• Journal of The Korean Astronomical Society
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• v.8 no.1
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• pp.29-34
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• 1975

Solar electrical conductivity has been calculated, making use of Yun and Wyller's formulation. The computed results arc presented in a tabulated form as functions of temperature and pressure for given magnetic field strengths. The results of the calculation show that the magnetic field does not play any important role in characterizing the electrical conductivity of the ionized gas when the gas pressure is relatively high (e.g., $P{\geq}10^4\;dynes/cm^2$). However, when the gas pressure is low (e.g., $P{\leq}10\;dynes/cm^2$), the magnetic field becomes very effective even if its field strength is quite small (e.g., $B{\leq}0.01$ gauss). It is also found that, except for lower temperature region (e.g., $T{\leq}10^{4^{\circ}}K$), there is a certain linear relationship in a log- log graph between the pressure and the critical magnetic field strength, which is defined as a field strength capable of reducing the non-magnetic component of the electrical conductivity by 20%.

• Progress in Superconductivity and Cryogenics
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• v.23 no.2
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• pp.24-27
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• 2021

This paper presents a design methodology of high-temperature superconducting (HTS) magnets. The magnet consists of several double pancake coils with a variety of wire width. This technique, named Multi-Width, is well known to make efficient use of the superconducting wire. It is common for design of high-temperature superconducting magnets to not only reduce wire consumption used, but also consider the homogeneity of the magnetic field. In this paper, we study a design method that efficiently reduces wire usage while considering magnetic field homogeneity. The design is carried out by calculating the critical current and the critical magnetic field according to the configuration of arranging the thickness of the wire to determine the number of windings. The width of wire comprising the magnet was set to 4 - 12 mm, and the number of double pancake coils was set to an even number to consist of top-down symmetry. To verify the validity of the design, we compared the progress of the design code with a complete enumeration survey. As a case study, we designed a magnet that generates a central magnetic field of 3 T or more in a 240 mm bore in diameter. Optimality can be evaluated by weighing wire consumption and field homogeneity according to the magnet's use or user preference.

• Progress in Superconductivity and Cryogenics
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• v.23 no.1
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• pp.12-16
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• 2021

The magnetic properties of heat treated O-series high temperature superconducting (HTS) GdBCO coated conductor (CC) tapes which were formed of Ag/GdBCO/Buffer-layers/Stainless Steel (SS), were investigated by employing a Quantum Design PPMS-14. Using a modified Bean model, the critical current density J_c values have been estimated from the 𝚫m_irr(H) data, which are obtained by measuring the magnetic moment m(H) loops. For a range of intermediate fields, which are interacting or collective flux pinning area, the magnetic flux behaviors were investigated from the relationship J_c ∝ H^-β. In addition, the changes of irreversibility magnetic field H_irr line of heat-treated O-series HTS GdBCO CC tapes were analyzed, according as the annealing temperature under oxygen flowing increases. Both weak and strong break-downs were found by examining the changes of irreversibility magnetic field H_irr lines.

• Progress in Superconductivity
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• v.5 no.2
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• pp.128-131
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• 2004

The resistive superconducting fault current limiters (SFCLs) are very attractive devices for the electric power network. But they have some serious problems when the YBCO thin films were used for the current limiting materials due to the in homogeneities caused by manufacturing process. When the YBCO films have some inhomogeneities, simultaneous quenches are difficult to achieve when the fault current limiting units are connected in series for increasing operating voltage ratings. Magnetic field application is one of the prospective way of inducing simultaneous quenches far the series-connected resistive FCL components. Magnetic field was typically generated by the fault current thorough a coil, which is connected to components of the fault current limiter in series, leaving the problem, which provides significant inductance to the power line and suppresses critical current density of the superconducting components. In this article we investigated the possible application of the protective current transformer (p-CT), which is available current source to the magnetic coil. This system inductively coupled to the circuit, therefore, remarkably reducing impedance to the circuit. The current by the protective current transformer was directly fed to the coil, generating magnetic field large enough to reduce critical current density of the components. This successfully induced simultaneous quenches of the series-connected resistive FCL components.

• Progress in Superconductivity and Cryogenics
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• v.17 no.1
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• pp.17-20
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• 2015

Coated conductor is an important candidate for power cable applications due to its high current density. Even for DC power cable transmission, we must study the transport properties of HTS tapes after slow and fast discharge. In order to evaluate relation of the magnetic field with applied current we developed a scanning magnetic field measurements system by employing a Hall probe. This work presents the measurements of the magnetic fields above a coated conductor by varying applied current pattern. In the work, a transport current of 100 A, less than the critical current, is applied to YBCO coated conductor. We measured the residual magnetic field distributions after cut off the transport current with slow and fast operations. The results show differences of the magnetic field profiles and the corresponding current profiles by an inverse solution from the magnetic field measurement between these two operations because of the hysteresis of coated conductor excited by the transport current.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.274-276
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• 2002

To enhance the critical current of superconducting coil, the magnetic field experienced by superconductors in a coil should be minimized. This is true for both low $T_{c}$ and high $T_{c}$ superconductors, and the difference between the two lays in their isotropic/an-isotropic characteristics. In this paper, we propose a shape optimization algorithm to reduce radial magnetic field components in HTS solenoid to enhance the critical current of a solenoid. In the algorithm, finite element method and continuum shape design sensitivity formula were employed. The objective function is to minimize the maximum radial magnetic fields in a solenoid with a constraint of constant solenoid volume condition. In this paper, the details on algorithm are introduced and the calculated optimized shapes are presented.

• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.260-263
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• 1997

In this paper, we describe the mechanical strain effects on the critical current density of HTS (BSCCO) pancake-type-magnet. Firstly the strain of pancake coil is calculated in terms of coil length, which is also a function of angle, and then the critical current density degradation due to strain is calculated along the coil. We assumed that the critical current density degradation pattern is same with that of $Nb_{3}Sn$. We also modelled the effects of magnetic field on the critical curent degradation, and the results are compared with those with null magnetic field.

• Progress in Superconductivity and Cryogenics
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• v.12 no.1
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• pp.28-31
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• 2010

A magnetic field calculation method for toroidal type winding which has circular section was developed. At first, the equation for magnetic field by single filament coil was extended using numerical integration to estimate the entire interesting region of solenoid, especially winding region itself. And then, the magnetic field by toroidal arrangement of solenoids was computed with a coordinate transformation of vector fields. The superconducting magnet with toroidal arrangement can be made up of several tens of solenoid type double pancake windings for some applications such as superconducting magnetic energy storage system(SMES). In this system, the field calculation on the high-Tc superconducting(HTS) tape itself is very important because the entire system can be reached to a fault by magnetic stress of conductor or the critical current of superconducting tape can be dramatically reduced under its self field condition. To make matters worse, 3-dimensional analysis is indispensable for this type of magnet and the most of commercial programs with finite element method can be taken too much time for analysis and design. In this paper, a magnetic field calculation method for toroidal type winding with circular section was induced.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.3
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• pp.384-389
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• 2008

The cental magnetic field of an HTS magnet consisting of pancake windings can be increased if the magnet is excited by multiple power sources. Multiple power sources enable all pancake windings to conduct their critical currents. The HTS magnet consisting of pancake windings was excited by separate power sources in this paper. Critical currents of each pancake winding were determined by using optimization technique. Fabrication of the BSCCO magnet consisting of 10 pancake windings is described and test results of the BSCCO magnet are given. Central magnetic field and perpendicular magnetic field of the magnet excited by multiple power sources were compared with those of the magnet excited by a single power source.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.15-18
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• 2003

HTS(High Temperature Superconductor) tapes have dependence on critical characteristics such as electric, magnetic field and temperature. In order to confirm these effects, we examined the current transport characteristics of HTS tapes. First, after being fed DC and AC, the dependence of HTS tapes of 10cm on external magnetic field was investigated. On centeral region of HTS tape, about 1cm, external magnetic field was applied. Second, after applying DC of 50A to HTS tapes, we applied time variable magnetic field about 100mT and investigated the quench characteristics. Finally, AC, which is about 10 times of I$_{c}$, was applied to HTS tapes and over current characteristics were investigated. The data acquired in this study will be used as a source for the study of HTS cable conductor which is supposed to carry on.n.