Simulations of magnetic properties of short superconducting cylinders and coils

Younas, Irfan (1997) Simulations of magnetic properties of short superconducting cylinders and coils. University of Southampton, Doctoral Thesis.

Abstract

This thesis presents an investigation into the magnetic properties of short cylindrical type II superconductors. Further to this problem, a preliminary simulation of a superconducting magnetic separator was undertaken using a high-T_c superconducting coil to energise an iron circuit. A configuration of the iron circuit together with an optimum position for the coil was determined. The results suggest that a magnetic separator using high-T_c coils can be built with present day technology.

A number of simulations have been carried out to determine the currents and fields within short cylindrical type II superconductors in the remnant state using the critical state model where the current is assumed field dependent. The aspect ratio of the cylinder has been varied from the short cylinder to the thin disc limit and important current and field profiles have been discovered explaining the remnant state of type II superconductors, where the demagnetising field has also been accounted for by reaching a self-consistent relation between the current and the local magnetic field. Results on extensive simulations of short cylindrical type II superconductors are also presented where the conductor is immersed in a uniform slowly time-varying applied magnetic field. A fundamental approach of energy minimisation has been applied to determine the position of the flux front as a function of the applied magnetic field. This method allows hysteresis loops to be determined, from which errors in the critical current can be estimated when using the Bean model to interpret the magnetisation. The simulations have been extended to cover the dependence of the flux front on the cylinder aspect ratio.

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