Longitudinal Magnetic Field Effect in Superconductors

Characteristic electromagnetic phenomena called longitudinal magnetic field effect are observed for a current-carrying superconductor in a parallel magnetic field. These phenomena and the mechanism of the longitudinal magnetic field effect are generally discussed from the viewpoint of flux motion in this article. This effect includes a significant enhancement of the critical current density from that in the transverse magnetic field, a deviation from Josephson's relation E= B×v for the induced electric field (B and v are the magnetic flux density and the velocity of flux lines), negative electric field in the resistive state, etc. These are attributed to the force-free torque to reduce the rotational shear in flux lines that appears in the force-free configuration and the resultant rotational flux motion. This is analogous to the electromagnetic phenomena in the transverse magnetic field in which the Lorentz force causes the flux motion. The similarity and difference of electromagnetic phenomena are discussed between the transverse and longitudinal magnetic field configurations.

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