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Quasi-Monoenergetic Electron-Beam Generation Using a Laser Accelerator for Ultra-Short X-ray Sources
J Kim,고도경,석희용,H Jang,김형택,I Hwang,최일우,J Lim,J. Lee,J. H. Sung,K.-H. Hong,허민섭,N Hafz,유승훈,유태준,T. M. Jeong,V Kulagin,Y.-C. Noh 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
Two types of electron acceleration methods have been conducted to generate quasi-monoenergetic electron beams. Multi-MeV quasi-monoenergetic high-charge electron beams were generated at Korea Electrotechnology Research Institute (KERI) from self-modulated laser wakefield acceleration by using a collimator with a 2 TW (1.4 J/700 fs) Nd:glass/Ti:sapphire hybrid laser system and a supersonic nitrogen gas jet. The peak electron energy was 3.6 MeV, and the energy spread was 4 MeV. These electron beams are useful for the generation of short-pulse X-rays in the water window region, which is 250 eV -- 500 eV (2.5 -- 5 nm), by using Thomson scattering. The calcualted photon spectrum indicates the scattered photon covers the water window region. This can be used for a high spatial and temperal resolution microscope for medical imaing. To generate higher-energy electron beams with small energy spread, a laser wakefield acceleration experiment with a sharp downward electron density gradient was conducted with a 100 TW laser system at Advanced Photon Research Insistitute (APRI). With the electron density gradient, some background plasma electrons could be locally injected in the laser wake wave and a small energy spread was expected. Using the pre-pulse, we could generate sharp downward electron density gradients. The gradient scale length was 20 $\mu$m for a 25 \% density change. With this electron density gradient, we could get more reproducible electron beams than we could without the density gradient.
G. H. Lee,남창희,이효철,이재혁,Kim T. K.,김형택,Park J. Y. 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.1
Revival structures (rotational coherence) of three linear molecules (N2, O2, and CO2) in a fieldfree alignment condition have been investigated using high-order harmonic generation. The harmonic yields of these molecules were measured in a pump-probe manner by using a weak femtosecond (fs) laser pulse for field-free alignment of molecules and another intense fs laser pulse for harmonic generation. The harmonic intensities from 23rd to 29th order with respect to the time delay between the pump and the probe pulses showed revival structures in the condition of a field-free alignment of molecules. While the revival structure of a N2 molecule had one-fourth the period of the full revival time and different degrees of modulation among different fractional revival times, the revival structures of O2 and CO2 molecules showed one-eighth the periods of the full revival time and similar degrees of modulation among all fractional revival times. The revival structures could be interpreted in terms of the nature of the highest occupied molecular orbital and the total nuclear spin.
Loop형 Thermal Diode의 열성능에 관한 기초 연구
천원기(W.G.Chun),Kuan Chen,이태규(T.K.Lee),김형택(H.T.Kim) 한국태양에너지학회 1994 한국태양에너지학회 논문집 Vol.14 No.3
본 논문은 루프형 열다이오드의 열 성능에 관하여 시험적 연구를 수행하였다. 다이오드는 두 개의 튜브로 만든 수평 부분과 이 두 수평부분을 연결하는 두 개의 PVC 튜브로 구성되어 있다. 작동유체로는 물과 공기가 사용되었으며, 특히 물의 경우 낮은 열전도도와 유동저항의 영향으로 좋은 열성능을 보여 주었다. 본 연구에서는 순방향과 역방향일 경우의 열전달율과 열전달 비를 구하였으며 여러 차례에 걸친 실험을 반복 수행하였다. 이와 같은 형태의 열다이오드는 바로 태양열의 이용에 효과적으로 응용될 수 있다. The thermal performance of a loop thermal diode is presented. This diode in composed of the horizontal segments(metal tubes) and two branches(PVC tubes) connecting the horizontal segments. For the working fluid(filling the loop), water and air are tested where water has shown remarkable performance due to its low thermal conductivity and frictional resistance. A number of tests are done to estimate the heat transfer rate and ratio of heat transfer rates of the diode under forward and reverse bias. This type of thermal could be used at hand to harness the solar energy.
OPR1000 원자로 격납건물 내 중대사고 시 수소 및 증기 거동에 대한 CFD 해석
홍태협(Tae Hyub Hong),최청열(Choengryul Choi),김형택(T. H. Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Hydrogen could be generated by an active reaction of the fuel-cladding and the steam in the reactor pressure vessel during a hypothetical severe accident in a nuclear power plant (NPP). In such situation, the generated hydrogen is released together with steam into the containment. In order to mitigate hydrogen hazards which could possibly occur in the NPP containment, a hydrogen mitigation system (HMS) is usually adopted, such as hydrogen igniters and passive autocatalytic recombiners (PAR). In this study, an analysis of the hydrogen and steam behavior has been numerically performed using fully 3-dimensional computational fluid dynamics (CFD) technique, during a total loss of feed water (LOFW) accident in the OPR1000 containment. During the accident, a huge amount of hot water, steam, and hydrogen are released into the containment. The possibilities of flame acceleration and a transition from deflagration to detonation (DDT) are evaluated by using the Sigma?ambda criteria.