We propose the novel magnetic compensation method which is suitable to compensate gradient magnetic fields. The method is to be applied to a conventional large-scale, tri-axial active magnetic shielding system such as spacecraft magnetic testing facility. The essences of this method are adoption of compensation coils which have degrees of freedom in their coil orientations, and their installation position, which is chosen to have certain distances from the center of the shielding area. The method works with at least 4 compensation coils. In this research, we actually demonstrated the method with scaled-down experiment. Disturbance magnetic field (B) at the target zone was suppressed from 21.33nT to -1.54nT and magnetic field uniformity (ΔB) within the test zone was improved from 2.3nT to 0.015nT. In terms of magnetic field gradient, improvement from over 4nT/m to below 0.5 nT/m was achieved.

Effect of secondary electron emission coefficient on accumulated charge density distributions in atmospheric pressure dielectric barrier discharges have been simulated using two dimensional fluid model. Spatio-temporal distributions of accumulated charge density on each side of dielectric have been examined. The differences of conventional waveforms of accumulated charge density and the simulated results were clarified. And when the dielectrics were negatively accumulated, charges were uniformly accumulated, while positive charges were not. Randomness of streamers occurrence, and self-organized structures have been also examined by the accumulated charge distributions.

Some safety-related low-voltage cables used in nuclear power plants are required to maintain the insulation performance even during severe accidents. It is not clear whether oxygen affects the insulation performance of the cable in the steam exposure during a severe accident. In this study, we investigated the influence of oxygen on the insulation performance in an assumed severe accident condition for flame-retardant ethylene propylene diene rubber insulation (FR-EPDM) cables used as safety-related cables. Cables pre-aged by accelerated aging and non-treated ones were used as samples. The following points were found. When oxygen is present in water vapor, the oxygen concentration decreases during the exposure since oxygen is consumed by the oxidation of insulators and other materials. Whether or not the cable was subjected to aging does not alter the insulation resistance of the cable significantly under the assumed severe accident condition. The oxygen contained in water vapor affects the insulation resistance of the cable scarcely under the condition.

Cr-doped vanadium dioxide, V_1-xCr_xO₂ (x = 0-0.20), thin films were fabricated by metal-organic decomposition. From X-ray diffraction patterns of the films at room temperature, VO₂(M₂)(201) and VO₂(M₂)(201) diffraction peaks were observed for x = 0.03-0.20, while a VO₂(M₁)(011) peak was observed for x = 0-0.01, where M₁ and M₂ represent different monoclinic structures of VO₂. Moreover, all the fabricated films showed a p-type conductivity, and the hole concentration in the films increased with increasing x. From R-T characteristics of the films at the temperature range from 20 to 90℃, abrupt resistance changes caused by the metal-insulator transition in VO₂ with a hysteresis loop were gradually suppressed with increasing x; especially x≥0.15, they were completely suppressed, since the transition temperature of the film shifted to a temperature above 140℃. Relatively flat temperature dependence of the temperature coefficients of resistance (TCR) as high as -3.9%/K in the range of 20-90℃ was obtained for the V_0.85Cr_0.15O₂ thin film. The TCR value of the film is almost same as that of a V_0.75Ti_0.25O₂ thin film, whereas a resistivity of the former at room temperature is one order lower than that of the latter.

This paper deals with partial discharge inception voltage (PDIV) and long-term voltage-time (V-t) characteristics of Polyvinyl Formal (PVF) wires in mineral oil under thermal and electrical aging. The reliability of the long-term insulation performance was evaluated considering the thermal aging of PVF wire and the aging due to humidification of the insulating oil. The results showed that PDIV decreases with an increase in the temperature of heat treatment in the oil. It was also found that the lifetime of specimens subjected to the thermal aging up to 180°C was reduced compared to that of non-treated specimens. In order to examine the reduction in the long-term charge life of thermally aged specimens, chemical analysis was performed using a Fourier transform infrared spectrometer (FT-IR). The results suggest that the decrease in the long-term voltage application lifetime of the thermally aged specimens is caused by the low molecular weight of the PVF wire coating due to thermal aging. From the above experimental results and discussion, it was concluded that the PVF wire thermally aged at 180°C for 2 months, which corresponds to 60 years of operation according to the 10°C half-life law, maintains sufficient insulation performance at 1 kV stressed to the coatings and can be expected to have a service life of more than 30 years.

To further validate the IEC specified waveform as an ideal contact discharge current presented in 2008 IEC 61000-4-2, a comparison is made with air discharge waveforms from an ESD generator measured under different temperature and humidity conditions by newly introducing the IEC non-specified waveform parameters of 60% time width T of the first peak and falling depth D from the first peak. The result shows that the air discharge waveform is closer to the IEC specified waveform than the contact discharge waveform in both T and D when the rise time and the first peak value meet the IEC requirements. This verifies that the IEC specified waveform has the validity in a sense of well representing the air discharge waveform from the generator.