

4. The method of any of claims 1 to 3, further comprising the step of cooling the molten metal to solidify the molten metal.

5. 5. The method of claim 1, wherein the support structure is a first support structure, and the method further comprises the steps of inserting a second HTS cable into a second groove of the second support structure, and pouring a second molten metal into the second HTS cable while the second HTS cable is in the groove.

6. The method of claim 5 further comprising the step of mounting the first support structure to the second support structure.

7. The method of claim 5 or 6, further comprising the step of electrically connecting the HTS cable with the second HTS cable.

8. A magnetic structure comprising: a support structure having a groove; a high temperature superconductor (HTS) cable having first and second HTS tape stacks and a former separating the first and second HTS tape stacks; Equipped with The HTS cable includes a metal at least partially filling the HTS cable and a magnetic structure disposed within the groove.

9. The magnetic structure of claim 8 , wherein the metal comprises a solder.

10. 10. The magnet structure of claim 8 or 9, wherein the shape of the HTS cable matches the shape of the groove.

11. the HTS cable comprises a plurality of flow paths and a plurality of HTS tape stacks disposed in each of the plurality of flow paths; The magnetic structure of any one of claims 8 to 10, wherein the plurality of HTS tape stacks includes a first and a second tape stack.

12. The magnetic structure according to any one of claims 8 to 11, wherein the former includes a conductive metal.

13. The magnetic structure according to any one of claims 8 to 12, further comprising an electrical insulator that insulates the plurality of sections of the former from each other.

14. The magnetic structure of claim 12 , wherein the conductive metal comprises copper or steel.

15. The magnet structure according to any one of claims 8 to 14, wherein the HTS cable comprises cooling channels.

16. The magnet structure according to any one of claims 8 to 15, wherein the first and second HTS tape stacks are twisted along the length of the HTS cable.

17. The magnetic structure according to any one of claims 8 to 16, wherein the support structure comprises an electrically conductive material.

18. The magnet structure according to any one of claims 8 to 17, wherein the HTS cable has a helical shape within the groove.

19. 19. The magnet structure according to claim 8, wherein the HTS cable has a plurality of windings, and the respective windings of the plurality of windings are electrically coupled to each other via the support structure.

20. A magnetic structure having a first magnetic structure and a second magnetic structure, The first magnetic structure is a magnetic structure according to any one of claims 8 to 19, The second magnet structure comprises: a second support structure having a second groove; a second HTS cable; and Equipped with the second HTS cable includes a second metal at least partially filling the second HTS cable and is disposed in the second groove; The HTS cable is electrically connected to the second HTS cable.

21. The magnet structure according to any one of claims 8 to 20, wherein the HTS cable comprises an outer sheath, and the first and second HTS tape stacks are disposed within the outer sheath.

22. 22. The magnet structure of claim 21, wherein said sheath and said first and second HTS tape stacks extend along the length of said HTS cable.

23. A magnet structure according to any one of claims 8 to 22, wherein the support structure comprises a plate.

24. A method according to any one of claims 1 to 7, wherein the first and second HTS tape stacks are capable of sliding along the length of the HTS cable when the HTS cable is inserted into the groove.

25. The method of any of claims 1 to 7 or 24, wherein pouring molten metal into the HTS cable comprises pouring the molten metal into a channel in the HTS cable.

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