• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.136-147
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• 1993

The paper describes : ⅰ) Mathematical modeling of poloidal flux to define and calculate the tokamak plasma position based on a property of the plasma boundary which is always a flux surface. Controlling the plasma boundary position is therefore equivalent to equalizing the flux value on several points belonging to a curve tangent to the limiter. ⅱ) Experimental method for determining the outmost poloidal isoflux surface by a linear combination of measurements of magnetic fluxes, fields and field gradients, without requiring knowledge of internal plasma parameters for the feedback control, i.e., with neither corrections for variation in the poloidal beta and the plasma current distribution, nor compensations for the induced currents in the vacuum vessel. ⅲ) Feedback control algorithm for the regulation of plasma boundary position and its electronics hardware based on the PID control theory. ⅳ) Experimental results obtained from the RTP tokamak experiments using the present plasma control system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2C
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• pp.10-15
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• 2005

In this paper, a simple but fast and reliable technique for the complex dielectric constant measurement of non-magnetic materials is introduced using a measured transmission coefficient (S21) and a genetic algorithm as an inversion process at microwave frequencies. In this experiment, it has been found that the transmission method is less susceptible with the measurement errors than that of the reflection method and the genetic algorithm can be efficiently used as a search technique. The suggested technique is validated with known and unknown conductor-loaded lossy materials and the conductor-loaded PCB at X-band.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.144-146
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• 1995

A superconducting 2 tesla MRI magnet for the animal magnetic resonance imaging has been developed as a basic model for the application of the precise supercoducting magnet technology. MRI cryostat with 210mm room temperature bore was designed and manufactured for this magnet. The cryostat was designed basically not only to extract the principal design parameters at the performance test but also for the convenience of the manufacturing. The most extinct feacture of the cryostat is that it does not have $LN_{2}$ tank and the 77K thermal shield is cooled by circuling $LN_{2}$ through copper pipe which is welded around the shield plate. It results in reduction of the total cryostat size(about 30%).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.11
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• pp.934-940
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• 2001

Magnetic properties were investigated for Si/SiO$_2$/NiFe(300 )/A1$_2$O$_3$(t)/Co(200 ) junction related with the parameters of $Al_2$O$_3$. Insulating $Al_2$O$_3$ layer was formed by depositing a 5~40 thick Al layer, followed by a 90~120s RF plasma oxidation in an $O_2$ atmosphere. Magnetoresistance was not observed for tunnel junction with 5~10 thick Al layer, but magnetoresistance was observed large for tunnel junction with 15~40 thick Al layer. Oxidation time did not largely influence magnetoresistance. Tunnel magnetoresistance effect depended on magnetization behavior of two ferromagnetic layers. Tunneling junction was confirmed through nonlinear I-V curve. In this work, tunneling magnetoresistance(TMR) up to 30 % was observed. This apparent TMR is an artifact of the nonuniform current flow over the junction in the cross geometry of the electrodes.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.3B no.4
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• pp.179-187
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• 2003

In the machine tool industry, direct drive linear motor technology is of increasing interest as a means to achieve high acceleration and to increase reliability. This paper analyzes and compares the characteristics of the tubular linear actuator with the cylindrical Halbach and radial array, respectively. A tubular linear actuator with cylindrical Halbach array, consisting of parallel magnetized arc segments instead of ideal radial and axial magnetized rings, is manufactured. The magnetic field solutions due to the PMs and to the currents are established analytically in terms of vector potential, using the 2-D cylindrical coordinate system. Motor thrust, flux linkage and back emf are then derived. Thrust characteristics according to such design parameters as magnet height and air gap length are also given. The results are validated extensively by comparison with finite element analysis (FEA). Test results such as thrust measurements are also given to confirm the analysis.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.1
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• pp.23-26
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• 2003

This paper presents conceptual design and 3-D electromagnetic analysis of IMVA transformer with BSCCO-2223 High Tc Superconducting (HTS) tapes. The rated voltages of each sides of the transformer are 22.9 kV and 6.6 kV, and double pancake windings were adopted. High voltage and Low voltage sides were composed of several double pancake windings. Four HTS tapes were wound in parallel for the windings of low voltage side and were transposed in order to distribute the currents equally in each conductor The transformer core was designed as a shell type core made of laminated silicon steel plates and the core is separated with the windings by a cryostat with Fiberglass Reinforced Plastics(FRP). A sub-cooling system using L$N_2$ were designed to maintain the coolant temperature 65K. Finally perpendicular components of magnetic field applied to tapes were calculated 0.247 in the rated operation using 3-D analysis. A real 1MVA HTS transformer will be manufactured in near future based on the design parameters presented in this paper.

• Proceedings of the KIEE Conference
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• summer
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• pp.812-814
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• 2004

AC loss is one of the important parameters in (High Temperature Superconducting)HTS AC devices. Among the HTS AC power devices, the transformer is the essential part in the electrical power system. But unfortunately, the transformer is the worst HTS device concerning AC loss because of very large magnetization loss due to high magnetic field applied to the HTS wire. We calculated the magnetization losses in HTS pancake windings for transformer according to the operating temperature. Two kinds of arrangement of HTS pancake windings were adopted for calculation of AC losses of a shell type transformer, and the analysis results were presented and discussed.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.1
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• pp.26-32
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• 1997

In this paper, numerical analysis of dynamic characteristics for the plunger-type solenoid was used for a high speed solenoid valve with fast switching is discussed. The theoretic analysis of the electromagnetic field including eddy currents in the solenoid is studied by using permeance. The optimum value of design parameters which are a mass and an area of the plunger, a source voltage, a elastic modulus of the spring, a stroke, a number of turns, are obtained by the results of the investigation on effect of a parameter on others. And dynamic characteristics of acting solenoid that is the variation of magnetic force, displacement, solenoid current are investigated.

• Journal of Powder Materials
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• v.27 no.4
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• pp.300-304
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• 2020

In this paper, a durability study is presented to enhance the mechanical properties of an Fe-Si-Al powder-based magnetic core, through the addition of graphite. The compressive properties of Fe-Si-Al-graphite powder mixtures are explored using discrete element method (DEM), and a powder compaction experiment is performed under identical conditions to verify the reliability of the DEM analysis. Important parameters for powder compaction of Fe-Si-Al-graphite powder mixtures are identified. The compressibility of the powders is observed to increase as the amount of graphite mixture increases and as the size of the graphite powders decreases. In addition, the compaction properties of the Fe-Si-Al-graphite powder mixtures are further explored by analyzing the transmissibility of stress between the top and bottom punches as well as the distribution of the compressive force. The application of graphite powders is confirmed to result in improved stress transmission and compressive force distribution, by 24% and 51%, respectively.

• Journal of Astronomy and Space Sciences
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• v.33 no.4
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• pp.335-344
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• 2016

Scientific CubeSat with Instruments for Global Magnetic Fields and Radiations (SIGMA) is a 3-U size CubeSat that will be operated in low earth orbit (LEO). The SIGMA communication system uses a very high frequency (VHF) band for uplink and an ultra high frequency (UHF) band for downlink. Both frequencies belong to an amateur band. The ground station that communicates with SIGMA is located at Kyung Hee Astronomical Observatory (KHAO). For reliable communication, we carried out a laboratory (LAB) test and far-field tests between the CubeSat and a ground station. In the field test, we considered test parameters such as attenuation, antenna deployment, CubeSat body attitude, and Doppler frequency shift in transmitting commands and receiving data. In this paper, we present a communication performance test of SIGMA, a link budget analysis, and a field test process. We also compare the link budget with the field test results of transmitting commands and receiving data.