A Boltzmann equation as a mathematical model of an electron swarm in a gas is generally solved by using numerical method because of its nonlinearity. In actual numerical calculation, several conditions such as the upper limit of electron energy should be given and needed to be optimized for execution of accurate and efficient calculation. To search optimal conditions, iteration processes in which a procedure for revision of the value associated with a condition is repeated until the optimal value is obtained, are generally used. Various experiential methods have been used for iteration processes in many previous cases and any attempts for optimization of a process have not been made yet, however the authors have been trying to optimize the method and analysis.
In this paper, a new method for optimization of iteration processes suggested by the authors is developed. More than one process can be optimized by using this method in whicha technique of modern control theory is adopted. Applying this method to determination of the upper limit of electron energy and to convergence of ionization coefficient, the iteration number of calculation decreased under all of various physical calculation conditions for a swarm comparing with the case previous methods which optimize only one process are used.

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On the surfaces of polymer films used for thermal control materials of spacecrafts, the electrostatic charging and discharge occasionally occur in space environment. The final potential of charging depends on the materiais. To investigate this dependency, the experiment of electron beam irradiation on two kinds of materials using a high vacuum chamber and the calculation using a one dimensional model are compared. The result is that the final potential is dependent especially on the secondary electron emission and the backscatter coefficient of the material rather than its resistivity. The relationship between the resistivity of materials and the surface potential is also shown.
The breakdown voltage on the surface of polymer films using electrodes are also measured. The result shows that it is necessary to take the effect of the surface charging and the irradiation of electron beam into consideration to estimate the charging potential.

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In this paper, we report effects of quantity and diameter of filler on treeing breakdown of alumina-filled epoxy resin under a needle-plane electrode geometry. Peak of breakdown voltage in epoxy resin appears with increasing the quantity of filler in spite of filler diameter. And the filler parts that indicates the maximum breakdown voltage shift according to diameter of filler.
The results are as follows.
(1) In case of applications of positive impulse voltage, when diameter of filler in epoxy resin is 5μm, breakdown voltage shows maximum at 40 filler parts. When diameter of filler is 250μm and 500μm, it shows maximum at 30 and 20 filler parts, respectively.
(2) In case of applications of negative impulse voltage, when diameter of filler is 5μm, the breakdown voltage shows maximum at 40 filler parts. When diameter of filler is 250μm and 500μm, it shows maximum at 30 and 15 filler parts, respectively.
(3) In case of positive and of negative impulse voltage, filler parts of 5μm and 250μm in diameter, which show maximum breakdown voltage, become larger than those of 500μm in diameter.

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The noble gas dilution effects on the plasma parameters have been studied both for Ar+O₂ and He+O₂ mixture gas positive column plasmas using the modified Schottky's theory. Theoretical results show that the dominant ion species in Ar+O₂ plasmas is O₂⁺ whereas it is O⁺ in He+O₂ plasmas. In Ar+O₂ plasmas, the density of O radicals is much smaller and the density of O^- negative ions is much larger than those of He+O₂ plasma. These differences can be explained by the difference between electron temperature in Ar+O₂ and He+O₂ mixture gas plasmas. Experiments have been carried out using the electrostatic probe, the quadrupole mass spectrometer and the optical spectroscopic methods to measure the electron temperature, the density of O radicals and O₂⁺ ions. Experimental results agree well with the theoretical results.

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In this paper a new method of estimating the width of an air layer and its position in a long distance parallel plate acrylic resin condenser by measuring capacitance while changing the size of supplementary plate electrodes is proposed and the usefulness of this method is discussed. The supplementary plate electrodes are placed on the same face of each measurement plate electrode and surround it.
At a given size and position of the air space, we obtained different measurement results of capacitance depending on the size of the supplementary plate electrodes. Using the data, we were able to form the approximate equations of capacitance relating the position and width of the air space. Then, substituting the measured values of capacitance in the condenser including an unknown air space to these equations, we obtained information to decide the position and width of the unknown air space.
As the result of this experiment, we found a great possibility to estimate the size of a different kind of dielectric and its position in a long distance parallel plate uniform dielectric condenser by changing the size of supplementary plate electrodes.

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We have confirmed the new method of probe measurement in N₂/SiH₄ plasma. Using this method, we have measured the spatial distribution of plasma parameters such as electron temperature Te, electron density ne, plasma space potential Vs, floating potential Vf and sheath voltage Vs-Vf with varying the gas flow rate of SiH4 in the chamber of the double tubed coaxial line type microwave plasma CVD (MPCVD) system. In this paper, we report the spatial distribution of these plasma parameters in the chamber of this MPCVD system. And it is cleared that the plasma is very uniform in the chamber.

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The drift and longitudinal diffusion of N₂⁺, Ar⁺ and Ne⁺ in CH₄ has been studied with a drift-tube mass spectrometer. Values of the reduced mobility and of the density-normalized longitudinal diffusion coefficient of these ions are reported over a range of E/N from 50 to 300 Td. Gaseous ion mobilities are mainly dependent on ion-neutral collision energies and it can be directly related to ion-neutral interaction potentials. We estimated the ion-neutral interaction potentials of these ions and CH₄ from the experimental results.

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In insulation design of superconducting coils, breakdown characteristics of helium gas are important because liquid helium, which is often used for oolant in superconducting coils, is vaporized by quenching of the superconductor or leak to vacuum. On the other hand, shortening of insulation clearance due to metal chips or solder whiskers can cause of accidental arc or short circuit in the coils. In this study, breakdown characteristics of helium gas at room temperature between 0.3μm and 10mm of gap spacing are investigated under equivalent condition of superconducting coil quenching. Apparent breakdown voltage in the left of Paschen minimum becomes lower than the value, which is predicted by the Paschen curve, depending on misalignment and surface roughness of electrodes. This deviation from Paschen curve is more remarkable at higher pressure. In extremely short gap typically below 1μm, breakdown voltage can be lower than Paschen minimum voltage. This seems to be caused by the high electric field at the cathode surface and resultant field emission.

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Thermal degradation behavior of Silicone/Aromatic polyamide insulation system was discussed. It was found that the flash- and fire- points decreased owing to the formation of low-molecular-weight by-products of such cyclic siloxane oligomers as D₃, D₄ and D₅. The GPC and HPLC analysis clarified that the depolymerization of siloxane molecules and also re-polymerization of the decomposed siloxane molecules happen during the thermal aging, resulting in the high and low molecular products formation. The TGI index obtained by the TG measurements and cyclic oligomers detection of the silicone fluid may provide an appropriate insulation diagnosis.

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This experiment was carried out to investigate the magnetic properties of Sr-M ferrite powders prepared by mechanical alloying method. The samples of SrO•nFe₂O₃ where n was varied between 6.0 and 4.0 were mechanically alloyed for 1-40hs. The mechanically alloyed powders were heat-treated at 700-1200°C for 1h in air. The optimum condition of preparing the single phase of powders with suitable properties was as follows: compositlon: SrO•4.5Fe₂O₃, mechanical alloying time: 5hs, heat-treatment condition: 1100°C×1h in air, the magnetic properties are σ_s=7.97×10^-5Wb•m/kg (63.46emu/g), σ_r=4.20×10^-5Wb•m/kg (33.96emu/g), H_cJ=401.87kA/m(5.O5kOe).

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High current arc ignition test is a method for testing flammabilty of polymeric insulating materials specified in UL standard. The determination of ignition point has a difficulty in distinguishing the ignition light of materials from the arc light of electrode itself. We analyzed the light generated during arc ignition test and found that mainly the ignition light of materials is generated while electrodes contact each other and that both light overlap while electrodes separate each other. We have designed a measuring circuit that can detect only the light generated while the electrodes contact each other.Accordingly the determination for ignition point was performed by measuring mainly the ignition light of materials with the circuit. Test results showed that the ignition point of several materials could be determined easily by using the light detecting circuit of our design.

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Many complex patterns in nature such as discharge phenomena are known as fractal objects. With the development of computer system, their spatial structures of discharge patterns have been analyzed using a computer simulation.
In this paper, we developed the 3-dimensional numerical simulation model of the electrical tree pattern considering growing probability and local electric field under a Laplace field. Using this numerical simulation model, we obtained the various shapes of electrical tree, such as tree-like, bush-like and densely bush-like (balllike) trees, and measured the fractal dimensions of these simulated patterns. Furthermore, we studied the relationship between fractal dimensions of 3-dimensional simulated patterns and those of 2-dimensionally projected patterns, and the results were compared with those of the real electrical trees.

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