A pulsed discharge, which is obtained by compressing and superimposing energy in a very short time, generates a non-thermal plasma over a wide area. Therefore, the gas molecules in the plasma can be activated more effectively, and charged particles, ions, and active atoms can be generated at high density. In addition, the pulsed discharge has a high sparkover voltage, and is expected to generate a stable discharge even in high temperature gas. In this study, the current characteristics and discharge stability of pulsed discharge were measured, and the pulsed rise time and discharge gap length suitable for discharge processing under high temperature conditions were investigated.

The loss current method and the residual charge method had been developed as diagnosis method for water tree deterioration of XLPE cable bodies. Fundamental investigation of these method is mainly for vented trees generated from inner or outer semiconducting layers. However, bow-tie trees generated from voids or contaminants in the insulation layer have become main degradation cause because of application of the triple extrusion method for forming the cable core in order to reduce the generation of vented trees. Therefore, evaluation of applicability of the loss current method and the residual charge method for the bow-tie trees is important for the insulation diagnosis of the present XLPE cable body with these methods.

From these viewpoints, firstly we established the development method of the artificial bow-tie trees in a XLPE sheet specimen. Then, we demonstrated that the bow-tie tree could be detected with residual charge method and loss current method. And space charges accumulated around the bow-tie tree were measured with PEA method to evaluate possibility of the residual charge method to diagnose the bow-tie tree degradation.

Electric field measurement using electric-field-induced second-harmonic generation (E-FISHG) has attracted attention because of its high temporal and spatial resolution. For the E-FISHG method, it is necessary to consider the fact that the electric-field-profile along laser path affects the E-FISHG signal. We have proposed a method that can handle this issue and restore one-dimensional electric-field-profile from a sequence of E-FISHG signals along the probing laser path. In this letter, the electric-field-vector-profile along the laser path is acquired by this means.

We studied three dimensional effect on reconnection speed in TS-6 tokamak merging experiment. When we merge two tokamak plasmas, we observed both of axisymmetric and asymmetric current sheet structures on the midplane with almost equal probability. We found that the reconnection speed of the asymmetric (three-dimensional) reconnection is about three times higher than the symmetric (two-dimensional) reconnection. This result indicates toroidal asymmetry of current sheet structure can be one of the fast reconnection mechanisms.

A high-current vacuum arc generated between long-gap CuCr electrodes often transits from an anode-spot mode type 2 to a plume mode. In this study, we show that there is a positive correlation between the duration time of these two modes and that there is a threshold duration time for a vacuum arc in type 2 mode to transit to the plume mode. These results suggest that the transition to the plume mode and its duration time depend on the amount of neutral vapor injected into the gap during the type 2 mode.