• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.124-132
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• 2003

This paper described the structural design and the fabrication procedure of KSR-III composite pressure tank. The type of the composite pressure tank was COPV(Composite Overwrapped Pressure Vessel). A non-load sharing liner was made of aluminum 6061-0 and the liner provided a helium gas seal. The composite pressure tank was winded using T700 carbon/epoxy on the liner. Because the aluminum liner was thin, multiple cure cycles were applied to the filament winding technique. The multiple cure cycles prevented the liner-cylinder from losing a circular shape. A fitting force at the metallic boss was spread to the carbon fiber by a boss ring. The boss ring also prevented a local deformation at the boss part.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.296-296
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• 2010

ICRF 시스템을 이용한 방전세정인 ICWC(Ion Cyclotron Wall Cleaning)는 ITER와 DEMO 같은 초전도 자석을 이용하는 토카막에서 토카막 shot 중간에 자장을 낮추지 않고 바로 방전 세정을 할 수 있는 방법이다. 토카막에서 방전세정은 탄소나 산소 화합물과 같은 불순물을 제거하여 방사에 의한 플라즈마 냉각을 막고 토카막 초기 start-up시 진공 챔버 벽면으로부터 의도하지 않은 연료주입을 제거하는 역할을 한다. 본 연구에서는 ICWC 방전 세정 최적화를 위해 플라즈마의 불순물 제거 특성을 수소 유량의 크기와 ICRF 펄스의 duty ratio를 바꿔가면서 관찰하였다. ICRF 전력은 44.2 MHz에서 20-50 kW 가 입사되었으며 자장은 3 T에서 고정되었다. 운전압력은 $10^{-4}$ mbar 정도이다. 헬륨의 유량을 400 sccm으로 고정한 후 수소의 유량을 40 sccm에서 160 sccm까지 증가시켜가면서 제거율을 관측하였다. 그 결과 수소 유량의 증가에 따라 제거율이 증가하는 불순물과 오히려 감소하는 불순물이 있음이 관측되었다. 제거율이 증가되는 불순물 group은 charge-to-mass ratio가 26, 28, 40, 44이고 감소하는 불순물 group은 18, 20, 32 이다. 펄스의 duty ratio를 1/9(on/off) 초에서 5/5(on/off) 초로 증가시킴에 따라 제거율이 증가하는 불순물과 감소하는 불순물이 또한 나타났는데 수소 유량 실험과 그 group에 차이가 없었다. 이러한 실험결과는 수소 유량의 증가나 펄스 길이의 증가에 따라 가스의 종류에 관계없이 모두 증가하거나 감소할 것이라는 예측과는 다른 결과로서 이것에 대한 명료한 해석이 필요하다. 왜냐하면 위와 같은 운전조건에서 효율적인 불순물 제거를 위해서는 불순물 제거 운전 방법이 불순물의 종류에 따라 모두 달라져야 하기 때문이다. 본 연구에서는 이러한 특성을 불순물의 dissociation 에너지 관점에서 해석을 시도하였다.

• Fire Science and Engineering
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• v.15 no.2
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• pp.91-95
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• 2001

Decays of the ceiling jet front velocity under a circular ceiling are investigated. To simulate the ceiling jet in fires He and $N_2$gas were injected from a nozzle to the center of the ceiling. The jet fronts in the form of turbulent eddies were traced by a high-speed camera system. The instantaneous locations of the front were obtained from visual readings of visualized front, and the radial velocity was calculated from the information of the time and the location with respect to the front. The similarity and dimensional analysis were also carried out to reveal the relationship between the velocity decay and the radial distance. It was shown that the radial velocity of the front was inversely proportional to the radial distance in the fully developed region from the experimental results and the theoretical analysis.

• Korean Journal of Optics and Photonics
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• v.11 no.2
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• pp.114-118
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• 2000

The paper presents the effects of outpLlt-coLLpling power and small SIgnal gain of a He-Se+ laser by discharge of either $^4He$ or $^3He$. A quartz plane-plate was installed to outpLlt-coLlple the laseI beam from the resonator in the eAperimental setup. The result shows tbat compared with those of ~He, tbe outPLlt-coupling power and small-signal gain of $^4He$ increase in the most of the lines. EspeCIally, the small-signal gain of $^3He$ for the strong lines (497.6 nm, 499.3 nm, 506.9 urn, 5176 nm, 522.8 mn, 530.5 nm) lies 25% higher than Ulat of 4He, and the output-coupling power doubles oubles

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.231-231
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• 2012

7개 나라가 참여해서 공동으로 제작하고 있는 국제핵융합실험로(ITER)는 2020년경에 제작 설치가 완료될 예정이다. ITER 장치에는 6개의 시험 블랑켓 모듈(Test Blanket Module : TBM)이 장착될 예정이며, 그 중에서 한국도 1개를 독자적으로 제작해서 설치할 예정이다. 한국형 헬륨 냉각 고체형 증식(Helium Cooled Solid Breeder : HCSB) TBM이며, 한국은 ITER 참여국 중 유일하게 중성자 반사 재료를 채택한 것이 특징이다. 중성자 반사재료로는 지름 1 mm 내외의 흑연 페블에 SiC를 코팅해서 사용할 예정이다. SiC는 고온저방사화 물질로 차세대 핵융합로의 구조 재료로도 개발되고 있는 물질로, 이렇게 하면 흑연의 단점인 기계적 특성 향상뿐만 아니라, 산화나 화재 등에 대한 사고의 부담도 크게 줄일 수 있는 장점이 있다. 흑연위에 SiC를 코팅하는 방법은 여러 가지가 있으며, 그 중에서 비교적 간단한 건식 방법은 RF Sputtering, PECVD 등이 있다. 건식은 코팅방법이 간단하고 비교적 쉬운 편이지만 페블표면에 양질의 SiC 박막을 얻기가 쉽지 않은 단점이 있다. 이들 방법보다 습식법은 코팅이 까다롭지만 양질의 코팅막을 비교적 쉽게 얻을 수 있는 장점이 있다. CVD의 경우 전구체 물질로 여러 가지 물질이 사용될 수 있으며 대표적으로 $SiH_4$, $Si(CH_3)_4$, $CH_3SiCl_3$ 등이 있으며, 캐리어 가스로는 $H_2$가 사용된다. 이렇게 얻어진 SiC 코팅페블은 흑연에 비해 파괴강도도 향상되고 마모 등에 강한 것을 확인할 수 있었다.

• Progress in Superconductivity and Cryogenics
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• v.14 no.3
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• pp.38-42
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• 2012

Fixtures such as bushings in terminations of high temperature superconducting(HTS) power cable systems are subjected to high voltages, which have to transition from ambient to cryogenic temperatures. As such it is imperative to ensure the integrity of the dielectrics under all operating conditions, including thermal aspects brought about by the passage of current. Gaseous helium(GHe) at high pressure is regarded as a potential coolant for superconducting cables. The dielectric aspects of cryogenic helium gas are both complex and demanding. In this experimental study we looked at the interface between a smooth epoxy surface and high pressure helium gas in a homogeneous electric field. The alternating current(AC) flashover voltages of epoxy samples are presented. The results have been analyzed by using Weibull statistics. In addition to the behavior of the epoxy in gaseous helium as a function of pressure and temperature we also present data of the characteristics of the epoxy in mineral oil and in liquid nitrogen($LN_2$). The breakdown characteristics of a uniform field gap in gaseous helium as a function of pressure and temperature under AC, direct current(DC) and lightning impulse voltages are also given. Electric field calculations have been made for one of the experimental geometries in an attempt to explain some of the anomalies in the experimental results.

• Progress in Superconductivity and Cryogenics
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• v.14 no.1
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• pp.25-29
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• 2012

The novel type of cable under consideration is cooled by gaseous Helium at elevated pressure. Helium is known for having poor electric breakdown strength; therefore the dielectric capabilities of this type of cable must be tested under conditions similar to the envisaged operation. In order to study the dielectric performance we have designed and built a novel high pressure cryostat rated at 2.17 MPa which has been used for testing model cables of lengths of up to 1 m. The cryostat is an open system where the gas is not re-circulated. This allows maintaining a high purity of the gas. The target temperature range is between 40 K and 70 K. This substantially increases the critical current density of the HTS compared to 77 K, which is the typical temperature of cables cooled by liquid nitrogen. The cryostat presented allows for adjusting the temperature and keeping it constant for the time necessary to run a complete dielectric characterization test. We give a detailed description of the cryostat. Measurements of partial discharge inception voltages as well as the temperature distribution along the model cables as a function of time are presented.

• Journal of the Korean Chemical Society
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• v.34 no.5
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• pp.396-403
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• 1990

We describe how to design and construct a LPCVD (Low Pressure Chemical Vapor Deposition) apparatus which can be applicable to the study of reaction mechanism in general CVD experiments. With this apparatus we have attempted to make diamond like carbon films on the p-type (111) Si wafer from (H$_2$ ＋ CH$_4$) gas mixtures. Two different methods have been tried to get products. (1)The experiment was carried out in the reactor with two different inlet gas tubes. One coated with phosphoric acid was used for supplying microwave discharged hydrogen gas stream, and methane has been passed through the other tube without the microwave discharge. In this method we got only amorphous carbon cluster products. (2) The gas mixture (H$_2$ ＋ CH$_4$) has been passed through the discharge tube with the Si wafer located in and/or near the microwave plasma. In this case diamond-like carbon products could be obtained.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.3
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• pp.279-284
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• 2008

Propellant pressurization system in liquid rocket propulsion system plays a role in supplying pressurant gas at a controlled pressure into the ullage space of propellant tanks. The most important design parameter for such propellant pressurization system is the temperature of pressurant gas fed from pressurant tank, which is placed inside of cryogenic propellant tank. Such pressurant is gaseous state, of which density is very sensitive to the temperature of pressurant. Previous investigation dealt with thermal correlation of pressurant and external fluid at room temperature. This study investigates the temperature variation of cryogenic pressurant (GHe) at the time when the pressurant is coming out of pressurant tank, which is submerged in a liquid oxygen, experimentally as well as numerically.

• Membrane Journal
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• v.6 no.2
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• pp.96-100
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• 1996

In order to improve the permeability of the homogenous membrane of poly(carbobenzoxy-L-lysin)(PCLL), which has very high selectivity of helium gas to nitrogen gas, asymmetric porous membranes of PCLL were prepared by casting from 20% solutions in dioxane and dimethylformamide(DMF), respectively. The membranes were characterized by measuring the number of the pores, the pore size distribution of the surface(the skin layer) and the thickness of the skin layer by scanning electron microscope and transmission electron microscope. The mean pore size and the pore density were lower for the membrane cast from dioxane than that from DMF, which was explained by the mechanism of the formation of the pores in the asymmetric porous membrane. The permeability coefficient observed could be roughly explained by the viscous flow through the skin layer. However, the selectivity observed was against the theory of the viscous flow.