Shinji Ibuka

Atmospheric dc discharges with miniature gas flow as microplasma generation method

An atmospheric microplasma is generated by direct-current (dc) discharge in air with a miniature gas flow through a nozzle, which limits plasma volume. Two discharge modes appear in a nozzle-to-mesh electrode system with helium or argon. One is a repetitive pulsed discharge with a current of 10?30?mA and a short pulse width. The fast pulsed current is powered by electric charges stored in the parasitic capacitance, which depends on the spatial arrangement of the electrodes and the power leads. The pulsed discharge makes it possible to develop a discharge scheme for microplasma generation without a high-voltage pulse generator. The other is a sustained dc discharge, which develops with increasing applied voltage. In the case of helium, a glow discharge configuration is observed with a positive column and a layered structure near the cathode. The length of the positive column is affected by electrode separation and gas flow rate.

Atmospheric DC Glow Microplasmas Using Miniature Gas Flow and Electrolyte Cathode

We developed a new scheme to generate atmospheric dc glow discharges with a combination of an electrolyte cathode and a miniature gas flow. Stable glow discharges were obtained for a gap separation of 100–700 µm with a cathode of a sodium sulfate solution. The gap voltage increased with increasing a current up to 15 mA, above which the voltage became constant as the low-pressure glow discharges. Local boiling by the discharge at the surface of the sodium sulfate solution began at 15 mA. At the same time, the emission of an intense sodium atomic line appeared in the negative glow region. The pH of the solution decreased when the discharge was generated in ambient air. The reduction of pH was attributed to the existence of nitrogen oxide, which dissolved in the solution.

Fast high-voltage pulse generator with nonlinear transmission line for high repetition rate operation

A new application of the nonlinear transmission line (NLTL) for high-voltage pulse generation is reported. In this NLTL, a rise time of an input pulse voltage of 20-kV amplitude can be reduced from 500 to less than 120 ns. Using this circuit, we demonstrated excitation of a pulsed CO/sub 2/ laser, and obtained output energy of 129 mJ at an efficiency of 4.3%. Moreover, we find that the head-on collision of two solitons is quite effective to generate a high-voltage and short-width pulse. The input pulse is doubled in amplitude and sharpened in width, from 3.6 kV-300 ns to 11 kV-76 ns. With this method, the utilization of semiconductor devices such as the SI thyristor is possible as a primary switching device. Finally, a xenon lamp has been flashed at a repetition rate of 1 kHz.

Voltage amplification effect of nonlinear transmission lines for fast high voltage pulse generation

The authors have proposed a new scheme of high voltage pulse generation utilizing a nonlinear transmission line (NLTL). The scheme is based on the voltage amplification effect of the process of the formation and collision of solitons in the NLTL with ferroelectric ceramic capacitors. Using the head-on collision scheme of two solitons, a fast high voltage pulse with 11 kV amplitude and 76 ns pulse width has been successfully obtained from a 3.6 kV, 300 ns initial pulse generated by a 3000 V class SI thyristor with a repetition rate of 1 kHz. In addition, they have employed stacked nonlinear transmission lines to obtain a much higher voltage amplification ratio. The scheme, known as stacked cable transformers, consists basically of equal lengths of transmission line connected in parallel at the input side, and in series at the output.

Fast high voltage pulse generator with nonlinear transmission line for high repetitive operation

The pulse sharpening effect of nonlinear transmission lines (NLTL) with nonlinear power capacitors has been applied to fast high voltage pulse generation. NLTL can be utilized for high repetitive operation, since NLTL consist of only passive elements. The main problem of the scheme is difficulty of obtaining nonlinear power capacitors with high withstand voltage. In this study, the authors employed commercially available BaTiO/sub 3/ ceramic capacitors as the nonlinear power capacitors, and confirmed the high voltage operation of NLTL in the voltage range of up to 20 kV.

Formation of Ethanol Filament and Its Pulsed Discharge for Microplasma Generation

One of the advantages of microplasmas is that it can be generated using any phase of materials, namely, gases, liquids, and solids. We developed methods to generate microplasmas by pulsed discharge utilizing ethanol filaments grown from the tip of a Taylor cone, which were created by the electrostatic force between electrodes in air. The structures of the filament and Taylor cone were affected by electrode separation, applied voltage, electrode shape, and the mass of liquid. Vaporization and dissociation of ethanol were confirmed in the pulsed discharge of the liquid filament, because the atomic line of hydrogen was observed in optical emission spectroscopy.

Atmospheric DC Glow Discharge Observed in Intersecting Miniature Gas Flows

In this paper, stable atmospheric DC glow microplasmas generated along two intersecting miniature gas flows through nozzle electrodes are observed. The intersecting angle was varied from 45deg to 135deg. If argon gas flow was used, striation structure can be noticed at the cathode side.

Self-Organization Pattern in the Anode Spot of an Atmospheric Glow Microdischarge using an Electrolyte Anode and Axial Miniature Helium Flow

An atmospheric glow microdischarge is generated with an electrolyte anode and axial miniature helium flow. A stable operation under atmospheric pressure can be achieved using an axial miniature helium flow. When the electrode separation is 10 mm and the discharge current is greater than 30 mA, self-organization patterns, which depend on the electrolyte anode concentration, are observed at the electrolyte anode surface, indicating that the anion and cation in electrolyte solution are important for electrolyte anode discharges.

SI-thyristor as a high power switching device for fast high voltage pulse generators

Characterization of SI-thyristors as a fast closing switch for pulsed power application was examined. Since the SI-thyristors employed in this study are normally on-state, a negative bias voltage is necessary at the gate electrode to establish hold-off-state. As a consequence, fast current rise rate can be strongly expected. A low impedance gate driving circuit built with MOSFETs improved turn-on characteristics. By adjusting anode voltage distribution and gate timing, carefully stacked SI-thyristors were successfully operated to make turn on. The highest di/dt obtained in this study is 55 kA//spl mu/s. A fast high voltage pulse generator with magnetic pulse compression scheme was built by using stacked SI-thyristors. To obtain a faster high voltage pulse a nonlinear transmission line as an additional circuit for pulse sharpening was employed.

Electrolyte-Cathode Atmospheric Glow Discharge With Wide-Gap Operation Using Miniature Gas Flow

Stable dc electrolyte-cathode atmospheric glow discharges with a wide-gap separation were obtained using a miniature helium gas flow. A thin discharge column formed because of the gas flow exhibited intense sodium atom line emission from the cathode region for high-current operation.