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Lee, SangMoo,Jung, YeHyun,Kwak, Kisung,Rhee, Joonkyu,Yoo, Jaeun,Youm, Dojun,Kim, Hosup,Ha, Hongsoo,Oh, SangSoo IOP Publishing Ltd 2010 Superconductor science & technology Vol.23 No.4
<P>A simple model for estimating the hysteresis energy loss of coated conductors under a general load line was studied. We took advantage of the characteristic line <I>I</I><SUB>b</SUB>(<I>H</I><SUB>a</SUB>) to determine the major parameters used in this model. The value of <I>I</I><SUB>b</SUB>(<I>H</I><SUB>a</SUB>) was based on the scanning Hall probe measurements (SHP) on a Sm<SUB>1</SUB>Ba<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7 − δ</SUB> coated conductor. During SHP measurement, a magnetic field (<I>H</I><SUB>a</SUB>) and current (<I>I</I><SUB>a</SUB>) were applied simultaneously and were varied along 11 different load lines. From the values of SHP measurements, the current density profiles, <I>J</I>(<I>x</I>, <I>H</I><SUB>a</SUB>, <I>I</I><SUB>a</SUB>), were calculated using a numerical inversion method. We define the quantity <I>I</I><SUB>b</SUB> = ∫ <SUB> − <I>w</I></SUB><SUP><I>w</I></SUP>|<I>J</I>(<I>x</I>, <I>H</I><SUB>a</SUB>, <I>I</I><SUB>a</SUB>)| d<I>x</I> and we calculated <I>I</I><SUB>b</SUB> at many points (<I>H</I><SUB>a</SUB>, <I>I</I><SUB>a</SUB>) in every load line. We found that when <I>I</I><SUB>a</SUB> is less than <I>I</I><SUB>b</SUB> and the flux trap regions are absent, the values of <I>I</I><SUB>b</SUB> for all points (<I>H</I><SUB>a</SUB>, <I>I</I><SUB>a</SUB>) constitute a single line <I>I</I><SUB>b</SUB>(<I>H</I><SUB>a</SUB>), which can be easily extrapolated to a high field. This line provided a major parameter for our model. </P>
Scanning Hall probe measurements of field distributions of a coated conductor under applied fields
Yoo, Jaeun,Jung, Yonghwan,Lee, Jaeyoung,Lim, Sunme,Lee, SangMoo,Jung, YeHyun,Youm, Dojun,Kim, Hosup,Ha, HongSoo,Oh, Sangsoo IOP Publishing Ltd 2006 Superconductor science & technology Vol.19 No.12
<P>We measured the field profiles near the surface of a coated conductor (CC) under various applied fields by using the scanning Hall probe method. The field, applied in the normal direction, was increased from zero to 171.5 Oe and then decreased to −58.8 Oe. We could not analyse our data completely by the direct use of Brandt’s calculation but by a modification with unusual field dependences of the introduced parameters. Since Brandt’s original calculation was based on homogeneous films, it was not suitable for CCs with coarse granular structures. The modified calculations with appropriate parameters are related to the coarse granular structures. Those parameters, <I>D</I>, <I>J</I><SUB>c</SUB>, and <I>R</I>, represent the three characteristics of the flux penetration network: the average distance of flux penetrations, the density of critical sheet currents, and the range of meandering of the flux penetration front, respectively. The external field dependences of these parameters were different from those of the classical critical state model. </P>
Yoo, Jaeun,Lee, SangMoo,Jung, YeHyun,Kwak, Kisung,Rhee, Joonkyu,Youm, Dojun,Kim, Hosup,Ha, Hongsoo,Oh, SangSoo,Oh, Sangjun IOP Publishing Ltd 2009 Superconductor science & technology Vol.22 No.4
<P>The hysteresis loss in a Sm<SUB>1</SUB>Ba<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7−δ</SUB> coated conductor was estimated from magnetic field profiles measured by the scanning Hall probe method. Current, <I>I</I><SUB>a</SUB>, and magnetic field, <I>B</I><SUB>a</SUB>, were applied simultaneously; <I>B</I><SUB>a</SUB> was applied in the normal direction with respect to the tape surface. <I>B</I><SUB>a</SUB> and <I>I</I><SUB>a</SUB> were varied from <I>B</I><SUB>peak</SUB> to −<I>B</I><SUB>peak</SUB> and from <I>I</I><SUB>peak</SUB> to −<I>I</I><SUB>peak</SUB>, respectively, with the ratio α = <I>I</I><SUB>a</SUB>/<I>B</I><SUB>a</SUB> fixed during the variation. Three values of α were taken for the three load lines. The values of <I>B</I><SUB>peak</SUB>/<I>I</I><SUB>peak</SUB> were varied from 0 mT/0 A to 10.7 mT/116 A, 99.1 mT/50 A, and 298.2 mT/46.1 A, respectively, for the three load lines. From the measured values of magnetic field profiles, the current profiles were calculated by the iterative inversion method. From the current profiles, the flux density profiles and the hysteresis loss, <I>Q</I>, were then calculated for various values of <I>I</I><SUB>peak</SUB>(= α<I>B</I><SUB>peak</SUB>) in each load line. The results were compared with theoretical calculations based on Brandt’s model. When <I>B</I><SUB>peak</SUB> was about 300 mT, the estimated values of <I>Q</I> were several times smaller than the theoretical values of <I>Q</I> with the self-field <I>I</I><SUB>c0</SUB>. The low value of <I>Q</I> in this case is due to the field dependent <I>I</I><SUB>c</SUB> and the saturation effect of the current profiles, which results in significant reduction of the induced magnetic moment, <I>M</I>. </P>