Plasma Mirrors Towards Extreme Intensity Light Sources and High-Quality Compact Electron Accelerators
The research programs conducted at the Lasers Interactions and Dynamics Laboratory of the French Atomic Energy Commission (CEA) aim to understand the fundamental processes involved in light-matter interactions and their applications. As part of the CEA-LIDYL, the Physics at High Intensity (PHI) group conducts studies of laser-matter interactions at extreme intensities, for which matter turns into an ultra-relativistic plasma. Using theory, simulations and experiments, researchers develop and test new concepts to control the laser-plasma interaction with the aim to produce novel relativistic electron and X-UV attosecond light sources, with potential applications to fundamental research, medicine and industry.
In collaboration with the Lawrence Berkeley National Laboratory, the group is a core developer of the exascale Particle-In-Cell (PIC) codes WarpX/PICSAR for the high-fidelity modelling of laser-matter interactions. It also pioneered the study and control of remarkable optical components called ‘plasma mirrors’, which can be obtained upon focusing a high-power laser with high-contrast on an initially solid target. In the past five years, the PHI group has developed two concepts exploiting plasma mirrors to manipulate extreme light for pushing the frontiers of high-field science. The first concept uses relativistic plasma mirrors to amplify the intensity of existing lasers by orders of magnitude and probe novel regimes of Strong-Field Quantum Electrodynamics (SF-QED). The second uses plasma mirrors as high-charge injectors to level up the charge produced in laser-plasma accelerators (LPAs) to enable their use for medical studies, industrial applications and fundamental research (collider design, electron-laser collisions for SF-QED studies).
In this context, the PhD candidate will first improve our simulation tool WarpX to speed-up plasma mirror simulations. They will then use WarpX to optimize the use of plasma mirrors as intensity boosters for the study of SF-QED. In collaboration with Brigitte Cros's team at CNRS and within the framework of novel collider designs based on Laser-Plasma Accelerators (LPAs), the PhD candidate will finally investigate and optimize the use of plasma mirrors as optical components for the coupling of multiple LPA stages. This will be crucial for developing compact acceleration schemes that can be scaled to produce high-energy, high-quality electron beams.
VHEE Radiotherapy with Electron Beams from a Laser-Plasma Accelerator
The research programs conducted at the Lasers Interations and Dynamics Laboratory of the French Atomic Energy Commission (CEA) aim to understand the fundamental processes involved in light-matter interactions and their applications. As part of the CEA-LIDYL, the Physics at High Intensity (PHI) group conducts studies of laser-matter interactions at extreme intensities, for which matter turns into an ultra-relativistic plasma. Using theory, simulations and experiments, researchers develop and test new concepts to control the laser-plasma interaction with the aim of producing novel relativistic electron and X-UV attosecond light sources, with potential applications to fundamental research, medicine and industry.
In collaboration with the Lawrence Berkeley National Laboratory, the group strongly contributes to the development of the code WarpX used for the high-fidelity modelling of laser-maIer interactuons. It also pioneered the study and control of remarkable optical components called ‘plasma mirrors’, which can be obtained by focusing a high-power laser with high contrast on an initially solid target. In the past five years, the PHI group has developed core concepts exploiting plasma mirrors to manipulate extreme light for pushing the frontiers of high-field Science. One of these concepts uses plasma mirrors as high-charge injectors to level up the charge produced in laser-plasma accelerators (LPAs) to enable their use for medical studies such very high energy electrons (VHEE) radiotherapy. This concept is being implemented at CEA on the UHI100 100 TW laser facility in 2025 to deliver 100 MeV - 200 MeV electron beams with 100 pC charge/bunch for the study of high-dose rate deposition of VHEE electrons on biological samples.
In this context, the PhD candidate will use our simulation tool WarpX to optimize the properties of the electron beam produced by LPAs for VHEE studies (electron beam quality and final energy). He/She will then study how the LPA electron beam deposits its energy in water samples (as biological medium) using Geant4. This will help assessing dose deposition at ultra-high dose rate and develop novel dosimetry techniques for VHEE LPA electron beams. Finally, the Reactive Oxygen Species (ROS) production and fate in water will be studied using the Geant4-DNA toolkit. This module has mainly data tabulated at electron energies below 10 MeV and will therefore require measures cross-section of water-ionization processes from experiments at 100 MeV. This will be performed on the UHI100 100 TW laser by the DICO group of the CEA-LIDYL, in collaboration with the PHI group.
Towards strong coupling between a single spin and a superconducting resonator via magnetic mode hyper-focusing
Magnetic resonance is a non-invasive tool that plays a central role in a wide range of fi elds, from medical imaging (MRI) to analyticalchemistry, and more recently in quantum computing, where it is used to control and read spin-based qubits. However, this techniquesuff ers from low sensitivity, requiring the collective response of a large number of spins to produce a detectable signal. Recent advancesin superconducting quantum technologies have dramatically improved this sensitivity—by more than ten orders of magnitude—bycombining the Purcell eff ect with novel detectors such as microwave photon counters.
This project builds on these breakthroughs by developing an innovative superconducting platform for the fast and effi cient readout of
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single electron spins, based on enhancing the spin-resonator coupling through magnetic mode hyper-focusing.
Using a specially designed parallel-plate capacitor geometry, featuring a central nanowire, the magnetic fi eld of the microwave mode canbe concentrated within a region of just a few hundred nanometers. This signifi cantly increases the local interaction between the fi eld andthe electron spin located just beneath the nanowire. The central objective of the project is to boost the Purcell factor by two orders ofmagnitude, from 10¹³ to 10¹5, in order to drastically reduce spin detection time and potentially reach the strong coupling regime at thelevel of a single spin.
In a first phase, the project will focus on Er³? ions implanted in crystals such as CaWO4, Y2SiO5, or directly in silicon, with the aim ofintegrating them into hybrid quantum computing architectures combining superconducting circuits and spin-based quantum memories.In a second phase, the platform will be extended to more realistic paramagnetic systems, such as organic radicals or metallic centers inproteins, paving the way for quantum spectroscopy of complex molecular compounds, well beyond the scope of current model systems.
Building on the expertise of the Quantronics group at CEA Saclay in superconducting circuits, nanofabrication, cryogenics, andmicrowave single-photon detection, the project will provide the PhD student with comprehensive training at the intersection ofexperimental physics, nanoscience, and quantum information, within a world-class research environment.
Evaluation of nanoscale surface coatings on high energy density positive electrodes for lithium-ion batteries.
Nickel-rich layered oxides LiNi1-x-yMnxCoyO2 (NMC) and LiNi1-x-yCoyAlzO2 (NCA) are exceptional materials for the positive electrode of lithium batteries due to their high reversible storage capacity. However, under real conditions, undesired reactions can lead to the dissolution of transition metals and electrodes cracking, thus affecting their electrochemical properties. This phenomenon is linked to the presence of hydrofluoric acid (HF) in the electrolyte, mainly due to the degradation of the LiPF6 salt. To address this problem, surface treatments are needed to protect the active material and improve performance. The EVEREST project proposes an innovative, flexible, and affordable method for creating inorganic coatings at the nanoscale. This method is based on a recent technique, coaxial electrospinning, which allows the production of nanofibers with a well-defined core-sheath structure. For this project, we propose to evaluate the impact of nanofiber shaping parameters on morphology, electrochemical performance and the underlying mechanism. The electrochemical performances of the coated and the pristine positive electrodes will be compared in a half-cell with Li metal as a counter electrode. Redox processes, charge transfer mechanisms and structural modifications will be studied in the operando mode using the synchrotron radiation beam.
Ultrafast spin currents and ferroic oxides
This PhD thesis lies at the intersection of ultrafast spintronics and the physics of spin currents on sub-picosecond timescales. Pure spin currents are currently attracting considerable attention due to their central role in the development of next-generation spintronic devices. As data consumption continues to grow exponentially, information and communication technologies must process increasingly large volumes at higher speeds, all while minimizing energy consumption. In this context, ultrafast information processing has become a major challenge.
Pure spin currents offer several decisive advantages: in addition to their dissipationless propagation, they can now be generated, transmitted, and detected on timescales of just a few hundred femtoseconds. This progress paves the way for the emergence of ultrafast spintronic components and devices operating in the terahertz range.
The aim of this thesis project is to investigate the fundamental mechanisms governing the generation and propagation of pure spin currents on picosecond and sub-picosecond timescales, with a particular focus on ferroic oxides. These materials exhibit a wide range of remarkable and tunable properties, making them ideal candidates for enabling ultrafast spin current functionalities and addressing the societal challenges of tomorrow.
The core of this thesis work will involve the implementation of time-resolved optical and magneto-optical techniques to probe the ultrafast magnetic dynamics in epitaxial thin films of ferromagnetic and antiferromagnetic oxides. The main expected outcomes include overcoming key bottlenecks: on one hand, the tunability of ultrafast spin current generation through the half-metallicity of selected ferromagnetic oxides; and on the other hand, the control of spin information propagation at terahertz frequencies in antiferromagnetic oxides.
Custom synthesis of diamond nanoparticles for photocatalytic hydrogen production
Diamond nanoparticles (nanodiamonds) are used in nanomedicine, quantum technologies, lubricants and advanced composites [1-2]. Our recent results show that nanodiamond can also act as a photocatalyst, enabling the production of hydrogen under solar illumination [3]. Despite its wide band gap, its band structure is adaptable according to its nature and surface chemistry [4]. Moreover, the controlled incorporation of dopants or sp2 carbon leads to the generation of additional bandgap states that enhance the absorption of visible light, as shown in a recent study involving our group [5]. The photocatalytic performance of nanodiamonds is therefore highly dependent on their size, shape and concentration of chemical impurities. It is therefore essential to develop a "tailor-made" nanodiamond synthesis method, in which these different parameters can be finely controlled, in order to provide a supply of "controlled" nanodiamonds, which is currently lacking.
This PhD aims to develop a bottom-up approach to grow nanodiamond using a sacrificial template (silica beads) to which diamond seeds < 10 nm are attached by electrostatic interaction. The growth of diamond nanoparticles from these seeds will be achieved by microwave-enhanced chemical vapor deposition (MPCVD) using a homemade rotating reactor available at CEA NIMBE. After growth, the CVD-NDs will be collected after dissolution of the sacrificial pattern. Preliminary experiments have demonstrated the feasibility of this approach with the synthesis of faceted <100 nm nanodiamonds (so called CVD-ND), as shown in the scanning electron microscopy image.
During the PhD work, the nature of the diamond seeds (ultra-small NDs [size ˜ 5 nm] synthesized by detonation or HPHT, or molecular derivatives of adamantane) as well as CVD growth parameters will be studied to achieve better controlled CVD-NDs in terms of crystallinity and morphology. Nanodiamonds doped with boron or nitrogen will be also considered, playing on the gas phase composition. The crystalline structure, morphology and surface chemistry will be studied at CEA NIMBE using SEM, X-ray diffraction and Raman, infrared and photoelectron spectroscopies. A detailed analysis of the crystallographic structure and structural defects will be carried out by high-resolution transmission electron microscopy (collaboration). CVD FNDs will then be exposed to gas-phase treatments (air, hydrogen) to modulate their surface chemistry and stabilize them in water. The photocatalytic performance for hydrogen production under visible light of these different CVD-NDs will be evaluated and compared using the photocatalytic reactor recently installed at CEA NIMBE.
References
[1] Nunn et al., Current Opinion in Solid State and Materials Science, 21 (2017) 1.
[2] Wu et al., Angew. Chem. Int. Ed. 55 (2016) 6586.
[3] Marchal et al., Adv. Energy Sustainability Res., 2300260 (2023) 1-8.
[4] Miliaieva et al., Nanoscale Adv. 5 (2023) 4402.
[5] Buchner et al., Nanoscale 14 (2022) 17188.
Hemoglobin S polymerization and diffusion in different hemoglobin mixtures HbYxHbS(1-x) with Y=At, A0, F…
Sickle cell disease (SCD) is a genetic disorder of the blood, causing anemia. It results from the polymerization of a mutated hemoglobin HbS, the oxygen-carrying protein found in red blood cells (RBCs), which causes the soft cells to deform into a rigid sickle shape under certain circumstances. Because the deformed cells induced by the polymerization will clog the blood capillaries, it induces an increase in blood pressure and ultimately degeneration of the various organs. Pharmacological treatments for sickle cell anemia include hydroxyurea, a molecule that promotes the synthesis of fetal hemoglobin (HbF) which leads to a mixture of hemoglobin HbFxHbS(1-x) in the blood, with HbF partially inhibiting polymerization of HbS. Gene therapy is also used for the treatment of this disease by stimulating the production of therapeutic hemoglobin (HbAt), or normal hemoglobin (HbA0). In collaboration with the Department of Genetic Diseases of the Red Blood Cell at Henri-Mondor hospital, we propose to study the effect of the addition of different types of hemoglobin on the polymerization process as well as the kinetics of oxygen capture at RBC level. This model study is directly linked to the treatments developed to cure this disease and aim to try to better understand them from a molecular point of view.
Monitoring the electrode-electrolyte interface and redox activity in aqueous water-in-salt Na-ion batteries
Using concentrated aqueous electrolytes (Water-In-Salt aqueous Electrolytes), a significant increase in the potential window of aqueous Li batteries can be achieved. This is due to the absence of free water molecules while the interfaces seem to play a crucial role. While WISEs pave the way for sustainable systems, the Li-based solutions use expensive and toxic salts. To look for more sustainable elements, one can envision sodium, which is less expensive and more abundant. While the systems based on Li imide salts have been quite thoroughly investigated, a fundamental understanding of the reactions at stake in sodium batteries based on WISEs, particularly at the interfaces, is needed. The project aims at identifying the reactions occurring at the interphase between the electrodes and the electrolyte in aqueous water-in-salt Na-ion batteries as well as the redox behavior of electrodes in these solutions. To do so, we propose to use cutting-edge in situ/operando techniques, namely infrared spectroscopy (IR) and X-ray absorption spectroscopy (XAS) at SOLEIL. The PhD student will first develop/adapt dedicated cells to perform these measurements. He/she will then conduct in-depth investigation of
the electrodes and interfaces reactivity in aqueous water-in-salt Na-ion batteries. This will provide insights into electrodes behavior in the bulk and also on the chemical composition of the interfaces, on their formation mechanisms and their stability upon cycling.
Development of microfluidic photoreactors for reproducible, quantitative evaluation of photoactive materials, coupled with on-line analysis by mass spectrometry and gas chromatography
The development of high performance photoactive materials (catalysts, semiconductors, sensitive films) for chemical conversion under light irradiation requires precise, reproducible and quantitative evaluation methods. Conventional batch approaches suffer from major limitations: poor control over residence time, temperature or light gradients, low exposed specific surface area and variable reproducibility. In this context, microfluidic photoreactors offer a promising alternative for structured screening and fine evaluation of photoactive materials, in particular thanks to their high surface/volume ratio, flow control and geometry adaptable to different irradiation configurations.
This work, linked to the PEPR LUMA SUNRISE project, aims to design, fabricate and characterize photonic microreactors specifically adapted to the fine evaluation of photoactive materials. The aim is to create a platform capable of generating quantitative and comparable data on the performance and stability of these materials, under well-defined conditions of throughput, irradiation and reaction environment, and then to couple them to high-level analytical techniques (GC, MS) for on-line identification of the products generated.
We propose to develop 4 axes during this thesis project: 1) development, characterization and optimization of the microfluidic platform for online liquid and gas measurement; 2) implementation of protocols for the deposition of photoactive materials 3) evaluation of photochemical performance and validation of the system with samples provided (SUNRISE partners) and on the degradation of pollutant by photochemistry (collaboration with a thesis in progress at the laboratory) and 4) Coupling of the reactor to online analytical methods (GC, MS).
Turbulent geophysical flows above topography
The project is focused on the large-scale organization and the energy budget of idealized oceanic flows above random topography. We will first characterize the enhanced energy dissipation due to the topography and its impact on the transport properties of an idealized parcelle of Ocean. To wit, we will consider models of increasing complexity, from quasi-two-dimensional to fully three-dimensional. We will then turn to the large-scale spatial organization of the flow, building on recent progress regarding the application of statistical mechanics to such flows. A special effort will be devoted to adapting these tools to forced-dissipative flows.