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Modelling nonlinear effects in high temperature superconducting magnets

Research output: Book/ReportDoctoral thesisCollection of Articles


Original languageEnglish
PublisherTampere University
ISBN (Electronic)978-952-03-1419-4
ISBN (Print)978-952-03-1418-7
Publication statusPublished - 10 Jan 2020
Publication typeG5 Doctoral dissertation (article)

Publication series

NameTampere University Dissertations
ISSN (Print)2489-9860
ISSN (Electronic)2490-0028


In the future particle colliders, the accelerator magnets keeping the particles on their tracks are required to produce magnetic fields above 20 T. This can be achieved only by using high temperature superconductors. The technology for producing the high temperature superconducting (HTS) conductors is relatively new and only recently the number of HTS conductor manufacturers has started to increase. It was only in 2016, when a 10 kA class Roebel cable made of REBCO tapes was tested in a small study coil, Feather-M0. Followed by that, in 2017 the first Roebel cable based 5 T accelerator magnet prototype Feather-M2 was constructed and tested to examine the prospects of HTS REBCO technology in accelerator magnets. The measurement results suggested that there is still a lot to learn in modelling those magnets.

This thesis begins by introducing the readers to the mathematical and physical background for understanding the research presented in the attached publications. The background is followed by the chapters reviewing and synthetizing the publications. The focus in this thesis is on the AC loss modelling and thermal stability modelling. First, AC losses and magnetic field quality are modelled in Feather-M0 using a self-implemented minimum magnetic energy variation principle based simulation tool. Then, the focus is moved on the thermal stability modelling of HTS magnets by formulating the thermal model utlized in this thesis work. Next, the thermal model is utilized for scrutinizing the behavior of Feather-M2 with an inverse problem based modelling approach. Using the Feather-M2 measurement data, the inverse problem solutions are obtained for the thermal model parameters characterizing the magnet in terms of the thermal model. Furthermore, the thermal model is utilized and an optimization problem is formulated in order to determine the maximum stable operation current of Feather-M2. Finally, an energy-extraction system (EES) design for 20 T range magnet is presented and optimized by formulating and solving an optimization problem.