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Charles Gurnham

PGR Student


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PGR Student in the Department of Physics  


I completed a 4-year master’s degree in natural sciences (MSci MA) from the University of Cambridge in 2016, specialising in physics, with an experimental project on aluminium foams. In 2018, I qualified as a secondary school physics teacher (PGCE) at the University of Durham. I am now working on an experimental PhD under the supervision of Professor Damian Hampshire, Dr Mark Raine and Professor Del Atkinson. I am a member of the Department’s Superconductivity Group and the EPSRC Centre for Doctoral Training in the Science and Technology of Fusion Energy, based in York ( The CDT is a collaboration between 5 major UK universities: The University of York, University of Durham, University of Oxford, University of Liverpool and University of Manchester.


Rare-Earth Barium Copper Oxide (REBCO) High Temperature Superconductors (HTS) offer a number of advantages over more established Low Temperature Superconductors (LTS) such as Nb3Sn and NbTi. In addition to the higher critical temperature (Tc) of about 90 K, the upper critical field (Bc2) and critical current density (Jc) are much higher, particularly at low temperatures where superconductivity persists in magnetic fields well in excess of 100 T [1]. This high Bc2 makes REBCO valuable for high-field magnet systems. REBCO for current transport is typically manufactured as a Coated Conductor (CC), a quasi-single-crystal layer a few μm thick and up to a few km long, deposited on a sophisticated substrate which controls the grain alignment and provides mechanical support.

In a high-field magnet system, the conductor will be subject to large Lorentz forces, which will induce strains. The superconducting properties of REBCO are sensitive to strain, so improving our understanding of this will inform future magnet design and manufacturing process for CCs.

REBCO has an anisotropic crystal structure and CCs have well-controlled grain alignment, leading to anisotropy in the superconducting properties of a CC. This means that the current that can be carried by a cable depends on the orientation of the magnetic field and the orientation of the strain. My work focuses particularly on biaxial strain measurements of CCs, where we can measure the effect of strain orientation on the superconducting properties, and understanding the strain behaviour from crystallographic texture and microstructure.

Experimental Apparatus and Facilities

Bending beams (springboards) have previously been used to apply both compressive and tensile uniaxial strains to REBCO CCs along the direction of current flow [2]. A newly modified form of the bending beam is used to apply in-situ x-strain with an additional y-strain applied at room temperature. This gives us control over the 2D strain state and allows the strain-surface to be mapped.

The bending beam is attached to a bespoke probe which can be used in our world class, 15 T horizontal magnet system. Using the horizontal magnet system, we can investigate the angular dependence of JC. Critical currents are measured using a standard 4-terminal technique.

Key Results

Above: The effect of magnetic field angle on Jc at two different field strengths. At fields close to 0.3 T, there is an asymmetry on rotation of 180o due to an asymmetry in flux nucleation from surfaces.

Below: Calculated field and current distributions in a thin superconducting strip in the self-field limit for a Josephson junction model of Jc(B).

  • Measurements of strain effects on current flow with a component orthogonal to the ab-planes [1] to determine the role of the plane spacing and the inter-plane layer on the superconducting properties of REBCO.

Poster Presentations:

  • 15th European Conference on Applied Superconductivity, 5th - 10th September 2021, Virtual;
  • 14th European Conference on Applied Superconductivity, 1st - 5th September 2019, Glasgow, UK;
  • Culham PhD Showcase, 22nd – 23rd July 2019, Oxford, UK;
  • Frontiers of Fusion, 29th April – 3rd May 2019, York, UK.

[1] Sekitani T., Miura N., Ikeda S., Matsuda Y.H. and Shiohara Y, 2004, “Upper critical field for optimally-doped YBa2Cu3O7−δ”, Physica B 346-7 319-24

[2] Sunwong P., Higgins J.S. & Hampshire D.P., 2014. “Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet.” Rev. Sci. Instrum. 85(6) 065111

Research groups

  • Superconductivity