Modern and planned state-of-the-art particle accelerators employ hundreds or thousands of superconducting radio frequency (SRF) niobium cavities to increase the energy of charged particles. Maintaining the large electromagnetic fields inside cavities leads to dissipation, which can be minimized using superconductors enabling continuous wave (CW) operation and superior beam quality. This technology enables many applications of great socio economic impact such as accelerator driven systems (ADSs) for transmutation of nuclear waste and energy production or compact CW accelerators for gamma ray production to probe nuclear waste/fissionable materials. The current technology of choice is producing cavities from niobium sheets. Using micrometer thick films of superconductors with a higher critical temperature on copper, cavities can potentially yield cheaper production and a better performance in terms of accelerating gradient and cryogenic efficiency, leading to multi-million-pound cost reduction for large scale projects. Furthermore this technology is being explored for quantum computing.
While there has been some success with Nb3Sn this material is currently limited to accelerating gradients below 20MV/m due to premature flux penetration. This is less than 50% of what has been achieved with niobium. As an alternative approach A. Gurevich (APL 88.1 (2006): 012511) suggested to use multilayers of insulators and type-II superconductors on niobium to prevent early flux penetration. While it is a challenge to deposit such a structure on a curved large object, like a cavity, several proof-of-principle experiments can be performed on small flat samples which can be produced more easily.
In this PhD project it is anticipated to explore several physical mechanism of multilayers which can potentially yield a higher accelerating gradient than niobium technology. Samples will be prepared at Daresbury Laboratory and characterized by surface analytical tools such as atomic force microscopy, ion cross section SEM, energy-dispersive X-ray spectroscopy (EDX), X-ray photoemission spectroscopy (XPS) and electron backscatter diffraction (EBSD) at Daresbury Laboratory and the universities associated with the Cockcroft Institute. The shielding potential of the samples will be measured under cryovacuum conditions at Daresbury using a dedicated instrument. Additionally measurements probing the field penetration as a function of depth in the nanometer scale shall be carried out with muon spin rotation at PSI in Switzerland and with betaNMR at TRIUMF in Canada.
Qualifications applicants should have/expect to receive: The successful candidate will have or expect to obtain a first or upper second-class degree or equivalent (e.g. MPhys, MSci) in physics or engineering. Experience in superconductivity, cryogenics, thin film deposition or surface characterization is an asset.
Funding and eligibility:
The project is fully funded by the Science and Technology Facilities Council for 4 years. A full package of training and support will be provided by the Cockcroft Institute, and the student will take part in a vibrant accelerator research and education community of over 150 people.