Motomune Kodama

Bio: Motomune Kodama is an academic researcher from Hitachi. The author has contributed to research in topics: Superconducting wire & Oxide. The author has an hindex of 7, co-authored 44 publications receiving 202 citations. Previous affiliations of Motomune Kodama include University of Tokyo.

High-performance dense MgB2 superconducting wire fabricated from mechanically milled powder

Abstract: Owing to the relatively high critical temperature and the low manufacturing cost, MgB2 superconducting wires are promising for liquid helium-free superconducting applications. Today, commercially available MgB2 wires are manufactured by either an in situ or ex situ powder-in-tube process, the in situ process being more effective to obtain high critical current density. In in situ-processed wires, however, the critical current density is seriously suppressed by the high porosity of MgB2 filaments. To resolve this problem, we propose an innovative method of using precursor powder prepared by mechanical milling of magnesium, boron, and coronene powders. This precursor powder has a metal–matrix–composite structure, in which boron particles are dispersed in a magnesium matrix. The plastic deformation of the precursor powder through wire processing leads to compact packing, and a dense MgB2 filament is generated after heat treatment. As a result, the limitation of critical current density that occurs for the typical in situ process is overcome, and the practical critical current density of 103 A mm−2 is obtained at 10 K and 6.1 T, at 15 K and 4.8 T, and at 20 K and 3.3 T.

Conduction-Cooled MgB2 Coil in Maximum Self-Magnetic Flux Density 2.3 Tesla Made With 300-Meter-Long Multifilamentary MgB2 Wire

Abstract: We fabricated a 300-m-long multifilamentary MgB 2 wire as a powder in tube wire by using an in situ method. The J e values were approximately 250 A/mm 2 from 2 to 3 T at 20 K and 3 to 4 T at 15 K. These J e values were interpolated by J c values on monofilament wire because I c measurements over 100 A were difficult due to joule heat on solders. By using this 300 m wire, a coil was designed to be driven in the maximum magnetic flux density in MgB 2 filaments (B max ) over 2 T. The coil was made by using a wind-and-react method and cooled by using conduction cooling. The coil was successfully driven at 24 K and 27 K as temperatures of coil winding, and calculated B max was 2.3 T in 24 K operation. The coil I c values measured at 24 K and 27 K agreed well with the estimated values based on I c values on short-length wire. This means that the 300-m-long multifilamentary wire has sufficient longitudinal homogeneity for designing MgB 2 coils and can be used at a maximum magnetic flux density over 2 T.

Superconducting switch, superconducting magnet and MRI

Abstract: A superconducting switch is provided in which the structural strength of the superconducting switch is kept, and thermal efficiency between a superconducting film and a heater is high when an ON state (superconducting state) and an OFF state (normal conducting state) of the superconducting switch are switched. The superconducting switch includes a substrate, a heater for generating heat by energization, a conductive film, and a MgB2 film evaporated on the conductive film. The heater, the conductive film and the MgB2 film are laminated in this order on one surface of the substrate.

Mechanism for high critical current density in in situ MgB2 wire with large area-reduction ratio

Abstract: A comparative study of in situ MgB2 wire and MgB2 bulk was carried out to clarify the mechanism for the high critical current density, Jc, in the practical in situ MgB2 wires. The in situ MgB2 wire was manufactured with an area-reduction ratio of 99.93%, which was one of the highest values in MgB2 superconducting wires previously reported. The electrical connectivity, K, and the flux pinning strength, Fp, which are important factors in explaining the behavior of Jc, could be determined in the same manner as those for the bulk sample; K was well understood with the three-dimensional percolation model, and Fp was effectively explained by the electron scattering mechanism by grain boundaries. On the other hand, the area-reduction process dramatically enhanced the value of K, leading to an increase in the value of Jc. The respective values of K and Jc(20 K, ~0 T) reached 0.24–0.34 and 6.0 × 103−8.4 × 103 A mm−2, which were twice or three times higher than those of typical in situ bulks. This is because the plastic deformation of magnesium particles increased the packing factor of raw powders through a repetitive drawing process.

Performance of MgB2 Superconductor Developed for High-Efficiency Klystron Applications

Abstract: An 8-km long MgB 2 wire for a prototype klystron magnet was made and evaluated. The wire was made by a typical in situ method; it has 10 filaments and 0.67 mm in outer diameter. The homogeneity of I c of this wire was evaluated by several methods. Deviation of I c values in short sample wires was very small. In addition, the current sharing temperature of the MgB 2 magnet (made of two reels of wire 2.9 km long each) agreed well with the estimated value of the I c -B-T properties in short sample wires. Based on the obtained results, it can be said that the I c properties of the entire wire length are quite uniform.

Display device and method of fabricating the same

Abstract: Provided is a display device. The display device includes a lower display element where a substrate, a first lower electrode, a liquid crystal part, and a second lower electrode are sequentially stacked, an upper display element stacked vertical to the lower display element, where a first upper electrode, a light emitting part, a second upper electrode, and a protective part are sequentially stacked, and a middle part configured to deliver a driving signal to the lower and upper display elements, between the lower and upper display elements.

Logging individuals for tv measurement compliance

Abstract: A TV audience survey system for determining the TV viewing activities of a plurality of individuals in a household includes a master device and multiple tags, each tag assigned to an individual. After an individual logs into the system and starts watching the TV, the master device communicates with the corresponding tag repeatedly to accumulate data representing the individual's TV viewing activities. Such data can be used to determine when the individual stops watching the TV for an extended period of time without logging out of the system and when the household member remains watching the TV after logging or being logged out of the system. The master device then reports the accumulated data to a remote server, which uses the data to determine whether the individual complies with the logging protocol defined by the TV audience survey system and update the TV viewership data associated with this household.

Electromagnetic Design of Superconducting Synchronous Motors for Electric Aircraft Propulsion

Abstract: This paper evaluates the electromagnetic characteristics as to two types of superconducting motors: one is the superconducting motors adopting high-temperature superconducting field coils and copper armature windings; and the other is fully-superconducting motors, which have high-temperature superconducting field coils and MgB 2 superconducting armature windings. Analytical formulas and FEM are employed for the designs of 1.5-, 3.0-, and 5.0-MW motors. We consider how to reduce ac loss in MgB 2 winding structure as well. The analysis of our results, which was conducted mainly over output density and efficiency, suggests that the adoption of superconducting motors is more realistic in realizing electrical aircraft propulsion system in terms of higher output; the analysis results show that the fully-superconducting motors have a potential to reach over 16 kw/kg.

Enhanced trapped field in MgB2 bulk magnets by tuning grain boundary pinning through milling

Abstract: The effects of the grain size, lattice strain, and microstructure on the trapped field properties of ball-milled MgB2 bulks were studied. A decrease in the in-plane lattice parameters and transition temperature and an increase in the in-plane x-ray diffraction peak widths occurred with milling as a result of grain refinement and carbon substitution. Microstructural analysis revealed that sub-micron-size fine MgB2 grains were well connected, resulting in increased grain boundary density. The trapped field of the magnetized bulk samples exhibited a large improvement with milling and reached 3.72 T at 5 K, which is the highest among MgB2 bulks prepared using pressureless synthesis. Excess milling resulted in degradation of the trapped field because of Tc reduction. The increased grain boundary density and electron scattering are considered to contribute to the high trapped field through quantitatively and qualitatively enhancing the grain boundary flux pinning.