An investigation of flux trapping in a superconducting tin sphere
McAshan, Michael Sanford
Houston, William V.
Master of Arts
Measurements have been made of magnetic dipole moments trapped in a superconducting tin sphere by transition at constant temperature and at constant field. These measurements were made by suspending the sphere in a torsion pendulum and observing the interaction of the grozen-in moment with a uniform magnetic field. The magnetic moment of the sphere was found to be the same roughly reproducible function of temperature for both types of transition, and it remained constant with time as long as the temperature was not changed. However, if the temperature was changed so as to make it possible, the moment would decrease toward the value given by this measured function. The angle between the direction at which the magnetic moment was trapped in the sphere and the direction of the applied magnetic field as also found to be a rough function of the temperature, the angle being greatest (about 45°) when the measured moment was smallest. The percentage of flux trapped was found to be constant (at about .05%) for low temperatures but to rise sharply near the critical temperature. Also noted near the critical temperature were some sort of electromagnetic losses in the superconducting sphere as evidenced by a greatly increased damping of the pendulum.