Hidetoshi Oguro

Upgrading Design to a 25 T Cryogen-Free Superconducting Magnet Based on Low Temperature and High Magnetic Field Properties of the Practical CVD Processed Coated Conductors

We evaluated critical current density and mechanical properties of the Y123 coated conductor (CC) tapes on buffered Hastelloy substrates prepared by the chemical vapor deposition method in high magnetic fields and low temperatures. The Jc values of the tape are about 1.1 MA/cm at 77.3 K, 0 T and 1.8 MA/cm2 at 4.2 K and 17 T for B//c. In addition, the hoop stress test of the single layer coil shows that the stress limit of the CVD-Y123 CC tapes on Hastelloy is over 1 GPa. On the basis of those experimental data, we designed the innermost high temperature superconducting insert coil for upgrading of the 18 T cryogen-free superconducting magnet (18 T-CSM) under the condition of the stress limit of 600 MPa. The coil, which consists of the 22 double pancake coils can generate 9.4 T with the operation current of 295 A in the backup field of 15.6 T. In this case, the central field of the 18 T-CSM can be improved up to 25 T from 18.1 T.

Neutron Diffraction Measurements of Internal Strain in

The superconducting properties of Nb3Sn strands are very sensitive to strain. Measuring internal strain of Nb3Sn in Cable-In-Conduit Conductors (CICC) is important for evaluating the superconducting performance of CICC. Internal strain can be determined by neutron diffraction measurement using Takumi of J-PARC. Neutron diffraction measurement becomes a strong tool for evaluating directly the internal strain of Nb3Sn in CICC.

{\rm Nb}_{3}{\rm Sn}

Residual strains for practical Nb3Sn superconducting wires were measured directly using neutron diffraction. Seven wires, stacked with epoxy resin, were measured under a tensile load at room temperature. As a result, the three-dimensional strain was obtained up to 0.5% axial tensile strain. We found that the neutron diffraction result is consistent with the strain measured using strain gauges and extensometers at the same time, although the strains increased due to the long measurement time. The ratio between the axial and lateral strains is about 0.33, although the Cu?Sn, Cu and CuNb were plastic in this region. The ratio is an important value for evaluating three-dimensional strain effects on the superconducting properties of Nb3Sn wires.

Cable-In-Conduit Conductors

Abstract-Concerning the strain effect of superconducting properties for Nb3Sn wires, it is necessary to investigate a three-dimensional strain state that Nb3Sn superconductors truly experience in the composite wire. However, it is very difficult for Nb3Sn wires to obtain the three-dimensional residual strain components experimentally. We adopted the strain gauge that is directly glued onto the 1 mm outer diameter Nb3Sn wire, in order to quantitatively measure the three-dimensional distortions. To evaluate axial and lateral distortions of the wire, strain gauges were set in both axial and lateral directions. This measurement system can obtain the distortion detail in fields up to 27 T at temperatures ranging from 4.2 to 20 K. We measured the upper critical field Bc2% in a three-dimensional strain state for Nb3Sn wires. It was found that the wire architecture changes each residual strain in axial and lateral directions of the wire. Moreover, the Bc2 strain sensitivity that is related to the Bc2 variation is also affected by its architecture. We found that the axial tensile strain variation 0.3% roughly corresponded to the lateral compressive strain variation 0.1% for Nb3Sn wires. This means that the ratio of the lateral strain and the axial one for Nb3Sn wires is 0.3. The ratio of both residual strains in the axial and lateral directions is very important to examine the strain effect of Nb3Sn wires in detail.

Residual strain measurement using neutron diffraction for practical Nb3Sn wires under a tensile load

Internal lattice strains under a tensile load for CuNb/Nb3Sn wires with and without prebending treatment were measured directly by neutron diffraction at room temperature. In the axial direction of the wire, the residual lattice strain was changed by 0.29% to the tensile side, while, in the lateral direction, the change was 0.03% to the compressive side due to the prebending treatment. The relationships between the axial and lateral lattice strains under axial stress are almost linear with a slope of about 0.3 for both wires; however, the absolute value of the lateral lattice strain differed at the same axial lattice strain. Tensile load dependences of the axial and lateral lattice strains of Cu and Nb in the wires were also obtained. The prebending treatment was found to affect the elastic–plastic deformation behavior of Cu and to change the internal lattice strains of Nb3Sn.

Strain Gauge Method for Evaluating a Three-Dimensional Residual Strain State in

We evaluated three-dimensional residual strains for practical Nb3Sn wires with different architectures and residual strains at low temperature by neutron diffraction, and the upper critical fields under the tensile strains were discussed on the basis of the three-dimensional strain model. We found that the angular dependence of the residual strain can be described well by the two representative strains, i.e. the axial and lateral strains. The differences in the three-dimensional residual strains, which depend on the wire architecture and mechanical treatment history, play an important role in the superconducting properties of composite Nb3Sn wires under axial stress/strain.

{\rm Nb}_{3}{\rm Sn}

The three-dimensional strain dependence of the superconducting property for an internal-tin Nb₃Sn wire was investigated, because three-dimensional strains are necessary to understand the strain effect of superconducting properties for Nb₃Sn wires. The three-dimensional strain dependence of <i>B</i>_c2 and residual strains were measured by the strain gauge method and neutron diffraction, experimentally. As a result, the three-dimensional strain model based on the experimental results for bronze route Nb₃Sn wires explained the strain dependence of superconducting properties for an internal-tin Nb₃Sn wire. We found that the strain effect of <i>B</i>_c2 for bronze route and internal-tin Nb₃Sn wires are expressed by three-dimensional strain model.

Wires

IBARAKI Materials Design Diffractometer (iMATERIA) is a high-throughput powder diffractometer. iMATERIA has a vacuum chamber, which is enclosed in a shield. Each sample is measured in 10 minutes, and must be placed in the vacuum chamber before being measured. If the vacuum in the chamber cannot be maintained while exchanging samples, the process of re-establishing the vacuum would become a bottleneck when samples are exchanged. To reduce exchange time, we developed and manufactured an automatic sample changer that can handle a large number of samples (up to 672) through both the vacuum chamber and shielding blocks.

Axial and lateral lattice strain states under a tensile load in as-reacted and prebent CuNb/Nb3Sn wires using neutron diffraction

Researches to study internal stress/strain behaviors in industrial superconducting composites have been started at TAKUMI of J-PARC, as soon as the completion of TAKUMI construction. Preliminary results obtained from strains measurements during tensile deformation of Nb3Sn strands and YBa2Cu3O7 tapes, strains measurements during heating of Nb3Sn strands and residual strains measurements in a Nb3Sn Cable-In-Conduit Conductors are briefly described. The results can demonstrate possibilities of neutron engineering diffraction to solve problems in industrial superconducting composites by using J-PARC high flux neutron beam, even the volume fractions of superconducting phases in the composites are small and the superconducting phases locate inside the real components.