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Title: Numerical solution of critical state in superconductivity by finite element method
Author: Hong, Z.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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Bulk high temperature superconductors have increasing potential to be used in a number of devices including motors, levitated transportation, flywheels, cables, transformers and fault current limiters, etc. To optimize the design of such systems, it is necessary to predict their behaviours. The research presented in this thesis aims to fulfil this need by implementing a range of critical state models using finite element method in order to calculate field distributions, current densities, trapped magnetic fields and AC losses. A numerical solver of critical state is proposed which is based on a set of Maxwell’s equations using magnetic field as the known. The equations are used with E-J constitutive law and are incorporated with commercial finite element software to give fast and accurate solutions. Four case studies surrounding the application of using superconducting materials as wires and trapped field magnets are investigated. The phenomenon of MgB­2 wires carrying transport current is investigated in order to determine the AC loss in the wires. Two finite element models based on different assumptions are introduced to solve the AC losses in YBCO coated conductors both in self field and external field conditions. The crossed field effects on bulk high-temperature superconductors are studied. A bulk YBCO single domain is premagnetized with the applied field parallel to their shortest direction and then subjected to several cycles of the application of a transverse magnetic field parallel to the sample surface plane. The decay of magnetization is investigated both experimentally and numerically. The remagnetization process is studied by applying rotational field to a bulk YBCO which has been partially demagnetized by a transverse field. It is shown that all principal features of the experimental data can be reproduced quantitatively or qualitatively by using the model proposed in this thesis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available