发明领域field of invention
本发明涉及将超导导线连接在一起的方法，以及可由此类方法制得的接头(joint)。The present invention relates to methods of joining together superconducting wires, and joints which may be made by such methods.
背景技术Background technique
当由超导导线制造如电磁体这样的设备时，通常要求将单独的导线长度连接在一起。如果必需在“持久化模式”下运行，为了保持设备的超导性，接头处也必须是超导的，或至少显示出非常低的电阻。通常情况下，需要约为10-13欧姆的接头电阻来启用这种运行模式。在“持久化模式”下运行是非常可取的，因为在初始通电后，这已经实现了电源供应的分配。When fabricating devices such as electromagnets from superconducting wire, it is often required to join the individual wire lengths together. If it is necessary to operate in "persistence mode", in order to maintain the superconductivity of the device, the junction must also be superconducting, or at least exhibit very low resistance. Typically, a tap resistance of about 10-13 ohms is required to enable this mode of operation. Running in "persistence mode" is highly desirable as this enables distribution of the power supply after the initial power-on.
超导材料的近期发展已带动二硼化镁MgB2作为超导材料使用。二硼化镁MgB2的优势是，其在较高的温度下能比更常规的材料表现出超导性，这避免了需要将超导体冷却到很低的温度。然而，该材料本身是脆性的，并且难以将其连接以形成持续的接头。The recent development of superconducting materials has led to the use of magnesium diborideMgB2 as a superconducting material. The advantage of magnesium diboride, MgB2 , is that it exhibits superconductivity at higher temperatures than more conventional materials, which avoids the need to cool the superconductor to very low temperatures. However, the material itself is brittle, and it is difficult to join it to form a continuous joint.
图1示出了典型的MgB2-芯超导体10的剖示图。超导细丝4包含基本上以颗粒状、粉末状的形式保持在铌金属护套2内的MgB2-芯1。这些MgB2填充的铌护套进一步被包裹在高强度的、导电的金属或合金(例如被称为“MONEL”的Cu-Ni合金)基体3中。基体3和细丝4构成超导导线7。铌2的目的是防止在导线制造过程中MgB2和基体材料之间发生不需要的反应。FIG. 1 shows a cross-sectional view of a typical MgB2 -core superconductor 10 . The superconducting filament 4 comprises a MgB2 -core 1 held in a niobium metal sheath 2 essentially in granular, powdery form. These MgB2 -filled niobium sheaths are further encased in a matrix 3 of a high-strength, electrically conductive metal or alloy (such as the Cu-Ni alloy known as "MONEL"). The matrix 3 and the filaments 4 constitute a superconducting wire 7 . The purpose of Niobium 2 is to prevent unwanted reactions between MgB2 and the base material during the wire manufacturing process.
在一种制造方法中，将颗粒状或粉末状的MgB2置于基体材料坯(a billet ofmaterix material)的铌内层的钻孔中，被称为非原位过程(ex-situ process)。然后，完整的坯被拉成最终所需的导线直径。铌加套(Niobium-cased)的超导细丝在拉丝过程中成形并被压实。In one manufacturing method, granular or powderedMgB2 is placed in drilled holes in the niobium inner layer of a billet of materialix material, known as the ex-situ process. The completed billet is then drawn to the final desired wire diameter. Niobium-cased superconducting filaments are shaped and compacted during the drawing process.
基体3配备有导电的分流器和散热片(thermal sink)。如有任何超导丝4骤冷，则热量会通过基体3被带离骤冷区域，并且电流将流经基体所提供的较低的电阻。这将使细丝的骤冷部分冷却到超导状态。基体也使得超导导线机械上更为坚固。The base body 3 is equipped with electrically conductive shunts and thermal sinks. If any of the superconducting filaments 4 are quenched, the heat will be carried away from the quenched area through the matrix 3 and current will flow through the lower resistance provided by the matrix. This will cool the quenched part of the filament to a superconducting state. The matrix also makes the superconducting wire mechanically stronger.
导体10通常还包括稳定导槽5(channel)。该稳定导槽5可以是铜或其它材料的，或者是组合材料的。该导槽应是能导电和导热的。在图示的例子中，导线7被焊接6到导槽5的空腔中。导槽5以参照基体3所阐释的相同的方式，进一步地增强了超导导线7的电和热稳定性，以及机械坚固性。The conductor 10 also typically includes stabilizing channels 5 (channels). The stabilizing channel 5 can be made of copper or other materials, or a combination of materials. The channel should be electrically and thermally conductive. In the example shown, the wire 7 is welded 6 into the cavity of the channel 5 . The guide grooves 5 further enhance the electrical and thermal stability, as well as the mechanical robustness, of the superconducting wire 7 in the same manner as explained with reference to the base body 3 .
为了制造超导接头，两种常规的方法已被采纳：第一，可以在待连接的导线的MgB2芯1之间直接形成接头。或者，使用另一种材料在超导装置中将导线的MgB2芯1电连接在一起，该材料在导线的运行温度下也是超导的。通常情况下，已知的连接方法涉及暴露出待连接的超导导线的MgB2芯，并且将暴露出的相应导线的MgB2颗粒机械性地挤压在一起，以形成超导接头。在一些已知的设置中，会将如超导材料的中间层，通常为金属(例如铟)置于相应导线暴露出的芯之间，以增加接触面的面积和提高相应导线颗粒之间的机械密合性。这些方法都要求对MgB2颗粒施加大的机械负荷。MgB2颗粒相对来说是脆性的，施加这样的大机械负荷有压裂MgB2超导材料的风险，会导致超导接头故障。To fabricate superconducting joints, two conventional methods have been adopted: first, the joint can be formed directly between theMgB2 cores 1 of the wires to be joined. Alternatively, the wire'sMgB2 core 1 is electrically connected together in a superconducting device using another material that is also superconducting at the wire's operating temperature. Typically, known joining methods involve exposing theMgB2 cores of the superconducting wires to be joined and mechanically squeezing together the exposedMgB2 particles of the corresponding wires to form a superconducting joint. In some known arrangements, an intermediate layer such as a superconducting material, usually a metal such as indium, is placed between the exposed cores of the corresponding wires to increase the area of the contact surface and improve the contact between the particles of the corresponding wires. mechanical tightness. These methods all require a large mechanical load on theMgB2 particles.MgB2 particles are relatively brittle, and applying such large mechanical loads risks fracturing theMgB2 superconducting material, leading to failure of the superconducting joint.
在一些已知方法中，例如在通过MgB2粉末或镁和硼的粉末之间的反应来连接时，MgB2颗粒被暴露出来并被加热。如果将MgB2颗粒暴露，就有被氧化的风险。在将接头设置在超导装置(如低温容器内的磁铁)中之后，故障可能会发生在连接过程后的一段时间。由于存在使接头与设置在低温容器和/或真空容器等中的超导装置接触的接触问题，修复这样的故障是非常昂贵和耗时的。因此，本发明的一个目的是提供一种用于连接MgB2芯超导导线的方法，该方法降低了MgB2颗粒的机械损伤或氧化的风险。In some known methods, for example when joining by reaction betweenMgB2 powder or powders of magnesium and boron, theMgB2 particles are exposed and heated. IfMgB2 particles are exposed, there is a risk of oxidation. Failure can occur some time after the joining process, after setting the joint in a superconducting device, such as a magnet inside a cryogenic vessel. Repairing such faults is very expensive and time consuming due to contact problems that bring the joints into contact with superconducting devices disposed in cryogenic vessels and/or vacuum vessels, etc. It is therefore an object of the present invention to provide a method for joiningMgB2 core superconducting wires which reduces the risk of mechanical damage or oxidation of theMgB2 particles.
然而，基于MgB2的超导导线之间的常规接头的测试已经表明，磁场容差值(magnetic field tolerance value)比预期的差。这被认为是由于实际发生的传导是通过护套2的铌的，而非通过对应导线的MgB2颗粒之间的超导接头。铌是一种“第二类”超导体，但相比于其它第二类超导体，如铌钛合金，它具有非常低的高临界磁场强度(uppercritical magnetic field strength)Bc2。铌的临界磁场在零点几特斯拉的范围内，其精确值取决于许多因素，最明显的是电流密度。因为非常希望的是用于超导磁铁中的接头应该能够承受相当高的磁场，因此对于电流传输，任何利用铌护套的连接方法可能是没有多大用处的。However, tests of conventional joints betweenMgB2 -based superconducting wires have shown that the magnetic field tolerance values are worse than expected. This is believed to be due to the fact that conduction actually occurs through the niobium of the sheath 2, rather than through the superconducting joints between theMgB2 particles of the corresponding wires. Niobium is a "type 2" superconductor, but it has a very low upper critical magnetic field strength Bc2 compared to other type 2 superconductors, such as niobium-titanium alloys. The critical magnetic field for niobium is in the range of a few tenths of a Tesla, the exact value of which depends on many factors, most notably the current density. Since it is highly desirable that joints used in superconducting magnets should be able to withstand relatively high magnetic fields, any connection method utilizing a niobium sheath may not be of much use for current transmission.
在WO2007/128635A1、US2008/0236869A1、US6921865B2和US7152302B2中描述了某些制造超导接头的常规方法。Some conventional methods of making superconducting joints are described in WO2007/128635A1 , US2008/0236869A1 , US6921865B2 and US7152302B2.
发明内容Contents of the invention
本发明从而提供用于制造有铌护套的超导导线(例如具有MgB2芯的，或具有NbTi芯的导线)之间的超导接头的方法，以及例如可通过本发明的方法制造的接头，正如在所附的权利要求书中所限定的那样。The present invention thus provides a method for producing a superconducting joint between niobium-sheathed superconducting wires, for example with aMgB2 core, or a wire with a NbTi core, and joints such as can be produced by the method of the invention , as defined in the appended claims.
附图说明Description of drawings
结合附图，通过以下本发明的某些实施方式的描述，上文所述的以及进一步的目的、特征和本发明的优点将变得更加显而易见。其中：The above and further objects, features and advantages of the present invention will become more apparent through the following description of certain embodiments of the present invention in conjunction with the accompanying drawings. in:
图1示出了一个典型的有铌护套的MgB2芯(niobium-sheathed,MgB2-cored)的超导体的剖视图;Figure 1 shows a cross-sectional view of a typical MgB2 core (niobium-sheathed, MgB2 -cored) superconductor with a niobium sheath;
图2示出了处在本发明连接方法的早期阶段的两根超导导线；Figure 2 shows two superconducting wires in the early stages of the connection method of the present invention;
图3示出了正在进行的本发明连接方法的后续步骤中的图2的导线；Fig. 3 shows the wire of Fig. 2 in the follow-up step of connection method of the present invention in progress;
图4A-4C示出了处在本发明连接方法的各个阶段中的有铌护套的、MgB2芯的超导细丝的横截面；Figures 4A-4C show cross-sections of a niobium sheathed, MgB core superconducting filament at various stages of the bonding method of the present invention;
图5示出了图4C的局部放大图；Figure 5 shows a partially enlarged view of Figure 4C;
图6示出了处在本发明方法的后一阶段的图2和图3中的导线；Figure 6 shows the wires in Figures 2 and 3 at a later stage of the method of the invention;
图7示出了在图6中所示的步骤之后的根据本发明的实施方式完成的接头；Figure 7 shows the finished joint according to an embodiment of the invention after the steps shown in Figure 6;
图8示出了通过如在图7中所示的根据本发明的接头的局部横截面；Figure 8 shows a partial cross-section through a joint according to the invention as shown in Figure 7;
图9示出了在图8中标识为IX的区域放大图；Figure 9 shows an enlarged view of the area identified as IX in Figure 8;
图10示出了根据本发明的另一个实施方式的用来准备连接的导线；FIG. 10 shows wires for preparing connections according to another embodiment of the present invention;
图11示出了根据本发明的一个实施方式的用来形成超导接头的方法的各个阶段；以及Figure 11 shows various stages of a method for forming a superconducting joint according to one embodiment of the invention; and
图12示出了可通过图11示出的方法形成的根据本发明的接头的横截面。FIG. 12 shows a cross-section of a joint according to the invention which may be formed by the method shown in FIG. 11 .
具体实施方式detailed description
本发明提供用于连接有铌护套的超导导线的方法和例如可通过这样的方法制备的接头。The present invention provides a method for joining superconducting wires sheathed with niobium and, for example, joints which can be produced by such a method.
根据本发明，将有铌护套的超导细丝4浸泡在液态的锡(Sn)中，使铌护套与锡反应生成Nb3Sn。按照惯例，在长时间的、高温的反应过程中通过锡扩散进铌细丝中来制备Nb3Sn超导体细丝。根据本发明，采用类似的过程来连接有铌护套的导线。According to the present invention, the superconducting filament 4 with the niobium sheath is immersed in liquid tin (Sn), and the niobium sheath reacts with the tin to form Nb3 Sn. Conventionally,Nb3Sn superconductor filaments are prepared by tin diffusion into niobium filaments during a long, high temperature reaction process. According to the invention, a similar procedure is used to connect niobium-sheathed wires.
Nb3Sn是一种超导体，其具有比铌(4K时，～0.5T)高得多的磁场容差(4K时，～18T)，以及约为18K的更高的临界温度Tc。Nb3Sn也具有更大的相干长度(coherencelength)，从而使得在反应后的护套和MgB2超导颗粒或粉末之间电流能无损耗地传输。相干长度显示出可能存在于超导体之间(但超导体之间仍然存在超导性)的间隙的大小。通过具有护套材料(例如具有较大相干长度的Nb3Sn)可以保持护套材料和包封的MgB2颗粒之间的超导性。因此，如果超导导线中的铌护套能被转化成Nb3Sn，接头的磁场容差应该能大幅度地增加，并且在MgB2颗粒和护套材料之间的传输电流应该能够被提高。Nb3Sn is a superconductor with a much higher magnetic field tolerance (~18T at 4K)than niobium (~0.5T at 4K), and a higher critical temperatureTc of about 18K. Nb3 Sn also has a greater coherence length, enabling lossless transmission of current between the reacted sheath and the MgB2 superconducting particles or powder. The coherence length shows the size of the gap that might exist between superconductors (but still have superconductivity between superconductors). Superconductivity between the sheath material and the encapsulatedMgB2 particles can be maintained by having a sheath material such asNb3Sn with a larger coherence length. Therefore, if the niobium sheath in the superconducting wire can be converted to Nb3 Sn, the magnetic field tolerance of the joint should be greatly increased, and the transmission current between the MgB2 particles and the sheath material should be improved.
在已知的连接MgB2芯导线的方法中，据认为大部分电流通过的是护套材料，而不是直接从一根导线的芯到另一根导线的芯。本发明提供了一种特别有利的护套材料，使得这样的电流传输能更有效地运作。In known methods of joining MgB2 -core wires, it is believed that most of the current passes through the sheath material rather than directly from the core of one wire to the core of the other wire. The present invention provides a particularly advantageous sheath material that enables such current transmission to function more efficiently.
将细丝4的反应后的护套2通过超导材料连接。本发明避免了暴露MgB2颗粒并且在它们之间建立机械连接的需要。据相信，MgB2向热的锡暴露，会导致形成不受欢迎的化合物作为污染物。这将降低交界处可获得的品质。The reacted sheaths 2 of the filaments 4 are connected by superconducting material. The present invention avoids the need to expose theMgB2 particles and create a mechanical connection between them. It is believed that exposure ofMgB2 to hot tin can lead to the formation of undesirable compounds as contaminants. This will reduce the quality available at the junction.
本发明的接头具有相对较高的磁场容差和相对较高的临界温度Tc。根据本发明的方法形成的接头被认为能在被连接的导线的超导细丝之间提供良好的导电和机械的连接；与类似导线间的常规接头相比能提高接头的磁场容差；并且能防止发生机械损伤。The joint of the present invention has a relatively high magnetic field tolerance and a relatively high critical temperature Tc . A joint formed according to the method of the present invention is believed to provide a good electrical and mechanical connection between the superconducting filaments of the wires being joined; to improve the magnetic field tolerance of the joint compared to conventional joints between similar wires; and Can prevent mechanical damage.
图2示出了本发明连接方法中的前期步骤。将两个待连接的导体12、14从它们的导槽5剥离，在一定的长度范围内暴露出导线7。将扎线(binding)18，例如不锈钢丝，围着两个导体未剥开的区域缠绕，以使它们机械性地固定在一起。为获得进一步的机械稳定性，可将导体12、14的导槽5在未剥开的区域焊接在一起。导线7各自被剥开的区域的特定长度20被以r为半径弯曲。应选择小的半径，但并不是小到要冒降低MgB2超导体的风险。对于该MgB2导线，可以优先考虑约为80mm～100mm的半径。优选进行弯曲使得形成的角度θ在45°～90°的范围内。Figure 2 shows the early steps in the connection method of the present invention. The two conductors 12, 14 to be connected are stripped from their guide grooves 5, and the wires 7 are exposed within a certain length range. A binding 18, such as stainless steel wire, is wrapped around the unstripped areas of the two conductors to mechanically secure them together. For further mechanical stability, the channels 5 of the conductors 12, 14 can be welded together in the unstripped areas. A certain length 20 of each stripped area of the wire 7 is bent with a radius r. A small radius should be chosen, but not so small as to risk degrading theMgB2 superconductivity. For this MgB2 wire, a radius of about 80 mm to 100 mm can be given preference. It is preferable to bend so that the formed angle θ is in the range of 45° to 90°.
图3示出了本发明方法的下一阶段，应用固定夹(retaining clip)22将导线7的弯曲部分20固定在稳定的位置。将在弯曲区域中的剥开的导线7浸泡在装有蚀刻剂(etchant)24的槽26中。该蚀刻剂的材料和温度的选择与材料有关，并且涉及拓扑结构(topology)。选择蚀刻剂来去除基体材料3并且暴露出细丝4的护套2。Figure 3 shows the next stage of the method of the invention, applying a retaining clip 22 to fix the bent portion 20 of the wire 7 in a stable position. The stripped wire 7 in the bend area is soaked in a groove 26 filled with an etchant 24 . The choice of material and temperature of the etchant is material dependent and involves topology. The etchant is chosen to remove the matrix material 3 and expose the sheath 2 of the filament 4 .
在一个典型的例子中，基体3为铜合金且护套2为铌。可以发现硝酸蚀刻剂24是合适的，因为它腐蚀铜，但不明显腐蚀铌。In a typical example, the substrate 3 is a copper alloy and the sheath 2 is niobium. Nitric acid etchant 24 was found to be suitable because it attacks copper but does not significantly attack niobium.
在其它例子中，可以发现在约为300℃的温度下的熔融锡(Sn)是合适的。铜和铜合金容易溶解在热的锡中。这种情况下，锡会同时刻蚀铜基体并且在一个步骤中形成NbSn。In other examples, molten tin (Sn) at a temperature of about 300°C may be found suitable. Copper and copper alloys dissolve readily in hot tin. In this case, tin simultaneously etches the copper substrate and forms NbSn in one step.
优选使用热锡，以及优选仅对于护套材料使用酸蚀，该材料与热锡的反应不明显或者用锡去除护套材料要花很长时间。Hot tin is preferably used, and acid etching is preferably used only for sheathing materials that do not react significantly with hot tin or that take a long time to remove the sheathing material with tin.
槽26必须选择对于蚀刻剂24是耐腐蚀的。在热锡蚀刻的情况下，槽可以是坩埚。可设置搅拌器28，使蚀刻剂24在导线7以及有护套2的细丝4之间循环。Groove 26 must be selected to be corrosion-resistant to etchant 24 . In the case of hot tin etching, the tank may be a crucible. An agitator 28 may be provided to circulate the etchant 24 between the wire 7 and the filament 4 with the sheath 2 .
一旦蚀刻完成，就会进行护套2材料的反应。在坩埚中，该坩埚可以是图3步骤中所使用的坩埚槽，在约为600℃的温度下，将弯曲区域20浸泡在热的锡(Sn)中。通过扩散，护套2中的元素铌(Nb)与热锡(Sn)反应生成超导体：Nb3Sn。Sn扩散进入Nb的速率高度依赖于熔融的Sn的温度。因此，优选锡的最高可行的温度。可提供惰性气体或真空氛围来防止锡的氧化。Once the etching is complete, the reaction of the sheath 2 material proceeds. In the crucible, which may be the crucible tank used in the step of Fig. 3, the curved area 20 is immersed in hot tin (Sn) at a temperature of about 600°C. By diffusion, the element niobium (Nb) in the sheath 2 reacts with hot tin (Sn) to form a superconductor: Nb3 Sn. The rate at which Sn diffuses into Nb is highly dependent on the temperature of the molten Sn. Therefore, the highest feasible temperature for tin is preferred. An inert gas or vacuum atmosphere can be provided to prevent tin oxidation.
图4A-4C示出了三个横截面视图，每一个视图通过单个有护套2的细丝4示出了反应进程。图4A中，将包围有MgB2芯1的未反应的Nb护套2浸泡在Sn浴24中。图4B中，护套2已经开始反应，并且护套的外侧部分已转化为Nb3Sn，而护套的内部仍然是元素Nb。通过扩散反应继续，直到护套2完全转化成Nb3Sn，如图4C所示。MgB2芯1保持未反应。4A-4C show three cross-sectional views, each showing the progress of the reaction through a single sheathed 2 filament 4 . In FIG. 4A , an unreacted Nb sheath 2 surrounding a MgB2 core 1 is soaked in a Sn bath 24 . In Fig. 4B, the sheath 2 has started to react and the outer part of the sheath has been converted to Nb3Sn, while the inner partof the sheath is still elemental Nb. The reaction continues by diffusion until the sheath2 is fully converted to Nb3Sn, as shown in Figure 4C. MgB2 core 1 remained unreacted.
然后，将导线7从坩埚中取出。图5示出了经过了上述步骤中的单根细丝4的局部横截面。MgB2芯1是未反应的。护套2现在完全为Nb3Sn，并且由于在坩埚中Sn的浸润，护套上存在薄的Sn涂层。示出了芯中的MgB2颗粒。因为细丝的制造方法，MgB2颗粒靠近护套材料：这个距离通常小于Nb3Sn的相干长度，使得通过护套2的Nb3Sn材料，在MgB2芯之间形成持久的超导接头。Then, the wire 7 is taken out from the crucible. Figure 5 shows a partial cross-section of a single filament 4 that has undergone the above steps. MgB2 core 1 is unreacted. The sheath2 is now entirely Nb3Sn and there is a thin Sn coating on the sheath due to the wetting of Sn in the crucible.The MgB particles in the core are shown. Because of the method of fabrication of the filaments, theMgB2 particles are close to the sheath material: this distance is usually smaller than the coherence length of Nb3Sn, enabling the formation of a durable superconducting joint between theMgB2 cores through the Nb3Sn materialof thesheath2 .
图6示出了本发明方法中的进一步步骤。将导线7的弯曲部分20(现在该导线7为在Nb3Sn护套中包括MgB2芯)放入另一个坩埚或模28内。或者，如果构造合适的话，可以使用同一个坩埚。将超导铸造材料30，例如伍德合金(Woods metal)或PbBi添加到坩埚或模28中，从而使细丝4的弯曲部分20浸泡在其中。在铸造过程中，可将固定夹22留在原处来协助机械定位。也可将导线7的相邻部件铸造成铸造材料30，以维持成品接头的机械强度。可以使铸造材料冷却和固化。如图7所示，将由此产生的接头40从坩埚或模28中移除。Figure 6 shows further steps in the method of the invention. The bent portion 20 of the wire 7 (now the wire 7 comprising a MgB2 core in a Nb3 Sn sheath) is placed into another crucible or mold 28 . Alternatively, the same crucible can be used if properly constructed. A superconducting casting material 30, such as Woods metal or PbBi, is added to the crucible or mold 28 so that the bent portion 20 of the filament 4 is immersed therein. During casting, retainer clip 22 may be left in place to assist in mechanical positioning. Adjacent parts of the wire 7 may also be cast into the casting material 30 to maintain the mechanical strength of the finished joint. The cast material can be allowed to cool and solidify. The resulting joint 40 is removed from the crucible or mold 28 as shown in FIG. 7 .
重要的是，不使细丝的末端32浸泡在蚀刻剂或超导铸造材料中，以防止MgB2芯的损坏或污染。It is important that the ends 32 of the filaments are not soaked in etchant or superconducting casting material to prevent damage or contamination of theMgB2 core.
图8示出了图7所示接头40的部分横截面。所示每根导线的细丝4仍然组合在一起。细丝4被包埋进超导铸造材料30中。图9示出了图8中注明的IX部分的放大图。将每根细丝4的MgB2芯1通过超导的Nb3Sn护套层2和超导铸造材料30，机械地并且导电地连接在一起。图5所示的Sn涂层已经进入超导铸造材料的溶液中。电流i可以流经MgB2芯1，通过Nb3Sn护套2、超导铸造材料30的一段距离、另一Nb3Sn护套2到达另一根细丝4的MgB2芯。以这种方式，可以实现本发明的超导接头。相比以往涉及机械压缩的连接方法，该方法不需要向超导导线施加机械负荷，从而降低了超导细丝损坏的风险。FIG. 8 shows a partial cross-section of the joint 40 shown in FIG. 7 . The filaments 4 of each wire are shown still grouped together. The filaments 4 are embedded in a superconducting casting material 30 . FIG. 9 shows an enlarged view of part IX noted in FIG. 8 . The MgB2 core 1 of each filament 4 is mechanically and electrically connected together through a superconducting Nb3 Sn sheath layer 2 and a superconducting casting material 30 . The Sn coating shown in Figure 5 has been put into solution in the superconducting casting material. The current i can flow through the MgB2 core 1 , through the Nb3 Sn sheath 2 , a distance of the superconducting cast material 30 , another Nb3 Sn sheath 2 to the MgB2 core of another filament 4 . In this way, the superconducting joint of the present invention can be realized. Compared with previous joining methods involving mechanical compression, this method does not require the application of mechanical loads to the superconducting wires, reducing the risk of damage to the superconducting filaments.
根据本发明，这种形成超导接头的方法的变体将参照图10加以讨论。A variation of this method of forming a superconducting joint in accordance with the present invention will be discussed with reference to FIG. 10 .
在该实施方式中，没有必要弯曲导线，并使最终的接头更加密实。In this embodiment, there is no need to bend the wires and the resulting joint is more dense.
图10示出了待连接的第一导线的一端。已将基体材料(如铜或MONEL)3，例如用酸蚀刻掉，让有Nb护套2的细丝在末端裸露出来。在浸入坩埚中的锡之前，先将细丝的末端42密封。这可以通过基体材料的焊接或机械卷边(mechanical crimping)来实现。Figure 10 shows one end of the first wire to be connected. The base material (eg copper or MONEL) 3 has been etched away, for example with acid, leaving the Nb-sheathed 2 filaments exposed at their ends. The ends 42 of the filaments are sealed before dipping into the tin in the crucible. This can be achieved by welding or mechanical crimping of the base material.
在卷边步骤中，相邻的MgB2颗粒被碾碎，并且从细丝上掉落，留下一段长度的空护套可通过卷边来密封。或者，通过焊接、铜焊或类似的方式，可使用在600℃下不受锡(Sn)影响的材料来密封细丝的末端。这样密封的目的是防止MgB2颗粒接触熔融锡。During the crimping step, adjacentMgB particles are crushed and fall off the filament, leaving a length of empty sheath that can be sealed by crimping. Alternatively, a material that is not affected by tin (Sn) at 600° C. may be used to seal the ends of the filaments by soldering, brazing, or the like. The purpose of this seal is to prevent theMgB2 particles from coming into contact with the molten tin.
在图3-7所示的方法中，使导线弯曲以防止护套的开放端浸泡在蚀刻剂、锡以及超导铸造材料中。通过使用图10所示的带有密封端的直导线，也使得护套的开放端受到保护，免于暴露在蚀刻剂或铸造材料中。在坩埚中将图10所示的导线铸造成接头，该坩埚可以远小于图7所示的坩埚：例如，窄缸。多部分模具(multi-part mould)可以用来形成此类接头的模腔，因为，如果将坩埚塑造成窄缸，该坩埚也许难以成形并且在使用中易碎。In the method shown in Figures 3-7, the wire is bent to prevent the open end of the sheath from soaking in the etchant, tin and superconducting casting material. By using straight wires with sealed ends as shown in Figure 10, the open end of the sheath is also protected from exposure to etchant or casting material. The wires shown in Figure 10 are cast into joints in a crucible which can be much smaller than the crucible shown in Figure 7: eg a narrow cylinder. A multi-part mold can be used to form the mold cavity for such joints because, if the crucible is molded into a narrow cylinder, the crucible may be difficult to form and brittle in use.
按上文所述形成的超导接头被认为适合应用在干磁铁的制造中，其可通过低温制冷器冷却至约为10K的温度。在这样的装置中，优选的是，应将超导接头放置在靠近制冷器的地方，以确保接头有效地冷却。A superconducting joint formed as described above is considered suitable for use in the manufacture of dry magnets, which can be cooled to temperatures of about 10K by means of a cryogenic refrigerator. In such an arrangement, preferably, the superconducting junction should be placed close to the refrigerator to ensure effective cooling of the junction.
现在将参照图11和12讨论另一种形成超导接头的方法。这种方法共有引起细丝的铌护套与锡反应生成Nb3Sn超导护套的特征。然而，所产生的接头是被压接(crimped)在一起，而不是被铸造进超导材料中。Another method of forming a superconducting joint will now be discussed with reference to FIGS. 11 and 12 . This method shares the characteristic of causing the niobium sheathof the filament to react with the tin to form a Nb3Sn superconducting sheath. However, the resulting joints are crimped together rather than being cast into the superconducting material.
图11(i)示出了待根据本发明的方法连接在一起的两根导线7。已经通过例如卷边、用能抵抗热锡的材料焊接或铜焊的方式将导线的末端密封44。Figure 11(i) shows two wires 7 to be connected together according to the method of the present invention. The ends of the wires have been sealed 44 by eg crimping, soldering or brazing with a material resistant to hot tin.
如图11(ii)所示，在其末端的一定长度范围内剥离基体3。细丝4从而暴露出来。密封件44的材料必须能抵抗任何用于剥离护套材料的蚀刻剂。密封件44防止了MgB2芯暴露在蚀刻剂中。As shown in FIG. 11(ii), the substrate 3 is peeled off within a certain length at the end thereof. The filaments 4 are thus exposed. The seal 44 material must be resistant to any etchant used to strip the jacket material. Seal 44 prevents exposure of theMgB2 core to etchant.
将圆柱形金属压接器(crimp)46(例如以铌为内层的铜管)置于细丝周围，如图11(iii)所示。铌内层可以是铜压接器内侧上的涂层，或是包围细丝的铌箔，并随后具有铜压接器置于该铌箔之上。压接器应松紧合适，但不紧迫，以免由于压接器的贴合对细丝造成损坏。然后实施由箭头47示意性地示出的机械压接工序。该工序把压接器的铌内层压至与细丝的铌护套接触，并且把细丝压至彼此互相接触。虽然涉及细丝4的一些机械压缩，但MgB2芯1保持被Nb护套2包裹在内，与最常规的方法相比，这降低了在机械压缩过程中损坏芯的风险。A cylindrical metal crimp 46, such as a niobium-lined copper tube, is placed around the filament, as shown in Figure 11(iii). The niobium inner layer can be a coating on the inside of the copper crimper, or a niobium foil surrounding the filament and then have the copper crimper placed on top of the niobium foil. The crimper should be tight and snug, but not tight enough to avoid damage to the filament due to the fit of the crimper. A mechanical crimping process, schematically indicated by arrow 47, is then carried out. This process presses the niobium inner layer of the crimper into contact with the niobium sheath of the filaments and compresses the filaments into contact with each other. Although some mechanical compression of the filaments 4 is involved, the MgB2 core 1 remains encased by the Nb sheath 2, which reduces the risk of damage to the core during mechanical compression compared to most conventional methods.
图11(iii)(a)示出了在此阶段经过压接的横截面。压接器的外表面48显示了由于压接过程而产生的机械变形50。压接器46的铌内层52是可见的。在压接器内，导线7的细丝4被压在一起形成机械接触。必须对压接过程加以控制，以免损坏细丝的MgB2芯。在这个阶段，通过铌金属护套2以及压接器的铌内层，将细丝4的MgB2芯1电连接。Figure 11(iii)(a) shows a crimped cross-section at this stage. The outer surface 48 of the crimper shows mechanical deformation 50 due to the crimping process. The niobium inner layer 52 of the crimper 46 is visible. Inside the crimper, the filaments 4 of the wire 7 are pressed together to make mechanical contact. The crimping process must be controlled so as not to damage theMgB2 core of the filament. At this stage, the MgB2 core 1 of the filament 4 is electrically connected through the niobium metal sheath 2 and the niobium inner layer of the crimp.
图11(iv)示出了该方法的进一步的阶段。将如图11(iii)和11(iii)(a)所示的被压接的细丝4浸泡在坩埚56内的熔融锡54中。熔融锡的温度约为600℃或更高。该步骤可以在真空中或惰性气体的氛围下进行，以防止大气成分与锡反应。就像参照图4所讨论的那样，将铌护套2浸泡在这样的热锡中通过扩散引起铌和锡反应生成超导铌-锡(Nb3Sn)。优选地，为使铌护套2完全地转化成Nb3Sn，该反应要在适合的温度下进行适当的时间，但让铌内层52完全转化成Nb3Sn不是必需的。Figure 11(iv) shows a further stage of the method. The crimped filament 4 as shown in FIGS. 11(iii) and 11(iii)(a) is immersed in molten tin 54 in a crucible 56 . The temperature of molten tin is about 600°C or higher. This step can be performed in vacuum or under an atmosphere of inert gas to prevent atmospheric components from reacting with the tin. As discussed with reference to Figure 4, immersion of the niobium sheath 2 in such hot tin causes the niobium and tin to react by diffusion to form superconducting niobium- tin (Nb3Sn). Preferably, the reaction is carried out at a suitable temperature and for a suitable time in order to completely convert the niobium sheath 2 into Nb3 Sn, but it is not necessary to completely convert the niobium inner layer 52 into Nb3 Sn.
类似于图(iii)(a)的横截面，图12示出了所得的经过压接的接头的横截面。压接器的外表面48显示了由压接过程而产生的机械变形50。压接器46的内层52已转化为Nb3Sn。在该压接器内，导线7的细丝4的护套2也已转化为Nb3Sn。它们被压在一起形成机械接触。通过Nb3Sn护套以及压接器的Nb3Sn内层，将细丝4的MgB2芯1电连接。正如上文所讨论的那样，Nb3Sn成分是超导的，它具有比铌更好的超导特性，例如，其具明显更大的磁场容差(4K时，约为18T)，以及更高的临界温度(约为18K)。Nb3Sn还具有相对更大的相干长度。除了获得锡涂层以外，浸泡在锡中不影响铜压接器46。Similar to the cross-section of Figure (iii)(a), Figure 12 shows a cross-section of the resulting crimped joint. The outer surface 48 of the crimper shows the mechanical deformation 50 produced by the crimping process. The inner layer 52 of the crimper 46 has been converted toNb3Sn . In this crimper, the sheath 2 of the filament 4 of the wire 7 has also been converted to Nb3 Sn. They are pressed together to form mechanical contact. The MgB2 core 1 of the filament 4 is electrically connected through the Nb3 Sn sheath and the Nb3 Sn inner layer of the crimper. As discussed above, the Nb3 Sn composition is superconducting, it has better superconducting properties than niobium, for example, it has significantly greater magnetic field tolerance (at 4K, about 18T), and more High critical temperature (about 18K). Nb3 Sn also has a relatively larger coherence length. The immersion in tin does not affect the copper crimper 46 other than to obtain a tin coating.
而图12所示的所得结构可以浸泡在熔融的超导填料中，如伍德合金或PbBi，其注入细丝4之间并且填充压接器，优选不包括此类连接材料。由本发明的这种实施方式所提供的在Nb3Sn护套和Nb3Sn压接器内层之间的机械和导电接触可足以提供所需的超导接头。预计在无填料的多重Nb3Sn连接之间所得接头能耐受相对高强度的磁场并在超过10K的温度下保持超导性。这种接头预计在通过热传导冷却、通过在约为10K时运行的低温制冷器制造干磁铁的过程中是有用的。Whereas the resulting structure shown in Figure 12 may be soaked in molten superconducting filler, such as Wood's metal or PbBi, which is injected between the filaments 4 and fills the crimpers, preferably excluding such connecting material. The mechanical and electrical contact between the Nb3Sn sheath and the inner layerof the Nb3Sn crimper provided by this embodimentof the invention may be sufficient to provide the desired superconducting joint. The resulting joints between filler- free multiple Nb3Sn connections are expected to withstand relatively high-intensity magnetic fields and maintain superconductivity at temperatures in excess of 10K. This joint is expected to be useful in the manufacture of dry magnets cooled by heat conduction by cryocoolers operating at about 10K.
因此，本发明提供了用于连接超导导线的方法，以及例如可用此类方法制造的接头。本发明涉及在具有铌护套的细丝(例如具有MgB2芯的超导导线、具有NbTi芯的超导导线)之间的接头，以及有MgB2芯的导线和有NbTi芯的导线之间的接头。根据本发明，将铌护套浸泡在热的锡(Sn)中，以将铌转化成Nb3Sn，所述Nb3Sn相比于铌元素而言是一种优良的超导体。所得Nb3Sn护套为向MgB2芯导线引入传输电流而充当高效和有效的导体。相比用于这类导线的常规连接方法，所得接头的磁场容差得到了显著的提高，在所述导线中，认为铌护套运载部分或全部电流通过接头。在接头的形成过程中MgB2芯不暴露在锡(Sn)中，从而降低了MgB2芯被污染或氧化的风险。Accordingly, the present invention provides a method for joining superconducting wires, and, for example, a joint that can be produced by such a method. The invention relates to joints between filaments with a niobium sheath (such as superconducting wires with aMgB2 core, superconducting wires with a NbTi core), and between wires with aMgB2 core and wires with a NbTi core connector. According to the present invention, the niobiumsheath is soaked in hot tin (Sn) to convert the niobium toNb3Sn , which is a superior superconductor compared to niobium element. The resulting Nb3 Sn sheath acts as an efficient and effective conductor for introducing transport current to the MgB2 -core wire. The magnetic field tolerance of the resulting joint is significantly improved compared to conventional joining methods for such wires where the niobium sheath is believed to carry some or all of the current through the joint. TheMgB2 core is not exposed to tin (Sn) during the formation of the joint, thereby reducing the risk of contamination or oxidation of theMgB2 core.
一些MgB2芯暴露在热的锡中是可容许的，其前提是锡不会在导线内渗透较长的距离从而接触接头的有效部分。Exposure of someMgB2 core to hot tin is tolerable, provided the tin does not penetrate a significant distance within the wire to contact the active part of the joint.
在本发明的一些实施方式中，多个接头可以在单一的锡加工工艺(tinartefact)中形成。每个接头可以是两根或多跟超导导线的接头。在这些实施方式的变体中，多个接头可以在单一锡加工工艺中形成，并且然后可以将锡加工的制品(tin artefact)隔开，以提供分开的接头。In some embodiments of the invention, multiple joints can be formed in a single tin artefact. Each joint can be a joint of two or more superconducting wires. In variations of these embodiments, multiple joints may be formed in a single tin fabrication process, and the tin artefacts may then be spaced apart to provide separate joints.
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1102153.2 | 2011-02-08 | ||
| GB1102153.2AGB2487926B (en) | 2011-02-08 | 2011-02-08 | Joints with very low resistance between superconducting wires and methods for making such joints |
| PCT/GB2011/052448WO2012107709A1 (en) | 2011-02-08 | 2011-12-09 | Joints with very low resistance between superconducting wires and methods for making such joints |
| Publication Number | Publication Date |
|---|---|
| CN103493232A CN103493232A (en) | 2014-01-01 |
| CN103493232Btrue CN103493232B (en) | 2016-11-30 |
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0148479A2 (en)* | 1983-12-30 | 1985-07-17 | General Electric Company | Methods of forming Superconducting joints for superconducting wires and coils |
| US20060240991A1 (en)* | 2004-12-14 | 2006-10-26 | Masaya Takahashi | Connecting structure for magnesium diboride superconducting wire and a method of connecting the same |
| US20100190649A1 (en)* | 2009-01-29 | 2010-07-29 | Doll David W | Low loss joint for superconducting wire |
| US20100317530A1 (en)* | 2006-12-12 | 2010-12-16 | Pyeong-Yeol Park | Superconducting wire and manufacturing method thereof |
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0148479A2 (en)* | 1983-12-30 | 1985-07-17 | General Electric Company | Methods of forming Superconducting joints for superconducting wires and coils |
| US20060240991A1 (en)* | 2004-12-14 | 2006-10-26 | Masaya Takahashi | Connecting structure for magnesium diboride superconducting wire and a method of connecting the same |
| US20100317530A1 (en)* | 2006-12-12 | 2010-12-16 | Pyeong-Yeol Park | Superconducting wire and manufacturing method thereof |
| US20100190649A1 (en)* | 2009-01-29 | 2010-07-29 | Doll David W | Low loss joint for superconducting wire |
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| TR01 | Transfer of patent right | Effective date of registration:20170110 Address after:Surrey Patentee after:SIEMENS health care Co., Ltd. Address before:Britain's Patentee before:Siemens PLC | |
| CF01 | Termination of patent right due to non-payment of annual fee | Granted publication date:20161130 Termination date:20191209 |