The triggering characteristics of a conventional triggered gap switch at main electrode voltage between 1.25 and 4kV are extremely inferior to those at voltage more than 10kV. Spontaneous discharge or discharge failure will frequently take place in the gap switch as the result of inadequate adjustment of electrode separation. A low pressure triggered gap switch put in a vacuum vessel made of pyrex glass has been made on an experimental basis. This consists of a pair of cylindrical main electrodes opposed to each other with a separation of 2mm, a pair of trigger electrodes made of close parallel wires and disposed at right angles to the main electrode and at a radial distance of 17mm from the axis of the main electrodes and a magnetic field coil provided so as to surround the rear portions of the trigger electrodes. A 100‰ trigger region without spontaneous discharge and discharge failure of the trial triggered gap switch has been obtained with the main electrode voltage from 1.25 to 4kV. The scatter in trigger time lag is evaluated by its standard deviation and it is shown that the standard deviation within the 100‰ bigger region is decreased from 26.4 to 8.8μs by applying magnetic field. The low pressure triggered gap switch was connected in the capacitor bank power source for the vertical field in a small tokamak HAMANA-T. It could be triggered by the detection of the initial phase luminescence in the tokamak and discharge satisfactorily the capacitor bank power source.

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To investigate the dependence of laser energy on a gas flow velocity in high repetition rate operations, the excimer laser energy was measured by varying the gas flow velocity up to a repetition rate of 3kHz. The laser energy decreased at a clearance ratio of around 2 and 4 in our apparatus. When the upstream pin electrodes for preionization were removed, these decreases were not observed. This suggests that the preionization discharge products flow into the main discharge region at an onset of the following discharge and decrease the laser energy.
In order to show the influence of the preionization discharge products, we have defined the avoidance ratio AR (=d*f/v, d: distance between pin electrodes and a center of main electrode, f: repetition rate, v: gas flow velocity). If AR becomes an integral number, the filamentation is occured in following main discharges, resulting in laser energy reductions.

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A superconducting magnetic energy storage (SMES) system has many advantages such as high storage efficiency and quick response to load fluctuation. However, the system contains the possibility of various failures, which are mainly generated from by a transition to normal conducting state. These system failures tend to result in arc discharge inside the system which gives a serious damage to the entire system. Based on above considerations, a superconducting pulsed power system (SPPS) with a mechanical opening switch as an energy transfer switching device was designed to clarify the electrical insulation problems of the superconducting magnet. In this study, the characteristics of internally induced voltage of the magnet during system discharge were investigated. Especially, generation mechanism of the oscillating waveform which appears between magnet terminals just before arc extinction was analyzed using the digital simulation program EMTP (Electromagnetic Transients Program) considering distributed constant circuit of superconducting magnet, load condition and time varying arc resistance of the switch. The experimental and theoretical investigations showed that the voltage waveform was strongly influenced by the load condition and arc discharge triggered by the switch operation. Finally, a suppression method of the oscillating surge is proposed based on the theoretical consideration.

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Luminosity of wire corona has been observed by the technique of the computed tomography. The light output from wirecorona has been compared with the calculated result. Spatial distributions of space-charge and current density of each type ofcharges carrier in a corona field has been also determined by computing the ionization and attachment process under the Deutschassumption and compared with experimental results.
The calculated results along the symmetry axis of the electrodes show very good agreement with measurements.Unfortunately, there is a slight difference between the experimental results and those of the calculation under the Deutschassumption in the distribution of luminosity.

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The authors deal with the surface discharges initiated from the triple junction at which a solid insulator, SF₆ gas and a metal electrode come in contact. The process of the surface discharges at impulse voltages has been measured optically. The voltages of the leader inception and the surface flashover increase with the gas pressure for positive polarity, while they are almost independent for negative polarity. The difference can be explained by the following polarity effect of the scaling laws on the leader transition and the leader propagation. (1) The streamer to leader transition time for positive polarity is inversely proportional to the gradient of impulse voltage dV/dt. The transition time for negative polarity is inversely proportional to the products of the pressure P and the gradient dV/dt. (2) The positive leader propagation speed is described by the products of the leaderinception voltage V_1d and the gradient dV/dt, while the negative speed is PV_1d (dV/dt). The polarityeffect can be accounted for by the difference in the pressure dependences of streamer channel radiusbetween positive and negative polarities.

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NbC_xN_1-x thin films were prepared on glass substrates by reactive sputtering in a mixture gases of Ar, CH₄ and N₂ using Niobium plate as a target. The substrate temperature was varied in the high temperature range from 500 to 900°C. Structural properties were investigated by X-ray diffraction. Preferred orientation was observed for the thin films deposited at the substrate temperature of 800°C. Thin films had smooth surface and high mechanical hardness. The Vickers hardness of NbC and NbC_xN_1-x thin film was about 1150 and from 600 to 700, respectively. The electrical conductivity of thin film was 1.0×10⁴[S/cm]. The highest turn on temperature of 16.2 [K] was observed for the NbC_xN_1-x thin film. These properties are of importance for the fabrication of NbC_xN_1-x superconducting devices.

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AC breakdown and ac partial discharge through narrow chink between two insulating walls were investigated, using a (knife edge)/(plane) electrode configuration. The chink was formed by two plane walls of PE insulator blocks. The maximum electrode distance studied was 70mm. The experiments were performed in air controlled at 20-25°C and 40-50‰RH.
AC breakdown characteristics depend on width(s) of the chink: In a range of the width(s) about 1mm _??_ s _??_ 20mm, the breakdown voltage decreases with the decrease in the width(s); In the range between about 100μm _??_ s _??_ 1mm, the voltages are higher than that at 2mm of the width(s); In the range between about 15μm _??_ s _??_ 100μm, the voltage decreases with the decrease in the width(s). It was found that these breakdown characteristics are corresponding to the dependence of ac partial discharge characteristics on the width of the chink: AC breakdown voltage is decreased with increases in the number and the maximum strength of positive pulse in ac partial discharges generated near the positive peak of ac applied voltage. The discussion was focused on the dependence of the number and the strength of the positive pulse on the width of the chink.

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PTFE (Polytetrafluoroethylene) is one of the most chemically stable polymers. This means the small surface energy and the poor wettability. However, it is difficult to change the surface properties of PTFE. In this study, PTFE surface was treated by reactive sputter etching using H₂O gas and irradiation of KrF excimer laser in H₂O. The contact angles to water and ESCA spectra were measured. As a result the contact angles decreased and the surfaces of PTFE were changed chemically. Therefore, it is conclused that PTFE surfaces change chemically and to be wettable by irradiation of ions or UV strong light in H₂O gas or H₂O.

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