Distribution of shielding currents in a cylindrical superconducting tube

Superconductive cylindrical tubes can be used to shield out magnetic flux for high energy physics use. The shielding currents in the tube are found based on a physical model. The model is based on the principle that the flux linked by a superconducting loop must be conserved. For a finite cylindrical superconducting tube, the axial distribution of shielding currents for a given shielded magnetic field is determined, which agrees with experiment. Some facts are found, that is, first, the external shielded magnetic field can partly penetrate into the bore at the two ends of a finite superconducting tube where Icis first reached; second, the shielding currents in the end region are about the same for different aspect ratio tubes; third, if the radii of the tube are properly reduced from the middle to the ends then the shielding currents can become uniformly distributed. These analytic results agree generally with experiment.