Kazunori Kadowaki

Repetitive Discharges in a Corona Reactor Produced by a Reciprocal Traveling Voltage Pulse in a Coaxial Cable

We propose a new method for a gas cleaning system with repetitive discharges produced by a reciprocal voltage pulse in a coaxial cable. When the cable is charged with a dc voltage and then grounded at one end of the cable without any resistance, a traveling wave is reciprocated in the cable because of a negative reflection at the grounded end and a positive reflection at the other end. The reciprocal traveling wave results in a voltage oscillation with a very high frequency. The repetitive pulsed discharges between a point-plane electrode gap with a dielectric barrier were observed for various charging voltages.

Effect of pre-charging to plasma reactor on repetitive barrier discharges produced by reciprocal traveling wave voltage pulse

This paper describes an experimental study for NO/sub x/ decomposition using repetitive streamer discharges produced by reciprocal traveling wave voltage pulse from a direct-grounded coaxial cable. When the cable is charged and then grounded at one end of the cable without any resistance, a reciprocal traveling voltage pulse is repeatedly applied to a barrier-type reactor at the opposite end with a change in its polarity. High-speed photographs of discharge light indicated that the voltage oscillation caused by one switching induced alternate propagation of positive and negative streamers with a very high frequency. The 50% streamer initiation voltage with the reciprocal pulse generator was much smaller than that with a single pulse generator having a matching resistance. The reason for the difference in the 50% voltage was explained by the effect of pre-charging to the dielectric barrier. In the case of the reciprocal pulse, a large number of space charges were accumulated on the barrier surface during the cable charging, so that the field strength in the gap was strongly enhanced after the polarity reversal. In the test of NO removal from a flue gas, high NO removal ratio was obtained under the low applied voltage when the reciprocal pulse generator was used. Removal weight of NO per unit discharge energy in the reciprocal pulse generator was lower than that in the single pulse generator. However, the total efficiency calculated with the stored energy in the reciprocal pulse generator gave a better performance.

Comparative Inactivation of Bacillus subtilis Spores Using a DBD-Driven Xenon Iodide Excilamp and a Conventional Mercury Lamp

In this paper, we compared the inactivation of Bacillus subtilis spores in water by means of a dielectric-barrier-discharge (DBD)-driven XeI* excilamp and a low-pressure mercury lamp. The main part ( ~ 76%) of the excilamp output was due to the B → X transition of XeI* exciplex at 253 nm. It is shown for the first time that a better sterilization action is achieved with the DBD-driven XeI* excilamp compared with the monochromatic mercury lamp at the same UV dose. The contribution of an atomic iodine emission in the range of 178-207 nm has been confirmed. Germ-reduction experiments with the XeI* excilamp have been carried out in a steady-state mode and in a water-flow reactor.

Space charge effect for streamer initiation and propagation in water subjected to reciprocal traveling wave voltage pulse

This paper deals with initiation and propagation processes of streamer discharges in water subjected to high-speed repetitive voltage pulse. The 50%-duty repetitive pulses were produced by the reciprocal traveling wave in a pulse forming cable which was connected with a point-plane electrode gap in a water-cell. Laue plot of time lag distributions for the streamer initiation indicated that the initiation probability during the second pulse application became much higher than that during the first pulse application. We concluded that the change in space charges distribution due to internal field during the rest-time after the first pulse enhanced the streamer initiation probability at the second pulse application. Temporal development in the positive streamers during the repetitive pulse application was observed using a gated image intensifies. When the pulse was relatively high, the streamer discharges started the propagation at the first pulse and then the discharge channel became long step by step at the subsequent pulse applications. It was also found that the periodical emission due to excitation of OH radicals was detected for a long period after the development of the streamer discharge in a spectroscopic measurement

Effect of Water-Surface Discharge on the Inactivation of Bacillus subtilis Due to Protein Lysis and DNA Damage

The effect of water-surface discharge on the inactivation of Bacillus subtilis ATCC6633 in water was examined by using a very short high-voltage pulse generator. The surviving number of spore cells at 104 CFU/ml in initial concentration exponentially decreased with increasing discharge-treatment time. The input energy into the water-surface discharge under an O2 gas flow for reduction in the survival number to 10% was lower than that under an air flow because many oxidation agents such as ozone and OH radical were produced under the O2 gas flow. The input energy density for the one-tenth reduction depended not only on the spore state but also on the initial cell concentration. The input energy for the high-concentration spore cells (107 CFU/ml) was much higher than that for the low-concentration spore cells (104 CFU/ml). Cellular proteins and DNA were degraded by a 30-min discharge treatment of vegetative cells, whereas DNA of the high-concentration spore cells was relatively resistant.

Photographic observation system for DC prebreakdown phenomena in dielectrics using the long image guide scope

The observation technique for dc prebreakdown in dielectrics was established by the use of a long image guide scope which was set in front of an image intensifier with a high speed gate. The passage time of a prebreakdown image through the scope was longer than the response delay time of the gate. Therefore the gate could be closed as soon as the prebreakdown image arrived at the image intensifier.

Transition process from film breakdown to complete breakdown in a silicone-oil/polymer-film composite under point-cathode/plane-anode

The purpose of this paper was to clarify the physical reason for the previously reported experimental results that a complete breakdown in a silicone-oil/PET-film composite for a negative point occurred after a considerable time had elapsed after the film breakdown due to charge deposition. It was concluded from some experiments that the breakdown in the composite was completed by a positive streamer propagation from the breakdown spot of the film which was induced by negative charges emitted from the point cathode immediately after the film breakdown. The minimum delay time between the complete breakdown and the film breakdown was approximately equal to the transit time of negative charges from the point cathode to the film.

DC voltage breakdown in silicone-oil/polymer-film composite

Breakdown phenomena in a silicone-oil/polymer-film composite subjected to DC ramp voltage (0.5 kV/s) and a step voltage were studied with point-plane and plane-plane electrode systems. When the film was placed on the plane anode, the breakdown voltage of the composite with the ramp voltage was less than that for oil alone for both electrode systems as long as the film thickness was thin. Although the breakdown of the film due to charge deposition caused the complete breakdown of the composite for both systems, there was a difference in the transition process from the film breakdown to the complete breakdown. For both electrode systems, when the film was placed on the plane cathode, the increasing rate of the breakdown voltage with the increase in the film thickness was less than that for the film on the anode. In the point-plane system though the film breakdown was brought about by the charge deposition, it could not cause the complete breakdown. The breakdown of the composite was completed by the positive propagation from the point anode. In the plane-plane system, the magnitude of depositing positive charges on the film was too little to cause film breakdown under the ramp voltage. The complete breakdown was induced by the discharge in oil.<<ETX>>

Photographic observation of DC prebreakdown in silicone-oil/PET-film composite using the long image guide scope

The paper describes the results of photographic observations on the complete breakdown in silicone-oil/PET-film composite under point-cathode/plane-anode conditions by the use of an optical system.

Effect of electrical stress produced by repetitive pulsed power on germination of naked barley seed between point-plane electrodes

This paper presents an experimental study on germination control for naked barley seed by using a repetitive pulsed power technique. Two kinds of tests, localized pulse electric field (PEF) treatment and dielectric barrier discharge (DBD) treatment, are carried out. In the first test, very short mono-polar pulses below 500 ns in width and below 5 kV in heights are applied to the seeds between point-plane electrodes with 500 pps repetition rate for 20 min. A fine stainless needle electrode is inserted into embryo region or endosperm region of the seed to clarify which region should be stressed by the localized PEF for the germination control. The germination rate of the seed after the PEF treatment is compared not only with that of the seed without any treatment (control) but also the seed with sham treatment, which means that the needle tip is inserted without voltage application. Results indicate that there is no effect of the PEF application into the endosperm region of the seed on the germination inhibition. On the other hand, the PEF application into the embryo region has an effect on the germination inhibition if the pulse width is long. In the second test, embryo region of the seed is exposed by the dielectric barrier discharges produced by the polarity-reversed voltage pulses with 100 ns in width. Evans Blue dyeing for the seeds is carried out to clarify the biological activity of the embryo cells. Embryo cell necrosis is caused by the 10 min discharge treatment. On the other hand, necrosis of the seed surface is not observed for the seed after the PEF treatment.