The Symposium on Electromagnetic Processing of Materials (EPM) was organized in the beginning of the 1990s in Japan in cooperation with France. EPM applies various electromagnetic phenomena to materials processing. In the early stages of EPM, it was mainly applied to steel-making processes like heating, melting, stirring, flow control and so on. However, its application has been extended recently to nonferrous metals like aluminum, and even to nonmagnetic materials by the use of DC superconducting magnets. In the present paper, examples of EPM are shown and the applicability of superconducting magnets to conventional EPM is investigated. If AC superconducting magnets are applied to conventional EPM, the limit of EPM due to the weakness of the magnetic field will be broken and a new stage of EPM applications will be opened.
This report describes the development of low vibration cooling systems with pulse tube (PT) cryocoolers. Generally, PT cryocoolers have the merit of lower vibration than GM cryocoolers. However, the cooling systems for a cryogenic laser interferometor observatory (CLIO), which is a gravitational wave detector, require sufficiently lower operational vibration than that of a commercial PT cryocooler. The required specification for vibration amplitude on cold stages is less than ±1 μm. Therefore, during development of the low vibration cooling systems for CLIO, we introduced advanced countermeasures for commercial PT cryocoolers. The cooling performance and the vibration amplitude were evaluated. Results revealed that, 4 K and 80 K PT cooling systems, which have a vibration amplitude of less than ±1 μm and respective cooling performances of 4.5 K at a heat load of 0.5 W and 70 K at a heat load of 50 W, were developed successfully.
The commercial-scale development and critical current density (Jc) improvement of (Nb, Ta)3Sn superconducting wires utilizing a Ta-Sn powder-in-tube process were carried out. In the commercial-scale wire, the necessary properties (RRR, 0.2% yield strength) required for practicable use were equivalent to a wire developed using the bronze-method. The Jc and n-value were uniform along the wire and higher than those of the bronze-method wire. In addition, we achieved an overall Jc of 110 A/mm2 (21 T, 4.2 K) by optimizing the core composition of the wire and heat treatment.
Recently, a tri-axial cable composed of three concentric phases has been intensively developed, because it has advantages such as reduced high-temperature superconducting (HTS) tape, small leakage field and small heat loss as compared with three single-phase cables. However, there is an inherent imbalance in the three-phase currents in tri-axial cables due to the differences in the radii of the three-phase current layers. The imbalance of the currents causes additional loss and a large leakage field in the cable, and deteriorates the electric power quality. We have already showed that it is possible to obtain a balanced three-phase currents by adjusting all of the twist pitches. To verify the theory, we have fabricated a 1-m-long tri-axial HTS cable and tested it. The balanced three-phase voltages of the cable were measured by imposing an AC transport current with a frequency in the range of 50-500 Hz at 77 K. From this test, we demonstrated that the balanced three-phase currents can be realized by adjusting all of the twist pitches.