Sn Wires Research Articles

Influence of trapped magnetic field of Sn-Pb solders on electrical resistivity measurement: an example of superconducting transition of Sn

We examined the effect of the flux-trapped states of Sn60-Pb40 solders on the superconducting properties of a Sn wire. The temperature dependence of electrical resistivity at H = 0 Oe after zero-field cooling (ZFC) showed a sharp superconducting transition at T = 3.7 K. In contrast, field cooling (FC) resulted in a broadening of the transition. The difference between ZFC and FC data evidences the critical effect of trapped fluxes at solders on superconducting states. We propose that, in electrical measurements where magnetic fields of several hundred Oe are critical, field experience should be seriously considered when using solders.

Numerical and Experimental Analysis of Thermomagnetic Instability in Nb3Sn Wires

Numerical and Experimental Analysis of Thermomagnetic Instability in Nb₃Sn Wires

Internal Strain Measurement by Neutron Diffraction Under Transverse Compressive Stress for Nb3Sn Wires With and Without Cu-Nb Reinforcement

Internal Strain Measurement by Neutron Diffraction Under Transverse Compressive Stress for Nb₃Sn Wires With and Without Cu-Nb Reinforcement

MAX phase-derived tin nano-/micro-wires with controlled diameter through seeded growth

Nano-scaled one-dimensional (1D) metallic materials show tremendous potential in various important technological applications, such as flexible transparent electrodes and catalysis. However, achieving scalable preparation of nanoscale 1D metallic materials remains a significant challenge for most metallic compositions. The phenomenon of A-site whisker growth from MAX phases provides an opportunity for innovative 1D metal fabrication techniques. However, the whisker diameters derived from MAX phases are often too large to satisfy the requirements of advanced technologies. Herein, we introduce Sn nanocrystals with different particle sizes as the initial seeds to tune the diameter of Sn whiskers, fed by the atomized tin resulted from the mechanochemical decomposition of Ti2SnC. It was found that incorporating nano-scaled (50–300 nm) and micro-scaled (0.5–1 μm) Sn crystal seeds resulted in the growth of whiskers with diameters matching the respective seed sizes, and the reduced melting point phenomenon of the nano-sized Sn wires conformed to the size-dependent behavior of metal nanowires. The diverse A-site elements within MAX phases implied that this method could be a generic strategy for synthesizing various nanoscale 1D metallic materials with controllable diameters.

X-Ray Absorption Spectroscopy to Investigate Precipitated Oxides in Nb3Sn Wires With an Internal Oxygen Source

X-Ray Absorption Spectroscopy to Investigate Precipitated Oxides in Nb₃Sn Wires With an Internal Oxygen Source

Study on the High Temperature Heat Treatment Process Optimization of Different Sizes High Jc Nb$_{\text{3}}$Sn Wire Produced by WST

Study on the High Temperature Heat Treatment Process Optimization of Different Sizes High Jc Nb$_{\text{3}}$Sn Wire Produced by WST

Development of Cu-Nb Reinforced Nb3Sn Wires Appropriate for Large Multi-Stage Stranded Cables With Short-Pitch Twisting and Low-Void Ratio

The strength of the conventional Cu/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires may be too low to be applied to much larger cable-in-conduit (CIC) conductors with the multi-stranded cable structure of short-pitch twisting and low-void ratio applied for ITER-CS conductors. In this study, the Nb-rod-method Cu-Nb reinforced ITER-type Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire was developed by using a bronze-process not only to realize superior superconducting properties under high electromagnetic stresses but also to mitigate damage to the superconducting wires during the cable manufacturing process. The critical current properties of the Cu-Nb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire were significantly higher performance under both tensile stress and transverse compression stress compared to a conventional non-reinforced Cu/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire. The Cu-Nb reinforcement had no detrimental effect on the AC losses of the wire. The trial production of short-pitch sub-cables was conducted, and it was confirmed that the Cu-Nb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires can improve the manufacturability of multi-stage stranded cables co-twisted with copper wires.

Mechanical Properties of Ultra-Thin Nb3Sn Composite Wires

Flexible Rutherford cables are needed to realize high field superconducting magnets with A15 conductors based on the react-and-wind (R&W) technology. Aiming such an application, ultra-thin A15 composite wires with a diameter of 0.03–0.05 mm have been developed by the National Institute for Materials Science (NIMS). Mechanical properties of such ultra-thin Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires were evaluated to determine the cabling parameters and mechanical analysis of twisted cables. Tensile tests were performed at room temperature for 0.05 mm-thick Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires before and after heat treatment for the first time. Basic mechanical parameters such as 0.2% proof strength and fracture strength were evaluated from a stress–strain curve. Young's modulus of such a thin wire was determined from unlading and reloading slopes of a load–stroke curve for the specimens with different gauge lengths. Fracture strain was estimated without using extensometers and strain gauges by correcting for machine deformation. Based on these results, we concluded that a simple technique to measure stress–strain curves for ultra-thin Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires was able to be established.

Design Optimization, Cabling and Stability of Large-Diameter High Jc Nb3Sn Wires

In the framework of the High Field Magnets (HFM) program, CERN is developing and qualifying Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn Rutherford cables to support magnet development towards the requirements of a future energy-frontier collider, using both state-of-the-art commercial wires and experimental wires under development with industrial partners. The trend towards higher current density and larger diameter wires imposes challenges for magneto-thermal stability. In this study, rolling trials and Rutherford cabling have been performed at CERN for two designs of a 1 mm diameter distributed tin Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire produced by KAT, and for 1 mm and 1.1 mm diameter RRP Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires procured from Bruker OST, and the self-field stability and cabling degradation have been analyzed. The 1 mm RRP wire shows significant degradation in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> and stability on cabling. Although the latter is not expected to impact the performance of research magnets, the potential of heat treatment optimization to improve stability has also been quantified. The distributed tin wire shows substantially poorer stability, but promising indications of low cabling degradation. The influence of wire design characteristics on cabling behavior and stability have been assessed, and the implications for future wire optimization towards high field accelerator magnet applications have been discussed.

RRP Nb3Sn Subelement Shear Dependence on Hexagonal Subelement Stack Orientation and the Strand's Position Within a Rutherford Cable

Superconducting strands built into Rutherford cables undergo high deformation at the cable edges. This deformation negatively impacts subelement integrity and subsequently the Residual Resistance Ratio (RRR) of the stabilization Cu in Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands after heat treatment due to compromised diffusion barriers [1]. Rutherford cables for the high luminosity upgrade of the LHC at CERN (HL-LHC) use Restack Rod Process (RRP) Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires with a 108/127 subelement stack. Numerous transverse cross-sectional samples from the cables made under the HL-LHC Accelerator Upgrade Project (“HL-LHC AUP”) [2] have been mounted, polished, and analyzed with light microscopy. The number of sheared subelements within a strand was seen to depend not only on a strand's position in the overall cable (i.e. center vs. edge), but also on its specific position within the cable edge. Moreover, the rotational angle of the subelement stack within a strand, relative to the cable's centerline plane, appears to play a role. There is a need to understand these dependencies, as they might impact the applicability of any criterion for a maximum number of sheared subelements (typically < 15% of subelements) applied to series production quality assurance, often imposed to ensure acceptable RRR degradation. By gathering data across many HL-LHC AUP cables and utilizing a more statistical approach, we aim to establish more accurate success criteria for future R&D cables using RRP wire when the available cable runs (and thus samples) are limited.

Experimental Study on the Critical Current Properties of Flexible Nb3Al Superconducting Wires in Cryocooler System

In recent years, Jelly-rolled Nb/Al composite monofilament Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al superconducting wires with an outer diameter of 30 μm, and multi-stranded Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al wires were successfully fabricated by NIMS in Japan. So, it is necessary to measure the temperature dependence of the critical current of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al wires in cryocooler system for development of superconducting applications cooled by conduction cooling method. The single and multi-stranded ultrafine Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al superconducting sample wires with different outer diameter were prepared to evaluate the critical current properties. The critical currents of sample wires were evaluated by the current sweep method and constant current method. In this study, the sample wires were soldered to the copper wire to prevent burnout of the sample wire during critical current measurements. Therefore, the amount of current shunted to the copper wire was estimated to accurately evaluate the critical current of the superconducting wire. Also, the critical current of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al wires due to bending strain (bending radius of 5 to 15 mm) was experimentally investigated. From the critical current measurement results of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al wires with different cross-sectional structures, it was confirmed that the superconducting properties of the wires were improved by reducing the wire diameter. It was shown that the critical current density of the developed Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al wire is lower than that of REBCO wire, but higher than that of commercial NbTi and Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires.

Influence of Axial Strain and Transverse Compressive Load on Critical Current of Nb3Sn Wires for the FCC

Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting wires are under consideration for producing high field accelerator magnets for the proposed Future Circular Collider (FCC) due to their high critical field. R&D studies are ongoing worldwide with a target non-Cu critical current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> ) of 1500 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 4.2 K, 16 T. As an accomplishment of this R&D, one of the conductor manufacturers, JASTEC, has developed Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires with non-Cu <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> higher than 1100 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 16 T, 4.2 K by a distributed-tin (DT) method. In high field Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnets, degradation of performance has been frequently reported due to the brittleness of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and the high electromagnetic force. To realize more robust Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn accelerator magnets, electro-mechanical properties of the conductors should be deeply understood. In this study, the variation of the critical current with mechanical loading is evaluated for a DT Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire in two configurations, i.e. under axial strain and under transverse compression.

Mechanical strain triggering flux jumps of multi-filamentary Nb3Sn wires

The composite multi-filamentary Nb 3 Sn wire with a high critical current density is a preferred option for fabricating the superconducting magnet beyond the limit of NbTi wire (9-16 T). However, one crucial issue stems from the fact that electromagnetic force in superconducting coils is very strong, and the critical physical properties of Nb 3 Sn, such as J c , are more sensitive to mechanical strain than those of other possible low-temperature superconductors. We theoretically investigated the impact of mechanical strain on the thermomagnetic instabilities such as the flux jump (FJ) and quenching of Nb 3 Sn wire exposed to a static magnetic field and transport current. The good agreements with H formulation or H-φ formulation implemented on COMSOL software confirm the validity of our numerical simulations using home-made codes. It is discovered that mechanical strain can trigger flux jumps even in a static magnetic field. Furthermore, the threshold value of mechanical strain to trigger the first flux jump is a monotonic function of the static magnetic field in the case of high transport current, while it is a non-monotonic function in the case of low transport currents. It is attributed to the fact that flux can be released by the mechanical strain first, causing smooth flux penetration before triggering the flux jump. We also present the stable/unstable regions by applying mechanical strain by varying transport current, magnetic field, and working temperature, which helps in avoiding thermomagnetic instabilities while designing the superconducting magnet.

X-ray tomography assessment of the heat treatment effect on Nb3Sn wires with different architectures

Two unreacted commercially available Nb 3 Sn precursor wires with different architecture were subject to a two-temperature heat treatment in vacuum at 650 °C for 72 h and at 700 °C for 168 h. Evolution of wires towards formation of the superconducting phase was assessed by the non-invasive X-ray computed microtomography (micro XRT) with a spatial resolution of ∼2 μm on the samples before and after the heat treatments. Statistical image analysis quantified the defects and quantitatively revealed the deviation of the geometrical perfection of the wire components comparative to designed parameters depending on the wire architecture and heat treatment conditions. Our results position XRT as a tool to evaluate the quality of Nb 3 Sn, also promoting it as a method capable for providing new insights that could be used in the optimization processes of Nb 3 Sn wires design, technology, and during operation. • Wires of Nb 3 Sn were heat treated (HT) and assessed by x-ray tomography (XRT). • Before and after HT, defects and deviation from design parameters were quantified. • Architecture has a strong influence on the HT processes and quality of the wires. • XRT emerges as a non-invasive tool with novel, unique characterization possibilities. • XRT contributes wires optimization, fabrication, application, and during operation.

Novel Pb-Free Superconducting Joint Between NbTi and Nb3Sn Wires Using High-Temperature-Tolerable Superconducting Nb–3Hf Intermedia

There was no other method but to use Pb-alloy solder intermedia to establish superconducting joints between NbTi and Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires beyond 0.5 T. However, Pb is environmentally hazardous. In this context, new alternative joint methods without using these substances were strongly desired in applications such as high-field NMR systems. Recently, we have developed a novel superconducting joint method using high-temperature-tolerable (HTT) superconducting Nb-alloy intermedia that enable us to establish the superconducting joint between NbTi and Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires by a combination of chemical and mechanical bonding processes. In this work, the joint was surely confirmed to have ultra-low resistance by current decay measurements. The yield rate of successful superconducting joint between Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and HTT Nb-alloy was almost 100% and the scattering of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> value was small. Meanwhile, the joint between NbTi and HTT Nb-alloy showed large scattering of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . We observed NbTi filament cracks in mechanically-pressed joints between NbTi and HTT Nb-alloy, using a high resolution X-ray CT device with micro X-ray source. The filament cracking could account for the large scattering of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> in the joints.

Microstructure and Superconducting Properties of Hf–Ta Addition Bronze-Route Nb3Sn Wire

The Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting wire is a promising candidate for cutting-edge high-field magnets such as the next generation particle accelerator and fusion reactor. Recently, Hf–Ta addition to Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires has attracted our great interest, because it results in significant grain refinement and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> enhancement, maintaining high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> . In this work, we studied how much effect the Hf–Ta addition has on the layer formation and superconducting characteristics, when it is applied to bronze-route Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires, through microstructural and microchemical analysis by using EBSD and EDS. For simplicity, single-core composite wires were fabricated and tested. The tested wires included conventional Ti-doped Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and Hf–Ta-doped Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires. As a result, grain refinement in Hf–Ta addition was not significant in bronze process, compared with internal-tin process. Apparently, the thickness of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn layer was thick especially when Ti was doped into the Cu-Sn bronze matrix. Sn content seems to be also high in Ti-doping to Cu-Sn bronze matrix. In the bronze-route process, impact of Ti addition on the promotion of Sn diffusion seems to be relatively large, compared with Hf–Ta addition.

Magnetic Alignment and Mechanical Analysis of Superconducting Bending Section for Proton Therapy

The last bending section of a proton therapy beam line may be mounted on a rotating gantry to target the cancerous cells of patients from all possible angles. To gain such capability, it is sensible to use superconducting magnets because of their high energy density providing a large reduction in weight. In the following work, a configuration of combined function magnets for rotating gantries is presented. It includes two conventional electromagnets and three superconducting magnets using Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn conduction-cooled at around 4.2 K. For such assembly, an alignment procedure is proposed to ensure that a large beam momentum acceptance can be achieved. Besides this proposal, additional 3D mechanical Finite Element analyses were conducted to check that the structural support of the most critical superconducting magnets made of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires and their coil thermal shields could handle their weight as well as the momentum due to the rotation.

Minimum Quench Energy of Nb3Sn Wires With High Specific Heat Tape

A major problem of state-of-the-art Nb$_3$Sn accelerator magnets is their long training due to thermo-mechanical perturbations. Increasing the specific heat, $C_p$, of the Rutherford cable would reduce and/or eliminate training by limiting the coils temperature rise. This paper studies feasibility of increasing the $C_p$ of Rutherford-type cables by using thin composite Cu/$Gd_2$O$_3$ and Cu/$Gd_2$O$_2$S tapes produced by Hyper Tech Research, Inc. The tape can be either wrapped around the cable, placed on the cable wide faces under the insulation, and/or inserted as a core. Wire samples outfitted with these high-$C_p$ ribbons, or tapes, were prepared and tested at FNAL for their Minimum Quench Energy (MQE). At 90%I$_c$ and 15 T, the average gain of MQE of the Nb$_3$Sn wire soldered to the Cu/$Gd_2$O$_2$S 55 micrometer thick ribbon was 2.5, and further increased at larger transport currents.

Co-Wound Superconducting Wire for Quench Detection in Fusion Magnets

High temperature superconducting (HTS) materials are widely utilized in various design proposals for fusion magnets, resulting in enhanced performance of the machines compared to the past. However, a reliable quench detection in HTS conductors remains an open issue. Using a co-wound superconducting wire of high normal state resistance as an electrically insulated and thermally coupled sensor provides strongly increased sensitivity for the voltage-based quench detection methods. Furthermore, resistance of the wire can be practically proportional to the size of the normal zone, even though the location of the hot-spot cannot be identified. We present adaptation of this method for fusion conductors by considering various wire options, such as MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires in a highly resistive matrix, non-stabilized Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires and (K,Na)-Ba122 wires. The insulated wire of a small diameter (<1 mm) can be embedded in the steel jacket, thus barely affecting the conductor design and manufacturing aspects. Alternatively, if installed within the cable space, the wires might even allow monitoring of quench dynamics among the strands. Our first experimental demonstration is planned in a sub-scale ReBCO cable-in-conduit sample, which will be tested in the SULTAN test facility recently upgraded for DC operation in resistive samples with the transport currents up to 15 kA and maximum voltage of 10 V.

Development of Ultra-Low-Resistance Splicing of Nb3Sn and NbTi Superconducting Wires

During the last decade, Budker Institute of Nuclear Physics (BINP) manufactured nine multipole superconducting wigglers on the basis of NbTi superconductor. These wigglers are operating at various synchrotron radiation centers worldwide. High magnet parameters were achieved due to using NbTi wire of high NbTi/Cu ratio, up to a factor of two, and by grading the current density in the coils. So, further increase in the magnet parameters is limited by the properties of NbTi conductor. Another important feature of the BINP wigglers is the magnet design, with superconducting coils manufactured separately and connected with a splicing resistance of well below 0.1 nΩ at an operating current of about 1 kA. That yields significant decrease in the heat load on cryocoolers because the total amount of splicings in one wiggler exceeds 200. The existing demand in superconducting wigglers and undulators for higher magnet parameters can be realized by using Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire. The ultimate aim of the on-going work at BINP is to make an Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting wiggler with separate coils, the terminals of which will be connected by NbTi wires with low splicing resistance, below 0.1 nΩ. During assembling of such a wiggler, these coils will be connected via NbTi terminals by the technology available at BINP. This article reports on first results of testing five samples of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn-NbTi wire splicing. The experimental setup is described. The samples are two-turn loops made of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and NbTi wires. The samples were charged by currents of up to 500 A, and the resistance of these superconducting wire connections was evaluated from the current decay using a Hall sensor. All samples have demonstrated very low resistance, estimated as several Ohm.