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Currently, progress is made globally to construct the ITER, to test the feasibility of fusion at a large scale. Currently cable in conduit (CIC) conductors are used for large scale magnet designs. Here the individual strand positions are a concern, due to the possibilities of non-uniform current distribution and the consequences that arise with it. Thus, knowing the position of individual strands is necessary. Many studies have been conducted in simulating the strand position. At the same time, it is necessary to physically map the positions of the strands, for confirmation and refinement of simulations. Our lab conducted measurements using thermal imaging by slicing a CIC conductor in sections, heating up a strand on one side and detecting the change in temperature on the other side by the thermal camera. The strand that heats up fastest should be the same one that was heated up on the other side, allowing a one-to-one matching. The results were promising, but struggled in identifying closely packed sections, due to response speed of the camera. To improve the response speed, it was suggested to use thermistor chips, capable of detecting changes in temperature in the form of voltage with little lag. This should allow the identification of the path that a single strand takes. In this paper, an array of thermistors was tested to see the feasibility of the method, and results will be shown.

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 (Ic). Thus, react-and-wind cables with ultra-thin Nb3Sn 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 Nb3Sn 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 Ic at 4.2 K after applying various uniaxial tensile loads at room temperature. The tensile stress limit of Ic was compared between the single wire and twisted cable.

To detect the particle energy with high resolution, the trace measurement is important. From this viewpoint, the detector magnets are designed as solenoids with a thinner thickness. What is also needed to maintain a high transparency of the particles is a lower mass of coil constituents. MgB2 has great potential not only to reduce mass density of detector magnets but also to simplify cooling systems, which lead to higher transparency of the particles. Focused on the stability of the magnet, the MgB2 conductor should be stabilized by various types of aluminum. To optimize the amount of the stabilizer, we have newly established two-dimensional governing equations for vector field of current diffusion and discretized for performing calculation by finite element method (FEM). The model is based on a demonstration with simplified conductor on which a specific heater attached at the center of the conductor to initiate quench to trigger the current diffusion into the stabilizer. The results show that the residual resistance ratio (RRR) of the stabilizer plays an important rule for current diffusion “depth” indicating optimum amount of aluminum stabilizer, which would enable us to design thinner conductors for particle-detection magnets with improved robustness.

10 kJ-Capacity Energy Storage Coil Made of MgB2 proposed in the Advanced Superconducting Power Conditioning System (ASPCS) was fabricated, and an electric current test was conducted with indirect liquid hydrogen cooling. This coil consists of three DP (double pancake) coils with an inner diameter of 400 mm and an outer diameter of 606 mm. The first DP was manufactured by the W&R (Wind and Reacted), and second and third DPs were manufactured by the R&W (React and Wind). A thermosiphon system is used for cooling the coils, in which the coolant is circulate without pump. For energization, several DC excitation and AC excitation tests were carried out with liquid hydrogen, and the rated current of 600 A was successfully achieved. The evaluation of both DC and AC losses were also performed, indicating needs to reduce the losses for stable operation under the indirect cooling conditions.

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 Nb3Sn 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 Nb3Sn 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 Nb3Sn wires was able to be established.