Active absorber spectrometer for Bremsstrahlung emitted during Laser-Plasma interaction
The SAABRE project involves the development of a new diagnostic tool to measure the continuous Bremsstrahlung X-ray radiation produced when a high-power laser interacts with matter.
Currently, the instrument known as the Bremsstrahlung Cannon (BC) uses a stack of X-ray-sensitive films separated by filters. Each film absorbs a portion of the incident radiation based on its energy, allowing the energy spectrum of the incident X-rays to be reconstructed. However, these films must be removed from the experimental chamber and scanned after each shot, which severely limits the use of the BC on the new generation of high-repetition-rate lasers (such as APOLLON, VEGA3, or ELI) and complicates its deployment on single-shot facilities like the LMJ.
The project therefore proposes replacing the films with millimeter-sized semiconductor crystals (Si, CdTe, CZT, GaAs, and perovskites). These sensors will enable instantaneous measurement of the radiation dose, conversion of the signal into digitized electrical data analyzed in real time, and adaptation of the instrument to different types of experiments by changing the configuration of the filters used (inertial confinement fusion or laser-plasma acceleration).
The postdoctoral fellow hired will lead the entire development of this new detector, from the study of the proposed semiconductors to the creation of a prototype simulated with GEANT4, which will then be calibrated and experimentally tested on facilities producing high-energy gamma rays. The device will be used in particular for the EUROPA project, dedicated to the production of innovative medical radioisotopes, and will lead to scientific publications and conference presentations.
In-situ 4D tracking of microstructural evolution in atomistic simulations
The exponential growth of high-performance computing has enabled atomistic simulations involving billions or even trillions of particles, offering unprecedented insight into complex physical phenomena. However, these simulations generate massive amounts of data, making storage and post-processing increasingly restrictive. To overcome this limitation, on-the-fly (in-situ) analysis has emerged as a key approach for reducing stored data by extracting and compressing relevant information during runtime without significantly affecting simulation performance.
In this context, tracking the four-dimensional (space and time) microstructural evolution of materials under extreme conditions is a major scientific challenge. Atomistic simulations provide a unique spatial resolution to analyze crystalline defects such as dislocations, twinning, vacancies and pores, which govern dynamic phase transformations, melting, damage and mechanical behavior. By capturing their spatio-temporal evolution, it becomes possible to study their statistics, correlations and collective effects in out-of-equilibrium regimes, leading to more accurate predictive material models.
This project builds on advances of the exaNBody high-performance computing platform and a recently developed in-situ clustering method in the ExaStamp molecular dynamics code at CEA. This method projects atomic information onto a 3D Eulerian grid to perform real-time clustering. The objective is to extend this approach to full 4D tracking, enabling the time-resolved monitoring of clusters. This will allow dynamic graph-based analysis of their evolution, including changes in size, shape and temporal behavior, providing new insights into microstructural dynamics at the atomic scale.