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노남균(Roh Nam Kyun),조영래(Cho Young Rae),문지호(Moon Ji Ho),이학은(Lee Hak Eun) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
Vortex induced vibration(VIV) may take place to a slender member at wind speeds considerably lower than their design wind speed. Vortex induced vibration cannot occur structual failures in itself but may cause fatigue problems and decline the servicability. So, VIV should be examined thoroughly. Particulary, Wide Flange Beams which were usually used to hanger have H shape section. H shape sections have wind resistant dynamic unstability. This research is performed to investigate the relation between aspect ratio and critical wind speed of vortex induced vibration. To verify the relation, this paper discusses aerodynamic characteristics of the H shape section with various aspect ratios based on the wind tunnel test result.
Roh, Hyun-Joon,Ryu, Sangwon,Jang, Yunchang,Kim, Nam-Kyun,Jin, Younggil,Park, Seolhye,Kim, Gon-Ho Institute of Electrical and Electronics Engineers 2018 IEEE transactions on semiconductor manufacturing Vol. No.
<P>A phenomenological-based virtual metrology (VM) technique is developed for predicting the silicon nitride film thickness in multi-layer plasma-enhanced chemical vapor deposition (PECVD). Particularly, the analysis of optical emission spectroscopy based on the excitation kinetics in nitrogen plasma is used to develop novel variables, named plasma-information (PI) variables. One variable, PI<SUB>Wall</SUB>, is determined by analyzing the light transmittances of the nitrogen emissions at the contaminated window, representing the drift of reactor-wall condition. The other variable, PI<SUB>Volume</SUB>, is determined by analyzing vibrational distribution of N<SUB>2</SUB>( <TEX>$\text{C}^{3} {\Pi }_{\text u}$</TEX>, <TEX>$\nu =0-4$</TEX>) states, representing the drift of plasma density and temperature. These PI variables are applied as part of input variables of VM to improve the prediction accuracy. The partial least squares regression is adopted as the statistical method and the contribution of PI variables on the VM are evaluated through the variable influence evaluation on projection. It demonstrates the necessity of PI variables in VM for PECVD and the reactor-wall condition is a major cause of drift in PECVD.</P>
Roh, Hyun-Joon,Kim, Nam-Kyun,Ryu, Sangwon,Jang, Yunchang,Kim, Gon-Ho Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.22
<P>A novel method is proposed to determine an electron energy distribution function (EEDF) that includes the highly populated tail originated by energetic beam-like electrons (>20 eV), which often occur in narrow gap, very-high-frequency capacitively coupled plasma (VHF-CCP). This method combines conventional Langmuir probe analysis to represent the EEDF in the low-energy regime and the line-ratio method taken from the optical emission spectrum to represent the highly populated tail of the EEDF. Here the emission lines are chosen with consideration of the excitation rates, which are a function of the shape of the cross-section of the spin- and dipole-forbidden states of an argon atom and the EEDF at corresponding energy. In this method, the analytical EEDF model is chosen for the composition of the Maxwellian for low-energy (bulk) electrons, and Schulze’s time-averaged form of the shifted Maxwellian (Schulze <I>et al</I> 2008 <I>J. Phys. D: Appl. Phys</I>. <B>41</B> 042003) is chosen for the highly populated tail of the EEDF. The variables of the time-averaged form of the shifted Maxwellian, the fraction and mean energy of the beam-like electrons, are determined using an emission model of line-intensity ratios, which describes the line-intensities as a function of the EEDF. This method is advantageous for the diagnostics of a time-averaged EEDF with a highly populated tail, especially where this is due to beam-like electrons that originate from stochastic heating, compared to a two-temperature EEDF.</P>
Kim, Nam-Kyun,Song, Jaemin,Roh, Hyun-Joon,Jang, Yunchang,Ryu, Sangwon,Huh, Sung-Ryul,Kim, Gon-Ho IOP PUBLISHING 2017 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.26 No.6
<P>Recent studies have demonstrated that the two-ion-stream-instability occurs near the plasma boundary and makes the ions reach the ‘modified Bohm velocity’ at the sheath edge. In most low-temperature plasmas, however, the ion-neutral collisions can disturb the growth of instability to occur frequently, and the ions exit the plasma boundary with their own Bohm velocities. We report some experimental observations regarding this issue. The spatial variations of the ion drift velocities and the space potential near the sheath edge were measured in Ar/Xe mixture plasmas by increasing the total pressure in the range of 0.5–2.1 mTorr. The results show that the instability cannot occur above a certain pressure condition and that is consistent with the theoretically driven pressure criteria for the onset of the instability.</P>
Enhancement of deuterium retention in damaged tungsten by plasma-induced defect clustering
Jin, Younggil,Roh, Ki-Baek,Sheen, Mi-Hyang,Kim, Nam-Kyun,Song, Jaemin,Kim, Young-Woon,Kim, Gon-Ho International Atomic Energy Agency 2017 Nuclear fusion Vol.57 No.12
<P>The enhancement of deuterium retention was investigated for tungsten in the presence of both 2.8 MeV self-ion induced cascade damage and fuel hydrogen isotope plasma. Vacancy clustering in cascade damaged polycrystalline tungsten occurred due to deuterium irradiation and was observed near the grain boundary by using all-step transmission electron microscopy analysis. Analysis of the highest desorption temperature peak using thermal desorption spectroscopy supports reasonable evidence of defect clustering in the damaged polycrystalline tungsten. The defect clustering was neither observed on the damaged polycrystalline tungsten without deuterium irradiation nor on the damaged single-crystalline tungsten with deuterium irradiation. This result implies the synergetic role of deuterium and grain boundary on defect clustering. This study proposes a path for the defect transform from point defect to defect cluster, by the agglomeration between irradiated deuterium and cascade damage-induced defect. This agglomeration may induce more severe damage on the tungsten divertor at which the high fuel hydrogen ions, fast neutrons, and self-ions are irradiated simultaneously and it would increase the in-vessel tritium inventory.</P>
Jang, Yunchang,Roh, Hyun-Joon,Park, Seolhye,Jeong, Sangmin,Ryu, Sanywon,Kwon, Ji-Won,Kim, Nam-Kyun,Kim, Gon-Ho Elsevier 2019 CURRENT APPLIED PHYSICS Vol.19 No.10
<P><B>Abstract</B></P> <P>A phenomenology-based virtual metrology (VM) for monitoring SiO<SUB>2</SUB> etching depth was proposed by Park (2015). It achieved high prediction accuracy by introducing newly developed plasma information (PI) variables as designated inputs, called PI-VM. The PI variables represent the state of the plasma, the sheath, and the target during the process. We investigate how a PI variable can help to improve prediction accuracy of VM and how it plays a special role in the statistical selection. We choose only PI<SUB>EEDF</SUB> among the three PI variables to focus on the investigation. The PI<SUB>EEDF</SUB> is determined from the ratio of line-intensities of optical emission spectroscopy. We apply Pearson's correlation filter (PCF), principal component analysis (PCA), and stepwise variable selection (SVS) as statistical selection methods on the variables set including PI<SUB>EEDF</SUB> or not. Multilinear regression is used to model the VM. This study reveals that PI<SUB>EEDF</SUB> variable is a good variable in terms of independence from other input variables and explanatory power for an output variable. Especially, VM using SVS method applied to variable sets including PI<SUB>EEDF</SUB> achieves the highest accuracy, comparable to Park's PI-VM. This study shows that PI<SUB>EEDF</SUB> variable is particularly useful for monitoring of the fine variations in semiconductor manufacturing process and it also extends the utilization of OES sensor data.</P>