Superconducting thin film coated radio-frequency cavities

About the project

About the Project Project Background The superconducting radio-frequency (SRF) cavities made of bulk niobium (Nb) are used in charged particle accelerators for more than 50 years. They exhibit a million times lower power dissipation than ones made of copper, and allow to accelerate charges particle with high acceleration field up to ~50 MV/m. However, the cost of Nb and liquid helium required for operation are increasing over recent years dramatically, and the performance of the Nb cavities reached the limitation in Nb physics properties. A way to improve is to employ copper (Cu) cavities coated with superconducting thin films (TF). Cu is a material with lower cost and higher thermal conductivity than Nb. The most promising TF materials are Nb3Sn, NbTiN, V3Si, …, that have higher super-conducting parameters such as critical temperature (Tc), critical magnetic field (Bc), etc. Further improvement can be achieved by employing multilayer structures of superconducting and insulating layers. Applying this technology should allow accelerators to reduce their operating power by a factor of 2 and/or increase the gradient to up to 100 MV/m in CW or long pulse machines. To facilitate this TF-SRF technology, the CI collaborating multidisciplinary team of ASTeC, Lancaster University and now Manchester is focused on the following technologies: copper cavity surface polishing, material science development (TF deposition and characterisation), superconducting property evaluation of deposited TF and, finally, an RF testing at cryogenic conditions. In Aug. 2025 this team, for a first time in the world, the bulk Nb cavity was coated with Nb3Sn thin film and send to HZB for RF testing (in a frame of IFAST collaboration). This has placed Cockcroft in a world leading position at the forefront of sustainable RF research. Daresbury Laboratory (DL), home for CI, is a unique place where all these technologies are developed in present, and the only one in UK. Only a few places worldwide have integrated deposition teams, surface/RF characterisation and SRF integration all in one institute. A key aspect of our approach is a suite of novel characterisation facilities with fast sample turn around allowing CI to optimise key deposition parameters in a few weeks that would take other groups years. This team has the leading role of thin film SRF workpackages in international projects such as ARIES (2017-2021), IFAST (2021-2025), iSAS (2023-2027), EPITA (2025-2029). Aim of project to develop all technologies for producing TF SRF cavities and test them at real accelerator conditions at DL, e.g.: CLARA beam loaded test. While thin-film Nb cavities are now fairly common, a beam test of a novel material TF cavity would be a major leap forward in development of these systems further cementing the CI team as a trailblazer in this critical technology. A long-term ambition of this project are producing acceleration structures for UK-XFEL, ISIS-II, participating in the international projects, e.g.: FCC, ILC, etc. Superconducting RF cavities: coating and characterisation Aim The aim is to develop the coating technology of superconducting materials with Tc higher than one of Nb and apply it for coating on the RF cavities. An ultimate aim is to produce SC cavities with Q(E) better or (at least) near than bulk ones. A major challenge in coating materials such as Nb3Sn compared to Nb is the need to ensure the material has the correct stoichiometry and phase, and that the superconducting properties are not modified by stress. There are also issues with thermoelectric currents running between the two materials during cooldown requiring buffer layers to prevent. Multilayers can also act as shielding layers using a nm scale film to sustain much higher surface currents. Getting the correct coating recipe and buffers will require detailed optimisation using a wide variety of characterisation techniques to understand how the parameters effect the operation of the cavity. Objectives This study requires a systematic study of coating parameters of superconducting metals (ex. Nb3Sn, NbTiN, and others) in a single or multilayer structure deposited on copper and bulk Nb substrates. The obtained result then should be applied to produce SC cavities. Ideally we should obtain Nb level gradients (50 MV/m) at temperatures 4.2K or higher using novel materials and gradients above Nb (80 MV/m) using multi-layer approaches. Proposed Scheme of Work Initially student will be introduced to existing deposition facilities and study basics of TF deposition on planar samples, and characterise them with surface characterisation facilities available in VISTA laboratory and through collaborating institution. Then he/she will be involved in designing, building and operation of cavity deposition with Nb3Sn, NbTiN, V3Si and other materials. The student will be responsible for: 1) Familiarisation with different type deposition methods: a. Knowledge of vacuum b. Physical vapour deposition c. Atomic layer deposition d. Deposition on 2 D surfaces and internal surfaces of 3D geometry cavity. 2) Thin film characterisation: a. Surface and depth characterisation techniques (XPS, RBS, EDAX, SEM, XRD, TEM, SIMS) b. Superconducting characterisation techniques (AC and DC superconductivity parameters such as Tc, Hc, RRR existing, surface resistance, and superconductive band gap. 3) Understanding for the film characterisation results are affected by deposition parameters and utilise this to feedback and optimise the deposition process. 4) Data analysis and participation in discussions, meetings and scientific events. Also, all PhD students attend a standard CI 2-year course of lectures on all aspects of charge particle accelerators. Funding and eligibility: Upon acceptance of a student, this project will be funded by the Science and Technology Facilities Council for 3.5 years. This consists of a tax free stipend at UKRI rates, university fees at the home (UK) rate, plus support for travel to conferences and workshops. 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. Contact for further information: Prof. Graeme Burt g.burt1@lancaster.ac.uk How to apply: Apply at the Cockcroft Institute PhD webpage . For full consideration for funded awards, please apply by Jan 31st 2026. Anticipated Start Date: October 2026 for 3.5 Years

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