Guided flux motion: models and experiment

TL;DR

This paper reviews models of guided flux motion in superconductors, compares their predictions with experiments on Nb-Ti tapes, and discusses how vortex behavior changes with driving force and pinning effects.

Contribution

It provides a comparative analysis of three models of flux guiding, validated by experiments on Nb-Ti superconducting tapes, highlighting the transition from plastic to elastic vortex motion.

Findings

The anisotropic pinning model semi-quantitatively predicts guiding angles.

Guiding angle varies along the sample at the critical electric field.

Vortex motion transitions from plastic to elastic mode with increased driving force.

Abstract

The article provides a brief overview of existing models describing guided flux motion. The first model was proposed by Niessen et al. This model works in the single-vortex approximation and provides qualitative explanation of the effect, but in most cases it gives an overestimated guiding angle. The stochastic model explains the experimentally observed effect of decreasing the guiding angle, the so-called slipping effect, by the influence of thermal fluctuations. However, the performed estimates show that thermal fluctuations should not be so significant. An alternative guiding model is the anisotropic pinning model. This model works in the critical state approximation, and the slipping effect is the result of the combined action of anisotropic pinning and vortex interaction. The predictions of all three models are verified by the example of a superconducting Nb-Ti tape containing about 6 vol. % {/alpha}-Ti, which acts as strong pinning centers. Cutting samples at different angles to rolling allows one to control the direction of the driving force. It was found that when the standard criterion of the electric field is reached, the guiding angle varies significantly at different places along the sample, which is explained by the plastic mode of the vortex matter motion. In this case, the anisotropic pinning model semi-quantitatively predicts the direction angle averaged over the sample length. With an increase in the driving force, the vortex matter motion passes into an elastic mode, and the guiding angle becomes uniform along the sample.