Bong Ju Lee

Plasma formation using a capillary discharge in water and its application to the sterilization of E. coli

An underwater electrical discharge in a narrow dielectric capillary provides the details of the evolution of microbubbles to plasma as formed by a tungsten electrode inserted in the capillary. An increase in the applied voltage forms microbubbles after water fills the capillary. A further increase in the voltage generates a surface discharge through the boundary of the bubble, elongating the bubble shape, and eventually forming plasma by electrical breakdown. This produces atomic oxygen, atomic hydrogen, and hydroxyl radicals from dissociation of water vapor. Also, a bactericidal test in normal saline solution showed that more than 99.6% of the bacterial cells were killed within 8 s, resulting from chlorine-containing species, in particular hypochlorous acid as a major bactericidal agent.

Generation of Plasma Using Capillary Discharge in Water

This paper is focused on providing a facile method for the production of underwater plasma by a capillary discharge in water. The underwater plasma is formed from a tungsten electrode inserted in a narrow dielectric capillary, showing the breakdown of water vapor in the capillary. This mainly produces atomic oxygen, atomic hydrogen, and hydroxyl radicals from the dissociation of water vapor, revealing different plasma species when the capillary electrode serves as the anode or the cathode.

Plasma-enhanced gasification of low-grade coals for compact power plants

A high temperature of a steam torch ensures an efficient gasification of low-grade coals, which is comparable to that of high-grade coals. Therefore, the coal gasification system energized by microwaves can serve as a moderately sized power plant due to its compact and lightweight design. This plasma power plant of low-grade coals would be useful in rural or sparsely populated areas without access to a national power grid.

Generation of High-Power Torch Plasma by a 915-MHz Microwave System

Large electrodeless plasmas at atmospheric pressure have been generated by making use of 915-MHz microwaves from a magnetron operated at high-power source. In comparison with 2450-MHz microwaves, a 915-MHz microwave source induces enlarged plasma based on waveguide. The plasma flames were sustained and stabilized in a discharge tube with an inner diameter of 80 mm by swirl gas flows. When 150-L/min air as a plasma-forming gas was injected, its diameter and length at an applied power of 20 kW were 6.5 and 130 cm, respectively, displaying a flame pillar in its appearance.

Plasma production by multi-phase alternating current underwater discharge and its applications to disinfection of micro-organisms

Abstract This work is concentrated on providing a novel way to produce underwater plasma. The underwater plasma is generated by taking advantage of a multi-phase alternating current voltage source with the frequency of a commercial electric power system. The multi-phase underwater plasma source is composed of 3-phase transformers to supply 12-phase alternating current voltage, a voltage regulator to control the output voltage of the transformers, capillary electrodes, and a water vessel for installation of the capillary electrodes. This arrangement can provide the stable, large-scale underwater plasma by giving the capillary electrodes independent powers without voltage drop due to phase difference made from the voltage source. This plasma system in flowing water would be useful as a continuous massive water treatment for the purification, sterilization, or disinfection of objects or materials.

Plasma Production by Multiphase Alternating-Current Underwater Discharge

The multiphase alternating-current (ac) voltage source ensures the formation of plasma in water by providing an efficient breakdown voltage for the electrodes connected in parallel. The voltage-driving source was composed of 3-phase transformers to supply 12-phase ac voltage and a voltage regulator to control the output voltage of the transformers. The arrangement provided the stable large-scale underwater plasma by giving the capillary electrodes in water independent powers without voltage drop due to phase difference made from the voltage source. This plasma system in a flowing water would be useful as a continuous massive water treatment for the purification, sterilization, or disinfection of objects or materials.

Current status of the development of the Kumgang laser

The Kumgang laser, a 4 kW (4 x 0.1 J @ 10 kHz / 8.5 ns) coherent beam combination laser using self-controlled stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs), is being developed. The front-end (FE) and the pre-amplifier (PA) are completed. The FE produces pulse energy of 0.51mJ and a pulse width of 8.5 ns with a 10 kHz repetition rate (0.51mJ @ 10 kHz / 8.5 ns) and a 95 MHz linewidth. The PA amplifies up to 200 W (20 mJ @ 10 kHz / 8.5 ns) with an input power 5.1 W.

Cu Nanoparticles From Evaporation of Cu Granule in a Microwave Torch Plasma at Atmospheric Pressure

The copper (Cu) nanoparticles (Cu-NPs) were obtained directly by evaporation of Cu granules in an atmospheric microwave plasma torch flame with a possibility for direct continuous preparation and mass production of Cu-NPs. The microwave plasma generated in a mixture of nitrogen (N2) and argon (Ar) gases evaporates Cu granules and produces Cu-NPs. This template- and catalyst-free process may be promising for the practical production and application of Cu-NPs.

Plasma Burner Enlarged by Coal Injection Into Microwave Plasma

An apparatus for generating a flame and, more particularly, a microwave plasma burner for obtaining a large-volume high-temperature plasma flame are designed using a coal injection into the microwave plasma. The plasma burner was mainly composed of a coal feeder and a stainless steel tube, as the exit for the plasma flame, in series with a 2.45-GHz microwave plasma torch, in which a mixture of air and oxygen could immediately burn the powdered coal, with the help of a high atomic-oxygen density and the high-temperature plasma. In order to examine the possibility of implementing microwave plasma burners at power plants, a feasibility test was conducted using the coal plasma burner, with information obtained on the optical emission lines of the plasma torch, the coal plasma flames, the temperature profile along the axis of the flame, gas compositions at different coal-injection rates, etc.