• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.10
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• pp.889-894
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• 2007

We investigated the quench velocity of superconducting fault current limiter (SFCL) dependent on the source voltage. $YBa_2Cu_3O_7$ (YBCO) thin film was used as the current limiting element for SFCL. The analysis on the quench velocity of SFCL is essential to determine the capacity of circuit breaker (CB) or coordinate with CB. Generally, the quench velocity of SFCL is related with the short-circuit current. To change the short-circuit current, in this paper, the amplitude of the power source voltage is adjusted. Through the fault current limiting experiments, the quench velocity of SFCL was confirmed to increase fast as the source voltage increased. On the other hand, the peak limited current was shown to increase with steady rate of increase.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.136-139
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• 2000

The relations between tensile stresses and critical current densities (J$_c$) of coated conductors were measured. Around 320 MPa of tensile stress, the critical current densities of coated conductor fabricated on pure Ni tape were reduced to zero at 77K, where J$_c$ for zero stress was order of 10$^5$A/cm. The critical tensile stress was much enhanced for the coated conductors fabricated on NiCr alloy tapes. However fabrication conditions for the growth on such alloys are much different from those on the pure Ni and it was not easy to get good textures and large critical currents. The detailed fabrication methods on those alloys will be presented.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.151-154
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• 2000

We have developed a YBCO SQUID gradiometer system for the measurement of a very weak magnetic field in an unshielded environment. The system consists of a SQUID gradiometer sensor, low noise pre-amp, and FLL(fluxlocked loop) control electronics. The gradiometer sensors have been fabricated on STO bicrystal substrates, and exhibit a magnetic noise of 300 fT/${\surd}$ Hz/cm at 100 Hz. The overall magnetic field noise of the SQUID gradiometer system was about 10 pT/${\surd}$ Hz/cm at 10 Hz without any magnetic shield. The system demonstrated a high stability for a long time, and real-time measurement resolution ${\le}$ 100 pT/cm in the unshielded environments.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.35-39
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• 2000

Large-area high-temperature superconducting (HTS) films, filter design and damage-free processing technique have been developed to fabricate low insertion loss and sharp skirt filters. Further, long life cryocooler, low temperature low noise amplifier (LNA) and cryocable have been developed to assemble HTS filter subsystem for IS-95 and IMT-2000 mobile telecommunication. The surface resistance of the films was about 0.2 milli-ohm at 70 K, 12 GHz. An 11-pole HTS filter for IS-95 telecommunication system and a 16-pole HTS filter for IMT-2000 telecommunication system were designed and fabricated using 60 {\times}$ 50 mm$^2$ and one half of 3-inch diameter YBCO films on a 0.5-mm-thick MgO substrate, respectively. We have assembled the filter and low temperature LNA in a dewar with the cryocooler. Ultra low-noise (noise figure: 0.5 dB at 70 K) and ultra sharp-skirt (40 dB/1.5 MHz) performance was presented by the IS-95 filter subsystem and the IMT-2000 filter subsystem, respectively.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.9-14
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• 2000

We report on the novel nonequilibrium nlicrowave emission from quasiparticle-injected high-Tc superconductors. The phenomena have been observed for the current-injected YBCO/I/Au or BSCCO/I/Au thin-film tunnel junctions and BSCCO single-crystal intrinsic Josephson mesa junction samples. For the thin-film tunnel junctions, the emitted radiation appears as broadband. For the intrinsic BSCCO mesa samples, the radiation appears as three different modes of emissions depending on the bias point in the hysteretic current-voltage characteristics; Josephson-emission, nonequilibrium broad emission and sharp coherent microwave emission. The results were interpreted by the Josephson plasma excitation model due to quasiparticle injection.

• Progress in Superconductivity
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• v.2 no.1
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• pp.15-19
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• 2000

[ $YBa_2Cu_3O_{7-\delta}$ ] thin films were deposited by laser ablation using modified melt-textured grown targets. As the laser energy density was increased, the films showed an increasing c-axis orientation and an improvement of superconducting properties. However, at 4 $J/cm^2$, the degree of c-axis alignment and $J_c$ of the film were considerably reduced. These were attributed to the enhanced a-axis outgrowths. It was shown that the increased laser energy density resulted in the formation of $Y_2O_3$ inclusions during the c-axis film growth, and that these inclusions nucleated the a-axis outgrowths.

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.84-84
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• 2004

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.83-83
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• 2004

• 한국초전도학회:학술대회논문집
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• 2007.07a
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• pp.94-94
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• 2007

• Progress in Superconductivity and Cryogenics
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• v.2 no.2
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• pp.44-48
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• 2000

The high temperature superconducting bulk can be used as the rotor of an ac motor. This paper presents the fabrication and test results of a ac motor with HTS bulk rotor. The rotor of a conventional squirrel cage induction motor was replaced with cylinder type YBCO bulk. Height and outer diameter of the HTS bulk was 15mm and 46mm, respectively. Eddy current brake using aluminium disk was used to measure the torque of the HTS motor. No load test, locked rotor test and load test were performed to examine the characteristics of the HTS motor. Test results show the motor can rotate at synchronous speed without any special starting circuit. Maximum output power of the constructed HTS motor was 408W.