The onset of dissipation in high-temperature superconductors: magnetic hysteresis and field dependence

Ae Pantoja,Ef Talantsev,James Storey,Jeffery Tallon,Justin Brooks,Nicholas Strickland,Rodney Badcock,Stuart Wimbush

doi:10.26686/wgtn.13175075.v1

Abstract

© 2018, The Author(s). Recently, we showed that the self-field transport critical current, Ic(sf), of a superconducting wire can be defined in a more fundamental way than the conventional (and arbitrary) electric field criterion, Ec = 1 μV/cm. We defined Ic(sf) as the threshold current, Ic,B, at which the perpendicular component of the local magnetic flux density, B⊥, measured at any point on the surface of a high-temperature superconducting tape abruptly crosses over from a non-linear to a linear dependence with increasing transport current. This effect results from the current distribution across the tape width progressively transitioning from non-uniform to uniform. The completion of this progressive transition was found to be singular. It coincides with the first discernible onset of dissipation and immediately precedes the formation of a measureable electric field. Here, we show that the same Ic,B definition of critical currents applies in the presence of an external applied magnetic field, Ba. In all experimental data presented here Ic,B is found to be significantly (10–30%) lower than Ic,E determined by the common electric field criterion of Ec = 1 µV/cm, and Ec to be up to 50 times lower at Ic,B than at Ic,E.

Highlights

We showed that the self-field transport critical current, Ic(sf), of a superconducting wire can be defined in a more fundamental way than the conventional electric field criterion, Ec = 1 μV/cm
In attempting to resolve this problem, recently[7,8] we showed that the definition of the dissipation-free critical current under self-field conditions, Ic(sf) can be arrived at in a more fundamental way, based not on a continuous onset of dissipation with an arbitrary threshold, but on an abrupt physical effect which we identified in high-temperature superconducting (HTS) tapes by measuring and analyzing the perpendicular component of the magnetic flux density, B⊥(x), generated across the surface of the conductor by the transport current
And 3 we present experimental results for SuNAM 2 G wire for which the Hall sensor array was centred at the position d = −0.5 mm. In this position all six Hall sensors are located inside the tape width, with sensor 1 located at a distance of 0.25 mm from the left edge of the wire

Summary

Introduction

In attempting to resolve this problem, recently[7,8] we showed that the definition of the dissipation-free critical current under self-field conditions, Ic(sf) (when no external magnetic field is applied) can be arrived at in a more fundamental way, based not on a continuous onset of dissipation with an arbitrary threshold, but on an abrupt physical effect which we identified in high-temperature superconducting (HTS) tapes by measuring and analyzing the perpendicular component of the magnetic flux density, B⊥(x), generated across the surface of the conductor by the transport current. The voltage taps for measuring critical current were positioned along the tapes approximately 12 cm apart, with a Hall sensor array placed half way between the two voltage taps, spanning the width of the conductor.

Results

Conclusion