• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.200-203
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• 2011

Supersonic ejectors are simple mechanical components, which generally perform mixing and recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for high altitude testing (HAT) of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser (SED). This paper aims at the improvement in HAT facility by focusing attention on the vertical firing rocket test stand with shock generators. Shock generators are mounted inside the SED for improving the pressure recovery. The results clearly showed that the performance of the ejector-diffuser system was improved with the addition of shock generators. The improvement comes in the form of reduction of the starting pressure ratio and the vertical height of test stand. It is also shown that shock generators are useful in reducing the total pressure loss in the SED.

• Journal of the Korean Vacuum Society
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• v.18 no.3
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• pp.197-202
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• 2009

The long term stability of ion current of QMS has been one of key parameters for monitoring gas process in vacuum. The time dependence of ionic current was monitored while the pressure of nitrogen gas was kept at a fixed pressure by introducing the gas into vacuum chamber. The chamber was evacuated to ${\sim}3{\times}10^{-9}\;Torr$ to reduce background signals before the measurement. Two ion sources were tested; one had brownish or black color due to gas contamination and the other one was new, i.e. cleaner. At a nitrogen pressure of $1{\times}10^{-5}\;Torr$, the ionic currents measured by the contaminated ion source decreased faster with time. The decrease rate was respectively ${\sim}46%$ for cleaner one and ${\sim}84%$ for contaminated one after ${\sim}5.5%$ hours. In order to test the effect of filament material on the ion current decrease, we fabricated a tungsten(W) filament which consisted of two parts; one half was made of W and the other was coated with yttria. The similar decrease of ionic currents were shown for the two types of filaments, indicating that slight change of temperature of filament due to material difference i.e. baking effect could not improve the origin of ionic current decrease. Overall the decreasing rate of ionic current is more closely associated with contaminated ion source of QMS rather than its filament materials.

• Journal of the Korean Vacuum Society
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• v.15 no.4
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• pp.347-353
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• 2006

A helium permeation type standard leak calibration system has newly developed by using dynamic gas expansion method. The measurement range was extended lower to $10^{-6}$ Pa L/s for participating CCM (Consultative Committee for Mass and Related Quantities) standard leak key comparison. For the system, pressure ratios of high and ultra-high vacuum chamber and porous plug conductance for helium gas were determined. By using the system, a permeation type standard leak of $5.6{\times}10^{-4}$ Pa L/s range was calibrated. The calibration result showed that the difference between standard commercial leak was 11.1 %.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.314-324
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• 2006

The vacuum characteristics of the KSTAR ICRF antenna were experimentally investigated. The fabricated antenna was installed in the RF Test Chamber(RFTC) which has a vacuum system with an effective pumping speed of 1015 l/s. The time variations of RFTC pressure, total gas load and ultimate pressure were measured before the RF test. RF conditioning effect was studied by repeating RF pulses at low power level. A time variation of the RFTC pressure was measured during a RF power was applied to the antenna. Threshold pressure at which a RF breakdown occurs was investigated. Whenever the pressure was higher than $10^{-4}$ mbar, the RF breakdown occurred. During a long pulse testing, the temperature of the antenna and RFTC pressure were measured to investigate long pulse limitation of the maximum available voltage without any cooling, which were compared with testing results with a water cooling of the antenna.

• Journal of the Korean Vacuum Society
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• v.19 no.5
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• pp.319-325
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• 2010

Pressure vacuum measurement technique using acoustic impedance change of ultrasonic transducers was studied. The sensor has been setup using two air-coupled ultrasonic transducers, one as a transmitter and the other as a receiver, and put it into vacuum chamber and measured pressure versus ultrasonic amplitude. The result confirms that the standard deviations of four repeat measurements were from 0.0093 to 0.3325 at pressure 6.66 kPa to 202.65 kPa(about two atmosphere), and the relative percents were 0.018% and 0.164% at pressure 133.32 kPa and 202.65 kPa, respectively.

• Aerospace Engineering and Technology
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• v.12 no.1
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• pp.32-39
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• 2013

All spacecraft components shall be checked for compatibility with vacuum using CVCM and TML in advance. CVCM and TML of the PZT-5 piezoelectric vibrator has to be less than 0.1% and 1.0% respectively. Also, it has less than $500ng/cm^2/hr$ of TQCM for vacuum bake-out test using high temperature and high vacuum. Thus, the piezoelectric vibrator may be employed in the vacuum environments. Finally, it can be confirmed that the characteristics change of the piezoelectric vibrator is less than 1% under vacuum environments. Also, the temperature dependency of the characteristics in the PZT-5 piezoelectric vibrator with the lateral mode was investigated in the range of $-100^{\circ}C$ to $90^{\circ}C$ using the thermal vacuum chamber to utilize the vibrator to the aerospace industries. As the results, at room temperature, the resonant and anti-resonant frequencies had the minimum value, whereas, the dielectric constant increased linearly from about 2500 to 7500 in the given temperature range. The mechanical loss decreased linearly from 0.08 to 0.03.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4178-4184
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• 2013

Nanoimprint lithography (NIL) is an emerging technology enabling cost-effective and high-throughput nanofabrication. Recently, the major trends of NIL are high throughput and large area patterning. UV curable type NIL (UV NIL) can be performed at room temperature and low pressure. And one advantage of UV NIL is that it does not need vacuum, which greatly simplifies tool construction, so that vacuum oprated high-precision stages and a large vacuum chamber are no longer needed. However, one key issue in non-vacuum environment is air bubble formation problem. Namely, can the air bubbles be completely removed from the resist. In this paper, the air bubbles formation by the method of droplet application in UV NIL with non-vacuum environment are experimentally studied. The effects of the volume of droplet and the number of dispensing points on air bubble formation are investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.153-153
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• 2012

Endpoint detection with plasma impedance monitoring and self-plasma optical emission spectroscopy is demonstrated for dielectric layers etching processes. For in-situ detecting endpoint, optical-emission spectroscopy (OES) is used for in-situ endpoint detection for plasma etching. However, the sensitivity of OES is decreased if polymer is deposited on viewport or the proportion of exposed area on the wafer is too small. To overcome these problems, the endpoint was determined by impedance signal variation from I-V monitoring (VI probe) and self-plasma optical emission spectroscopy. In addition, modified principal component analysis was applied to enhance sensitivity for small area etching. As a result, the sensitivity of this method is increased about twice better than that of OES. From plasma impedance monitoring and self-plasma optical emission spectroscopy, properties of plasma and chamber are analyzed, and real-time endpoint detection is achieved.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.58.2-58.2
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• 2010

This paper deals with the simulation of solid particle coating technology via supersonic nozzle in vacuum environment to devote as an aerosol-deposition device. In order to improve efficiencies of nozzle and coating process, effects of shockwave, nozzle geometry, and substrate location were studied computationally under a fixed chamber pressure of 0.01316 bar which is nearly vacuous. Shockwave is the important factor affect to entire flow because shockwave in the jet flow dissipates the kinetic energy of the flow in the supersonic condition. Results show that various nozzle geometries have significant effect on the supersonic flow and we know that the supersonic nozzle should be optimized to minimize the loss of the flow. Another parameter, the distance between substrate and nozzle tip, shows little effect in this study.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.370.1-370.1
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• 2016

Volatile organic compounds (VOCs) are considered hazardous air pollutants and these are emitted from building materials and household products. VOCs can cause global warming as well as human sickness, and even cancer. Photocatalysis provides a way of converting VOCs into harmless materials. Various researches have shown that $TiO_2$ is the most efficient photocatalysts due to its excellent activity. In this study, metal/non-metal doped $TiO_2$ particles are synthesized for the enhancement of the photocatalytic properties of pure $TiO_2$. By metal/non-metal doping, band gap energies of prepared samples were analyzed by UV/Visible spectrophotometer. The physical and chemical properties of synthesized powder were characterized by field emission scanning electron microscope, by BET for measuring their specific surface area, and by XRD for phase identification and particle size determination. Degradation ability for p-xylene was evaluated through monitoring the concentration in a closed chamber. Relation between their properties and decomposition abilities for VOC were evaluated based on the experimental results.