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Ochiai S.,Kyoto University | Okuda H.,Kyoto University | Arai T.,Kyoto University | Nagano S.,Kyoto University | And 3 more authors.
Cryogenics | Year: 2011

Transport current and n-value of DyBCO-coated conductor pulled in tension were measured experimentally and their relation to crack-induced current shunting was analyzed with the partial crack-current shunting model. The following features were revealed. The shunting current increases with increasing transport current and with increasing crack size. At low voltage where shunting current is low, the transport current of cracked sample normalized with respect to the transport current in non-cracked state is described with the modified ratio of non-cracked area to overall cross-sectional area of superconducting layer. At high voltage where the shunting current is high, the normalized transport current becomes higher than the modified ratio of non-cracked area. The increase in shunting current with transport current (and voltage) leads to a decrease in n-value at high current (voltage). This phenomenon is enhanced by crack extension. © 2011 Elsevier Ltd. All rights reserved. Source


Ochiai S.,Kyoto University | Okuda H.,Kyoto University | Arai T.,Kyoto University | Sugano M.,High Energy Accelerator Research Organization | And 2 more authors.
Materials Transactions | Year: 2013

The influence of the volume fraction (Vf) of copper, plated at room temperature over a DyBa2Cu3O7-δ- coated conductor, on the tensile strain tolerance and stress tolerance of critical current at 77K was studied over a wide range of copper Vf values. The copper plating exerts a tensile stress during cooling because copper has a higher coefficient of thermal expansion than the substrate conductor. Before application of tensile strain, the copper plated at room temperature yielded at 77K when the copper Vf was lower than a critical value, and was in an elastic state at 77K when the copper Vf was higher than the critical value. The strain tolerance of critical current increased with increasing copper Vf due to an increase in thermally induced compressive strain in the substrate tape. The stress tolerance of critical current decreased with increasing copper Vf because copper is softer than the substrate tape. These results, together with the trade-off between strain tolerance and stress tolerance (i.e., stress tolerance decreases with increasing strain tolerance), were analyzed by modeling. The results show that the restriction imposed by the trade-off, which limits the ability to simultaneously obtain a high strain tolerance and a high stress tolerance, can be relaxed by strengthening the copper. © 2012 The Japan Institute of Metals. Source


Ochiai S.,Kyoto University | Okuda H.,Kyoto University | Sugano M.,High Energy Accelerator Research Organization | Osamura K.,Research Institute for Applied science | Prusseit W.,THEVA Dunnschichttechnik GmbH
IEEE Transactions on Applied Superconductivity | Year: 2012

This paper was carried out to reveal the influence of plated copper onto the substrate tape constituting of DyBa 2Cu 3O 7-δ, MgO, Ag, and Hastelloy C-276 on the stress-strain behavior, and tensile strain and stress tolerance of critical current at 77 K. From the analysis of the stress-strain relation of the copper-plated tape at 77 K, it was shown that the copper plated at room temperature is yielded in tension at 77 K due to the higher coefficient of the thermal expansion of copper than that of the substrate tape. The plated copper gave compressive strain to the substrate tape and, hence, the superconducting layer at 77 K, due to which the strain tolerance of critical current was improved. The observed improvement of the strain tolerance with increasing volume fraction of plated copper was quantitatively described from the viewpoint of the stress balance at 77 K between the substrate tape and yielded copper. The tolerant strain increased, but the tolerant stress decreased with increasing copper volume fraction. Such a tradeoff correlation between the tolerant strain and stress was well described by modeling analysis. © 2006 IEEE. Source


Ochiai S.,Kyoto University | Arai T.,Kyoto University | Toda A.,Kyoto University | Okuda H.,Kyoto University | And 3 more authors.
Journal of Applied Physics | Year: 2010

Influences of cracking of coating layer under applied tensile strain on V (voltage)-I (current) curve, critical current, and n -value of DyBa2 Cu3 O7-δ coated conductor were studied experimentally and analytically. The experimentally measured variations in V-I curve, critical current, and n -value with increasing applied strain and the correlation of n -value to critical current were described well by the partial crack-current shunting model of Fang Also, the variations in the ratio of shunting current to overall critical current and the ratio of voltage developed in the cracked region to overall voltage with extension of crack, and the variation in critical current with the ratio of noncracked area to overall cross-sectional area of superconducting layer were revealed. © 2010 American Institute of Physics. Source


Grosse V.,Institute For Festkorperphysik | Grosse V.,THEVA Dunnschichttechnik GmbH | Schmidl F.,Institute For Festkorperphysik | Seidel P.,Institute For Festkorperphysik
Applied Physics Letters | Year: 2012

We report on the study of the low temperature electronic transport in strontium titanate thin films having a thickness of 25-30 nm. I-V characteristics measured below 4.2 K show unique structures which are evidence for the occurrence of a Coulomb blockade. Simulations of the measured characteristics suggest that this behavior is closely related to the formation of nanoscopic metallic islands within an insulating matrix which arrange in a network connected via tunneling currents. © 2012 American Institute of Physics. Source

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