Beam dynamics for a multi-stage laser-plasma accelerator
Laser–plasma wakefield accelerators (LWFAs) can provide accelerating gradients exceeding 100 GV/m, providing a pathway to reduce the size and cost of future high-energy accelerators for applications in synchrotron radiation, free-electron lasers, and emerging medical and industrial uses.
Scaling this technology to higher beam energies and charges requires both technological maturity and innovative acceleration schemes. Multi-stage configurations — connecting several plasma acceleration stages — offer key advantages: increasing beam energy beyond single-cell limits and enhancing total charge and/or repetition rate. These systems aim to overcome single-stage limitations while maintaining or improving beam quality at higher energies.
Designing an accelerator delivering stable, reproducible, high-quality beams requires comprehensive understanding of plasma acceleration physics and beam transport between successive stages.
Building on expertise at CEA Paris–Saclay's DACM, this PhD will focus on physical and numerical studies to propose a fully integrated multi-stage LWFA design, with particular attention to optimizing all components — plasma accelerating section and transport lines — to preserve beam quality in terms of transverse size, divergence, emittance, and energy spread.
Investigation of Lanthanide Salt Interactions with Lipid Systems
Lanthanide–lipid interactions have gained significant attention due to their importance in biophysical and technological applications, including magnetic resonance imaging, fluorescence-based cell labelling and drug delivery. This project aims to investigate the interactions between different lanthanide salts (LnX3, where X = Cl?, ClO4?, NO3?, etc.) and lipid aggregates, focusing on the precipitation and gelation phenomena that occur when their concentration exceeds a certain threshold. Understanding these phenomena is essential for studying self-assembly and phase behaviour in soft matter systems. By examining how lanthanide ions interact with lipid aggregates—particularly in the presence of different anions—this study seeks to elucidate their roles in inducing precipitation and gelation. To this end, a combination of spectroscopic, scattering, microscopy, and rheological techniques will be employed to characterize the molecular interactions in lanthanide–phospholipid systems. These investigations will provide insights into the structural and dynamic properties of such systems and support their application in both biophysical and technological contexts.
Exploring trends in rocky exoplanets observed with JWST
One of JWST’s major goals is to characterize, for the first time, the atmospheres of rocky, temperate exoplanets, a key milestone in the search for potentially habitable worlds. The temperate rocky exoplanets accessible to JWST are primarily those orbiting M-type stars. However, a major question remains regarding the ability of planets orbiting M-dwarfs to retain their atmospheres.
In 2024, an exceptional 500-hour Director’s Discretionary Time (DDT) program, entitled Rocky Worlds, was dedicated to this topic, underlining its strategic importance at the highest level (NASA, STScI).
The main objective of this PhD project is to: 1) Analyze all available JWST/MIRI eclipse data for rocky exoplanets from Rocky Worlds and other public programs using a consistent and homogeneous framework; 2)Search for population-level trends in the observations and interpret them using 3D atmospheric simulations.
Through this work, we aim to identify the physical processes that control the presence and composition of atmospheres on temperate rocky exoplanets.
Stochastic Neutron Noise Estimation Using a Rare-Event Simulation Approach. Application to the Monitoring of Nuclear System Reactivity
This PhD project aims to develop an innovative method to characterize the reactivity of fissile systems by analyzing their stochastic fluctuations, known as zero-power neutron noise. In a subcritical fissile medium, neutrons originating from spontaneous fission can initiate short and random chain reactions, generating a fluctuating signal. This noise carries essential information on the distance of the system to criticality, a key parameter both for the safety of nuclear installations (prevention of criticality accidents) and for the detection of undeclared fissile materials (nuclear security and non-proliferation).
Existing theoretical approaches to infer system reactivity from neutron noise are limited to idealized situations and become unsuitable in realistic configurations, particularly when the system is strongly subcritical or when significant uncertainties exist regarding its geometry or composition (as in the case of the Fukushima Daiichi corium or spent fuel storage). Monte Carlo simulations then appear as a natural alternative, but current simulations rely on variance reduction techniques that fail to correctly preserve stochastic fluctuations.
This thesis proposes to address this scientific challenge by adapting a relatively recent variance reduction method known as Adaptive Multilevel Splitting (AMS), originally developed to efficiently sample rare events while preserving their statistical properties. The goal is to extend this method to neutron transport in multiplying media and to make it a tool capable of faithfully simulating the temporal correlations characteristic of neutron noise. Following the theoretical developments, the algorithm will be implemented in Geant4, compared to analytical benchmark solutions, and experimentally validated through in situ measurements (using neutron sources or research reactors). In the long term, this work may lead to direct applications in nuclear monitoring, safety diagnostics, and detector physics, while also opening perspectives in fundamental physics and medical physics.
Spatiotemporal shaping of high-order harmonic emission in nanostructured crystals
We propose to study the spatiotemporal manipulation of radiation emitted by high harmonic generation, leveraging advances in nanofabrication technologies. The approach involves transposing methods developed for meta-optics to the strong-field regime specific to harmonic generation. The candidate will explore various design strategies to control the spatiotemporal properties of this radiation, which is intrinsically linked to the broad spectral bandwidth of attosecond pulses. These concepts will then be implemented and experimentally validated. This project aims to enhance the integration of high harmonic generation into optoelectronic devices, paving the way for new applications in ultrafast photonics.
Magnetar formation: from amplification to relaxation of the most extreme magnetic fields
Magnetars are neutron stars with the strongest magnetic fields known in the Universe, observed as high-energy galactic sources. The formation of these objects is one of the most studied scenarios to explain some of the most violent explosions: superluminous supernovae, hypernovae, and gamma-ray bursts. In recent years, our team has succeeded in numerically reproducing magnetic fields of magnetar-like intensities by simulating dynamo amplification mechanisms that develop in the proto-neutron star during the first seconds after the collapse of the progenitor core. However, most observational manifestations of magnetars require the magnetic field to survive over much longer timescales (from a few weeks for super-luminous supernovae to thousands of years for Galactic magnetars). This thesis will consist of developing 3D numerical simulations of magnetic field relaxation initialized from different dynamo states previously calculated by the team, extending them to later stages after the birth of the neutron star when the dynamo is no longer active. The student will thus determine how the turbulent magnetic field generated in the first few seconds will evolve to eventually reach a stable equilibrium state, whose topology will be characterized and compared with observations.
Understanding the signals emitted by moving liquids
Elasticity is one of the oldest physical properties of condensed matter. It is expressed by a constant of proportionality G between the applied stress (s) and the deformation (?): s = G.? (Hooke's law). The absence of resistance to shear deformation (G' = 0) indicates liquid-like behavior (Maxwell model). Long considered specific to solids, shear elasticity has recently been identified in liquids at the submillimeter scale [1].
The identification of liquid shear elasticity (non-zero G') is a promise of discoveries of new liquid properties. For example, do we know that a confined liquid changes temperature under flow? Yet no classical model (Poiseuille, Navier-Stokes, Maxwell) predicts the effect because without long-range correlation between molecules (i.e. without elasticity), the flow is dissipative, therefore athermal. For a change in temperature to be flow induced (without a heat source), the liquid must have elasticity and this elasticity must be stressed [1,2].
The PhD thesis will explore how the mechanical energy of the flow is converted in a thermal response [2]. We will exploit the capacity of conversion to develop a new generation of microfluidic devices (patent FR2206312).
We will also explore the impact of the wetting on the liquid flow, and reciprocally, we will examine how the liquid flow modifies the solid dynamics (THz) of the substrate [3]. Powerful methods only available in Very Large Research Facilities such as the ILL will be used to probe the non-equilibrium state of solid phonons. Finally, we will strengthen our existing collaborations with theoreticians.
The PhD topic is related to wetting, macroscopic thermal effects, phonon dynamics and liquid transport.
1. A. Zaccone, K. Trachenko, “Explaining the low-frequency shear elasticity of confined liquids" PNAS, 117 (2020) 19653–19655. Doi:10.1073/pnas.2010787117
2. E. Kume, P. Baroni, L. Noirez, “Strain-induced violation of temperature uniformity in mesoscale liquids” Sci. Rep. 10 13340 (2020). Doi : 10.1038/s41598-020-69404-1.
3. M. Warburton, J. Ablett, P. Baroni, JP Rueff, L. Paolasini, L. Noirez, “Identification by Inelastic X-Ray scattering of bulk alteration of solid dynamics due to Liquid Wetting”, J. of Molecular Liquids 391 (2023) 123342202
Exploration of VACNTs in Anode-less Batteries: Mechanism and Cell Optimization
Anode-less or anode-free batteries are getting increasing attention owing to their excellent energy density, cost efficiency, and ease of process upscaling. Exploring anode-less battery will offer a breakthrough in energy storage devices by using the lithium reserve already present in the NMC cathode to reversibly cycle after an initial formation process, which will reduce the overall thickness, processing steps, and cost of materials, and provide excellent energy density. Vertically aligned CNTs (VACNTs) on metal substrates can be an interesting choice for this application due to their low thickness, reproducible synthesis process, and uniform surface properties, which have already proven their applicability in supercapacitors. In this PhD project, we will investigate their newer avenue of applications- anode-less batteries, where VACNTs act as the lithium or sodium plating substrate. We will study the electrochemistry of VACNT in lithium anode-less batteries (in liquid and solid electrolytes) and in sodium anode-less batteries in a liquid electrolyte. The PhD student will work on the synthesis optimizations of VACNT to tune the thickness and density to match their electrochemistry. Post-cycling studies (Raman and SEM) will be carried out to study the effect of cycling and the electrolytes on the VACNT layers. The project aims to explore the possibility of the application of VACNTs in various energy storage systems, which can open up new application possibilities and valorization
Understanding the origin of the remarkable efficiency of distant galaxy formation
The James Webb Space Telescope is revolutionizing our understanding of the distant universe. A result has emerged that challenges our models: the extremely high efficiency of star formation in distant galaxies. However, this finding is derived indirectly: we measure the mass of stars in galaxies, not their star formation rate. This is the main weakness of the James Webb. The aim of this thesis is to remedy this weakness by using its angular resolution capacity, which has not been taken into account until now, in order to obtain a more robust measurement of the SFR of distant galaxies. We will deduce a law that will improve the robustness of SFR determination using morphological properties and combining data from the James Webb Space Telescope with data from ALMA (z=1-3). We will then apply it to the distant universe (z=3-6, part 2) and use it as a benchmark for numerical simulations (part 3).
Spectro-temporal analysis of Gamma-Ray Burst afterglows detected with SVOM
Gamma-Ray Bursts (GRB) are the most powerful explosions in the Universe. They last a few tens of seconds and emit the same amount of energy as the Sun during its entire lifetime. They gamma-ray emission is followed by a long lasting (hours to days) emission from the X-rays to the radio band. This "afterglow" emission is rich on information about the GRB nearby environnent and host galaxy. SVOM (Space based astronomical Variable Object Monitor) is a Sino-French mission, dedicated to GRB studies, and has been successfully launched in June 2024. It carries a multi-wavelength payload covering gamma-rays/X-rays/optical and includes two dedicated ground based robotic telescopes in Mexico and China.
The PHD project is focussed on the exploitation of the SVOM data for GRBs. The successful candidate will join the MXT science Teal at DAp. MXT is a new type of X-ray telescope, for which the DAp is responsible and its Instrument Centre is also hosted at DAp.
The PHD student will participate actively to the spectral and temporal analysis of MXT data. These data will be compared
to the other data acquired by the SVOM collaboration, especially in the optical an infrared domains.
This dataset will be used as a support to the physical interpretation of GRBs. More specifically, the aspects related to the modeling of the energy injection in the first phases of the afterglow will be used to determine the nature of the compact object at the origin of the relativistic flux, generating the electromagnetic emission observed.