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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this bu den estimate or any other aspect of this collection of information, including suggestions for reducing this burden, ABSTRACTAn YBCO coated conductor with a zipper pattern striation is investigated by scanning laser microscopy (SLM). The distribution of transport current deduced from the VTSLM images shows that striations act as artificial barriers forcing the current to flow around them. Current sharing and redistribution are observed at the zipper area. We find the major dissipation mechanism in the sample in the superconducting state to be the current crowding at bottleneck areas. The bottleneck seems to be caused by the disabled filaments at and around the zipper area. Some filaments show the dissipation away from the zipper area. In general, we find that the lower J. areas have lower Tc and high EiVm, which we consider as a sign of the current crowding. For the first time, we have demonstrated that there is a high temperature signature of the lower J e (high dissipation) area and VTSLM can detect the signature. SUBJECT TERMSCritical current density, the distribution of transport current, YBCO coated conductor, zipper striations SECURITY CLASSIFICATION OF: 17. LIMITATION NUMBER OF PAGES 1019a. NAME OF RESPONSIBLE PERSON (monitor) Paul N. Barnes Index Terms-Critical current density, the distribution of transport current, YBCO coated conductor, zipper striations.

We have investigated the spatial distribution of superconducting transition in an epitaxial YBa 2 Cu 3 O 7 film using variable temperature scanning laser microscope (VTSLM). VTSLM creates an image of the ac voltage response, ( ), due to an ac modulated laser beam, which is proportional to d d (). In the resistive transition region, there is a strong correlation between the VTSLM images and the resistance of the sample. When the sample is making a poor thermal contact to the heat bath, the large ( ) region shifts toward the ends of the bridge while the sample resistance decreases. This result is due to the variation of surface temperature along the sample created by the heating at the contact resistance and/or the poor thermal contact between the sample and the heat bath. However, even after improving thermal contact, we still observe the distribution of superconducting transition. Since the local superconducting transition occurs within 1 K, we conclude that any samples with superconducting transition width larger than 1 K have local nonuniformity.Index Terms-Critical temperature, films, high temperature superconductor, nonuniformity, scanning laser microscope.

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