2015 Volume 56 Issue 9 Pages 1558-1564
We have determined experimentally that the n-value of tension-damaged bismuth strontium calcium copper oxide (BSCCO, Bi2223) filamentary superconducting tape decreases very sharply with decreasing critical current, compared with bending-damaged tape. In this work, the sharp decrease in the n-value associated with decreasing critical current under applied tensile stress/strain was studied with a current shunting model that assumes cracks in filamentary and coated superconductors. In a filamentary conductor containing collective filament cracks, defined as cracks composed of successively cracked filaments in a transverse cross-section, the decrease in the cross-sectional area of the superconducting current transportable-filaments reduces the critical current, and the shunting current at the crack reduces the n-value. In addition, the decrease in the electrical resistance in the current shunting circuit increases the critical current slightly and decreases the n-value sharply. The experimentally measured relationship between the n-value and the critical current for two BSCCO samples from different manufacturers was described by the upper and lower bounds calculated with the current shunting circuit resistance as a variable. The experimentally measured relationship between the n-value and the critical current for two different coated conductors were described in a similar manner.
