Ultra-thin A15 composite wires with a diameter of 0.03-0.05 mm are being developed by National Institute for Materials Science (NIMS) to realize flexible Rutherford cables for high field ...superconducting accelerator magnets. Since the bending strain is approximately proportional to the wire diameter, a cable composed of thin wires can be bent to a smaller bending diameter without the degradation of critical current ( I c ). Thus, react-and-wind cables with ultra-thin Nb 3 Sn wires are expected to be realized. In our previous study, the basic mechanical properties including fracture strength and Young's modulus of 0.05-mm-thick bronze-processed Nb 3 Sn wires were evaluated by a single- fiber tensile test. As a next step, in this study, a tensile test was conducted for a twisted cable with 19 0.05-mm-thick wires at room temperature to confirm whether the mechanical strength of the twisted cable can be predicted from that of the single wire. The stress tolerance of the single wire and twisted cable was assessed by measuring I c at 4.2 K after applying various uniaxial tensile loads at room temperature. The tensile stress limit of I c was compared between the single wire and twisted cable.
This paper presents the experimental results of the (Bi,Pb)2Sr2Ca2Cu3O10 (BSCCO) coils impregnated with low-melting point metal, whose melting point is 60°C. The coils were layer-wound without ...turn-to-turn insulation, i.e., no-insulation (NI). We fabricated the coils with polycarbonate bobbin and casing and the coils with aluminum alloy bobbins and casing. The coils with polycarbonate bobbin and casings showed severe degradation after impregnation. The coils with aluminum alloy ones showed less degradation. A long decay time of the magnetic field during a sudden discharge was measured. The decay time was shortened to be 1/39 by an inter-layer insulation with polyimide sheet. Partial insulation, i.e., electrical insulation between adjacent layers, was effective in reducing this long time constant, even for a BSCCO NI coil.
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 3 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 3 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 3 Sn wires was able to be established.
Superconducting Magnetic Energy Storage (SMES) has been a promising option amongst potential other storage devices to support world-wide demands for introducing more renewables into the utility grid. ...If MgB 2 strands are used for SMES, liquid hydrogen, one of the renewables, could be used not only as a clean energy source but also as a coolant for the superconducting device. For large-scale coil design, mechanically fragile multi-filament strands should be used for their low AC loss feature considering that the transport current inside the coil would be always changing. To realize such a design, we designed and fabricated the large current capacity for AC-use Rutherford cable, together with experimental tests for its feasibility assessment. Based on the latest test results and development of commercial MgB 2 strands with high mechanical strength, and this research and development of kA-class cable at liquid helium temperature for extrapolating the critical current ( I c ) at hydrogen temperature, we believe this approach has the potential to make a practical SMES device with MJ capacity. In this paper, the world's largest-capacity AC cable design and test results including critical current evaluation under several background field strengths are shown, and the stability and current re-distribution are also discussed.
The strain tolerance of magnesium dioboride (MgB 2 ) wire should be enhanced at room temperature for fabricating MgB 2 coils by using the react and wind method. The irreversible external-compressive ...strain of MgB 2 filaments was measured by evaluating the critical current degradation of bent sample wires. From the results, MgB 2 filaments can accept -1.77% strain, and the pre-compressive strain should be -0.88% at room temperature to minimize its reversible bending radius. A stainless-steel reinforced 18-filament MgB 2 wire was fabricated and its strain tolerance was evaluated through bending and tensile tests at room temperature. The irreversible strain of this wire is 0.60%, and this wire seems to be suitable for the react and wind method. The filling factor of MgB 2 of this wire is 17%, so this wire has both suitable strain tolerance for the react and wind method and higher engineering current density.
New generation accelerators, such as future circular collider (FCC), require superconducting wires with non-copper J c of 1500 A/mm 2 at 16 T and 4.2 K. Kobe Steel Ltd. developed Nb 3 Sn conductors ...with elemental addition to achieve the target J c for FCC. The effect of zinc addition to the copper matrix on the superconducting properties and mechanical strength of the distributed tin (DT) method processed Nb 3 Sn wire is studied. In the present study, the I c -strain characteristics were evaluated using Walters springs (WASP) at 16 T and 4.2 K to investigate the impact of copper (Cu) and brass (Cu-Zn) matrix on further J c improvement and mechanical robustness.
