Pulse power has expanded its regime in technological and application fields. The state-of-art of switching technology shifts the trend of pulse power from huge and single shot systems to compact and highly repetitive generators. This extends the pulse power application into industrial, environmental, biological, medical, and also scientific fields. The progress has enabled us to have high energy density plasma and/or well-defined extreme conditions with low cost and good reproducibility. Plasmas produced by compact pulse power devices are proposed as a new tool in small laboratories for high energy density physics and its applications.

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Characteristics of soft X-ray radiation from nitrogen filled Z-pinch plasma columns energized by capillary discharge are reported in order to evaluate optimum plasma parameters for an H-like N recombination pumped soft X-ray laser, wavelength of which is 13.4 nm emitted by quantum transition from n=3 to n=2. The discharge system used in this experiment consists of a 3-stage Marx generator, a step-up transformer and a 3-nF water capacitor. Soft X-ray radiation from Z-pinch nitrogen plasma was measured by using a transmission grating spectrometer with a CCD array detector. Multiply-ionized ions up to N VII were confirmed to exist, and existence of N VIII was anticipated. This suggests that a plasma temperature at the pinch time is the order of 100 eV and might reaches over 150 eV. From these experimental results, plasma parameters and the discharge current required for realizing an H-like N recombination soft X-ray laser were estimated.

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Studies of an oversized BWO with a novel cathode and a rectangular corrugation are presented. The beam voltage is weakly relativistic, less than 100 kV. We propose to use a disk cathode made of metal only. The disk cathode can generate a uniformly distributed annular electron beam even in the weakly relativistic case. By using the annular electron beam, a weakly relativistic oversized BWO consisting of rectangularly corrugated cylindrical waveguide is demonstrated. The oscillation starting energy is about 60 kV for a 10-period rectangular corrugation. The maximum output power is estimated about 200 kW. The operation mode between axisymmetric and nonaxisymmetric modes can be controlled by changing the end condition of BWO.

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Studies of the concept of direct excitation of the TE₁₁ mode in a coaxial vircator using three-dimensional particle-in-cell simulations is presented. The excitation of the TE₁₁ mode is made possible by sectioning the emitting surface of the cathode, thus creating two interacting virtual cathodes. It is shown that the two virtual cathodes formed oscillate in push-pull mode as previously has been described for a planar geometry.

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Now the distribution cables are often used as armature winding in high voltage motor. The effect of cable semi-conductive layer dielectric performance on electric field distribution was studied by finite-element method (FEM). Then the probability of corona discharge in the winding cables was analyzed. The computed results indicate the maximum electric field intensity in the cable increases and electric field intensity in the internal semi-conductive layer reduces with the increase of the internal semi-conductive layer dielectric constant. In other words, rather large value of the internal semi-conductive layer dielectric constant will cause the electric field distortion in the insulation layer. On the other hand, lesser dielectric constant value will cause the electric field concentration in the internal semi-conductive layers and then may bring tree discharge. The results also indicate that the electric field intensity and potential in the external semi-conductive layer sharply reduce with the decrease of the external semi-conductive layer resistivity, which provides theoretic foundation for reducing the corona discharge on the high-voltage cable surface. Meanwhile, the research indicates near the outlet of stator slot and bad grounding spot the corona discharge will first occur.

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In this review we present main results of experimental research of passive and active plasma sources for high-current electron beam generation obtained during the last few years in our Plasma & Pulsed Power Laboratory. We will describe passive plasma sources (ceramic-metal, velvet and carbon fiber cathodes) based on flashover plasma and active plasma sources based on a ferroelectric plasma source (FPS) as well as on an FPS-assisted hollow anode (HA) plasma source. The main data concerning the plasma parameters (plasma density and temperature, plasma uniformity and plasma potential) and the main features of these plasma sources (plasma formation, life time, vacuum compatibility) will be discussed. Also, data concerning electron diode operation and parameters of the generated electron beam while using these plasma sources will be presented.

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For the preliminary design of an augmented railgun, the electromagnetic repulsive forces on the rails and the self and mutual inductance gradients were determined by simulation. This design is meant for the realization of an augmented railgun at the French-German Research Institute in Saint-Louis, France. The simulated railgun has a 25 mm × 25 mm square calibre and both the inner and outer rails have a rectangular cross-section. In our study the geometry of the inner rails is fixed while the dimensions of the outer rails were altered. A 2D transient analysis for the determination of the magnetic forces on the rails was carried out with the finite element method program ANSYS. The EM force on the projectile is analytically calculated with the force-equation based on values of the inductance gradients determined with 3D AC-analyses. The influence of the ratio between the currents in the inner and outer rails on the electromagnetic forces has also been investigated. We have shown that the EM force acting on the projectile increases when the height of the outer rails and the distance between the inner and outer rails decrease. However this also leads to higher repulsive forces between the rails. For the theoretically best geometry, based on the electromagnetic forces, a 3D transient analysis was carried out. The electromagnetic force determined directly with the 3D transient analysis is then compared with the one obtained with the analytical method. A good agreement was found.

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This paper deals with the discharge properties in low vacuum region of practical vacuum interrupter filled with SF6 gas. In field, the vacuum interrupter inside the cubicle-gas insulated switchgear is surrounded by SF₆ gas. If the leakages occur, the surrounding gas may invade the vacuum interrupter and increase the internal pressure. Thus, the pressures are set at 1.3 Pa to 2.6 kPa to simulate the leakage. The measurement of discharge occurring inside the vacuum interrupter was performed with a photomultiplier tube. From the result of the experiment, it is found that the pressure of vacuum interrupter below and above 50 Pa can be distinguished on the basis of the rise time, peak intensity and width of the discharge light pulse. The result reveals that the discharge pulses at pressures below 50 Pa have the relatively larger rise time of 100ns order, and larger pulse width of 2μs order. While, for pressures above 50 Pa, the rise time have relatively smaller value of 10 ns and pulse width of 0.1μs order. The result also shows significant difference in discharge characteristics compared with those in low vacuum of vacuum interrupter filled with air that we have investigated previously.

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The RF (13.56 MHz) gas breakdown in Ne-N₂, Ne-Ar and He-N₂ mixture systems are investigated experimentally in a parallel plate capacitively coupled device with varying the pressure, the mixing ratio and the electrode separation, specifically focussing on the breakdown at the small values of the mixing ratio. The breakdown voltage curves obtained have the V-shaped or L-shaped characteristics. The breakdown voltage decreases with the addition of a small amount of N₂ or Ar in each mixture system, and the ratios of decrease in breakdown voltage to rare gas breakdown voltage in these mixture sysytems are about 22, 32 and 30 % at the maximum, respectively. The decrease of breakdown voltage is observed in a certain restricted pressure range, which is narrower in Ne-N₂ system than in Ne-Ar one. This feature in Ne-N₂ system is probably due to the decrease of electron energy attributed to the vibrational excitation of N₂ by electron impact. Compared with the DC breakdown and the microwave one, the decrease ratio in the RF breakdown is relatively small, suggesting that there exist some competitive ionization processes accompanied by excited particles including the Penning ionization.

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This paper presents a capillary discharge in water, which was applied to sterilize tiny apertures of medical equipments due to the penetration of dissolved sterilization agent in water. In order to obtain stable and energetic discharge for sterilization, a capillary dielectric tube was used as a barrier material. Discharges in the tube can generate high electrical fields, ultraviolet rays, as well as various chemically active species which can be utilized for sterilization and decomposition of toxins and bacteria in water. The sterilization results of Escherichia coli (E. coli) were successful after 1 hour of treatment.

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Influence of corona discharge on the precessional motion of a wire particle located in a dc electric field formed by a parallel plate electrodes system was investigated experimentally. A copper wire with 0.25 mm in diameter and 6 mm in length was used as a wire particle. When an applied voltage to the parallel plate electrodes exceeded the lift-up voltage for the wire particle placed at the lower electrode, the particle moved in several manners depending on the polarity of applied voltage or polarity of the particle. A negative particle kept standing or precessional motion stably while a positive particle tended to cause spark or to leave the lower electrode and cross the gap. During precessional motion of a negative particle, a micro gap often formed between the wire particle and the lower electrode. From the analysis of high speed pictures of precessional motions, it was shown that the rotation speed of the particle was strongly affected by the edge shape of the wire particle. Corona discharge is a source of rotational and precessional motion. Space charge formed at a vicinity of the wire particle would inevitably play an important role to make a particle rotate and tilt associating with induced charge at the tip of the particle.

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Partial discharge (PD) is one of the major factors causing insulation damage of power transformers. PD signal usually mixed up all kinds of noise, it had some limitation to extract faint PD impulse signal from powerful noise with traditional analytic methods. Based on the analysis of the noise's correlation, spectral relative distribution and frequency, the noise's unique characteristics were obtained. Adaptive algorithm based on wavelet packet theory was presented to suppress the periodic noise. The wavelet transform was used to reject white noise and extract characteristic parameters from PD signal. Piecewise cubic spline interpolating algorithm was presented to reconstruct the wavelet coefficients. Compared with the alternate projection method, the algorithm is effective and easy to implement, which can get higher signal-to-noise ratio gain and smaller root mean square error than the alternate projection method. The results show the method can be used for noise recognition and suppression on-line monitoring of partial discharge in transformers.

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