Trapped fields in tape-wound cylindrical superconducting magnets

Diamagnetic effects are most pronounced when shielding supercurrents have unimpeded paths over wide dimensions. Flat tape superconducting windings provide a good basis for study in that the shielding currents are large and calculable, and so are the resulting trapped fields at zero winding current. The investigation shows under what conditions it is necessary to allow for shielding currents, and how this may be done for maximum field calculations for magnets of cylindrical geometry. Field-dependence of critical current Jcis included in both maximum field and trapped field cases. Measurements of trapped fields on two tape-wound niobium-tin magnets are shown to be in reasonable agreement with calculations. The results have been presented mainly in the form of lines of B plotted by computer. These have been most revealing, both for the trapped field, and for the maximum field where they have been compared with field lines resulting when diamagnetism is neglected.