Mikio Ohuchi

The axial distributions of optical emission and metastable density: comparison between experiments with DC and RF helium glow discharges

The axial distributions of the optical emission intensity and metastable atom density are shown experimentally for DC and RF helium discharges. Significant differences in the cathode glow adjacent to the cathode sheath are perceived between the DC and RF discharges. These differences seem to lead to differences in the consistencies of their cathode sheaths. It is found that the RF glow is caused by a direct excitation of non-thermalized high-energy electrons; on the other hand, the DC glow is caused by a dissociative recombination of old molecular ions and thermalized low-temperature electrons in addition to the former process. A theoretical model of metastable atoms in the cathode glow region is proposed, and the theoretical curves are compared with the experimental results of metastable density distribution. The validity of this model is then assured, at least qualitatively.

Improved RF-driven probe method for RF discharge plasma diagnostics

The authors describe an electrostatic probe technique for radio-frequency (RF) plasmas. The presence of RF potential fluctuations between probe and plasma distorts the Langmuir probe characteristic; it therefore introduces large errors into plasma parameters. The method presented an improved version of that proposed by Braithwaite et al. to remove the effect of an RF fluctuation on probe characteristics. It consists in superimposing the fluctuation of the space potential measured by an emissive probe to the DC voltage applied to the probe. This technique is applied to the measurement of electron temperature and density in 13.56 MHz RF discharges in helium and argon. The results are compared with direct-current (DC) discharge plasmas with identical input power. The electron temperature in the RF plasmas is higher than that in the equivalent DC plasmas and the electron density in the RF plasmas is lower than that in the equivalent DC plasmas.

Prebreakdown Phenomena and Formation Processes of Low-Pressure Glow Discharges in Ar, Ar/N2 and Ar/O2 Mixtures

In this research, both the prebreakdown phenomena and the transient processes from the prebreakdown phenomena to the glow discharge in low-pressure Ar gas, Ar/N2 and Ar/O2 mixtures were investigated by electrical and optical methods. The prebreakdown phenomenon in the Ar/N2 mixture was similar to that of Ar gas, and a pulseless component has been observed. The prebreakdown phenomenon in the Ar/O2 mixture differed from those in the Ar gas and Ar/N2 mixture, and formed a pulse discharge. Thus, the prebreakdown phenomenon in the Ar gas has been changed to pulse discharge by mixing a small amount of O2 gas which played an important role in the formation of pulse discharge.

Field-emission properties of diamond grains grown on textured Fe/Si substrates

Diamond grains were produced by the hot-filament chemical-vapor deposition technique using a mixture of CH4/H2 as the synthesis gas. The Si substrates were textured (random pyramids) by chemical etching before growth of diamond grains, because emission of electrons is facilitated at the top of the pyramids. In order to increase the diamond nucleation density, an iron thin film (Fe) was deposited on the textured Si substrate by a radio-frequency plasma sputtering technique. Moreover, partial iron thin films (20% surface coverage) were fabricated for application as field emitter displays using a metal mask. The relationship between the nucleation density and the thickness of the iron films has been investigated by scanning electron microscopy (SEM). The samples were placed in a high-vacuum chamber with a pumping system and the emission current was measured as a function of the applied voltage. The voltage–current (V–I) characteristics were estimated for the field emitter. In order to etch nondiamond compone...

Virtual Blood-Flow Controlling System: Optimization of Human Bioactivity Under Exposure to Magnetic Fields

The purpose of this paper is to investigate the effects of extremely low-frequency magnetic fields on the nature of artificial blood solutions, using an artificial blood-circulation system. We first measured induced electromotive forces in our test fluid, using two measurement points with test equipment electrodes inserted in the flow channel near the coil surface. No significant difference in the electromotive forces at the insertion points of the electrodes could be detected. When the positions of the exposure coils were shifted a little from each other on the outside of the flow channel near two measurement points with test equipment electrodes, we were able to detect some slight differences between them. This result showed the possibility that the magnetic fields induced from the coil distinctly generated effective electromotive forces in several fluids among the artificial blood solutions. In addition, we investigated the direct-current magnetic fields for the most effective blood flow on our artificial blood-circulation system. This system may provide new knowledge about the mechanism of blood massotherapy by electromagnetic stimulations as a therapy for many diseases.

Extremely Low-Frequency Electromagnetic Control of Bloodstream on Imitative Blood-Circulation System

In this paper, we designed an artificial blood-circulation system and an original medical device for the improvement of blood flow. First, we prepared an electromagnetic flowmeter and an adaptable coil conformed to the imitative system. The sinusoidal and rectangular signals emitted were sampled with a differential amplifier. Under a constant liquid-flow rate of 7.5 L/min at the alternating electromagnetic field strength of 20 mT, we were able to obtain an induced electromotive force of approximately 2.8 mV. In addition, we investigated the potential of some frequency-changing items to act as a new life-support device for clinical applications. By modifying a commercial magnetic field machine, we designed a prototype equipped with frequency switching of 50 and 0.5 Hz to trial a cure for poor lower limb intravenous flow, lower limb edema, and venous thrombus formation. These systems may provide new knowledge about a mechanism of blood massotherapy by electromagnetic stimulations in the developments of alternating magnetic field machines.

Time-Averaged Electric Field Profiles in a Capacitive Coupling Parallel Plate Electrode RF Discharge Helium Plasma

Time-averaged electric field profiles in a capacitive coupling parallel plate electrode RF discharge with Balun circuit have been measured for a helium plasma. The experiment was conducted at a gas pressure from 0.3 to 3 Torr and RF power from 10 to 30 W. The results show that the time-averaged electric field in the central region of the discharge tube is observed to be relatively uniform for the present range of experimentation except for the gas pressure near 0.7 Torr for higher RF power conditions, where nonmonotonic potential profiles are observed.

Prebreakdown phenomena and formation processes of low pressure glow discharges in N2, O2, and N2/O2 mixtures

The prebreakdown phenomena and the resulting transient processes from the prebreakdown phenomena to the glow discharge in low-pressure N2, O2 gases, and N2/O2 mixtures were investigated. When the applied voltage was a lower overvoltage ratio less than about 2%, nonprebreakdown phenomenon was observed, and the overvoltage ratio was independent of the gas materials. This phenomenon, however, was observed at the overvoltage ratio of higher than about 3%. The prebreakdown phenomenon in N2 gas differed from those in O2 gas, and formed pulseless components. On the other hand, those in O2 gas formed pulsed components. The prebreakdown phenomenon in N2 gas changed to a pulsed discharge by mixing it with a small amount of more than 0.3% O2 gas. These transient processes from the prebreakdown phenomena to the glow discharges were also observed by a high-speed video camera. As a result, the formation processes of the glow discharge became clear.

Prebreakdown phenomena and formation process of the glow discharge in low-pressure Ar gas

The prebreakdown phenomena and the formation process of the glow discharge in a low-pressure Ar gas were investigated under a uniform field gap. Prebreakdown phenomena were observed for 0.5 Torr cm⩽pd⩽2 Torr cm (where p is pressure, d the gap distance) in Ar gas under conditions of a slowly increasing voltage. It was observed that the prebreakdown phenomena formed pulse discharges up to the transition to the glow discharge. The amplitudes of the photon and current pulses due to the pulse discharge increased with time, and then decreased as soon as the transition to a steady glow discharge occurred. When the overvoltage or external series resistance was increased, the pulse amplitudes increased with the applied voltage and decreased with the resistance. The characteristics of the prebreakdown phenomena were changed by the shape of the electrodes. The formation mechanism of the glow discharge can be qualitatively explained by that of the streamer in a high-pressure discharge. The transient glow discharge wa...

Metamorphic behaviors of T 4 -administrated Mexican axolotl under exposure to gradient magnetic field

Objective The Mexican axolotl (Ambystoma mexicanum) has been known as a precious model for regenerative capacity and postembryonic development research for a long period of time.