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  4. No.46 November,2016
Fujikura Technical Review

No.46 November,2016


Y-based Coated Conductors for High-field Applications
Y-based coated conductors can be applied to the superconducting magnet with a magnetic field over 20 T which was not realized by conventional materials, due to their high critical current performance in strong magnetic fields and robust property in mechanical strength.. In this section, applications for the strong magnetic fields, for example, nuclear magnetic resonance (NMR) instrument with extra-high resolution utilizing a resonance frequency over 1 GHz are briefly introduced, and our recent R&D activities for those applications are also reported.
Multi-filamentary Yttrium-based Coated Conductors
With high critical current in magnetic field at a high temperature of above 20 K, Yttrium(Y) -based coated conductors are expected to apply to superconducting coils such as MRI (Magnetic Resonance Imaging). This is because expensive liquid helium which is required for conventional superconductors becomes unnecessary for Y-based coated conductors. To decrease screening current which becomes serious for superconducting coil, we developed multi-filamentary Y -based coated conductors. Here we report the overview.
Thermal Stability of Yttrium Based Superconducting Coil for Accelerator Application
Yttrium(Y)-based coated conductors are expected for miniaturization and higher performance of superconducting devices by applying to the coils, because of their high critical current characteristics in a high magnetic fields and relatively high temperatures above 20 K. As an application study of Y-based superconducting coils for a sextupole magnet considered by the High Energy Accelerator Research Organization (KEK), we evaluated the thermal stability of the Y-based superconducting coil.
Reducing Transmission Loss of the High Temperature Superconducting Power Cable
High temperature superconducting (HTS) cables are expected to be adapted to compact type large power transmission cables. HTS cables have not only high current density and low AC loss but also some environmental merits such as energy saving, CO2 gas reduction and magnetic shielding. In general, HTS tapes of the HTS conductor and shield layer in the HTS cables are wound in a spiral manner, and become a multi-layer winding with large current. Asa result, since the HTS conductor and shield layer has a multiple coil structure with different winding pitches, the internal magnetic flux is generated in the longitudinal direction. Therefore, the eddy current loss is generated in the former of such HTS AC cables. In addition, since the eddy current is induced in circumferential direction in the cryostat pipe in the case of the single- core cable, the joule loss is generated. It is considered that the magnitude of the magnetic flux (loss) depends on the winding direction, winding pitch of the HTS tape and the magnitude of the current, and comes actualized together with the large current. Therefore, in order to reduce the loss of the entire cable, each loss reduction for the former, the HTS conductor, the HTS shield and the cryostat pipe is necessary. In this paper, these low-loss measures of Fujikura Ltd are reported. Together, analytical considerations utilizing elliptic functions are also introduced.
2 kW single-mode fiber laser
Recently fiber lasers attract much attention due to their high power and excellent beam quality. Suppression of stimulated Raman scattering (SRS), which is a kind of nonlinear optical effects, is very important to realize a high power single-mode fiber laser. We have achieved a 2 kW single-mode fiber laser that shows well-suppressed SRS and excellent beam quality even with a 20 m long delivery fiber by properly designing the parameters of the fibers in the laser.
High Brightness Pump Module
We report the development of high brightness laser diode modules used as pump sources for high power fiber lasers. Laser diode modules are key devices which characterize the performance of the fiber lasers. We have achieved the highest brightness by combining the new packaging technology and high power laser diode technology developed by OPTOENERGY Inc.
High Power Semiconductor Laser Diode for Fiber Laser Pumping
We report performance improvement of single emitter laser diodes based on Asymmetric Decoupled Confinement Heterostructure (ADCH). Laser design optimization in vertical layer and lateral current injection structure enabled high power operation of 915 nm laser diodes up to 17 W and high power conversion efficiency more than 60 %. Mean time to failure of random mode is estimated to be over 600,000 hours for 17 W operation at room temperature. These results prove high reliability of ADCH at high power.
2000-fiber Ultra-high Density Underground Cable
In order to construct optical access networks economically and efficiently, we have successfully developed the ultra-high density 2000-fiber cable using innovative optical 8-fiber ribbon “Spider Web Ribbon (SWR) “ for underground networks. By employing high packing technology of SWR with simple cable design, the 2000-fiber cable has achieved the same diameter as existing 1000-fiber slotted core cable and the highest level of fiber packing density in the world. In addition, the cable has advantage of fiber joint workability such as mass fusion splice and unit identification by optimizing ribbon and bundle unit structure.
LCP Based Dipole Antenna Fed by Rectangular Waveguide Operating at 60-GHz band
In recent years, wireless communication with high speed and huge capacity data transmission at 60 GHz band is focused. Kiosk downloading which is a short-range wireless communication is one of 60 GHz applications. Requirements for millimeter-wave devices such as antenna are low loss and broadband operation whose bandwidth is up to 9 GHz. In the short-range wireless communication application, omni-directional radiation or large beam coverage is also required. In this paper, the design and evaluation of a dipole antenna fed by rectangular waveguide at 60 GHz is reported. The antenna is fabricated on liquid crystal polymer (LCP) substrate. The proposed antenna has broadband operation and broad beam radiation so that it is suitable for the short-range wireless communication at 60 GHz band.
B-Surface SBR of Load Detection Type
Many vehicles are now equipped with a Seat Belt Reminder (SBR) system. The system detects occupants in the front seat and reminds unbuckled occupants to fasten their seat belt by giving a warning light or an audible sound. We manufacture SBR sensors with membrane switches placed between the trim cover and the cushion pad of a passenger seat. Recently, customers have required us to develop a new type of SBR sensor, which is mounted on the bottom surface of a cushion pad, for the standardization of sensor shapes. Consequently, we have developed a new SBR sensor of load detection type using a metal film.