• Journal of the Korean Magnetic Resonance Society
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• v.10 no.1
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• pp.74-88
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• 2006

Since the first commercial NMR spectrometer came out in 1953 from Varian, much of the hardware development has been improved and matured through commercial equipments. Many of magnetic resonance laboratories however still build and use home-built spectrometers, which are satisfactory even with the consideration of educational purpose only. The home-built NMR spectrometer could be further advantageous and could be often an only option for investigating new ideas with demanding experimental conditions or new hardware support. A solid state NMR spectrometer was designed with extra interest in stochastic experiment and built for an 8.93 T superconducting magnet from Oxford instrument. Super-heterodyned system was implemented for the transmitter and receiver parts. Intermediate frequency (IF) for the heterodyne system was chosen to 70 MHz for the first and the second channels, with additional 120 MHz for the third channel for maximum NMR frequency capability. We will show overall schematics, and discuss the designs with detailed diagrams, then demonstrate the applicability of home-built spectrometer with stochastic-excitation in solid state NMR and in applications to quadrupolar nuclear Spins.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.229-232
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• 1999

We have measured the temperature dependence of thermoelectric power (TEP) and resistivity for the Sr$_{1-x}K_xBiO_3$ superconductor (x=0.45-0.6). At T=10.2K, the resisitivity starts to increase from zero and a rather broad superconducting phase transition (${\Delta}$T ${\sim}$ 2.3K) is observed. TEP at room temperature has a small negative value ( S =-1.96${\mu}$V/K), characteristic of metallic-like TEP. The temperature dependence of TEP shows two distinct features. With decreasing temperature from room temperature, the absolute value of TEP decreases and the sign of TEP changes from negative to positive around 200k. Also, the negative slope of TEP(dS/dT) decreases substantially and becomes rather flat at around 160k, which is a feature already noted in Ba$_{1-x}K_xBiO_3$[1].

• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.13-19
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• 2020

This study presents the experiment and simulation results on the magnetic field response and electrical stability behaviors of no-insulation (NI) and metal insulation with stainless steel tape (MI-SS) which wound in form of racetrack type coils. First of all, the structural design of the racetrack type bobbin was shown along with its parameters. Then, the current-voltage tests were carried out to measure the critical current of both test coils. Also, the sudden discharging and charging tests were performed in the steady state to estimate the decay field time and magnetic field response, respectively. Finally, the overcurrent tests were conducted in the transient state to investigate the electrical stability of these test coils. Based on the experimental results, the contact surface resistances were calculated and applied to the field coils (FCs) of 10-MW-class second generation high temperature superconducting generator (2G HTSG) used in wind offshore environment. The charging delay time and electrical stability for NI and MI-SS HTS FCs of 10-MW-class 2G HTSG are analyzed by the equivalent circuit model and the key parameters which were obtained from the electromagnetic finite element analysis results.

• Progress in Superconductivity
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• v.9 no.1
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• pp.119-125
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• 2007

We investigated recovery in $Au/YBa_2Cu_3O_7$ (YBCO) thin film meander lines on sapphire substrates. The meander lines were fabricated by patterning YBCO films coated with gold layers. The lines were subjected to simulated AC fault current and then small current was applied for recovery measurements. The samples were immersed in liquid nitrogen during the experiment. After the fault, the resistance decreased linearly, first slowly and then fast to zero. The initial slow decrease was due to the decrease of the meander line temperature, whereas the fast decrease was originated from the transition from the normal state to the superconducting state. The recovery speed depended on the size of samples, and was faster in the smaller samples during the whole period of recovery. The experimental results were analyzed quantitatively with the concept of heat transfer within the sample and to the surrounding liquid nitrogen. A heat balance equation was solved for the initial phase of recovery, and an expression for the time dependence of resistance was obtained. The result agreed with data well.

• Journal of Electrical Engineering and Technology
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• v.10 no.5
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• pp.2083-2088
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• 2015

The transient characteristics of the tri-axial High Temperature Superconducting (HTS) power cable are different from those of a conventional power cable depending on whether the cable is under a steady or transient state due to the quench. Verification using simulation tools is required to confirm both the characteristics of the cable and the effect of the cable when it is applied to a real utility. However, a component for the cable has not been provided in simulation tools; thus the RTDS-based model component of the tri-axial HTS power cable was developed, and a simulation was performed under the transient state. The considered properties of model component include resistance, reactance and temperature. Simulation results indicate the variation of HTS power cable condition. The results are used for the transient characteristic analysis and stability verification of the tri-axial HTS power cable. In the future, the RTDS-based model component of the cable will be used to implement the hardware-in-the-loop simulation with a protection device.

• Progress in Superconductivity
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• v.6 no.2
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• pp.138-141
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• 2005

Bi-2223/Ag tapes need to be safe, even it is under the over-critical current state for the protection of a superconducting power machine. However, it is not easy to identify the condition for the safe operation because of their broad S/N transition region. In this paper, for the study of the operation condition of Bi-2223/ Ag tapes, we investigated the V-I curves and the temperature variation of Bi-2223/ Ag tapes experimentally, applying alternating over-currents, and analyzed the relationship between resistance and temperature increase. For the experiments, a Bi-2223/Ag tape of 57 A $I_c$ was prepared, and the over-critical current characteristics under adiabatic state from $LN_2$ was measured. From the experiments, we confirmed that the Joule heating predicted by V-I curve corresponded with the increase of the measured temperature exactly. Using the results, a safe operation condition of Bi-2223 tape was discussed.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1669-1671
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• 1997

Liquid nitrogen has many adventages. It is cheaper than other cooling medium. It is easy to obtain high purity. It's utilized with easy. In future, liquid nitrogen is able to be accepted cooling medium for the superconducting and cryogenic applicated equipments. Cryogenic liquid may be atmospheric pressure state because thermoinsulation is ineffective, airtight decreasing by long time using and bubble occured by flowing current. If it is to be atmospheric pressure state, the electrical insulation strength is dropped and processed partial discharge, finally breakdown. Processing of breakdown has anticipated by measuring radiated-electromagnetic wave which is happened in time of breakdown. There is a measurement of radiated electromagnetic wave as a method that proceeding breakdown is anticipated. In this paper, radiated electromagnetic wave was measured in arc discharge by above conditions as a basic experiment.

• Progress in Superconductivity and Cryogenics
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• v.22 no.4
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• pp.14-19
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• 2020

Here we present the comparative experimental study of the stability of the superconducting state in 4 mm YBCO tapes with copper lamination against local heat disturbances at 77 K. The samples are either directly cooled by immersing a bare YBCO tape into a liquid nitrogen pool or operate in nearly-adiabatic conditions when the tape is covered by a 0.6 mm layer of Kapton insulation. Main quench characteristics, i.e. minimum quench energies (MQEs) and normal zone propagation (NZP) velocities for both samples are measured and compared. Minimum NZP currents are determined by a low ohmic resistor technique eligible for obtaining V - I curves with a negative differential resistance. The region of transport currents satisfying the stationary stability criterion is found for the different cooling conditions. Finally, we use the critical temperature margin as a universal scaling parameter to compare the MQEs obtained in this work for YBCO tapes at 77 K with those taken from literature for low-temperature superconductors in vacuum at 4.2 K, as well as for MgB2 wires cooled with a cryocooler down to 20 K.

• Korean Journal of Acupuncture
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• v.21 no.2
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• pp.1-28
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• 2004

Objectives : Human physiological changes in the state of qigong has been measured using EEG(Electroencephalography), functional MRI(functional Magnetic Resonance Image), EAV(Electro-Acupuncture according to Voll) and SQUID(Superconducting Quantum Interference Device) measurements. Methods & Results : EEGs were measured to study the differences between Qigong masters and Qi receiver on the changes of EEG. During Qigong, an alpha waves were increased. The power spectra indicate that the peak frequency of alpha waves increased during Qigong. Qi receiver's EEG signals seemed to affected by the state of himself. Brain activation did not observed when qigong master concentrates the Qi at Laogong(P8). But a localization of fMRI signal in the sensory cortex was observed by electric acupuncture stimulation at Laogong(P8). Five phase deviation of EAV were clearly changed in the both cases of Qigong master and Qi receiver. When a Qigong master concentrates the Qi at Yintang, Laogong(P8), Qihai(CV6) meridian points during Qigong state, the change of magnetic field around acupoints Yintang, Laogong points has been measured using 40-Channel DROS-SQUID apparatus. After smoothing process of the continuously measured magnetic signal around acupoints for a few minutes, we could observe that a series of peaks, magnitude of -1.0~2.5pT appeared. But there was no significant difference in changes of magnetic signal around acupoints. Physical signals of magnetocardiogram has been measured by using 2-Channel DROS SQUID(Magnetocardiogram). Physical signals of magnetocardiogram were clealy changed at the ST segments after S-wave when qigong master concentrates the Qi.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.58-66
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• 2008

The KSTAR Current Lead System(CLS) with network based real-time distributed control system is implemented using an EPICS as a middle-ware software. The current lead system transfers current from magnet power supplies to superconducting magnet system and simultaneously supply the coolant to maintain superconducting state. To control the CLS at main control room an EPICS IOC server is installed in local control area. Using this server, it is able to be controlled and monitored the system in main control room through operator interface(OPI) which uses "caget" to read status and "caput" to write command with a unique name called PV. The EPICS IOC is developed using "ether-ip" driver to communicate with PLC. Also we achieved satisfactory results in operation and stability aspects from a long period commissioning test.