Fluxoid Conservation by Superconducting Thin Film Rings

Citation

Hunt, Thomas Kintzing (1964) Fluxoid Conservation by Superconducting Thin Film Rings. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1DEJ-RD23. https://resolver.caltech.edu/CaltechETD:etd-09202002-142839

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. A torque method for measuring the persistent current in superconducting rings has been used to investigate the conservation of the fluxoid originally predicted by F. London. The fluxoid through a superconducting ring is the action integral of the canonical angular momentum of the superconducting electrons taken around the ring. This is comprised of two parts, one describing the mechanical angular momentum of the electrons and the other describing the magnetic flux trapped by the ring. The mechanical angular momentum depends on the penetration depth ([lambda]) and therefore on temperature. If the fluxoid is conserved, temperature variations should alter the balance between the mechanical and electromagnetic angular momenta. As a consequence, the amount of trapped flux, and hence the persistent current, should vary with temperature even though the ring remains at all times entirely within the pure superconducting state with zero resistance. Very thin films of tin have shown experimentally a decrease in persistent current with increasing temperature and an increase with decreasing temperature which agrees with that to be expected on the basis of the fluxoid conservation predicted by London.

Thesis Files