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Characteristics of a repetitive nanosecond pulsed gliding arc discharge in an air flow at atmospheric pressure driven by a SiC MOSFET inverter power supply are reported for the first time. The gliding arc discharge is produced using two diverging electrodes. The repetition frequency of the pulsed voltage is set from 10 to 300 kHz, and the pulse duration is 500 ns. The propagation distance of the gliding arc discharge almost linearly increases with increasing the repetition frequency of the applied pulsed voltage, resulting in an increase in the discharge reaction area. Dynamics of ignitions and propagation of the gliding arc discharge are revealed with a high-speed camera imaging synchronized with the applied pulsed voltage. The result shows that a shortcut discharge with a different generation mechanism appears. It is found that formation of a shortcut current path between the two legs of the stretched arc discharge occurs, resulting in a new ignited arc discharge. Thus, the pulsed gliding arc discharge can be repeatedly generated without a reignition at the shortest gap between the electrodes. The probability of the occurrence of the shortcut discharge increases as the repetition frequency of the pulsed voltage increases. Additionally, measurements of optical emission spectra of the gliding arc discharge show the presence of excited N2, OH, and NH radicals. The OH emission dominates in the gliding arc discharge with the shortcut events. It can be concluded that the repetition frequency of the applied pulsed voltage becomes the control knob for chemical reactions in future industrial applications. [ABSTRACT FROM AUTHOR]

Characterization of a pulsed plasma formed with a plasma gun device was performed. The averaged electron density was measured with an interferometer system using a Zeeman laser at 633 nm. It was found that the plasma with the density of \sim 10^22~m^-3 was successfully formed. The temporal evolution of the plasma was observed with a fast framing camera. It was found that the shape of the plasma was significantly varied temporally. From the intensity profile, the vertical emission profile was obtained using Abel inversion. The emission profile had a flat top shape with the radius of \sim20~mm, and gradually decreased with the radius. The penetration behavior of the gun plasma across the magnetic field was observed. [ABSTRACT FROM PUBLISHER]

In order to examine the interface magnetic anisotropy at the interface between an L10-FePt layer and a nonmagnetic layer, the magnetic properties for thin films with Au\ buffer/L10-FePt/capping\ layers were investigated, where MgO or Au was used as a capping layer. When the thickness of the L10-FePt layer (tFePt) was reduced from 5 nm to 1.5 nm, MgO-capped L10-FePt showed larger perpendicular magnetic anisotropy than those of Au-capped L10-FePt and uncapped L10-FePt. The plot of the magnetic anisotropy energy per sheet area as a function of tFePt suggested that the existence of the interface magnetic anisotropy between L10-FePt and MgO layers, value of which was estimated to be 630 \muJ/m^2. [ABSTRACT FROM PUBLISHER]

We investigated the characteristics of the partial discharge (PD) with twisted enameled wires by optical emission spectroscopy (OES) in atmospheric humid air. The electric field strength in the gap of the twisted enameled wires during the discharges was estimated from intensity ratio of the spectrum bands of nitrogen molecules obtained by the OES. It was found that the electric field strength was increased when increasing the relative humidity, and the increasing rate was different depending on the temperature. The increase of the electric field strength in the gap of the twisted pair could be related to a reduction of PD inception voltage (PDIV) observed in the experiment. The reduction of the PDIV could be determined by not only dielectric properties of enameled wires such as permittivity and surface conductivity but also changes of the discharge phenomena in the humid air. In this study, effects of the increase of the permittivity of the enameled wire due to the moisture absorption into the insulating layer were quantitatively discussed as one of the candidates to explain the reduction of the PDIV in the humid conditions. On the other hand, the discharge current amplitude was decreased with the increase of relative humidity at high temperature. It was considered that the discharge could be quenched by dissociative electron attachment to the large number of water molecules. The observed PD phenomena with respect to the change of the humidity are very important for quality management of low voltage inverter-fed random wound motors. [ABSTRACT FROM AUTHOR]

A compact-sized magnetized coaxial plasma gun (MCPG) with a single discharge stage is developed in order to simulate transient heat loads such as type I edge-localized modes (ELMs) in ITER. The MCPG produces hydrogen plasmas with an electron density of 1-4 x 1021 m-3, an ion energy of 15 eV and a pulsewidth of 0.5 ms. It is found that the absorbed energy density measured by a calorimeter reaches 0.9 MJ/m² which is comparable with a transient heat load of type I ELMs expected in ITER. Erosion of tungsten due to the plasma irradiation produced by the MCPG is confirmed only at the edge parts of the specimen in this experiment. [ABSTRACT FROM AUTHOR]

Effects of ambient humidity and temperature on partial discharge (PD) characteristics in twisted pairs with conventional and nanocomposite enameled magnet wires have been investigated. Measurements of the PD inception voltage (PDIV) and the apparent PD charge were performed by applying an ac sinusoidal waveform voltage of 60 Hz to the twisted pair. The observed PDIV in this study can be classified into the following three behaviors. First, the PDIV in both wires decreases with increasing relative humidity (RH) at low temperature. Secondly, the PDIV in both wires slightly increases when increasing the RH at high temperature. Thus, there is a certain value of the absolute humidity to determine the lowest PDIV in both cases with the conventional and nanocomposite enameled wires. Thirdly, the PDIV in the conventional enameled wire significantly decreases at the RH of 95 %,while the decrease rate of that in the nanocomposite enameled wire is relatively small. The observed PD phenomena are discussed in terms of material characterization of the enameled wires such as changes in permittivity due to moisture absorption and wettabilitiy under voltage application. [ABSTRACT FROM AUTHOR]