Neutron irradiation effect on superconductivity of Nb3Sn wire - 50 Hz data acquisition system -

A research facility for neutron irradiation effect on superconducting materials has been installed at Oarai center in Tohoku University in 2012 as part of a post irradiation experiment. It consists of a 15.5 T superconducting magnet, a variable temperature insert and a data acquisition and control system. Since the sample holder is cooled by thermal conduction with G-M refrigeration, there is a small temperature difference between positive and negative electrodes and the sample temperature rises during the critical current test due to joule heating. To evaluate the temperature rise precisely, a new data acquisition system with a sampling rate of 50 Hz has been installed. By measuring the temperatures of both electrodes and the voltage at the center of the sample, the temperature of the sample was estimated and the measured critical current (IC) was converted to the current at 4.2 K with a critical surface equation. The comparison of IC at different conditions including neutron irradiated samples was implemented and the neutron irradiation effect on superconductivity of Nb3Sn wire is discussed based on the 4.2 K superconductivity. This paper will describe the outline of the new data acquisition system and some results of neutron irradiated Nb3Sn wires.journal articl

Microstructure of Oxide Insulator Coating before and after Thermal Cycling Test

Erbium oxide (Er2O3) was shown to be a high potential candidate for tritium permeation barrier and electrical insulator coating for advanced breeding blanket systems such as liquid Li, Li-Pb or molten-salt blankets. Recently, we succeeded to form Er2O3 coating layer on large interior surface area of metal pipe using Metal Organic Chemical Vapor Deposition (MOCVD) process. In this paper, we investigated the microstructure of Er2O3 coating layer on stainless steel 316 (SUS 316) plate before and after heat treatments with hydrogen or argon gases. From the results of TEM observations, we confirmed that Er2O3 coating layer with 700 nm thickness was formed on the SUS 316 plate and this layer was identified to poly-crystal phase because the diffraction fleck which was arranged like a ring was observed in the selected electron diffraction pattern. No macroscopic defects such as crack and peeling in Er2O3 coating layer were observed before and after thermal cycling test. The change of microstructure of the Er2O3 coating layer on before and after heat cycling test was reported

Microstructure of Erbium Oxide Thin Film on SUS316 Substrate with Y₂O₃ or CeO₂ Buffer Layers Formed by MOCVD Method

Er2O3 has been known the best candidate material for insulating coating for liquid metal breeding blanket system. The formation of Er2O3 layer by MOCVD method can be succeeded on SUS316 substrate with CeO2 and Y2O3 buffer layers (100 nm and 500 nm) fabricated by RF sputtering, and their microstructures have been confirmed by SEM, TEM and STEM. The surface morphology of their layers was smaller granular structure than the previous study without buffer layer. According to cross sectional TEM (X-TEM) observation, Er2O3, CeO2/Y2O3 buffer, unknown layers and SUS substrate can be confirmed. CeO2 buffer layer has a granular structure, while Y2O3 has a columnar structure. Er2O3 layer formed on each buffer layer had finer structure without buffer layer. It has been also detected that each element does not exist so much in each layer by diffusion during fabrication according to STEM-EDS and HAADF imaging

Asymmetrical normal-zone propagation observed in the aluminum-stabilized superconductor for the LHD helical coils

Transient normal-transitions have been observed in the superconducting helical coils of the Large Helical Device (LHD). Stability tests have been performed for an R&D coil as an upgrading program of LHD, and we observed asymmetrical propagation of an initiated normal-zone. In some conditions, a normal-zone propagates only in one direction along the conductor and it hence forms a traveling normal-zone. The Hall electric field generated in the longitudinal direction in the aluminum stabilizer is a plausible candidate to explain the observed asymmetrical normal-zone propagation

Effect of atmospheric control during MA-HIP process on mechanical properties of oxide dispersion-strengthened Cu alloy

In this study, mechanical properties of Dispersion Strengthened (DS)-Cu-Al (aluminum) and Zr (zirconium) alloys, which were fabricated by an MA-HIP method, were investigated for application to the heat sink materials of fusion reactors. The effect of air exposure before the HIP process was studied using a NIFS-Sealing Device. Cu–Al specimen with air exposure before HIP was broken during wire-electrical discharge formation. Cu–Al specimen without air exposure exhibited high fracture strength, but without yielding. Cu–Zr specimen, both with and without the exposure, yielded and exhibits elongation. An increase in yield and tensile strength by approximately 61% and 45%, respectively, were obtained for Cu–Zr specimen by avoiding air exposure. The results showed that Cu–Zr specimen is less susceptible to the atmosphere of the MA-HIP process than Cu–Al

Transformation super plasticity deformation of reduced activation ferritic/martensitic steel

0000-0001-9016-2318Reduced Activation Ferritic/Martensitic (RAFM) steel is a promising candidate for the blanket structural materials of fusion reactors. One of the key issues in the use of RAFM for the blanket is its low workability. As a solution of this issue, innovative processing technology based on the transformation super plasticity (TSP) was proposed. In general, TSP is known as high temperature creep deformation which is induced by phase transformation. In this study, tensile tests under constant load were carried out with cyclic temperature variation for a RAFM steel to investigate the effect of cyclic temperature variations on elongation. The result of the tensile test under constant load for the RAFM steel with cyclic temperature variations exhibited a macro-elongation to 172%. The results of the tensile tests with varying loads showed the possibility of reducing the necessary time and enhancing the controllability for the formation of RAFM steel products using TSP.journal articl

Moderation of Negative Oxygen Effects by Small Yttrium Addition to Low Activation Vanadium Alloys

In order to improve irradiation embrittlement of vanadium alloys for fusion reactors, yttrium (Y) has been added reducing the interstitial oxygen impurity. However Y addition can also degrade high-temperature strength, because Y could scavenge oxygen in solid solution, which is a strong hardening agent in vanadium alloys. In this study, the effect of Y addition and oxygen level on the mechanical properties was investigated from the view points of both the high-temperature strength and low temperature ductility. Y addition was suggested to moderate the hardening and embrittlement induced by oxygen impurity sustaining the high-temperature strength within an acceptable level

Nd3+-activated CaF2 ceramic lasers

Nd,Y:CaF2 and Nd,La:CaF2 ceramics featuring good optical quality have been fabricated by reactive sintering and a hot isostatic pressing method. The transmission spectra, emission spectra, and fluorescence decay curves were measured. Lasing at 1064 and 1065 nm was observed in Nd,Y:CaF2 and Nd,La:CaF2, respectively, upon quasi-continuous-wave pumping by a diode laser emitting at 791 nm. To the best of our knowledge, this is the first demonstration of Nd3+-activated CaF2 ceramic laser

Microstructure development and high tensile properties of He/H2 milled oxide dispersion strengthened copper

This study describes the effect of microstructural development on high tensile properties of a newly developed He/H2 milled oxide dispersion strengthened copper in a large centimeter sized spherical morphology. Electron back scattered diffraction showed development of a strong texture of (110) plane in micron sized (1.2 μm) grains on the surface of milled spheres. A combination of microstructural features of inhomogeneous grain size, nanoscale lenticular/rectangular deformation twins, high dislocation density and fine oxide particles distribution induced a very high ultimate tensile strength (688 MPa)-ductility (8.6% elongation)

Fabrication and Superconducting Properties of the Bronze-Processed Nb3Sn Multifilamentary Wire Using Cu–Sn–Zn Alloy Matrix

0000-0002-5112-3065We developed several new Cu-Sn-Zn-(Ti) alloys, which are so-called “CSZ alloy,” for practical bronze-processed Nb 3 Sn wires. Several CSZ alloys were fabricated via the Mizuta method. The Zn was uniformly dissolved in the α phase of the Cu-Sn alloy, and the Zn-Ti compounds were not found in the CSZ alloy. Various 19 Nb-filament CSZ Nb 3 Sn precursor wires were fabricated using CSZ matrices with different Sn and Zn nominal compositions. We also found that the CSZ/Nb composites showed excellent workability at room temperature. In this paper, changes in microstructure and superconducting properties of Nb 3 Sn wires with different CSZ matrices as a function of the heat treatment condition were investigated. We clearly observed that the amount of Zn in the matrix remained constant after the Nb 3 Sn formation. Thicker Nb 3 Sn layers were formed by the Zn addition. T c transitions of about 18 K have been obtained. Finally, we have succeeded in fabricating multifilamentary wires using CSZ matrices through the restacking method. The number of Nb filaments is 7771 with a diameter of 3.4 μm. The effect of the Zn addition on microstructures and superconducting property of the CSZ wires are also reported.journal articl