• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.16-16
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• 2011

Plasmas in saline solutions receive considerable attention in recent years. How the operating parameters influence the plasma characteristics and how the electrode erosion occurs have been topics that require further study. In the first part of this talk, the effect of the frequency on the plasmas characteristics in saline solution driven by 50~1000 Hz AC power will be presented. Two distinct modes, namely bubble and jetting modes, are identified. The bubble mode occurs under low frequencies. In this mode, one mm-sized bubble is tightly attached to the electrode tip and oscillates with the applied voltage. With an increase in the frequency, it shows the jetting mode, in which many smaller bubbles are continuous formed and jetted away from the electrode surface. Multiple mechanisms that are potentially responsible to such a change in bubble dynamics have been proposed and the dominant mechanism is identified. From the Stark broadening of the hydrogen optical emission line, electron densities in both modes are estimated. It shows clearly that the driving frequency greatly influences the bubble dynamics, which in turn alters the plasma behavior. In the second part, the study of the erosion of a tungsten electrode immersed in saline solution under conditions suitable for bio-medical applications is presented. The electrode is immersed in 0.1 M saline solution and is positively or negatively biased using a DC power source up to 600 V. It is identified that when the electrode is positively biased, erosion by the surface electrolytic oxidation is the dominant mechanism with an applied voltage below 150 V. An increase in the applied voltage leads to the formation of the plasma and the damage by the plasma and the thermal effect becomes more prominent. The formation of the gas film at the electrode surface leads to the formation of the plasma and hinders the electrolytic erosion. In the negatively-biased electrode, no electrolytic oxidation is seen and the damage is mostly likely due to the plasma erosion and the thermal effect.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.144-144
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• 2013

Non-thermal atmospheric pressure plasmas have recently garnered much attention due to their unique physical and chemical properties that are sometimes significantly different from those of low pressure plasmas. It can offer many possible application areas including nano and bio/medical areas. Many different types of plasma sources have been developed for specific needs, which can be one of the important merits of the atmospheric pressure plasmas since characteristics of the produced plasma depend significantly on operating parameters such as driving frequency, supply gas type, driving voltage waveform, gas flow rate, gas composition, geometrical factor etc. Among many source configurations, parallel plate type geometry is one of the simplest configurations so that it can offer many insights for understanding basic underlying physics. Traditionally, the parallel plate type set up has been studied actively for understanding low pressure plasma physics along with extensive employment in industries for the same reason. By considering that understanding basic physics, in conjunction with plasma-surface interactions especially for nano & bio materials, should be pursued in parallel with applications, we investigated atmospheric pressure discharge characteristics in a parallel plate type capacitive discharge source with two parallel copper electrodes of 60 mm in diameter and several millimeters in gap distance. In this presentation, some plasma characteristics by varying many operating variables such as inter-electrode distance, gas pressure, gas composition, driving frequency etc will be discussed. The results may be utilized for plasma control for widening application flexibility.

• Journal of Astronomy and Space Sciences
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• v.17 no.2
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• pp.233-240
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• 2000

Five scientific instruments are planned on KAISTSAT-4 that is scheduled to be launched in 2002. A far ultra-violet imaging spectrograph and a set of space plasma instruments are currently being designed. The imaging spectrograph will make observations of astronomical objects and Earth's upper atmosphere. The plasma instrumentation is capable of fast measuring the thermal magnetosphere plasmas, cold ionospheric plasmas and the Earth's magnetic fields. Major system drivers and constraints on the payloads as well as the spacecraft are identified. A preliminary analysis of the K-4 mission has been undertaken with the system requirements that are derived from the system drivers. Detailed investigation shows that Sun-synchronous orbits with approximate altitudes of 800km are optimal to satisfy the identified requirements. Comparisons with other orbits of different inclinations are also shown. Four operation modes and a daily schedule of spacecraft maneuver are found from the Sun-synchronous orbital model. It is shown that the scientific objectives of K-4 can be achieved with moderate levels of design and operation risks.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1362_1363
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• 2009

In this study, we predicted the thermal breakdown of high-voltage interrupter with the characteristics of thermal plasmas such as temperature, pressure and concentration of the ablated material by using a commercial CFD program. The results showed that the pressure build-up inside the chamber was proportional to the magnitude of arcing current because the quantities of heat energy and ablated mass also increase together with the current during the compression process. And during the decompression process, the reverse flow was not coincided with the magnitude of the applied current due to the compressibility of the gas through backflow channel. The present method is expected to be useful for the design of guideline and interruption capacity on the thermal breakdown of a PASB chamber.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.77-77
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• 2016

Thin films synthesized by plasma processes have been widely applied in a variety of industrial sectors. The structure control of thin film is one of prime factor in most of these applications. It is well known that the structure of this film is closely associated with plasma parameters and species of plasma which are electrons, ions, radical and neutrals in plasma processes. However the precise control of structure by plasma process is still limited due to inherent complexity, reproducibility and control problems in practical implementation of plasma processing. Therefore the study on the fundamental physical properties that govern the plasmas becomes more crucial for molecular scale control of film structure and corresponding properties for new generation nano scale film materials development and application. The thin films are formed through nucleation and growth stages during thin film depostion. Such stages involve adsorption, surface diffusion, chemical binding and other atomic processes at surfaces. This requires identification, determination and quantification of the surface activity of the species in the plasma. Specifically, the ions and neutrals have kinetic energies ranging from ~ thermal up to tens of eV, which are generated by electron impact of the polyatomic precursor, gas phase reaction, and interactions with the substrate and reactor walls. The present work highlights these aspects for the controlled and low-temperature plasma enhanced chemical vapour disposition (PECVD) of Si-based films like crystalline Si (c-Si), Si-quantum dot, and sputtered crystalline C by the design and control of radicals, plasmas and the deposition energy. Additionally, there is growing demand on the low-temperature deposition process with low hydrogen content by PECVD. The deposition temperature can be reduced significantly by utilizing alternative plasma concepts to lower the reaction activation energy. Evolution in this area continues and has recently produced solutions by increasing the plasma excitation frequency from radio frequency to ultra high frequency (UHF) and in the range of microwave. In this sense, the necessity of dedicated experimental studies, diagnostics and computer modelling of process plasmas to quantify the effect of the unique chemistry and structure of the growing film by radical and plasma control is realized. Different low-temperature PECVD processes using RF, UHF, and RF/UHF hybrid plasmas along with magnetron sputtering plasmas are investigated using numerous diagnostics and film analysis tools. The broad outlook of this work also outlines some of the 'Grand Scientific Challenges' to which significant contributions from plasma nanoscience-related research can be foreseen.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.101.2-101.2
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• 2012

Shocks are ubiquitous in astrophysical plasmas: bow shocks are formed by the interaction of solar wind with planetary magnetic fields, and supernova explosions and jets produce shocks in interstellar and intergalactic spaces. The global morphologies of these shocks are usually described by a set of magnetohydrodynamic (MHD) equations which tacitly assumes local thermal equilibrium, and the resulting Rankine-Hugoniot shock jump conditions are applied to obtain the relationship between the upstream and downstream physical quantities. While thermal equilibrium can be achieved easily in collisional fluids, it is generally believed that collisions are infrequent in astrophysical settings. In fact, shock widths are much smaller than collisional mean free paths and a variety of kinetic phenomena are seen at the shock fronts according to in situ observations of planetary shocks. Hence, both the MHD and kinetic equations have been adopted in theoretical and numerical studies to describe different aspects of the physical phenomena associated with astrophysical shocks. In this paper, we present the results of 3D relativistic particle-in-cell (PIC) simulations for ion-electron plasmas, with focus on the shock structures: when a jet propagates into an unmagnetized ambient plasma, a shock forms in the nonlinear stage of the Weibel instability. As the shock shows the structures that resemble those predicted in MHD systems, we compare the results with those predicted in the MHD shocks. We also discuss the thermalization processes of the upstream flows based on the time evolutions of the phase space and the velocity distribution, as well as the wave spectra analyses.

• Food Engineering Progress
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• v.14 no.3
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• pp.202-207
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• 2010

Low-pressure plasmas (LPPs) were generated with different gases such as air, oxygen and nitrogen, and their inactivation effects against Escherichia coli were compared in order to evaluate the potential as a non-thermal microbial disinfection technology. Homogeneous plasmas were generated under low pressure below 1 Torr at gas flow rate of 350 mL/min regardless the types of gases. Temperature increases by LPPs were not detrimental showing less than ${10^{\circ}C}$ and ${25^{\circ}C}$ increases after 5 and 10 min treatments, respectively. The smallest temperature increase was observed with air LPP, and followed by oxygen and nitrogen LPPs. More than 5 log reduction in E. coli was achieved by 5 min LPP treatment but the destruction effect was retarded afterward. The LPP inactivation was represented by a iphasic first order reaction kinetics. The highest inactivation rate constant was achieved in air LPP and followed by oxygen and nitrogen LPPs. The small D-values of the LPP also supported its potentialities as a non-thermal food surface disinfection technology in addition to the substantial microbial reduction of more than 5 logs.

• Journal of the Korean institute of surface engineering
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• v.29 no.1
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• pp.45-59
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• 1996

Ultrafine powders(UFPs) of aluminum nitride(AlN) have been synthesized by chemical reactions in the nitrogen atmosphere and the gaseous aluminum evaporated from Al powders in thermal plasmas produced by a DC plasma torch. A synthesis system consisting of a plasma torch, a finely-controllable powder feeder, a reaction chamber, and a quenching-collection chamber have been designed and manufactured, and a filter for gathering AlN UFPs produced by the quenching process subsequent to the synthesis is set up. The synthesis process is interpreted by numerical analyses of the plasma-particle interaction and the chemical equilibrium state, respectively, and a fully-saturated fractional factorial test is used to find the optimum process conditions. The degrees and ultrafineness of synthesis are evaluated by means of SEM, TEM, XRD, and ESCA analyses. AlN UFPs synthesized in the optimum process conditions have polygonal shapes of the size of 5-100 nm, and their purities differ depending on collecting positions and filter types, and the maximum purity obtained is 72 wt% at the filter.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.3
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• pp.415-425
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• 1996

This study presents an analytical method of solving the behaviors of arc plasma in a nozzle constricting transferred-type torch and purposes to obtain the basic data for the design of a plasma torch, which can be obtained from the temperature, pressure, velocities and voltage distributions. We have to solve some conservation equations simultaneously and need to know the exact thermal gas properties in order to obtain the correct behaviors of arc plasma. It is also necessary to give the relevant physical or geometric boundary conditions. For the simplicity of analysis, we assumed that (a) the plasma flow is laminar, (b)the local thermodynamic equilibrium, i.e. LTE, prevails over the entire arc column region. The electrode sheath effects were neglected and the nozzle area was excluded from the analysis by assuming that the current flow into the nozzle is zero. We solved the momentum transfer equation including the self-magnetic pinch effect, and obtained the temperature distribution from the energy conservation equation. From this temperature, we could get arc voltage distribution. (author). refs., figs., tabs.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.70.1-70.1
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• 2019

Multiple-harmonic electron cyclotron emissions, often known in the literature as the (n + 1∕2)fce emissions, are a common occurrence in the magnetosphere. These emissions are often interpreted in terms of the Bernstein mode instability driven by the electron loss cone velocity distribution function. Alternatively, they can be interpreted as quasi-thermal emission of electrostatic fluctuations in magnetized plasmas. The present paper carries out a one-dimensional relativistic electromagnetic particle-in-cell simulation and also employs a reduced quasi-linear kinetic theoretical analysis in order to compare against the simulation. It is found that the Bernstein mode instability is indeed excited by the loss cone distribution of electrons, but the saturation level of the electrostatic mode is quite low, and that the effects of instability on the electrons is rather minimal. This supports the interpretation of multiple-harmonic emission in the context of the spontaneous emission and reabsorption in quasi-thermal magnetized plasma in the magnetosphere.