Recent progresses in amorphous and microcrystalline silicon materials are reviewed. Photo-induced degradation is controlled not completely but strictly in amorphous silicon deposited at high growth rate of 2nm/sec and stable solar cell showing an efficiency of 8.2% is demonstrated. Mechanism of the growth of microcrystalline silicon is started to be understood using surface-reaction diagnostic techniques, which enables us to fabricate high efficiency microcrystalline silicon solar cells at low temperature as low as 140C.

View full abstract

Electrostatic Precipitators (ESP) are used extensively for decontaminating of industrial gaseous pollution and air cleaning of building. One application of the ESP is decontaminating polluted gases and increasing the visibility index in expressway tunnels. However, the collection efficiency of large particle decreases due to particle re-entrainment phenomena, since lots of particles in expressway tunnels are made of carbon that has low resistivity. Therefore, large particle has the adverse effect of decreasing visibility index. It is important to prevent re-entrainment for increasing the visibility index. In this work, we discussed the method preventing particle re-entrainment, and devised applying rectangular AC high voltage to the collecting electrodes. DC voltage is applied to precharger in all test conditions. The collection efficiency of large particle decreases due to particle re-entrainment with DC high voltage applied to electrode in collecting section. However, when rectangular AC high voltage applied to the collecting electrodes, the collection efficiency of large particles improves with increasing frequency. The re-entrainment phenomena are prevented on applying rectangular AC high voltage (1Hz). And then, the collection efficiency of submicron particles on applying rectangular AC high voltage (1Hz) is as high as DC high voltage.

View full abstract

A Trichel pulse (TP) corona has been extensively studied by many investigators. From these results of investigations, it is obvious that the interval of each negative corona pulse is not constant and is fluctuating in time. This paper describes experimental results and the analysis at each frequency component of negative corona pulse in the VHF band. Because it is necessary to study the property at each frequency component in detail, Continuous Wavelet Transformation (CWT) was applied. However, in spite of such an idea no detailed study has been carried out up to now. From the obtained wavelet spectrum, it is clear that the generating mechanism of enhancement of TP corona due to accumulation of negative ion which tends to reduce the strength of the electric field and ionization zone in the near cathode region as increasing applied voltage.

View full abstract

Interest in the earth environmental problem has been rising year after year. Air pollutants such as NOx, SOx are contained in exhaust gases from car engines and electric power generators and they are one of the causes of the environmental disruption. From now on, countermeasures have to be taken especially for exhaust gas from diesel engines, because high concentration of NOx, higher remaining oxygen and soot make the development of selective catalyzer difficult. A diesel engine generator of 2.4kVA was selected as a target of exhaust gas cleaning, and the non-thermal plasma technology was applied to reduce NOx in the exhaust gas. A system composed of gas cooler, flow lines, discharge reactor of silent discharge type and scrubber was constructed and NOx removal experiments were carried out under various conditions. The system was operated successfully and the maximum NOx removal rate of 60% at the half engine load was attained. The NOx removal efficiency, the effect of hydrocarbon injection and the practical problems experienced in these experiments were described.

View full abstract

One of the problems of NO removal method by silent discharge is said to be low energy efficiency. This investigation was carried out in order to find determinative factors for improving the energy efficiency. Factors investigated were gas residence time, discharge area density and discharge volume density. The results showed that the NO removal efficiency became relatively high at the residence time in a range of 50 to 160[ms], but both the discharge area density and discharge volume density had almost no effects on the efficiency. It was also found that the discharge volume density has relation to the initial NO concentration.

View full abstract

For the past fifteen years, the TS-3 merging project has explored several new type of CT/ST(Compact tori and Spherical tokamak): merging formation of FRCs(Field Reversed Configuration), magnetic reconnection experiment, and ultra-high beta ST formation. The successful results of these experiments have enabled us to construct an up-scaled merging device; namely the TS-4. The new device TS-4 has two flux cores(major radius=0.5m) for inductive plasma formation, a center coil(external toroidal field coil and OH coil) for q value control and plasma sustainment, and DC external field coils. The initial operation of the TS-4 (since 2001) demonstrated co-helicity and counter-helicity merging of two spheromaks. The counter-helicity merging revealed annihilation of toroidal magnetic field with a significant overshoot motion of reconnected field lines. It resulted in the formation of an high-beta (≈0.8) FRC. The produced FRC has a significant field deformation, suggesting contribution of toroidal plasma flow to its equilibrium. The co-helicity merging doubled the toroidal fluxes of spheromak, causing its flux conversion from toroidal to poloidal. The merging spheromaks relaxed into another spheromak with beta ≈0, suggesting the large thermal energy loss due to its non-aximetric dynamo activity.

View full abstract

This paper describes local corona behavior and creeping discharge on composite electrodes in N₂. The composite electrode was consisted of a needle contacted with a borosilicate glass or ZnO disc on a needle-plane configuration. The discharge voltages increased when the needle was contacted with the glass with increasing creeping distance (L) from the needle tip to the bottom of the disc. The discharge voltages showed the polarity effect reversed bordering on L=4mm. In the case of the needle contacted with ZnO, the discharge voltages increased with increasing distance within L=2mm. However, they decreased beyond L=2mm. From the observation using an ultrahigh-speed camera, discharge behavior was different between for the glass and for ZnO. From the photographs of corona taken by a camera with an image intensifier, corona generated at the triple junction in the case of ZnO. The differences on the discharge voltage characteristics and the discharge behavior between for the glass and for ZnO were associated with the corona properties.

View full abstract

High-T_c superconductors (HTS), which have a characteristic of the critical current density over 3×10⁴ A/cm² in liquid nitrogen temperature (77K) and 1T, can be produced. Thus, they are promising for many practical applications such as a magnetic bearing, a magnetic levitation, a flywheel, a magnetic shielding and etc.. Since the HTS characteristics are not homogeneous in some specimens due to grain boundaries and cracks, the distribution of magnetic characteristics should be assessed. Thus, we have measured the distribution of the magnetic flux density on the surface of the HTS using a hall element, and have evaluated its magnetic characteristics. The measurement of magnetic characteristics using a hall element is difficult for measuring the distribution of the magnetic flux density on the actual surface and the inside of the HTS sample. In this research, we examined a quantitative evaluation of the magnetic shielding characteristics of the HTS including weak links under the static magnetic field with the three-dimensional finite element method analysis.

View full abstract

Extended chain crystal(ECC) polyethylene exhibits some unique properties. It is possible to make transparent highly crystallized polyethylene in the ECC phase. Electrical treeing discharges were investigated using a needle to plate electrode system under an application of lightning impulse voltage. The propagation of trees was observed using a high-speed image converter camera. The formation of tree channels was a very rapid phenomenon, 1μs. The discharge current accompanying the trees consisted of two kinds: A large current pulse, occurring just after voltage application, appeared to be a combination of injection current and charging current. Immediately following this large pulse, small current pulses appeared intermittently in the wave tail of the applied voltage. It is thought that these small current pulses are attributable to the rearrangement of charges in the gas phase on the inside surfaces of tree channels.

View full abstract

Crosslinked polyethylene(XLPE) has been widely adopted as insulating material for high voltage power cables up to 500kV. Further improvement of electrical and thermal properties on insulating material is required in order to increase cable operation efficiency. Therefore, the development of novel insulating material possessing high thermal properties will be necessary. Recent progress of catalysis technology contributes to obtain new polymeric materials which may be applied to electrical insulation. The authors investigated the basic properties of newly developed stereoregular syndiotactic polypropylene(s-PP) which is synthesized with homogeneous metallocene catalyst. Though recycling of crosslinked polymers such as conventionally used XLPE may be difficult because of its poor heat deformation, the s-PP which is not crosslinked must be suitable for recycle. A series of experiments on its physical and electrical properties gave following results.
(1) S-PP has sufficient flexibility compared with isotactic polypropylene (i-PP).
(2) Both AC and Lightning Impulse breakdown strength of s-PP in spite of no cross-linking are superior to those of XLPE in the range of temperature 25°C to 90°C.
(3) Degradation by copper of s-PP is less than i-PP.
(4) S-PP/VLDPE blend shows sufficient brittleness temperature for use.
These results suggested that s-PP would be available as insulating material for power cable at higher temperature operation.

View full abstract

The sterilization effect of ozone to Corticium rolfsii, one of the diseases for konjac plant, is examined quantitatively. The critical value for 0% survival ratio of Corticium rolfsii is found to be (99.2±2.8)×10³ ppm h, which is held in the range from 400 ppm to 1400 ppm of ozone. This suggests that a similarity law between ozone volume density and the treatment time may exist. The critical value is tested for the sterilization of the Corticium rolfsii in the soil.

View full abstract