Mitsubishi Electric Corporation and KEK have been developing internal‐tin‐route Nb3Sn conductors with high critical current density Jc and low magnetization for high energy accelerators. The non‐Cu Jc values of the conventional internal‐tin wire at 12 T and 4.2 K were about 1700 A/m2. These wires showed relatively high Jc values but their large effective filament diameter deff indicated that they also had very large magnetization. To further improve the Jc and deff of these wires, we have developed a wire with a new configuration. Called the Distributed Tin (DT) wire, it consists of Nb‐filaments/Cu‐matrix modules and Sn‐core/Cu‐matrix modules. The DT wire shows excellent superconducting properties, such as a non‐Cu Jc of 2120 A/mm2 and a deff of 75 μm, which is almost as small as the diameter of Nb/Cu modules. In addition to having a high Jc at 12 T, its Jc at 20 T was also improved to 207 A/mm2 because of the increase of Bc2 and Tc. The grain size distribution of the Nb3Sn filaments is far more uniform than that of the conventional wires, and we think this uniformity contributes to the improvement of these superconducting properties.
Field operation and cooling test of high Tc coil made of Bi-based pancake coil were carried out. By the measurement of critical current distribution inside the high Tc coil, we found that the critical current of the edge pancake coil is lower than that of the center pancake coil. This result is explained quantitatively in consideration of field and field angle dependence of critical current for the tape-shaped conductor and field distribution inside the coil. Magnet system assembled GM-refrigerator, high Tc current lead and the high Tc coil was tested. As a result, it was found that thermal load into the coil was low and field operation up to 90% of critical current of the high Tc coil was stable.
We investigated the critical current density and the flux creep in melt-processed Bi-Pb-Sr-Ca-Cu-O for the purpose of studying the existence of strong flux pinning forces due to normal conducting precipitates. We fabricated samples with a similar microstructure to melt-processed Y-Ba-Cu-O and Tl-Sr-Ca-Cu-O having a strong pinning force. When the matrix was (Bi, Pb) 2 Sr 2 Ca 1 Cu 2 O y (2212) phase, the irreversibility field B irr was expressed as B irr \propt(1- T / T c ) 3/2 , which suggested that the expected flux pinning was due to normal conducting precipitates. A part of the matrix was transformed to (2223) phase by the postannealing of the sample; however, the superconducting properties were inferior to those observed in (2223) polycrystals.
Multiband terminals, which can be used for W-CDMA, and digital TV and WLAN, will be strongly required in the future. In this paper, we describe the newly developed modified slot antenna. This new built-in antenna can realize multiband operation with a simple structure.
The Bi-based (2212) single grains including a large number of normal particles, (Ca,Sr)2Cu1O3, were synthesized by a melt process. To characterize the flux creep behavior in such a superconductor, magnetization measurements were performed at various temperatures and magnetic fields. The flux creep rate exhibited a maximum at 20 K in both magnetic fields parallel and normal to c axis. The magnetic field dependence of the pinning potential, U0, evaluated from the residual magnetization was not represented by the expression, B−α, in Y1Ba2Cu3O7 superconductors. The relation between U0 and the critical current density is discussed.
We have investigated the effect of Pt on crystallization of Bi 2 Sr 2 Ca 1 Cu 2 O y prepared by the melt process. By observing the microstructure of specimens rapidly cooled in the process of crystallization, we found that the Pt restrained the growth of the Ca 2 Cu 1 O 3 phase and even of superconducting phases. It was found that Pt formed oxides preferentially with Ca and Sr early in the crystallization process, however, such products didn't seem to grow coarsely.
The microstructure and superconducting properties for samples with the nominal composition of Bi 2 Sr 2 Ca 1+2 x Cu 2+ x O y ( x =0, 0.2, 1.0) prepared by a melt process have been examined. The magnetic field dependence of the intragrain critical current density was improved by enriching the Ca and Cu contents. Such samples included two kinds of precipitates, (Ca, Sr) 2 CuO y and Sr-Pt-O compounds. The latter precipitates were much smaller in size than the former, and this suggests that they may be more effective in enhancing the pinning force.
The development of high performance Nb3Sn wires with an internal-tin route was reviewed. The internal-tin wires have excellent productivity and low production cost because the drawing process does not require intermediate annealing. This process has the advantage of producing several types of wires with wide superconducting properties for practical applications. We have been producing wires with high critical current density (Jc) and low hysteresis loss for fusion applications such as the ITER and KSTAR. We have also developed internal-tin wires with Jc>1600 A/mm2 at 12 T, 4.2 K for general high field magnets. Recently, we have been developing a new wire configuration for next generation high energy accelerators in collaboration with the KEK High Energy Accelerator Research Organization. The wire, called a distributed-tin (DT) wire, has an original structure in which the multi-Nb filament modules and Sn rods are uniformly distributed in a Cu matrix. The values of Jc of the DT wire are 2120 A/mm2 at 12 T, 4.2 K, which was obtained by increasing the Nb and Sn fractions of the wires, and 207 A/mm2 at 20 T, 4.2 K, because of the improvements in Bc2 and Tc. It is anticipated that the DT wires will be applied to not only next generation accelerators, but also high resolution NMRs.
In this paper, a planar antenna and the 6-sector arrangement for a small card type mobile terminal used in the wireless local area network (WLAN) system are proposed. The radiation characteristics, particularly the tilted main beam in vertical plane and current distribution are calculated and discussed. We show that the 6-sector beams of half power width of 60 degrees are obtained by the proposed arrangement that is in a rectangular configuration of 10.6 mm /spl times/ 44 mm at 25 GHz band, and this is suited to a built-in antenna mounted on the edge of the card type mobile terminal like a PCMCIA card.
