Taihyeop Lho

Optimizing Factors on High Concentration of Ozone Production with Dielectric Barrier Discharge

The gap distance, electrode material, voltage and gas flow velocity were optimized with gas pressure variation of dielectric barrier discharge (DBD) for producing high concentration of ozone. There exists an optimum gas pressure at which the highest ozone concentration is produced with other parameters being fixed. This optimum gas pressure value changes accordingly as the other parameters changed. As the discharge continues at the optimum pressure, the ozone concentration could increase or decrease slowly. This aging effect has different characteristics with the metal electrode material and the impurity level of the oxygen gas used for ozone generation. The aging effect is supposed to be related with the catalytic effect of metal oxide, which is generated in the discharge zone. The change in the characteristic of optimum pressure by the other parameters, indicate that the ozone concentration is deeply related with the filament self-organization characteristics of DBD. At the final optimized condition, the ozone concentration was higher than 22.5 wt.%.

A method for generating plasma activated water and its biological assessments

Summary form only given. Plasma water treatment is starting to be applied in Advanced Oxidation Processes (AOP). It was experimentally established that water plasmas contain a lot of chemically active species such as OH radical, O radical, H radical which have strongly oxidized agents[su[1]}. in this study, we propose researches on electrical discharge condition having a high impulse current as well as formation of radicals in water and other fluid mediums. the treatment results show that the activated water has the possible biological effects on microorganisms. a method to generating plasma activated water (PAW) was based on a well-known electrolytic method consists of a constant electrical current between unlike electrodes submerged in treated water (WO 96/06048, SU 882944, RU 21133411)[2]. another presumable application for PAW is about to effectively remove chlorine disinfection by-products from water supplies facilities in sufficient quantities, as a substitute for drinkable water. the activated water received by this method can be easily used in waste water treatment, sterilization and other chemical processing.

Experimental visualization of the cathode layer in AC surface dielectric barrier discharge

A narrow etched polyimide line at the bottom edge of a biased electrode (BE) and a non-etched dielectric surface near the biased electrode were observed in an atmospheric AC flexible surface dielectric barrier discharge of polyimide dielectric. These findings are attributed to the bombardment of positive oxygen ions on the bottom edge of the BE and the electron breakdown trajectory not contacting the polyimide surface following the electric field lines formed between the BE edge and the surface charge layer on the dielectric. The length of the non-etched dielectric surface during the first micro-discharge was observed as 22 μm. This occurred, regardless of three different operating durations, which is in good agreement with the length of the cathode layer according to Paschens law.A narrow etched polyimide line at the bottom edge of a biased electrode (BE) and a non-etched dielectric surface near the biased electrode were observed in an atmospheric AC flexible surface dielectric barrier discharge of polyimide dielectric. These findings are attributed to the bombardment of positive oxygen ions on the bottom edge of the BE and the electron breakdown trajectory not contacting the polyimide surface following the electric field lines formed between the BE edge and the surface charge layer on the dielectric. The length of the non-etched dielectric surface during the first micro-discharge was observed as 22 μm. This occurred, regardless of three different operating durations, which is in good agreement with the length of the cathode layer according to Paschens law.

Study on the discharge under water and micro bubble generation

Summary form only given. Mechanism and electrical characteristics of the discharge under 0.9% saline water have been studied. The discharge under water needs Ohmic heating to generate a void around the cylindrical electrode. The void around the electrode provides the discharge space at high voltage. Hence the electrical power dissipated in to two channels, heating the water to generate the void and generating the plasma in the void. The discharge power has been measured by a I-V Lissajous curves. After discharge in the void around the electrode, the void split into micro size bubbles and scattered in the water. The size of micro bubbles has a Gaussian distribution. However the average micro bubble size depends on the diameter of the electrode.

Amorphous silicon & silicon nitride etching with NF 3 DBD plasma

Summary form only given. Amorphous silicon (a-Si) and silicon nitride (SiNx) etching process using atmospheric pressure plasma has been studied. As etchant, a small quantity of NF3 was mixed to nitrogen based DBD (Dielectric Barrier Discharge) plasma for the thin film etching. Test specimen was processed by passing through the downstream plasma zone under the specially designed plasma module with the speed of 50 mm/sec and with 3 mm of module-specimen spacing. The net treatment size of the plasma module (i.e. size of plasma jet nozzle) was 410 mm in width and 0.7 mm in length. The etch rate of the both film was increased with applied power and NF3 flow rate in the range of 0~3 lpm (liter per minute). The SiNx etch rate was dramatically increased by addition of oxygen at the elevated temperature with PR (Photo Resist) patterned specimen. At the optimized condition, the a-Si and SiNx etch rate was about 150 A/scan and about 200 A/scan at 50mm/sec scan speed, respectively. With PR patterned specimen the SiNx etch rate was increased about four times higher than the other case by addition of O2. In this experiment, the applied power range was 0.7~1.6 kW. And the etch rate results of the both layer did not show plateau in that power range.

The effects of plasma density and magnetic field on ion temperature and drift velocity in a LaB6 direct current plasma

In a LaB6 direct current plasma, parallel and perpendicular ion temperatures (Ti∥ and Ti⊥) were measured as a function of plasma density and magnetic field by a laser-induced fluorescence technique. In order to study the impacts of magnetic field and plasma density on ion temperature and drift velocity, the plasma density was controlled by a magnetic field and discharge current under the following plasma conditions: The magnetic field intensity at the measurement position, BD, was 186–405 G; discharge voltage, Vdis, was 29.9–32.1 V; discharge current, Idis, was 10–22 A; neutral pressures, Pn, were 130 mTorr (in the source region) and 2.2 mTorr (at diagnostic region); plasma density, np, was (2–8)×1012 cm−3; and electron temperature, Te, was ∼2.6 eV. Parallel ion temperature (Ti∥), perpendicular ion temperature (Ti⊥), and drift velocity, vD∥ (or drift kinetic energy, ED) all increase as a function of BD and Idis, such that the total ion energy, Et (=Ti⊥+Ti∥+ED), increases as a function of BD and Idis. From...

Development of Steam Plasma-Enhanced Coal Gasifier and Future Plan for Poly-Generation

A microwave plasma torch at the atmospheric pressure by making use of magnetrons operated at the 2.45 ㎓ and used in a home microwave oven has been developed. This electrodeless torch can be used to various areas, including industrial, environmental and military applications. Although the microwave plasma torch has many applications, we in the present work focused on the microwave plasma torch operated in pure steam and several applications, which may be used in future and r ight now. For example, a high-temperature steam microwave plasma torch may have a potential application of the hydrocarbon fuel reforming at one atmospheric pressure. Moreover, the radicals including hydrogen, oxygen and hydroxide molecules are abundantly available in the steam torch, dramatically enhancing the reaction speed. Also, the microwave plasma torch can be used as a high-temperature, large-volume plasma burner by injecting hydrocarbon fuels in gas, liquid, and solid into the plasma flame. Finally, we briefly report treatment of soils contaminated with oils, volatile organic compounds, heavy metals, etc., which is an underway research in our group.

Deduction of Mach numbers with charge-exchange and recombination

Summary form only given. For the analysis of atomic processes in the divertor-edge plasmas, a new fluid model on the ion collection to a probing object is developed for the magnetized flowing plasmas including electron-ion recombination, molecular activated recombination, charge-exchange and ionization processes. Spatial variations of plasma density and flow velocity along the field lines are calculated, in terms of the normalized shear viscosity, drift flow velocity and ratio of each atomic process to the cross-field transport contribution, by assuming that electrons are governed by the Boltzmann relation, ions are warm, and cross-field diffusion is anomalous. Applications of this theory to the Mach probe data of linear divertor simulators and majors tokamaks will be given along with the impact on the deduction of plasma density by electric probes used in the divertor-edge plasmas.

Development of an impedance monitoring system for the Hanbit device

Summary form only given, as follows. The impedance monitoring system to make use of a voltage and current probe has been developed for the Hanbit Mirror device. The impedance monitoring system installed in the matching network and measured the whole impedance of the system including matching circuit, RF antenna and plasma. The Hanbit Device is typically operated during 100/spl sim/300 ms over 10/sup -4/ Torr. However, it is almost impossible to adjust the matching condition during the discharge. The impedance monitoring system is the fastest way to find the best power coupling condition and necessary to keep the consistent discharge in the modulated discharge. The system consists of the V-I probe and phase detection circuit. The impedance data from the phase information and measured reflected power can cast in the Smith Chart. In this presentation, the characteristics of the impedance monitoring system and the experimental data will be discussed.

Characteristics of dielectric barrier discharge

Summary form only given. The frequency characteristics of dielectric barrier discharge (DBD) have been studied for optimizing discharge efficiency. The experiment was performed with various experiment conditions to find the relation between the discharge frequency and power consumption. There is the optimum discharge frequency, which minimizes the consumption of the electrical power. Physically, the optimum discharge frequency means the inverse of the charge build-up time on the dielectric materials. Hence, the optimum discharge frequency depends on the capacitance of a reactor, which is a function of the geometry of the reactor and dielectric materials, and discharge conditions, which depends on the discharge voltage, and gases. From the experimental results, a semi empirical relation on the optimum frequency can be expressed as a function of the discharge gap, dielectric materials, sort of electrodes, and discharge gases.