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Pressure drops and temperature rises caused by the cooling with liquid nitrogen are evaluated for two typical examples of HTS cables. One is the three-in-one-type AC cable located inside a corrugated pipe, and the other is the single-core-type DC cable located inside a straight pipe. The theoretical expressions of pressure drop and temperature rise indicate the contributions from three components such as the friction between the liquid nitrogen and the wetted surfaces, the ratio of the heat input to the mass flow rate of liquid nitrogen and the vertical change of position along the cooling pipe. The numerically estimated results are validated by comparing them with the test results carried out by the other groups. Furthermore, the maximum feeding distance of HTS cable can be determined by adjusting the flow rate of pump if the maximum permissible pressure drop and temperature rise are fixed in advance.

The development of a liquid nitrogen submerged pump for HTS applications is underway. A cryogenic active magnetic bearing is the main component of the pump. The bearing makes the maintenance interval of the pump longer than 3years such interval is essential for the pump in commercial use of HTS applications such as long HTS cable. The bearing will be set in a HTS motor shaft of the pump. In experiments, a shaft without an HTS motor is used and the bearing was immersed in liquid nitrogen. The rotation of the shaft is made by a high-speed motor at room temperature. The bearing consists of two radial bearings and one axial bearing. The shaft was floating by the bearing and was rotated by the motor at room temperature. The steady rotation speed of 2,000, 3,000, 4,000 and 5,000 rpm were achieved, and the rotation speed satisfied the design speed of the pump which is 5,000rpm.

Optical and magneto-optical properties of one-dimensional magneto-optical photonic crystal (1-D MPC) prepared by the sol–gel dip-coating method, including a magnetic defect layer composed of mixture of CoFe 2 O 4 and SiO 2 , are investigated from both the experimental and theoretical standpoints. The resonant transmission of light was observed around 570 nm in the photonic band gap. The Faraday rotation angle θ F showed two maxima at 490 and 640 nm, and the wavelength dependence of θ F above 760 nm was similar to that of the CoFe 2 O 4 +SiO 2 single-layer film. The two maxima of θ F are attributed to the enhanced Faraday rotation of nonmagnetic TiO 2 layers in the cavity structure and that in magnetic CoFe 2 O 4 +SiO 2 layer through the light localization in MPC. The maximum value of θ F due to the magnetic CoFe 2 O 4 +SiO 2 layer in the MPC was 22-times larger than that in the single-layer film. The simulation study of MPC with CoFe 2 O 4 +SiO 2 magnetic defect layer, based on the matrix approach method, showed that the resonant light transmission was accompanied by the localization of electric field, and large enhancement of θ F appeared at different wavelengths so as to agree with the experimental features. This can be explained in terms of the wavelength dependent off-diagonal components of the dielectric constant tensor in addition to the large extinction coefficient in the CoFe 2 O 4 +SiO 2 magnetic defect layer.

A facile synthesis method for monodisperse Fe nanoparticles has been developed by the injection of iron carbonyl into kerosene in one pot. By controlling reaction parameters, 3–12 nm Fe nanoparticles were prepared. The size distribution is very narrow and any size-selective treatment is not required, even when several grams of Fe nanoparticles are synthesized. Magnetic measurements reveal that the saturation magnetization (Ms) of the 9.3 nm Fe nanoparticles is always over 150 emu g−1 at room temperature.

We are developing 10 kW class turbo-Brayton refrigerator whose working fluid is neon gas. Its high pressure value is 1 MPa and its low pressure value is 0.5 MPa. The refrigerator consists of two turbine-compressors and a heat exchanger. The turbine-compressor has a turbo-expander on one side of its shaft and a turbo-compressor on the other side of the shaft. Two turbo-compressors are connected in series and two turbo-expanders are set in parallel. So, all amount of neon gas is compressed by two stages and each half a mount of neon gas is expanded by one stage. Two turbinecompressors are the same machines and development cost and time are minimized. In this stage, we made one prototype turbine-compressor and installed it in a performance test facility. This paper shows details of the turbine-compressor and refrigerator cooling power simulation results.

We developed a prototype sub-cooled liquid nitrogen (LN) circulation system for HTS power equipment. The system consists of a neon turbo-Brayton refrigerator with a LN sub-cooler and LN circulation pump unit. The neon refrigerator has more than 2 kW cooling power at 65 K. The LN sub-cooler is a plate-fin type heat exchanger and is installed in a refrigerator cold box. In order to carry out the system performance tests, a dummy cryostat having an electric heater was set instead of a HTS power equipment. Sub-cooled LN is delivered into the sub-cooler by the LN circulation pump and cooled within it. After the sub-cooler, sub-cooled LN goes out from the cold box to the dummy cryostat, and comes back to the pump unit. The system can control an outlet sub-cooled LN temperature by adjusting refrigerator cooling power. The refrigerator cooling power is automatically controlled by the turbo-compressor rotational speed. In the performance tests, we increased an electric heater power from 200 W to 1300 W abruptly. We confirmed the temperature fluctuation was about ±1 K. We show the cryogenic system details and performance test results in this paper.

We developed a prototype turbo-Brayton refrigerator whose working fluid is neon gas. The refrigerator is designed for a HTS (High Temperature Superconducting) power transformer and its cooling power is more than 2 kW at 65 K. The refrigerator has a turboexpander and a turbo-compressor, which utilize magnetic bearings. These rotational machines have no rubbing parts and no oil-components. Those make a long maintenance interval of the refrigerator. The refrigerator is very compact because our newly developed turbo-compressor is volumetrically smaller than a displacement type compressor in same operating specification. Another feature of the refrigerator is a wide range operation capability for various heat-loads. Cooling power is controlled by the input-power of the turbo-compressor instead of the conventional method of using an electric heater. The rotational speed of the compressor motor is adjusted by an inverter. This system is expected to be more efficient. We show design details, specification and cooling test results of the new refrigerator in this paper.

The Faraday rotation in Bi-substituted yttrium-iron garnet thin films, in which an artificially fabricated Au nanoparticle array is embedded, is studied as a function of lattice spacing compared with the extinction spectra. With decreasing lattice spacing in the Au array, the wavelengths corresponding to the enhanced Faraday rotation and the extinction peak showed blueshifts in the same manner. This indicates that Faraday rotation can be manipulated by means of the wavelength shift of localized surface plasmon resonance that originates from the change in electromagnetic interaction between Au nanoparticles.

Faraday rotation spectra of Co nanoparticles embedded in polymethylmethacrylate (PMMA) matrix were investigated by the theoretical and experimental approaches. Co nanoparticles were synthesized by means of the thermal decomposition method, which makes it possible to control the particle concentration without changing the particle size distribution. The amplitude of Faraday rotation is dependent on the particle concentration, and the Faraday rotation spectra show the blueshift accompanied by the decrease in size of Co nanoparticles. The experimental results of Faraday spectra were consistent with the calculation using the Maxwell-Garnett model which is considering the size-dependent free-electron contribution and size independent bound-electron contribution. It was found that the spectral shift was caused only by the size-dependent diagonal element in the dielectric constant tensor, which originates from the confinement of the free electrons in nanoparticles.

Frictional behaviors of flake and adsorbed monolayer on substrate can be observed by Frictional force microscope and Quartz crystal microbalance experiments and are typical problems in nano-friction. Computer simulations had been played important roles in understanding those behaviors, but in most of them the driving direction coincides with one of the crystal axes of the substrate. Here we report our numerical results of direction dependence of friction of flake and adsorbed monolayer. We found a new kind of dynamical phase transition in which flake and adsorbed monlayer change their structure relative to the substrate and make incommensurae structure to reduce kinetic frictional force after certain transition time. When the driving velocity is decreased the transition time tends to diverge at certain critical velocity for the flake. For the adsorbed monlayer the transition time tends to diverge at certain critical magnitudes of the external force or the interaction strength between adsorbates when they are decreased.