This paper summarizes the cryogenic electrical insulation with polymers and its interesting features. At cryogenic temperature, polymers show high electric strength, extremely higher ac treeing inception voltage, low tanδ, no thermal and chemical degradation, no water tree degradation, very limited space charge injection and resulting high short-circuit treeing inception voltage, etc. Based on these features, we can call polymer at cryogenic temperature as “super electrical insulator". Water is an enemy of electrical insulation at room temperature, but at cryogenic temperature it is frozen and becomes an electrical insulation material. A paper-ice composite insulation system shows superior electrical insulation performance compared with conventional paper- liquid nitrogen system and is expected to be one of good candidates for cryogenic electrical insulation system.

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An ESD (electrostatic discharge) testing is specified in the IEC 61000-4-2, in which the detailed waveform of the discharge current injected by an ESD-gun is prescribed. However, due to lack of understanding of the discharge process, it is difficult to confirm whether or not such the IEC current waveform be injected onto actual equipment. We thus previously proposed an equivalent circuit model for the ESD-gun based on its geometrical structure, and showed decisive factors for the discharge current. In this study, in order to confirm the feasibility of the above equivalent circuit model, we measured with a 6-GHz wide-band digital oscilloscope the discharge current through an SMA connector and the resultant magnetic near-field for the contact discharge of an ESD-gun. As a result, we found that both the measured waveforms approximately agree with those calculated from our equivalent circuit model. We then measured with respect to charge voltages the magnetic near-fields for the contact discharge of the ESD-gun to the ground, which showed that the measured waveform around the first peak fairly agrees with the calculated one. Furthermore, we also found that the magnetic field peak increases with increasing the charge voltage, whose dependence can be predicted from our equivalent model.

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Titanium iron oxide (Ti-Fe-O) thin films have been successfully synthesized by irradiating laser to Ti and Fe plates in a vacuum. The titanium, iron and oxygen contents in the thin films were controlled by changing the surface area ratio of the Fe plate to whole plates (S = S_Fe / (S_Fe + S_Ti)). As a result, the phase transition from Ti-Fe-O or β-Ti dissolving iron of 35 % to TiFe occurred in the S range from 60 to 70 %. In addition, the composition of the thin films prepared at S = 60 and 70 % was Ti_0.27Fe_0.40O_0.33 and Ti_0.15Fe_0.62O_0.23.

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A numerical simulation study of a virtual cathode oscillator withannular cathode has been performed by a 3 dimensionalparticle-in-cell (PIC) code called MAGIC. Also the experimentalstudies are performed for comparison of numerical results. Theannular diode consists of circular anode mesh and annular typecathode. The object for this investigation is to find theoptimized width and radius of the annular cathode in our highpower microwave pulser, “Chundoong". Both of simulation andexperimental results show that the output microwave power andfrequency depend on emission width and radius of annular cathode, and the dominant mode of output microwave is TM₀₁ under theoptimized width 4 mm and radius of 20 mm.

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Gas desorption from an insulator excited by electron impact is regarded as one of major causes of surface flashover in vacuum. To enable analysis of gases only from an electron emission site on insulator surface a liquid nitrogen cooled shroud was used to prevent gases from a vacuum chamber entering into a quadrupole mass spectrometer (QMS). We observed gases released from the alumina sample and found that their mass numbers were m/e=2 (main), 18 and 28(very few). It was found that they were same components as residual gas species of a vacuum chamber. Furthermore, we investigated the effect of heat treatment on the desorbed gases from alumina.

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In this study, an experimental model is made on the basis of the Whitehead abc model and the properties of partial discharge (PD) breakdown in the micro gap are investigated. The quite unique properties of the PD breakdown in the micro gap are obtained: The voltage dependence of time to the PD breakdown and spread of residual negative charge distributions in the micro gap become discontinuous at a certain voltage amplitude. The discontinuousness in the PD breakdown properties is found to be due to the difference in surface discharge patterns in the micro gap: Polbüschel-type at lower voltage and Gleitbüschel-type at higher voltage. This paper aims at discussing the PD breakdown process at higher voltage. Time to the PD breakdown in the micro gap is analyzed using the Weibull probability distribution. The result suggests that the PD breakdown processes are classified into two different types: fatigue-failure-type and early/random-failure-type. Assuming that the PD breakdown of fatigue-failure-type is a thermally activated degradation process of Ahrenius type, the activation energy is caluculated . The value is in good accord with activation energy required for polymer bond scission caused by interaction with oxygen and ozone. The result suggests that the PD breakdown of fatigue-failure-type is caused by oxidative degradation. On the other hand, residual negative charges in the micro gap play an important role in the PD breakdown process of early/random-failure-type. In view of previous studies, it is possible that the PD breakdown process of early/random-failure-type is governed by the existing probability of structural defects where a great deal of the negative charges accumulates.

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This paper describes a generation method of ozone using a silent discharge ozonizer, which is cooled down to cryogenic temperature by liquid nitrogen. The ozonizer was consisted of two metal electrodes and one dielectric barrier covering the lower electrode surface. In order to cool down the discharge space between the dielectric barrier and the upper electrode, the ozonizer was placed in an inner vessel of a metal cryostat whose outer vessel was filled with liquid nitrogen. It was found that the ozone concentration and ozone yield were increased with decreasing temperature. Especially, the cooling effects were remarkable in high specific energy region. The maximum ozone concentration of 146 g/m³ and ozone yield of 212.5 g/kWh were achieved at 170 K. Temperature distribution within the ozonizer was theoretically analyzed inorder to clarify the effects of the dielectric barrier material and the electrode gap space.

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The authors have developed a new method for detecting position and direction in weld zone of steel structures such as oil-storage tanks and bridges without removing their anticorrosion paint. The method uses a special eddy current probe and detects the position and direction by utilizing the difference of electromagnetic characteristics between the base material and the heat affected zone. The probe comprises two large tangential exciting coils wound orthogonally each other and a small pancake detecting coil. The exciting coils induce uniform eddy current rotating its direction synchronizing to the alternating exciting current. The signal amplitude from the probe provides information on its position in the weld zone and the signal phase indicates the direction of the probe. Thus the probe generates the weld signal to effectively follow the weld line in steel structures. The experimental results have shown that the proposed method is promising because the probe provides clear weld signal with little noise and the change of the probe lift-off from the material causes little variation in the signal.

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This paper proposes an earthing resistance measurement method for a simple earthing electrode without two axially electrodes. The proposed method can measure the earthing resistance by evaluating loop impedance of an earth return circuit composed by an earth electrode of under the test and a lead wire, a return wire, the earth soil. The return wire is only put on the soil surface without any terminations. The earthing resistance of the electrode of the under test can be given by the earth return circuit impedance at a resonate frequency designed between 100 kHz and 1 MHz. The measurement conditions for the proposed method are determined by numerical calculations. Earthing resistance deviations between the proposed method and the existing method are -13%-+22% for earthing resistance values with 50Ω, 100Ω, 300Ω. It is found that the proposed method can be applicable to evaluate an earthing resistance around 100Ω for a simple earthing electrode.

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A high-temperature heat treatment of polyimide (Kapton) film yielded a highly oriented graphite film, composed of thin graphite layers with 6-7nm in thickness. The hexagonal lattice formation of graphite depends on the heat treated temperature (HTT), and the orientation of the graphite layer preferentially proceeds from the surface of the film. As the results, the orientation of the graphite layer at the surface is superior than inner parts. The graphite films are particularly suitable for constituting optical components for X-ray monochromater.

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From viewpoints of environmental protection and reduction in manufacturing cost, it is desirable to use non-crosslinked polyethylene as an insulating material for power cables. A new type polymerized polyethylene using a single-site catalyst has an advantage of its high melting point, but its processability is very poor because of its high viscosity. Therefore, blends of this polyethylene and conventional low-density polyethylene with different blending ratios are examined in this research. As a result, it has become clear that the blend with a blending ratio of 1:1 has an appropriate melting stress and an adequate viscosity at a shear velocity suitable for cable manufacturing. Furthermore, the blend has a superior thermal property and a high dielectric strength for both dc and impulse voltages.

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The pulsed laser deposition (PLD) of GaN with Zn-dopant was closely investigated. The particular emphasis was placed on the PLD target consisting of liquid alloy of Ga and Zn. Throughout the work, an ArF excimer laser (193-nm wavelength and 20-ns duration) was used. Both Ga and Zn atoms could be simultaneously ablated from the alloy target, and ablation ratio of Zn/Ga was found to markedly depend on the laser fluence. Namely, lower laser fluence led to less Ga content in the ablated particles, and with high laser fluences the congruent ablation developed. Image of plume emission revealed that plume dynamics of Ga and Zn is very close to each other. Zn-doping to the GaN by the PLD method is carried out using the liquid Ga-Zn alloy target in N₂ ambient. PL spectrum of the film shows the clear evidence of Zn incorporation to the GaN film.

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It is well known that water-tree propagation in XLPE cable is significantly influenced by inorganic impurities in water. Therefore, we investigated both changes in concentration and deviation of isotopic content of inorganic elements in XLPE samples by water-tree experiments under clean environment. The concentration of several kinds of elements, e.g., Li, Na, Mg, Al, K, Ca, Fe, Ni, Pb and Bi, in water-treed sample showed anomalous increase or decrease dependent on cation (K⁺, Na⁺ or Ag⁺) in water solution compared with blank or original sample. Furthermore, the isotopic content of Zn deviated over 6% from natural abundance. These results suggest that water-tree propagation is concerned with unknown physical or electro-chemical reactions.

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Effects of ion bombardment on a-Si and a-SiGe film deposition have been studied by a large-area solar cell production equipment using plastic film substrates. We propose that a ratio between peak-to-peak voltage (Vpp) of electrodes and deposition pressure (P) gives information about ion damage during the film deposition. Single-junction a-Si solar cells were fabricated under conditions with various Vpp/P, and photovoltaic properties of the solar cells were measured in order to evaluate the dependence on Vpp/P. Conversion efficiency of the solar cells is strongly dependent on Vpp/P, which validates our ion damage model. The ion damage model is effective on both a-Si and a-SiGe film growth processes.

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