Recently, we have developed a first-principles based multi-scale modeling approach for studying carrier transport properties in polymeric dielectric, and have successfully modeled hole transfer in polyethylene (PE). In this study, in order to see if we can model carrier transport in more complex polymers, we have utilized the multi-scale modeling method to simulate electron and hole transfer in polyethylene terephthalate (PET). The agreement between computed and experimental electron and hole mobilities in PET demonstrated the robustness of the modeling technique. The multi-scale modeling approach enabled us to understand the microscopic origin of the carrier transport properties; unlike carrier transport in PE where the energetic disorder is dominated by the conformational disorder of the polymer chain, that in PET was strongly affected by the electrostatic disorder (disorder of the electrostatic potential due to surrounding environment). It is shown that this difference comes from the fact that (1) the charge localized region in PE chain is determined by the conformational disorder whereas that in PET is determined by the chemical structure of the polymer chain, and (2) PET chain has large local dipole compared to PE chain.

Epoxy resin not only has excellent insulation properties, but also has properties such as heat resistance, water resistance and so on. For these reasons, epoxy resin is used in various applications. It is necessary to pay attention to the deterioration of partial discharge and electrical tree, when the epoxy resin is used as an insulating material for DC high-voltage equipment, because they are exposed to a high DC electric field. In addition, it is known that the insulation performance of the epoxy resin is significantly reduced, when a foreign matter or air void is mixed in them, because non-uniform electric field will be generated. The electrical tree generated by non-uniform electric field increases the risk of dielectric breakdown and reduces the reliability of equipment. Therefore, it is necessary to accurately diagnose the deterioration of the epoxy resin and to clarify the risk before dielectric breakdown. It is expected that the accurate degradation diagnosis for DC high-voltage equipment will be possible by using the current integrated charge method. The equipment can be operated safely by clarifying the correlation between the integrated charge and the electrical tree. In this study, the electrical tree in epoxy resin was diagnosed by the current integrated charge method under non-uniform DC electric field. As a result, several information on the electrical tree was obtained before dielectric breakdown.

Pulsed electroacoustic (PEA) space charge measurement of low density polyethylene using a spin-coated Poly(vinylidene fluoride-trifluoroethylene) thin film is demonstrated. The space charge profile of a low density polyethylene film with a thickness of 150 µm is measured by PEA method. Compared with conventional 9-µm and 30-µm piezoelectric films, the space charge profile obtained by the 3-µm spin-coated film shows better spatial resolution. Furthermore, acoustic attenuation of a PEA signal is also analytically studied using the Kelvin-Voigt model for viscoelastic materials.

Sheets of cross-linked polyethylene (XLPE), which is believed to be the same as that for electrical insulation in safety-related cables in nuclear power plants, were aged under simulated severe accident conditions. Infrared absorption spectroscopy, indenter modulus measurement, and tensile tests were conducted to investigate the correlation between the aging-induced changes in chemical structure and those in the mechanical properties of XLPE. As a result, it has become clear that XLPE is oxidized to form carbonyl groups and becomes slightly brittle by the gamma-irradiation at 100°C. The gamma-irradiation at room temperature scarcely changes the chemical structure and softness. Instead, such gamma-irradiation apparently slows down the progress of embrittlement induced by the subsequent steam exposure at 220°C due to the presence of cross-linked structures.

Various methods have been proposed to evaluate hydrophobicity of silicone rubber used for sheds of polymeric insulators. CIGRE WG D1.14 has proposed Dynamic Drop Test (DDT) method to evaluate the hydrophobicity changes of the materials. In this paper, we measured static contact angle, hydrophobicity class in spray method, and drop velocity of water droplets, in order to observe the change in hydrophobicity of silicone rubber surface suffered to local arc discharge at DDT. Because of the hydrophobicity decreases due to the local arc discharge, the water droplet changes from a spherical to a water film. In particular, changes of initial state in hydrophobicity can be observed by measuring the drop velocity of water droplets. And the correlation was confirmed with the cumulative charge of local arc discharge. Therefore, the water drop velocity was effective for the evaluation of hydrophobicity change.

Some safety-related cables installed in boiling water reactors in Japan are likely to be exposed to an aqueous solution of sodium hydroxide (NaOH) during a severe accident (SA). For examining the degradation mechanism of cables insulated with silicone rubber (SiR) by the aqueous solution of NaOH sprayed during a SA, various tests to simulate a SA were conducted. Namely, after sample cables were pre-aged to simulate the degradation induced in the normal operating conditions, they were irradiated by gamma rays to simulate radiation exposure during a SA. Then, their insulated cores were immersed in the aqueous solution of NaOH with a pH of around 13 at 170 °C. It was found that the scission of siloxane chains in SiR on the surface of insulation and the generation of silicon dioxide occur with the increase in aging time and that the cable insulation is eroded from their surface contacted with the aqueous solution of NaOH.

A linear inertial electrostatic confinement fusion neutron source equipped with a cooling system for high power operation was developed and its discharge characteristics and neutron production performance were tested under a wide range of discharge conditions. Four different types of discharge anodes were prepared and the dependencies of the device performance on the anode shape were precisely investigated. A maximum neutron production rate of 3.4×10⁶ n/s was achieved when the device was operated with single-cylinder-type anodes under a discharge voltage of 94 kV, a current of 20 mA , and a deuterium gas pressure of 0.5 Pa. By comparing the discharge characteristics and neutron generation rates under different anode shapes, we found that the larger inner diameter of the anode leads to longer effective gap length and lower operating pressure, which may result in relatively high fusion reaction rate observed with the single-cylinder-type anodes.

We investigated and compared the alternate current (AC) and lightning impulse (LI) breakdown voltages (BDVs) of mineral oils that had been treated to nitrogen gas filling, nitrogen bubbling addition, and nitrogen fine bubbles (FBs) addition respectively after degassing. As a result, it was found that there was almost no effect on AC and LI BDVs by the difference of the nitrogen addition treatment methods. Additionally, the LI ratio of mineral oils were found to be approximately 2.41 to 2.68. Furthermore, nitrogen FB equal or less than 2 µm in diameter was not considered to be a factor in reducing BDV and breakdown electric field (BDE) of mineral oil.

In the growth study of agricultural crops, it is important to measure photon flux density (PFD) on each wavelength region such as ultraviolet, blue, green, red, and far-red. In our previous study, a simple band-spectra quantum meter was developed using photovoltaic (PV) cells, however the space resolution for measurement area was low owing to the large device size. Developed band-spectra quantum meter with the size of 70 mm length × 35 mm width × 10 mm height was configured using ultra-small PV cells and optical bandpass filters. A cover with the role to reduce the light reaching to the PV cells was equipped to maintain linear correlation between short-circuit current output of the ultra-small PV cells and outdoor solar radiation intensity. Band-spectral PFD according to the irradiated light wavelength was obtained from the developed quantum meter irradiated with green light.