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Flux Pumping for No-Insulation High Temperature Superconducting REBCO Magnets



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The high temperature superconducting (HTS) REBCO magnet has many advantages compared to the low temperature superconducting (LTS) magnet, including high operating temperature, high critical current under high magnetic fields, and strong mechanical properties. Due to these excellent properties, HTS REBCO magnets have huge potential in high-field high-current applications, such as accelerator magnets, tokamak fusion magnets, magnetic resonance imaging (MRI) systems, ultra-high-field magnets. It can pave the way for a more compact and economical superconducting magnet system, including. Currently, a novel no-insulation (NI) type HTS REBCO magnet has a self-protection ability, which has solved a long-lasting “thermal quench” problem. The self-protection ability has significantly improved the reliability of HTS REBCO magnets and makes the NI HTS REBCO magnet very advantageous in practical use.

However, lossless superconducting joints for HTS REBCO coated conductors are not available. To maintain a stable magnetic field for the HTS REBCO magnet, an external power supply is required via a bulky no-superconducting copper current leads. The copper current leads consume a huge amount of electricity and increase the size of the magnet system. In order to reduce energy loss and the size of the magnet system, flux pumping technology was invented, which is a contactless charging technology and removes the no-superconducting resistive current leads. Up to now, however, flux pumping technology only focuses on conventional insulated type HTS REBCO magnets. The novel NI HTS REBCO magnet has different characteristics from the conventional insulated HTS REBCO magnet, such as bypass current and characteristic resistance (Rc).

This thesis studies the flux pumping technology for the no-insulation type HTS REBCO magnet, figures out the technical challenges, and improves the flux pumping performance for NI HTS REBCO magnet with a very low Rc. Chapter 2 introduces the basic theory of superconductivity, the development of superconductors, and various superconducting applications. Chapter 3 reviews the flux pumping technology, including LTS and HTS flux pumps. Chapter 4 presents an active-switching HTS transformer rectifier flux pump (TRFP), including the fundamental physics, key components, and overall system. Chapter 5 presents the design and fabrication of the NI HTS REBCO magnet and proposed a novel solder impregnated NI HTS REBCO magnet. The characteristics of this novel NI HTS magnet are discussed. Chapter 6 studies the flux pumping performance of the HTS TRFP for different NI HTS REBCO magnets, analyses the unique flux pumping characteristics, and improves the flux pumping performance for NI REBCO magnet with a very low Rc. Chapter 7 designs high-performance switches for active-switching HTS TRFP via a multi-physics FEM COMSOL model.

This thesis will help promote the use of the flux pumping technology for the NI HTS REBCO magnets systems, and it will be of interest to physicists and engineers who want to build an energy-efficient, compact, and reliable superconducting magnet system.





Coombs, Tim


High-Temperature Superconductor (HTS), flux pump, superconducting magnets, no-insulation, wireless charging, dynamic resistance, multiphysics modelling, ReBCO coated conductor


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Cambridge Trust-CSC International Scholarship