AC Current Driven Flux Dynamics in YBCO Coated Conductors
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1001-M11-02
AC Current Driven Flux Dynamics in YBCO Coated Conductors Andrea Lucarelli1, Ran Yang1, Gunter Luepke1, George Levin2, Timothy Haugan2, and Paul Barnes2 1 Department of Applied Science, College of William and Mary, McGlothlin Street Hall, Williamsburg, VA, 23187 2 Power Generation Branch, Air Force Research Laboratory, 1950 Fifth Street, Bldg 18, WPAFB, OH, 45433
ABSTRACT We present a time-resolved magneto-optical imaging study of YBa2Cu3O7-δ coated conductors in alternating current regime. The evolution of the magnetic flux density distribution in the superconducting samples is imaged at small steps of the phase of the applied AC current. The flux penetration during the phase evolution is inhomogeneous due to the grain structure of the coated conductor. A quantitative analysis of the images show how grain boundary network affects the overall behavior of the flux and current density evolution. INTRODUCTION In recent years significant progress has been made towards the development of the so-called “second-generation” high-temperature superconducting (HTS) wires. The second-generation HTS conductors, also refereed to as “coated conductors” (CC), represent one of the most exciting developments in HTS technology, since they can be used advantageously in many traditional copper wire based high power and transport applications with enormous dollar and energy savings [1]. The introduction of flexible metallic substrates upon which epitaxial thick films can be grown made it possible to use the excellent superconducting properties of YBa2Cu3O7-δ (YBCO) up to 77K [2]. Since then, the HTS community interest has been mainly focused on developing long length robust cables with critical current density (Jc) in excess of 106 A/cm2 [3]. Magneto-optical experiments have strongly contributed to the analysis of current-limiting features like cracks, grain boundaries (GBs) and precipitates in technical materials, such as coated conductors [4], tapes and melt-textured bulk samples [5]. However, a full quantitative understanding of the current distribution is necessary for reliable operation of these materials. The time evolution of flux pattern in CC has to be taken into account. In particular, in regions with inhomogeneous Jc such as GBs, it has been shown experimentally that the electric field pattern and the related time decay of the current pattern are strongly inhomogeneous [6]. Time-resolved magneto-optical (TRMO) imaging technique is particularly effective to study spatial and time-dependent magnetic flux distribution in HTS samples. Here we present TRMO imaging measurements of YBCO coated conductors in the AC current regime. We studied the magnetic field and current evolution during the simultaneous application of a perpendicular magnetic field and an alternating current.
EXPERIMENTAL DETAILS Two-dimensional maps of the magnetic field perpendicular to the YBCO coated conductors are recorded with TRMO imaging. Time resolution is achieved by stroboscopic imaging using a q-switched frequency-doubled Nd:YLF laser (10
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