Two different surface treatments (mechanical polishing, thin film deposition) were done on cathode surfaces, and the field emission current from the cathodes were measured by using MCP. In order to discuss a relationship between the breakdown voltage and pre-breakdown current in vacuum gap, breakdown voltage was measured after a field emission measurement. The V-I characteristics of field emission and breakdown voltage were influenced by surface treatment, the breakdown voltages of mechanical polished cathodes were lower than thin film deposited cathodes. It was found that the probability of breakdown was higher as the field emission current was reached at 10^-11A. From atomic force microscope (AFM) measurement, there were a lot of protrusion on the cathode surface at a case of thin film deposition treatment, and we estimated by using finite element method that these protrusions, however, make field enhancement effect low. It was supposed that the breakdown voltage in vacuum gaps could be increased by thin film deposition method.

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Analytical and experimental investigations have been carried out to clarify the characteristic and the mechanizm of surface flashover in vacuum. Various insulator profiles made of PMMA having a certain contact angle with the cathode have been investigated. The simulation of surface charging based upon a secondary electron emission process is performed, which analyzes the electric field strength near the cathode triple junction considering the surface charge. It has been shown the flashover voltage of spacers experimentally obtained significantly depends on the electric field strength near the triple junction at the cathode.

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The authors have studied about the electron multiplication mechanism of discharge in the left side of the Paschen minimum. In this region, ionization by electron collision, so called a effect, is not so expected to sustain steady state discharge. Then, other electron supply processes may be important to maintain discharge in the region. The authors paid attention to the anode. Because, electrons with high energy accelerated in the space bombard the anode surface and many secondary electrons or reflected electrons may be generated.
In this study, chemical change of sample exposed to the high E/n discharge was detected by the XPS (X-ray Photoelectron Spectroscopy) and a yield of electrons at the sample surface was also measured. From the results, a qualitative relationship between the composition of element deposited at sample surface and the yield change was obtained.

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Analytical and experimental investigations have been carried out to clarify the charging mechanism on the surface of an insulating spacer in vacuum. A cylindrical insulator made of PMMA, PTFE, Polyimide, or Al₂O₃ has been examined. The distributions of charges measured by means of an electrostatic probe have been compared with results predicted from a charge-simulation technique for equilibrium conditions, based on a secondary electron emission process. For equilibrium conditions fairly good agreement has been established between measured and calculated. data except for positions on the insulator surface close to the cathode.

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This paper deals with the surface flashover characteristics of dielectrics during low-energy electron beam irradiation in vacuum, considering large and high-power space systems to be constructed in low earth orbit in future and/or charged-particle beam apparatuses such as cathode ray tube (CRT). The flashover voltage was measured as functions of the dielectric distance and the time of voltage application. As results, the flashover voltage during electron irradiation was lower than that without electron irradiation, especially in case of longer dielectric distance. In V-t characteristic during electron irradiation, n value in V_f∝ ^T-1/n (V_f: flashover voltage, T: time to breakdown) was about 23. Methods to improve the flashover characteristic were also investigated.

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Mass spectra and ion energy distribution in a conventional reactive vacuum arc deposition apparatus with Ti chathode and N₂ gas flow were measured. The experiment was carried out at different distances from the cathode surface as a function of gas pressure with an energy quadrupole probe analyzer. From the result of mass spectroscopy, it was found that Ti and N₂ existed in the plasma as neutral particles, and that N might exist as well.
From the data of ion energy measurement, very few N₃⁺ and TiN⁺ were also identified as well as Ti⁺, Ti⁺⁺, N⁺, and N₂⁺. It was found that their energies and relative quantities depended on the distance from the cathode surface and the gas pressure. Ti⁺⁺ had the highest energy as high as 130 eV and the widest distribution among the ions concerned, and its energy distribution had two peaks at lower pressure and at the position near the cathode. The energy of Ti⁺⁺ decreased with the distance from the cathode surface and increasing the gas pressure. The amount of Ti⁺ increased with distance and the energy was relatively low. The profile of the energy distributions of N⁺ and TiN⁺ showed a similarity to that of Ti⁺⁺. The peak energy of N₂⁺ also had lower energy of about 10 eV, compared with Ti⁺⁺, N⁺ and TiN⁺.
Taking into account the potential hump theory of the cathodic arc, we proposed a novel reaction process in the plasma based on the results obtained here.

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In order to clarify the instability phenomena of a low current vacuum arc, characterized by noise on the current trace prior to the actual current chopping, an analysis of copper cathode spot has been made. For the analysis, cathode spot region is recognized as the collisionless space charge sheath connected with singly ionizad collisional plasmas.
It is proposed that a current level below that no real solution exists is unstable current and this current corresponds to the point at which a vacuum arc turns into unstable.
It is found that there is no real solution when the current is below 25A. The physical explanation is considered that the electrons returning to the sheath region from the plasma one dominate over positive ions and, consequently, the electric field at the cathode surface is F₀²≤0 below 25A.

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To clarify factors influencing the conditioning effect brought by repetitive breakdowns of a vacuum gap, changes of electrode surface conditions before and after 500 breakdowns caused by impulse voltage application has been investigated. Changes of prebreakdown current characteristics has been also investigated. Electrode material used was copper. Electrode surfaces were analyzed by the X-ray photoelectron spectroscopy (XPS). The XPS analysis revealed that electrode surfaces were completely cleaned by repetitive breakdowns. Prebreakdown characteristics were classified into 3 patterns;(1) displacement current alone, (2) field emission current as well as the displacement current, (3) explosive current increase. The patterns (1) and (3) were observed mainly at the early stage of repetitive breakdowns, while the pattern (2) was at the later stage. It has been concluded that the breakdown mechanism alters during conditioning by repetitive breakdowns.

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The effect of mutual coupling between two cylindrical and parallel wires was studied at high frequencies. Currents into two wires were separately supplied with a different phase angle from two current sources.The vector diagrams for the voltage for the two-wire system were drawn under various phase differences and were compared with those of a single wire system. The inductive and resistive components of the voltage in the two wire-system were analyzed from the voltage differences of both systems. These voltages were also considered theoretically using the equivalent circuit and electomagnetic theory.
As a result, it was found that the increase of inductive components of the volage is nearly zero at the phase angles of 90° and 270° different from that of a single wire system. This result suggests that the increase of proximity resistance can be suppressed considerably even at a high frequency.

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AC partial discharge (PD) characteristics in air gap in series with fissure-like interface between solid insulating materials under needle-plate electrode system are studied at room temperature. The interface was formed by two insulating plates of epoxy resin and the minute interfacial gap and the surface roughness of the plates were changed artificially and their effects on the PD characteristics were studied. PD characteristics of specimens were measured with a pulse method using a computer aided partial discharge analyzing system.
The PD inception voltage is scarcely changed with the interfacial gap from 0μm to 400μm but becomes slightly lower for the specimen with smooth interface than that with roughened interface. The influence of conditions of the interface on PD characteristics, especially for the positive PD pulses, tends to be conspicuous. The roughened interfacial surface gives the larger positive PD magnitude with the minute interfacial gap near 0μm. When the interfacial gap thickness becomes large, however, the larger surface roughness is considered to prevent the surface discharge along the interface, resulting in the smaller positive PD magnitude.

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Outdoor HV polymer insulating materials could be aged by acid rain so that the insulator surface becomes rough, and hydrophobicity changes. The tracking and discharge may then occur, leading to insulation breakdown or flashover. In this paper, the relation of hydrophobicity and surface roughness of hlgh temperature vulcanizing silicone rubber (HTV SR) insulator aged in artificial acid rain is investigated. The experimental phenomena of variation, degradation and recovery of hydropbobicity of silicone rubber insulator before and after aging are discussed from a fractal theoretical point of view, The rough surface of whether a virgin or aged insulator presents the appearance of a fractal surface. Research results show that due to fractal phenomenon, the hydrophobicity of the moderately roughened virgin sample may increase with the surface roughness. After aging in acid rain, the insulator surface becomes rougher, and the hydrophobic groups in surface layer are wom away. The fractal surface of the aged insulator for lack of hydrophobic materials may become hydrophilic so that surface hydrophobicity degrades. In the following dry condition, the hydrophobic polymer liquid bulk diffuses and migrates to surface layer. The fractal surface of the aged insulator with the supplement of hydrophoblc polymer liquid may become more hydrophobic. The degraded hydrophobicity is therefore restored to some extent.This research shows that the outstanding performances of silicone rubber insulator are available to outdoor application in severe environmental stress.

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It has been expected that the ac conductivity σ _AC of conductive particle-polymer composites varies as a power of frequency f, such as σ _AC ∝ f_q with q=0.8-0.9 above the percolation threshold p_c. In this paper, how finite carbon black (CB) clusters contribute to the ac electrical conduction in CB-polyethylene composites below and above p_c is discussed. It was found that the frequency dependence of σ _Ac below p_c is directly proportional to f, being due to ac loss current, and a tunneling current taking place between the finite CB clusters appears in addition to the ac loss current for the volume fraction of CB very close to p_c. Above p_c, the ac loss current still appears, indicating that a hopping conduction between finite CB clusters does not take place and conducting pathways between electrodes govern the ohmic electrical conduction at least till 1 MHz.

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High-Tc superconductor Bi₂Sr₂CaCu₂O_y was prepared by melt-casting process (MCP). The MCP was achieved by raising the temperature of the furnace up to 1000°C. The MCP samples are subjected to a heating procedure at 840°C in order to reach the two-CuO layer phase. The oxygen concentration, that results from the final annealing condition, was optimized in order to obtain the highest value of the critical temperature Tc. Measurements of electrical resistance as a function of temperature for MCP samples have shown sharp drops associated with the onset of intragranular superconductivity. The enhancement of superconducting properties is due to the addition of strontium sulfate (SrSO₄). The value of Tc increases for SrSO₄ addition up to approximately 10wt%. The zero resistance is observed at 90.4K for the 10wt% SrSO₄ added sample annealed at 800°C in air.

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The method based on intergral from of preservation rule is simple form and high accuracy in comparison with FEM. This paper shows that variable decreases adding a condition defined by the integral form of gauge enclosed nodal point. The decrease number agrees with the rank number of a matrix of homogeneous linear equation derived from the condition. For a numerical result, it is clear that this method removes redundant part into the linear equation derived from the integral form.

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