The effect of self field on the critical current determination of multifilamentary superconductors

Abstract

In determining the short sample critical current of conductors of large cross section or high current density (he self field produced by the transport current must be taken account in order to obtain a "true value" for the critical current. A simple model calculation for determining this effect is described. Measurements on wires, cables, and monoliths show the validity and self consistency of the procedures.

Critical Current in High-J$ _{\rm c}$ Nb$_{3}$Sn Rutherford Cables Affected Substantially by the Direction of the Applied Magnetic Field

“…1). This would result in a different performance depending on whether the peak field is located in a more degraded part of the cable or in a less degraded part of the cable, as was previously shown for Nb-Ti in [2]. Here it will be demonstrated that in experiments performed on recent high-Nb Sn conductors comparable results are found.…”

“…It is assumed that the magnetic field induced by the coil shape of the sample can be ignored and that the peak magnetic field can be approximated by an infinitely long wire in a homogenous applied magnetic field. The peak magnetic field is now found on the edge of the strand at the point where the self field around the strand points in the same direction as the applied magnetic field [2]. This results in a simplified equation of (1): (2) where is the applied magnetic field, is the current in the strand and is radius of the filamentary zone in the strand cross section.…”

“…The peak magnetic field is now found on the edge of the strand at the point where the self field around the strand points in the same direction as the applied magnetic field [2]. This results in a simplified equation of (1): (2) where is the applied magnetic field, is the current in the strand and is radius of the filamentary zone in the strand cross section. It is known [3] that this is not completely correct, but the approximation suffices.…”

Thermo-magnetic instabilities in Nb₃Sn superconducting accelerator magnets

“…I c itself is obtained by integrating different critical current densities along the cross section of the strand. Although naturally one would pick the average field value of the strand, it has been shown [103] that the relevant field value to apply, which works for the parameterization described in the previous paragraph, is the peak field value.…”

Stability measurements on cored cables in normal and superfluid helium

“…Following the usual convention, I, is defined at an effective resistivity of a -m where the area is taken as the total strand cross-section in the cable.) In this determination, the self-field produced by the high currents in the cable has to be taken into account in determining the field at various points in the cable cross-section [7]. As with I, meashrements, the MQE of a conductor at a given field and current depends on the cable orientation relative to the applied field.…”