ENGINEERING SUPERCONDUCTING SURFACES FOR PARTICLE ACCELERATORS AND QUANTUM DEVICES
This project will establish atomic layer deposition (ALD) as a versatile surface engineering approach for superconducting resonators, addressing two complementary objectives for particle accelerators and quantum technologies.
The first objective is controlled doping of bulk niobium superconducting radiofrequency (SRF) cavities. Conformal films up to 10 nm thick will provide solid dopant sources, followed by high-vacuum annealing to tailor dopant profiles within the RF-active region. This strategy aims to improve uniformity, explore alternative dopants and eliminate subsequent electropolishing. Particular attention will focus on suppressing hydride formation while preserving the superconducting energy gap. Target performances include quality factors of 8 × 10¹° at 2 K and accelerating gradients of 40–45 MV/m. Supported by the European EPITA project, this work addresses requirements for future accelerators, including the Future Circular Collider.
The second objective is developing protective coatings with minimal dielectric losses by mitigating defects, particularly two-level systems. Building on CEA treatments combining dielectric oxide coatings and annealing that achieved record quantum-regime quality factors, alternative compounds will be investigated.
Ultimately, one treatment could enhance performance across quantum and accelerator operating regimes. Tunneling spectroscopy, X-ray spectroscopy and TOF-SIMS will correlate local superconducting properties with surface chemistry and dopant distributions. Two ALD systems will support development on coupons and transfer to resonators, building on demonstrated coating uniformity inside cavities. RF measurements will be conducted at CEA and partner laboratories, with Fermilab evaluating promising treatments at millikelvin temperatures. These investigations will clarify performance-limiting mechanisms and guide the rational design of optimized superconducting surfaces for both application domains.
In-depth understanding of the dedensification phenomenon during MOX sintering and during a pseudo-thermal stability test
MOX (mixed uranium and plutonium oxide) is a civil nuclear fuel. It comes in the form of cylindrical pellets with a diameter and height of approximately 10 mm. It is produced using a process that includes a high-temperature sintering step in a controlled atmosphere. During the sintering of MOX fuel pellets—formed via uniaxial pressing from a previously prepared granular feedstock—a phenomenon of dedensification resulting in swelling may occur under certain conditions. This swelling can persist during thermal stability tests intended to simulate specific in-reactor irradiation conditions.
The aim of this thesis is to identify the physicochemical mechanisms underlying this dedensification phenomenon and to formulate them mathematically in order to develop a model.
The thesis therefore includes an experimental component—to be conducted at Cadarache (using UO2) and Marcoule (using MOX)—to provide data for the model, which will be mathematically formulated during a theoretical phase carried out in collaboration with modelers at Cadarache.
Accelerated design of High Entropy Oxide thin films for carbon-free energies
Over the past decade, high-entropy oxides have emerged as a promising new class of materials for energy-related applications and corrosion resistance in extreme environments, both of which are central areas of CEA's activities.
However, their optimization remains limited by the vast compositional space that needs to be explored, leading most studies to focus on equimolar compositions.
This PhD project aims to overcome this limitation by combining combinatorial PVD using HiPIMS technology with artificial intelligence approaches based on Bayesian optimization, an approach that has not yet been explored for these materials.
The objective is to master the deposition of high-entropy oxides and optimize their properties for corrosion protection in high-temperature electrolyzers dedicated to low-carbon hydrogen production.
The deposited coatings will exhibit controlled stoichiometry, structure, microstructure, and texture, and will be characterized both in situ and ex situ using complementary techniques.
The project will provide a proof of concept for coupling combinatorial PVD with Bayesian optimization to accelerate the discovery and optimization of new materials.
This PhD project is part of the international doctoral programme of PEPR DIADEM and will bring together CEA (Saclay), ESRF (Grenoble), and NIMS (Japan).