Hidenori Akiyama

Drilling and demolition of rocks by pulsed power

There are various methods of rock drilling and demolition. Recently, a method utilizing pulsed power technology has appeared. This method is based on the difference of the dynamic breakdown field strength of liquid and solid dielectrics. The applicability of this method was examined. The features of the rock destruction have been studied. The mechanism explaining the breakdown of the dielectrics with high intrinsic inhomogeneity like natural rocks and concrete is proposed and proved experimentally. An inductive energy storage-opening switch system for the destruction of solid materials is designed allowing higher destruction efficiency. The experimental results using advanced diagnostics such as an image converter camera and X-ray computer tomography of samples are presented. High pulse energy experiments (up to 60 kT in pulse) have been conducted.

Application of pulsed power to mushroom culturing

Recently pulsed power has been broadly applied to biology. In this work we used pulsed power in order to generate more mushrooms as electrical stimulation to mushroom culturing. The aim of this paper is to report the results of three experiments to prove the effectiveness of the application of pulsed power technology to mushroom culturing. The first experiment was carried out as an attempt to increase the yields of shiitake mushrooms. The pulsed high voltage up to 140 kV was applied to logs for mushroom culturing. The result showed that the yield of shiitake mushrooms to which the pulsed high voltage was applied was twice as many as that of shiitake mushrooms to which the pulsed high voltage was not applied. The second experiment was performed to examine the effect of electrical stimulation on the growth of shiitake hyphae. The effect was estimated by the spreading ratios of shiitake hyphae on the surface and cut-ends of logs. That experimental result showed little influence on the growth of shiitake hyphae. However, before declaration of this result further experiment under other experimental conditions will be required. The third experiment was carried out as an attempt to control the growth of unwanted fungus. Trichoderma fungus was used as an unwanted one. The experimental result showed that there is a possibility that this method can reduce the growth of unwanted fungus without any damage to shiitake mushroom fungus.

Production of nitric monoxide in dry air using pulsed discharge

Nitric monoxide (NO) is widely used in the medical treatment of acute respiratory distress syndrome (ARDS) and thus a safe and an effective production of NO is of interest to the medical community. The present work reports on: (1) the production of NO in dry air and in a mixture of O/sub 2/ (26%) and N/sub 2/, and (2) the byproducts in the mixture of O/sub 2/ (26%) and N/sub 2/ subsequent to the application of a pulsed arc discharge. The byproducts which were measured using Fourier transform infrared spectroscopy (FTIR) in a mixture of O/sub 2/ (26%) and N/sub 2/ included NO, NO/sub 2/, N/sub 2/O, H/sub 2/O, CO, CO/sub 2/, and CH/sub 4/. It is shown that in dry air, nitric oxide can be produced with the lowest ratio of NO/sub 2//NO/sub X/ where NO/sub X/=NO+NO/sub 2/. The generation of NO using dry air is economical and effective for medical applications.

Ozone production by pulsed power in dry air

Experimental investigations of high voltage short pulsed streamer discharges in dry air-fed ozonizer under various operating conditions are reported. Ozone concentration, energy input and ozone production yield were measured at various voltages (14 to 37 kV), pulse repetition rates (25 to 400 pulses per second, pps), fixed flow rates (1.5 to 3.0 l/min) and different gap spacings (10 to 20 mm) at a pressure of 1.01/spl times/10/sup 5/ Pa in dry air. A spiral wire made to a cylindrical configuration in concentric coaxial electrodes of varying dimensions was employed. A magnetic pulse compressor provided the voltage and current pulses. Higher voltage and higher repetition rates yielded higher concentrations of ozone at a fixed flow rate. Additionally the present investigations were extended to assess the performance of pulsed ozone generators using dry air under industrial conditions, where both the concentration of ozone (in parts per million, ppm) and its yield (in g/kWh) were maintained at high levels.

Water treatment by pulsed streamer discharges

The reliable and durable reactor for wastewater treatment by pulsed streamer discharges is designed and tested. Uniform streamer discharges were obtained in water at pulsed electric loading. The volume of these discharges exceeds 200 cm/sup 3/ and the energy delivered to the discharge reached 40-400 J depending on the applied voltage. High amplitude of the voltage pulse applied to the reactor requires improved electric insulation to prevent the flashovers along the reactor surface both in water and air. High energy deposition due to high discharge current adds the requirements to the mechanical durability of the system. Small-size reactor with the volume of approximately 1 liter withstands successfully both high electrical and mechanical stresses. The reactor is designed for research purposes, however it can be upgraded to use in high repetition-rate regime necessary for applications.

NO/sub x/ and SO/sub 2/ removal by pulsed power at a thermal power plant

Recently various methods involving gas discharges and electron beams have been studied for the removal of NO/sub x/ and SO/sub 2/ from flue gases. The recent development of repetitive pulsed power generators gives the pulsed streamer corona discharges a chance of success in the removal of NO/sub x/ and SO/sub 2/. Experiments for the removal of NO/sub x/ and SO/sub 2/ using actual flue gases were performed at a thermal power plant. The results showed that about 90% of NO and about 50% of SO/sub 2/ were removed at a flow rate of 0.8 l/min and a repetition rate of 7 pulses per second (pps). The removal ratio of NO varied inversely proportional to the gas flow rate. The energy efficiency of NO removal was 900 /spl mu/mol/Wh when 50% of NO was removed.

Development of repetitive opening switches using exploding wires

An inductive pulsed power generator is very attractive in size, weight and cost, compared to a capacitive one. Compact, light and repetitive pulsed power generators promise a progress in a variety of pulsed power applications. In order to realize inductive pulsed power generators, the development of repetitive opening switches to interrupt a high current rapidly is necessary. Two repetitive opening switches based on exploding wires have been developed at Ariake National College of Technology and Kumamoto University. Both of them are designed for fast replacement of thin copper wires with a diameter of 30 /spl mu/m and can operate at repetition rate up to 6 pps.

Ozone synthesis in oxygen using a pulsed discharge

Ozone is a strong oxidizing and bleaching agent, which makes it a potent germicide, viricide and bactericide. Therefore, ozone can be used as an alternative to chlorination processes with low energy consumption and without detrimental effects to the environment. Ozone can be applied to numerous industrial applications including treatments of water, industrial wastes and removal of NO/sub x/ and SO/sub x/ from flue gases, bleaching processes, in the semiconductor industry and other applications. Therefore, it is necessary to investigate the effects of various parameters on the production of ozone both experimentally and by numerical simulation. A numerical simulation of the products created in oxygen which is widely used in the production of ozone and employing very short pulsed streamer discharges at atmospheric pressure was performed. A simulation has been made of the rate coefficients of various plasma chemical reactions including electron impact dissociation of molecular oxygen, which occurs in the streamer corona discharge as functions of the electric field and the ambient gas temperature in a wire-to-cylinder configuration. The influence on the production of ozone of a single pulse, multiple pulses, gas temperature and gas pressure have been investigated. This study was aimed at understanding the discharge phenomenon in an ozonizer after applying a short pulsed voltage for 100 ns in more details that could not be observed by experiments. The dependence of the concentration of ozone on the parameters studied, generally agreed with the trends of the experimental results and with the published literature thus confirming the validity of the simulation model.

Influence of gas density distribution on the pinch process in gas-puff Z-pinch scheme

Spatial distribution of the incident gas significantly influences the pinch process in gas-puff Z pinch schemes. This paper shows the dependence of the plasma formation on the distribution of the gas puffed into the discharge region. Temporary and spatially resolved gas density between the Z-pinch electrodes was measured by using a high-sensitive multi-channel laser interferometer. Also, plasma density distribution was measured by using a pulsed laser interferometer. The gas, which was puffed from the anode nozzle toward the center axis, quickly spread out to the radial direction and formed a conical shape. This resulted in the significant gas density gradient along z-axis. The pulsed laser interferometer showed a discharge took place at the contour of the gas distribution. The pinch process was significantly influenced by the initial gas distribution. In addition, the double layer structure was observed before implosion.

Ozone production using cylindrical reactors with and without solid dielectric layers in dry air

An investigation into ozone production in dry air-fed ozonizers under different operating gas discharge conditions at a pressure of 1.01/spl times/10/sup 5/ Pa using a spiral wire made to a cylindrical configuration is reported. A magnetic pulse compressor provided voltage and current pulses with a repetition rate of up to 500 pulses per second (pps). A cylindrical configuration with ceramic and polyvinyl chloride (PVC) on the outer electrode and without solid dielectric were used. High production yields were obtained of ozone of about 122, 60 and 57 g/kWh by the ceramic, PVC and without dielectric layers, respectively for 15.7-cm length reactor. The length of the cylindrical reactors was varied from 15.7 cm to 1 m. The flow rate of the gas was varied from 1.5 to 3.0 1/min. The dependence of the concentration and the production yield of ozone on different pulse voltages (17 to 63 kV) and varying pulse repetition rate (25 to 400 pps) with and without solid dielectric layer is reported. This investigation has industrial applications for construction of advanced ozone generators.