Transport-current–induced magnetic field profiles of Nb3Sn superconducting tape

Abstract
We have developed a new Mössbauer‐effect magnetic field microprobe and have used it and Hall probes to study the zero‐applied‐field large‐transport‐current‐density (3×106 A/cm2) magnetic field profiles of Nb3Sn superconducting tapes for TTc. Our data did not agree well with predictions of critical‐state models but did fit a model based on an elliptical approximation to the tape’s cross section with a current distribution having the property that where the field is zero the current density is also zero.