Stability of the Hard Superconduductor in the Changing Magnetic Field plus Sperimposed Direct Magnetic Field

Abstract

To investigate the stability of the superconducting magnet placed in the changing magnetic field, some fundamental experiments have been carried out.
The behaviors of the persistent current flowing in the superconducting closed circuit have been examined in the sinusoidally alternating magnetic field at fixed frequency of 50c/s, plus superimposed direct magnetic field. The amplitudes of the alternating magnetic field and direct magnetic field were varied from 0KG to 3.5KG and from 0KG to 10KG, respectively. The samples were Cu (0.14mm in the thickness) clad Nb-Ti wire (0.27mm in the diameter). Under the good cooling condition, after the persistent current decreased to a certain degree according to the applied magnetic fields, they became stable and didn't decay any more. The relations for the dependence of this stable persistent current on the applied magnetic fields have been derived by using the Bean's model for the magnetic field distribution in the superconductor. The measurements can be well explained by this relations.
We will be able to predict the stable current flowing in the supercondctors placed in the changing magnetic field by considering the magnetic characteristics of the superconductors.