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Field Dependence of Current Profiles Induced in a Superconducting Film under a Magnetic Field
유재은,염도준,Jaeyoung Lee 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.5
The field dependence of current profiles induced in a superconducting $\rm SmBa_2Cu_3O_7$ (SmBCO) film grown on an ion beam assisted deposition (IBAD) template in the coevaporation method was investigated. The field profiles near the surface of the film under external fields were measured using a scanning Hall probe method. The magnetic field was normal to the film surface and was increased monotonically from 0 to 1800 Oe in 90 Oe step. The corresponding current profiles in the superconducting thin film were obtained by using a numerically iterative inversion of the measured field profile data. We found that the sheet current density profile was very different from the theoretically calculated one based on the Bean model. When the applied field, $H_a$, was increased up to 270 Oe, the maximum values of the current profiles reached the highest value, which was similar to its critical current density at $H_a = 270~ \rm Oe$ and which decreased for further increases of $H_a$. We investigated the field profiles, $H_{super}(x)$, produced only by the superconducting current. The values of $H_{super}(x)$ saturated under the conditions of $H_a = 270~\rm Oe$. We think that these features may be due to a mixture of the shield current and the critical current induced in the granular structure of the sample. After the Meissner region disappeared at higher fields, the values of $J(x)$ showed the field dependence feature of the critical current.
Critical current densities of bicrystalline HTSC film under various magnetic fields
임선미,정예현,염도준,정용환,장경진,이상무 한국초전도.저온공학회 2006 한국초전도저온공학회논문지 Vol.8 No.2
Critical current densities were measured for a bicrystalline (Sm0.8Dy0.2)Ba2Cu3O7 film under various magnetic fields ( ). The fields were varied from to for various orientations with respect to the film surface. The curves of the critical current densities ( ) vs showed the well known butterfly-like hysteretic curves. Our data could be analyzed for the two components of field, which are normal and parallel to the film surface, respectively. We combined the effect of deduced from the data for the normal field ( ) and the effect of deduced from the data for the almost parallel field ( ). Our analyses indicate that depends on the two components of flux density at the grain boundary. All the experimental data for various s fit well to this new formula which was obtained by multiplying the factors deduced from the field dependences of these two components.
Hysteretic Magnetization Curves of Coated Conductors Calculated Using Measured Field-Profile Data
유재은,이재영,염도준,송규정 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.4
The hysteretic magnetization curves of superconducting ReBa2Cu3O7 (ReBCO,RE:Y,Sm) films were investigated. The YBCO and the SmBCO films were grown on ion-beam-asisted-deposition (IBAD) templates by using the pulsed laser deposition (PLD) method and the coevaporation method, respectively. The field profiles, H(x), near the surfaces of the samples in a magnetic field applied in a direction perpendicular to the surface, Ha, were measured using a scanning Hal probe method. The coresponding sheet curent profiles, J(x), in the superconducting thin films were obtained by numerical inversion of the measured field profile data. The negative magnetic moment, M(Ha), per unit length was estimated from J(x). The calculated magnetization hysteresis loops for Ha cycled with amplitude -Hpeak were in remarkable agreement with that measured by using a magnetometer. The differences in the hysteresis loops between the two samples are due to the granular characteristics of the samples.
이상무,정예현,곽기성,이준규,염도준,김호섭,하홍수,오상수,유재은 한국초전도학회 2009 Progress in superconductivity Vol.10 No.2
The magnetic field profiles near the surface of a SmBa2Cu3O7−δ coated conductor (CC-tape) under magnetic field and current that were applied simultaneously with phase differences φs were measured using scanning Hall probe method. Measurements were carried out along the elliptic load lines with φ = 90° and 45° for some Bpeak, Ipeak values. From the measured field profiles, sheet current density J(x, Ba, Ia) and magnetic flux density B0(x, Ba, Ia) profiles in the CC-tape were calculated. Using these J(x, Ba, Ia) and B0(x, Ba, Ia) profiles, we estimated the hysteresis energy loss Q in the CC-tape. The estimated Qs, together with our previous results for φ = 0° from [9], were compared with theoretical values based on Brandt’s calculation.
Jae Hun Lee,이상영,염도준,Sunme Lim 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.1
Observation of a reduced critical current density Jc for thick-film hightemperaturesuperconductor (HTS)-coated conductors has been an issue with regard to applications of HTScoated conductors. We investigated the thickness dependence of the microwave surface resistance of a 1.2-μm-thick SmBa2Cu3O7− (SmBCO) film grown in situ on biaxially textured Ni tape by using the co-evaporation method. The microwave surface resistance and the penetration depth were measured by using a dielectric resonator method as the SmBCO-coated conductor was etched down from 1.2 μm to 0.08 μm by using a 0.1 vol.% Br - methyl alcohol solution. Except for the 0.08-μm-thick bottom layer right on top of the Ni substrate, the intrinsic surface resistance Rs appeared to increase continuously as the thickness increased from 0.08 μm to 1.2 μm throughout the temperature range of 7 K − 77 K. The values were 380 μ for the 0.3-μm-thick top layer and 1270 μ for the 0.07-μm-thick layer grown on top of the 0.08-μm-thick bottom layer at 7 K and 8.5 GHz. Interestingly, the 0.08-μm-thick bottom layer still showed strong superconductivity unlike the observation of a dead layer at the bottom by Jo et al. [10]. The penetration depth at 0 K (0) vs. thickness data also appeared consistent with the results from the Rs measurements; 0 increased from 215 nm for the 1.2-μm-thick SmBCO film to 260 nm for the 0.08-μm-thick bottom layer. Our results show that the appearance of dead layers can be avoided by controlling the growth conditions, including the growth temperature and the deposition rate, and that the depth profile of microwave Rs with progressive etching processes can be used as a way to assess the thickness dependence of Jc for thick-film HTS-coated conductors in a non-invasive way.
유재은,곽기성,이준규,박찬,염도준,박병준,한영희 한국초전도.저온공학회 2010 한국초전도저온공학회논문지 Vol.12 No.4
The Lorentz force distribution of a high Tc superconducting tape with increasing transport currents in magnetic field (Ha) was visualized. The external magnetic field was applied normally to the coated conductor tape surface after zero-field cooling, and the transport current (Ia) was increased stepwise from 0 to 90 % of the values of the critical current (Ic (Ha)) at applied filed, Ha. The field distribution (H(x)) near the sample surface across the tape width (2w) was measured using the scanning Hall probe method. Applying an inversion to the measured field distribution, we obtained the underlying current distribution (J(x)), from which the magnetic induction, B(x) was calculated with Biot-Savart law. Then Lorentz force per unit length was calculated using F(x)=J(x)×B(x), which appears to be very inhomogeneous along the tape width due to the complicated distributions of J(x) and B(x).