DC Breakdown Voltage of Carbon Dioxide Medium under Needle to Plane Electrode

This paper reports the experimental results on thecorona onset voltage and breakdown voltage by positiveand negative dc discharges in carbon dioxide mediumwithin the pressure range of 0.1 to 15MPa under theneedle to plane electrode. From the experimental resultsof dc discharge, negative corona discharges are observedmore clearly in liquid and supercritical phase than in gasphase of carbon dioxide. However, in our experimentalcondition, positive corona discharge was not found for dcdischarges. The breakdown mechanism in liquid can beclassified into two categories on account of the bubbletriggeredformation

Negative DC Prebreakdown Phenomena and Breakdown-Voltage Characteristics of Pressurized Carbon Dioxide up to Supercritical Conditions

This paper deals with the experimental results on prebreakdown phenomena and breakdown voltage characteristics of a negative dc point-to-plane gap in-compressed carbon dioxide up to the supercritical pressure as the first step to develop a plasma reactor with supercritical carbon dioxide. The gap length and the curvature radius of the point tip were 200 and around 35 $muhbox{m}$, respectively. The experimental results show the following: 1) corona discharge preceding complete breakdown is observed more clearly in liquid and supercritical fluid than in gas; 2) the estimated discharge onset voltage according to the streamer theory is in fairly good agreement with the measured breakdown voltage in the gas density region of 0.1–30 $hbox{kg}cdot hbox{m}^{-3}$; 3) the breakdown mechanism in liquid can be classified into two categories: bubble-triggered breakdown at lower pressure and non bubble-triggered breakdown at higher pressure; 4) the breakdown mechanism in supercritical fluid is similar to that in higher pressured liquid; and 5) the density and temperature dependences of breakdown voltage in liquid and supercritical fluid are related closely with the breakdown mechanism

Electron Temperature and Electron Density of Underwater Pulsed Discharge Plasma Produced by Solid-State Pulsed-Power Generator

A pulsed discharge produced underwater has been an attractive method to treat waste water. For the optimization and realization of the water treatment system utilizing underwater pulsed discharge, modeling analysis could be one of the essential works. However, there is still no simulation work about the underwater pulsed discharge due to the lack of knowledge about its characteristic parameters such as electron temperature, electron density, and so on. In this paper, the temperature and the electron density in a pulsed discharge plasma produced underwater are measured and presented. A magnetic pulse compressor (MPC) was developed and used to create the electrical discharge in water. The developed MPC is all-solid state and is, therefore, a maintenance-free generator. To define the temperature and the electron density in an underwater pulsed discharge plasma, two kinds of spectroscopic measurements, called the line-pair method and Stark broadening, were carried out. According to the experimental results, the temperature and the electron density in the pulsed discharge plasma between point-plane electrodes immersed in water are determined to be 15 000 K and $10^{18}/ hbox{cm}^{3}$, respectively

チョウ リンカイ リュウタイ チュウ デノ ホウデン ゲンショウ ノ カイメイ ト ソノ オウヨウ

本論文では超臨界二酸化炭素中での放電特性の調査及び再臨界水中でのパルス放電プラズマの化学反応の有効性について検討した。特に二酸化案その放電特性実験では、超臨界二酸化炭素中での絶縁破壊特性および極性効果について詳細に調べた

Anomalous plasma temperature at supercritical phase of pressurized CO2 after pulsed breakdown followed by large short-circuit current

The relation between breakdown characteristics and plasma temperature of a pulsed arc discharge in highly pressurized CO2 was investigated up to a supercritical phase. A transient arc discharge was generated by applying nanosecond pulsed voltage with a rising rate of 0.7 kV/ns to a point-to-plane gap of 1 mm. The breakdown voltage, arc current, and consumption energy increased with the CO2 density in the gas phase. However, they were constant at the CO2 densities in the supercritical phase. The plasma temperature determined from the blackbody radiation ranged from 8000 to 12000 K and its dependence with respect to the CO2 density was all similar to the breakdown voltage, arc current, and consumption energy characteristics except under the critical density of CO2 (469 kg/m3). Although the breakdown voltage, arc current, and consumption energy in supercritical phase were also constant against the CO2 density, the plasma temperature demonstrated a local decrease around the critical density. The anomaly of the plasma temperature is consistent with the calculated result of the isochoric specific heat of CO2 which has a local maximum around the critical density

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Innovative Ph.D. program has been conducted to produce young scientists of a top level in the world. This program has been supported by the Ministry of Education, Japan, as one of 21st century COE (Center of Excellence) programs. Ten professors with different specialty educate Ph.D. students through a weekly COE seminar, a training camp, an international workshop and others. The web-based e-learning and web-based meeting systems are used extensively in this program. New authoring software, which can build high quality e-learning contents efficiently, has been developed and used here. This program has been producing about 10 Ph.D. scientists every year since 2003