Minimizing size of a gas circuit breaker (GCB) and progressing reliability moreover, the fundamental investigation has been needed. In this review, the fundamental investigations of a GCB in Japanese universities were described. In general, a large scale experimental facility is needed for a circuit breaker development. To make experimental facilities minimized, several new approaches were adopted. A MEMS sensor application was aimed for a diagnosis of mechanical failure of a circuit breaker. The mechanical circuit breaker model was constructed to obtain an acceleration characteristic in a mechanical failure mode. A small scale facility made an arcing phenomenon research possible by using the Thomson scattering measurement. An accurate transformer model investigation was focused in a transient analysis. It was found that the transformer impedance had a frequency dependence, which cannot be simulated in the EMTP.

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As a basic step in the study of the biological effects of power frequency magnetic field (60-Hz, 0.05 μT-60 mT) on creatures, a series of experiments were carried out to examine the acute, chronic, and genetic toxicities of fruit flies. Specimens were exposed to magnetic fields for 30 seconds on acute toxicity experiments, for most of the life on chronic experiments, and for five days on genetic toxicity experiments. The behavior, longevity and mutation rate were analyzed by counting the number of files transferred to higher magnetic field side, the number of dead specimens, and the number of mutated specimens, respectively. Statistical analysis of the results showed that there was no obvious evidence that magnetic field level affects the behavior, longevity, and mutation of fruit flies.

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10 kHz repetition rate operation of an ArF excimer laser for microlithography is studied by focusing on the spatial separation between the discharge and the gas density depletion that is created by the previous discharge and that moves out of the discharge area due to the enforced laser gas circulation. The widths of discharge and the gas-density depletion were measured in detail by Mach-Zehnder interferometry. As a result, the minimum required distance between the center of the discharge and the center of the gas-density depletion area was found to be 1.4 times larger than the width of the discharge and is 12 % larger than the center-to-center distance at which the discharge area is just detached from the gas-density depletion area. This minimum required distance is 4.9 mm and 2 times as large as the distance estimated only from the absolute value of the gas density depletion.

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Neutral beam injectors (NBI) used for JT-60 are required to generate negative ions of 500 keV energies. To produce such high-energy ions, the electrostatic accelerators consisting of 3-stage of electrodes and three insulator rings are applied. The insulators are made of Fiberglass Reinforced Plastic (FRP) which is composed of epoxy resin and glass fibers. The surface discharges along the insulators are one of the most serious problems in the development of NBI. To increase the hold-off voltage against surface flashover events, it is necessary to investigate the FRP and epoxy resin insulator properties related to surface discharges in vacuum. This paper describes surface flashover characteristics for epoxy resin, FRP and Alumina samples under vacuum condition. In addition, the measurements of secondary electron emission (SEE) characteristics are also reported. These are important parameters to analyze surface discharge characteristics of insulators in vacuum.

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The characteristics of rare gas RF (13.56 MHz) breakdown are investigated, focusing our interest on the effect of excited particles on electron production specifically. First of all the pressure dependence of breakdown voltage, the breakdown voltage curve, is measured in parallel plate capacitively coupled RF discharge devices for four rare gases, He, Ne, Ar and Kr. For Ar and Kr typical well-known V-shaped type curves composed of the left and right branches are obtained, while for light rare gases, He and Ne, the L-shaped ones which show flat characteristics over a considerably broad range of pressure in the right branch are obtained. According to the similarity law for pd (p: pressure; d: electrode separation) which holds roughly in the right branch for any gases studied here, it is found that the breakdown voltage in the right branches of light gases increases with pressure through three regions, namely the gradual increase one, the flat one and the abrupt increase one. The numerical results by Kihara's breakdown criterion and the conventional Boltzmann analysis are as follows: as the working pressure increases, the dominant electron production process in the right branches of light gases shifts from the direct ionization which is the main electron production process in heavy rare gas breakdown, to the processes accompanied by excited particles and the flat region in the breakdown curve corresponds to the transition region of the dominant electron production process.

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To study the characteristics of breakdowns in different materials under a high RF field, a high-gradient experiment was proposed with using narrow waveguides having a field of around 140 MV/m at 50 MW power. Two experiments, one on copper (OFC) and another on stainless-steel (AISI-316L), were done. The breakdown rate of the copper waveguide was found to be larger than that of the stainless-steel waveguide at fields higher than several tens of megavolts per meter. The surfaces of both materials were observed after high-field experiments. The area suffering from heavy breakdowns was found to be rugged for the copper waveguide, while that of the stainless-steel smoother than the copper case, even though the heights of dips and bumps were almost the same at 20∼30 microns for the two materials. From these results, it was proven that the breakdown study using narrow waveguide under the high gradient field offered great potential.

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It is essential to measure dielectric properties of human tissues for the safety evaluation of electromagnetic field exposures. In this paper, towards developing an in-vivo measurement method for living human tissues, we employed an open-ended coaxial probe together with a time domain reflectometry (TDR) technique, which probably enables us to extract a reflected waveform from some specified tissues in the time domain. We compared the TDR-measured dielectric properties for human surface tissues with those derived from a conventional frequency-domain technique. As a result, we found a fair agreement between them in the frequency range from 300 MHz to 6 GHz. This result suggests the possibility of in-vivo dielectric property measurement for superficial human tissues by using the proposed TDR technique.

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Human exposed to electric and/or magnetic fields at low frequencies may cause direct effect such as nerve stimulation and excitation. Therefore, basic restriction is regulated in terms of induced current density in the ICNIRP guidelines and in-situ electric field in the IEEE standard. External electric or magnetic field which does not produce induced quantities exceeding the basic restriction is used as a reference level. The relationship between the basic restriction and reference level for low-frequency electric and magnetic fields has been investigated using European anatomic models, while limited for Japanese model, especially for electric field exposures. In addition, that relationship has not well been discussed. In the present study, we calculated the induced quantities in anatomic Japanese male and female models exposed to electric and magnetic fields at reference level. A quasi static finite-difference time-domain (FDTD) method was applied to analyze this problem. As a result, spatially averaged induced current density was found to be more sensitive to averaging algorithms than that of in-situ electric field. For electric and magnetic field exposure at the ICNIRP reference level, the maximum values of the induced current density for different averaging algorithm were smaller than the basic restriction for most cases. For exposures at the reference level in the IEEE standard, the maximum electric fields in the brain were larger than the basic restriction in the brain while smaller for the spinal cord and heart.

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Laser Thomson scattering (LTS) has been developed to diagnose high pressure plasmas such as a discharge plasma produced in the plasma display panel (PDP) and a laser produced plasma for the extreme ultra-violet light source. In the LTS diagnostics of the high pressure plasmas, plasma disturbances caused by lasers have to be paid much attention. For the case of PDP plasmas, the multi-photon absorption ionization of Xe atoms at the ground state and the meta-stable states can be the obstacle for the diagnostics. This was shown to be solved by using an infrared laser as a light source of LTS and adjusting the laser power density to be in the linear signal range. For the case of the laser produced plasma, electron heating by absorbing energy of the diagnostic laser beam can be a problem. In order to know the phenomenon quantitatively, increases of electron temperature were measured as a function of the laser energy. Measured results were compared with calculations based on the model taking account of the energy absorption by the process of inverse bremsstrahlung and the heat diffusion to the volume surrounding the laser beam during the laser pulse. Both results agreed well if the electron heating is less than a few tens of percent of the electron temperature. This shows that the model can quantitatively evaluate the electron heating.

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The electric charge accumulation under an electron beam irradiation (40 keV and 60 keV) was measured by using the pressure wave propagation (PWP) method in the dielectric insulation materials, such as polar polymeric films (polycarbonate (PC), polyethylene-naphthalate (PEN), polyimide (PI), and polyethylene-terephthalate (PET)) and non-polar polymeric films (polystyrene (PS), polypropylene (PP), polyethylene (PE) and polytetrafluoroethylene (PTFE)). The PE and PTFE (non-polar polymers) showed the properties of large amount of electric charge accumulation over 50 C/m³ and long saturation time over 80 minutes. The PP and PS (non-polar polymer) showed the properties of middle amount of charge accumulation about 20 C/m³ and middle saturation time about 1 to 20 minutes. The PC, PEN, PI and PET (polar polymers) showed the properties of small amount of charge accumulation about 5 to 20 C/m³ and within short saturation time about 1.0 minutes. This paper summarizes the relationship between the properties of charge accumulation and chemical structural formula, and compares between the electro static potential distribution with negative charged polymer and its chemical structural formula.

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