• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.269-269
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• 2012

A new ion source has been designed, fabricated, and installed at the NBTS (Neutral Beam Test Stand) at the KAERI (Korea Atomic Energy Research Institute) site. The goalis to provide a 100 keV, 2MW deuterium neutral beam injection as an auxiliary heating of KSTAR (Korea Super Tokamak Advanced Research). To cope with power demand, an ion current of 50 A is required considering the beam power loss and neutralization efficiency. The new ion source consists of a magnetic cusp bucket plasma generator and a set of tetrode accelerators with circular copper apertures. The plasma generator for the new ion source has the same design concept as the modified JAEA multi-cusp plasma generator for the KSTAR prototype ion source. The dimensions of the plasma generator are a cross section of $59{\times}25cm^2$ with a 32.5 cm depth. The anode has azimuthal arrays of Nd-Fe permanent magnets (3.4 kG at surface) in the bucket and an electron dump, which makes 9 cusp lines including the electron dump. The discharge properties were investigated preliminarily to enhance the efficiency of the beam extraction. The discharge of the new ion source was mainly controlled by a constant power mode of operation. The discharge of the plasma generator was initiated by the support of primary electrons emitted from the cathode, consisting of 12 tungsten filaments with a hair-pin type (diameter = 2.0 mm). The arc discharge of the new ion source was achieved easily up to an arc power of 80 kW (80 V/1000 A) with hydrogen gas. The 80 kW capacity seems sufficient for the arc power supply to attain the goal of arc efficiency (beam extracted current/discharge input power = 0.8 A/kW). The accelerator of the new ion source consists of four grids: plasma grid (G1), gradient grid (G2), suppressor grid (G3), and ground grid (G4). Each grid has 280 EA circular apertures. The performance tests of the new ion source accelerator were also finished including accelerator conditioning. A hydrogen ion beam was successfully extracted up to 100 keV /60 A. The optimum perveance is defined where the beam divergence is at a minimum was also investigated experimentally. The optimum hydrogen beam perveance is over $2.3{\mu}P$ at 60 keV, and the beam divergence angle is below $1.0^{\circ}$. Thus, the new ion source is expected to be capable of extracting more than a 5 MW deuterium ion beam power at 100 keV. This ion source can deliver ~2 MW of neutral beam power to KSTAR tokamak plasma for the 2012 campaign.

• Journal of Welding and Joining
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• v.26 no.1
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• pp.63-68
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• 2008

This paper has aimed to prevent excessive heat input by controlling arc distribution and heat input capacity with pulse GTAW in order to improve weld quality in 0.08mm pressure gauge diaphragm and flange welding parts. A design of experiment was designed using Box-Behnken method to optimize a welding process. The pulse GTAW parameters such as pulse current, base current, pulse duty, frequency and welding speed were set to input variables while hydraulic pressure that represents welding characteristics in diaphragm and flange joint were set to output variables. Based on the test result, a second regression equation was obtained between input and output variables and turned out significant. Besides, an influence of parameters has been confirmed through response surface analysis using the second-order regression equation and optimum welding condition was obtained through a grid-search method. The optimum welding condition was set to pulse current 84.4(A), base current 29.6(A), pulse duty 58.8(%), frequency 10(%), and welding speed 596(mm/min). Then, decent bead shape was acquired with no excessive heat input under the $2.3kgf/cm^2$ of hydrostatic pressure.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.20-20
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• 2010

GTA (Gas Tungsten Arc)용접은 불활성 분위기에서 용접이 이루어지기 때문에 타 아크용접법에 비해 용접부 품질이 우수하여 고품질이 요구되는 산업분야에 널리 이용되고 있다. 하지만 스테인리스강으로 pipe를 제조하기 위해 GTA 용접을 적용할 경우, Laser 및 고주파 용접 (HFIW)에 비해 용접부 품질 및 용접속도가 낮기 때문에 pipe를 제조하는 산업에서 적용에 제한을 받고 있다. 하지만, GTA는 laser 혹은 HFIW에 비해 가격이 1/10수준으로 낮고, 용접부 gap tolerance 및 용접면 관리범위가 넓은 장점이 있기 때문에 GTA의 용접속도 및 용접품질을 향상시키기 위한 연구가 꾸준히 진행되고 있다. 일반적으로 스테인리스강 GTA용접 시 용접속도를 향상시키기 위해, 모재의 성분 제어 (합금성분 최적화-Al, S, Se, O등), Flux 도포 기술 (산화물을 용접전에 도포하여 용접속도 향상) 및 혼합보호가스 적용 등이 있다. 스테인리스강 용접 시 보호가스로는 용접부 품질을 확보하기 위해 Ar을 주로 사용하고 있다. 하지만 용입 특성을 향상시키기 위해 아크의 온도를 높일 수 있는 He, 혹은 $H_2$ gas를 단독 혹은 혼합하여 사용하고 있다. 오스테나이트계 스테인리스의 경우 용입특성을 향상시키기 위해 Ar에 $H_2$를 2~10%정도 혼합하여 사용하고 있다. 페라이트계 스테인리스강은 수소에 대한 고용도가 상대적으로 작아 용접부 수소 취화를 일으킬 수 있기 때문에 적용에 제한을 받고 있어 그 대안으로 산소를 극히 소량을 혼합하여 용입성 향상에 대한 연구가 보고 되고 있다. 따라서 본 연구에서는 페라이트계 스테인리스강의 용입특성을 향상시킬 목적으로 Ar에 산소를 미량 첨가 (1%미만) 하여 용접전류 및 산소 함량에 따른 용입특성의 변화에 대해 연구하였다. 또한 기계적인 물성 및 부식특성을 평가하였고, 최종적으로 실용화 가능성을 파악하기 위해 용접전극의 수명 테스트를 실시하였다. 실시한 결과, 산소가 첨가량 증가 할수록 용입특성은 상승하였으며, 기계적인 물성 또한 산소를 첨가하지 않은 경우에 비해 거의 유사한 값을 얻을 수 있었다, 하지만 산소함량이 증가 할수록 전극의 수명은 감소하여 교체주기가 증가함을 알 수 있다. 본 연구를 통해 얻어진 기술을 상용화시키기에는 극복해야할 문제가 있지만, 소재 합금성분 설계 시 용접생산성 향상위한 산소성분 범위를 제시할 수 있으리라 판단된다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.12
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• pp.2446-2452
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• 2009

A Ceramic Metal-halide lamp is achieved by adding multiple metals to a basic mercury discharge. Because the vapor pressure of most metals is very much lower than mercury itself, metal-halide salts of the desired metals, having higher vapor pressures, are used to introduce the material into the basic discharge. The metal compounds are usually polyatomic iodides, which vaporize and subsequently dissociate as they diffuse into the bulk plasma. Metals with multiple visible transitions are necessary to achieve high photometric efficiency and good color. Compounds of Sc, Dy, Ho, Tm, Ce, Pr, Yb and Nd are commonly used. The maximum visible efficacy of a Ceramic Metal Halide lamp, under the constant of a white light source, is predicted to be about 450lm/W. This is controlled principally by the chemical fill chosen for a particular lamp. Current these lamps achieve 130lm/W and these life time are the maximum 16,000[hr]. So factors of performance lower are necessary to improve lamp performance. In this paper, we analyzed factors of performance lower by accelerated deterioration test. The lamp was operated with short duration turn-on/turn-off procedure to enhance the effect due to electrode sputtering during lamp ignition. The tested lamp that was operated with a longer turn-on/off(20/20 minutes) showed blackening, changed distance between electrodes and lowered color rendering & color temperature by losses of Dy at 421.18nm, I at 511nm, T1 at 535nm and Na at 588nm compared with the new lamp.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.298.2-298.2
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• 2016

가공이 까다로운 소재를 가공하기 위한 공구에 적용하기 위해서 Al의 함량이 높은 AlTiN 소재가 개발되어 적용되고 있으며, 이 소재는 공구의 수명향상을 위한 표면처리 소재로 각광을 받고 있다. 본 연구에서는 음극 아크 증착 시 거대입자가 박막에 증착되어 결함을 만들기 때문에 그 밀도를 낮추기 위해서 음극 아크 증착을 이용하여 공정 변화에 따른 AlTiN 박막의 표면형상을 관찰하고 특성을 평가하였다. 또한 빗각 증착을 적용하여 제작한 AlTiN 박막의 특성을 평가하였다. Al-25 at.%Ti 합금타겟을 음극 아크 소스에 장착하여 AlTiN 박막을 코팅하였다. 시편은 스테인리스 강판(SUS304)과 초경(tungsten carbide; WC)을 사용하였다. 음극 아크 소스에 인가되는 전류가 낮을수록 AlTiN 박막 표면에 거대입자의 밀도가 낮아졌으며, 기판 전압과 공정압력이 높을수록 AlTiN 박막의 표면에 존재하는 거대입자의 밀도가 낮아지는 경향을 보였다. 이를 통하여 거대입자밀도를 낮추는 기초공정을 도출하였다. AlTiN 박막 제작 시 빗각을 적용한 결과 $60^{\circ}$의 빗각을 적용한 다층 박막에서 약 33 GPa의 경도를 보였다. 본 연구를 통해 음극 아크 증착을 이용하여 거대입자의 밀도가 낮은 박막을 제작할 수 있는 공정을 도출하였고, 빗각증착을 적용하면 경도가 향상되는 결과를 확인하였다. 이를 통해 절삭공구 등과 같이 고경도의 코팅물성 유지를 위한 코팅분야에 응용이 가능할 것으로 판단된다.

• Journal of Welding and Joining
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• v.32 no.6
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• pp.47-55
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• 2014

The purpose of the study is to produce a mechanically improved weld and minimum variation of color through comparing unpulsed and pulsed GTAW (Gas Tungsten Arc Welding) for pure titanium (CP grade7) tube. Pulsed GTAW using 60 A peak current and 20 A background current (1:9) achieved the wider window of welding conditions having part and full penetration without burn-through than the case of unpulsed GTAW. Moreover, the pulsed welding reduced a discoloration on the back bead of the weld and the size of microstructures (basket weave and serrated ${\alpha}$). That is because the pulsed welding has it's a low heat input and severe weld flow induced from electric current variation. Furthermore, the pulsed welding improved the bending property of the welded Ti tube. The enhanced bending property for the pulsed GTAW was due to the insignificant discoloration on the weld surface with maintaining the metal polish.

• International Journal of Korean Welding Society
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• v.3 no.1
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• pp.29-33
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• 2003

The ferritic stainless steels are generally considered to have poor weldability compared with that of the austenitic stainless steels. However the primary advantages of ferritic stainless steels include lower material cost than the more commonly used austenitic stainless steels and a greater resistance to stress corrosion cracking. Thus, the weldability of ferritic stainless steels was investigated in this study. In concerning the weldability, Grain size measurement test, Erichsen test and Varestraint test were involved. full penetration welds were produced by autogeneous direct current straight polarity (DCSP) and pulsed currents gas tungsten arc welding (GIAW) and the effect of pulsed currents welding on the welds was compared to that of DCSP welding. The results showed that pulsed current was effective to refine grain size in the weld metal and the finest grain size was obtained at the frequency of 150Hz. In addition, the ductility of welds was lower than that of base metal. Finally, autogeneous type 444 welds were less susceptible to macro solidification cracks, but more sensitive to micro cracks; SEM/EDS analysis indicated that all the inclusions in the crack showed enrichment of Mn, Si, O and S.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2256-2261
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• 2017

Carbon nanotube (CNT) and alumina ($Al_2O_3$) are synthesized into hybrid composites, and an advanced electrical discharge machining (EDM) system is developed for the machining of hard and conductive materials. CNT nanoparticles are mixed with $Al_2O_3$ powder and the $Al_2O_3$/CNT slurry is sintered by spark plasma. The hardness and the electrical conductivity of the $Al_2O_3$/CNT hybrid composite were investigated. The electrical discharge is controlled by a capacitive ballast circuit. The capacitive ballast circuit is applied to the tungsten carbide and the $Al_2O_3$/CNT hybrid composite. The voltage-current waveforms and scanning electron microscope (SEM) images were measured to analyze the characteristics of the boring process. The developed EDM process can manufacture the ceramic based hybrid composites, thereby expecting the variety of applications.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.632-638
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• 2002

Electron beam (EB) and Gas tungsten arc (TIG) welds were performed on 12.7 mm thick Ti-6Al-4V plate (ASTM Titanium Grade 5). Charpy-V toughness and hardness, as well as, microstructure of the welds and penetration from the macrostructure were studied. It appears that by EB welding rather smaller $\beta$-grains than with TIG welding can be obtained. Next to the fusion line the $\beta$-grain size in the HAZ was 50 ${\mu}{\textrm}{m}$l while in the weld metal it was 150 ${\mu}{\textrm}{m}$. Charpy-V toughness of the EB weld metal was equal or even better to that of base metal, which shows that the $\alpha$-martensite per se is not particularly brittle if only the grain size is fine enough. This is similar to behavior of low carbon martensite in steel. The grain size was studied with light optical and scanning electron (SEM) microscopes. Thus for products, for products which can be manufactured automatically with very narrow fit, the EB welding of Ti-6Al-4V appears to yield satisfactory toughness without any complex post weld heat treatment. ill this study as in earlier studies the TIG welds gave lower toughness than that of the base material due to the higher heat input and slower cooling as compared to EB welding.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.89-93
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• 2002

A study of noticeable improvement in welding speed in thin-plate Type 304 stainless steels gas tungsten arc (GTA) welding was investigated. The welding speeds were increased to more than 3m/min, up to 8m/min. During the welding, Direct Current Straight Polarity (DCSP) and pulsed current GTA welding processes were carried out, respectively. The appropriate high speed welding parameters were established while achieving a high quality weld. After this, Erichsen test and tensile test were performed. The results obtained wert summarized as following: ultra high speed welding for thin-plate Type 304 could be satisfactorily welded with high speed from 3m/min to 8m/min in both DCSP and pulsed GTA welding; Increasing welding speed was found to decrease the ductility, tensile strength md elongation of welded joint; The optimal frequency would be 200Hz-500Hz for high speed welding in pulsed current welding; DCSP welding could obtain the better results of Erichsen test and tensile test than those of pulsed current welding obtained.