• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.186-187
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• 2013

The paper presents a long-pulse modulator for klystron using a high-voltage solid-state switch and a droop compensator. The modulator guarantees the safe of klystron by limiting the amount of energy transferred to klystron in case of arc. The high performance of the modulator is also achieved by the fast transition time, high flatness and average power. The proposed prototype has produced pulses with a flat-top voltage -90[kV], pulse width 1ms and pulse frequency 200[Hz]. The validity of the long-pulse modulator for klystron has been verified by the simulation and experimental works.

• Progress in Superconductivity and Cryogenics
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• v.13 no.2
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• pp.25-28
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• 2011

A compact phase controller of pulse tube refrigerator is proposed in this paper. Most pulse tube refrigerators available now consist of a long inertance tube and reservoir as the phase controller. The long inertance tube and reservoir present a challenge for compact packaging in some applications. To overcome this disadvantage, the long inertance tube and reservoir are replaced with the compact phase controller consisted of mass, spring and damper in pulse tube refrigerator. This process is achieved using similarity of mechanical, electrical, and acoustic system and the specific configuration of the compact phase controller is designed. From the simulation code in this paper, the performance of pulse tube refrigerator with the designed compact phase controller is confirmed to be comparable to pulse tube refrigerator with the long inertance tube and reservoir.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1543-1546
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• 2008

Modified pulse waveforms were applied to an AC plasma display panel with an auxiliary electrode in order to improve the operation voltage margin. Reciprocal sustain pulse waveforms and modified auxiliary pulse waveforms were applied to the sustain and auxiliary electrode, respectively. During the sustain period, the influence of the address electrode on the luminous efficacy of long-coplanar gap discharges was mitigated by application of reciprocal sustain pulse waveforms. Modified auxiliary pulse waveforms maintained the high efficacy obtained from the AC PDP with an auxiliary electrode. The proposed reciprocal sustain and modified auxiliary pulses waveforms can induce stable discharges in long-coplanar gap discharges and can control wall charges with a wider auxiliary pulse voltage margin, thereby enhancing the luminous efficacy of the AC PDP with an auxiliary electrode.

• KIEE International Transactions on Electrophysics and Applications
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• v.2C no.6
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• pp.304-308
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• 2002

We demonstrate a simple pulsed $CO_2$ laser with millisecond long pulse duration in a tube at a low pressure of less than 30 Torr. The novel power supply for our laser system switches the voltage of the AC power line (60Hz) directly. The power supply doesn't need elements such as a rectifier bridge, energy-storage capacitors, or a current-limiting resistor in the discharge circuit. To control the laser output power, the pulse repetition rate is adjusted up to 60Hz and the firing angle of SCR(Silicon Controlled Rectifier) gate is varied from 30。 to 150。. A ZCS (Zero Crossing Switch) circuit and a PIC one-chip microprocessor are used to control precisely the gate signal of the SCR. The maximum laser output of 35 W is obtained at a total pressure of 18 Torr, a pulse repetition rate of 60 Hz, and a SCR gate firing angle of 90。 . In addition, the resulting laser pulse width is approximately 3㎳(FWHM). This is a relatively long pulse width, compared with other repetitively pulsed $CO_2$ lasers.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.3
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• pp.120-126
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• 2005

The Korean Superconducting Tokamak Advanced Research (KSTAR) tokamak device is being constructed to perform long-pulse, high-beta, advanced tokamak fusion physics experiments. The long-pulse operation requires the non-inductive current drive system such as the Lower-Hybrid Current Drive (LHCD) system. The LHCD system drives the non-inductive plasma current by means of C-band RF with 2-MW CW power and 5-GHz frequency. For the LHCD test experiments, an RF test system is developed. It is composed of a 5-GHz, 1.5-MW pulsed magnetron and a compact pulse modulator with $4\;{\mu}s$ of pulse width. The pulse modulator provides the maximum output voltage of 45 kV and the maximum current of 90 A. It is composed of 7 stages of Pulse Forming Network (PFN), a thyratron tube (E2V, CX1191D), and a pulse transformer with 1:4 step-up ratio. In this paper, the detailed design and the performance test of the pulse modulator are presented.

• Journal of Physiology & Pathology in Korean Medicine
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• v.24 no.6
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• pp.1077-1081
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• 2010

In this work, we report the diagnostic relations among some primary pulse conditions such as the floating/sunken, deficient/forceful, large/fine, and the long/short pulses. For this purpose, we carried out a clinical test, in which 11 Oriental medical doctors had participated to diagnose the pulses for 1566 healthy subjects. The subjects were divided into 11 subgroups and each subgroup was allocated to an individual doctor. It resulted in that, for 847 subjects (54%), two or more than two pulse conditions were felt simultaneously, for which we counted the frequency of the pairs of the pulse conditions. For the statistical analysis, we used a Chi-square test. As a result, at high frequency, the forceful, large, and the long pulses were diagnosed in pairs or in their triplet, and a similar close relation was found between the deficient, fine, and the short pulses. The pairwise diagnoses of the pulse conditions between the forceful, large, and the long pulses, and between the deficient, fine, and the short pulses imply their close relatedness in clinics. This result is supported by the theory of deficiency/excess syndromes. Moreover, we show that the close relatedness among the pulse conditions can be understood in terms of the geometric features of the radial artery near the prominent bone. This is the first work which reports the relatedness between the primary pulses by an objective clinical test.

• Journal of the Optical Society of Korea
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• v.7 no.3
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• pp.135-138
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• 2003

A chirped-pulse amplification femtosecond Ti:sapphire laser operating at 1 KHz has been developed. The laser system consisted of a long-cavity femtosecond oscillator, a four-pass grating pulse stretcher, two multi-pass amplifiers and a double-pass grating pulse compressor. Thermal lensing at the amplifiers was reduced by cooling Ti:sapphire crystals using Peltier coolers. Gain narrowing and residual phase errors were compensated for by the use of an acousto-optic pulse shaper. The final laser output had an energy per pulse of 2.0 mJ and a pulse duration of 19.5 fs, reaching 0.1 TW at 1 KHz.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1729-1731
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• 2003

Recently many solid-state laser systems were widely used in the medical applications. So it is necessary to study various optimal laser parameters for adopting new medical treatments. Alexandrite laser using switching mode power supply has designed and experimented to adjust a pulse repetition rate by PIC one-chip microprocessor. The fundamental results have been obtained during the first financial year in 2002. We will be able to find out the optimal hair removal characteristics by the repetitive experiments of Alexandrite laser as the parameters such as pulse repetition rate, pulse width, and pulse energy etc.

• Nuclear Engineering and Technology
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• v.36 no.4
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• pp.357-363
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• 2004

A prototype long pulse ion source was developed, and the beam extraction experiments of the ion source were carried out at the Neutral Beam Test Stand (NBTS) of the Korea Superconducting Tokamak Advanced Research (KSTAR). The ion source consists of a magnetic bucket plasma generator, with multi-pole cusp fields, and a set of tetrode accelerators with circular apertures. Design requirements for the ion source were a 120kV/65A deuterium beam and a 300 s pulse length. Arc discharges of the plasma generator were controlled by using the emission-limited mode, in turn controlled by the applied heating voltage of the cathode filaments. Stable and efficient arc plasmas with a maximum arc power of 100 kW were produced using the constant power mode operation of an arc power supply. A maximum ion density of $8.3{\times}10^{11}\;cm^{-3}$ was obtained by using electrostatic probes, and an optimum arc efficiency of 0.46 A/kW was estimated. The accelerating and decelerating voltages were applied repeatedly, using the re-triggering mode operation of the high voltage switches during a beam pulse, when beam disruptions occurred. The decelerating voltage was always applied prior to the accelerating voltage, to suppress effectively the back-streaming electrons produced at the time of an initial beam formation, by the pre-programmed fast-switch control system. A maximum beam power of 0.9 MW (i.e. $70\;kV{\times}12.5\;A$) with hydrogen was measured for a pulse duration of 0.8 s. Optimum beam perveance, deduced from the ratio of the gradient grid current to the total beam current, was $0.7\;{\mu}perv$. Stable beams for a long pulse duration of $5{\sim}10\;s$ were tested at low accelerating voltages.

• Journal of the Optical Society of Korea
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• v.8 no.1
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• pp.29-33
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• 2004

We propose and demonstrate a novel optical pulse multiplier applicable to OTDM (Optical Time Division Multiplexing) systems using cascaded long-period fiber gratings. We have exploited the fact that each mode in a fiber has a different propagation constant to obtain time delays among optical pulses. The proposed scheme could realize high-frequency optical pulse multiplication for optical short pulse trains. We have successfully implemented two, four, and eight times multiplications with the maximum repetition rate of 416.7 ㎓. The obtained pulse delays are well matched with the simulated ones.