Organisation
The French Alternative Energies and Atomic Energy Commission (CEA) is a key player in research, development and innovation in four main areas :
• defence and security,
• nuclear energy (fission and fusion),
• technological research for industry,
• fundamental research in the physical sciences and life sciences.
Drawing on its widely acknowledged expertise, and thanks to its 16000 technicians, engineers, researchers and staff, the CEA actively participates in collaborative projects with a large number of academic and industrial partners.
The CEA is established in ten centers spread throughout France
Reference
2024-32520
The aim of this post-doctorate is to develop a measurement chain dedicated to the observation and characterisation of Rapid Transient Phenomena (RTP) using X-ray phase contrast imaging (XPCI). The challenge is to provide a measurement system that can be deployed in the laboratory on a wide range of experiments that cannot be moved to the synchrotron. The performance targets are justified by the problems associated with additive manufacturing, the propagation of shock waves in low-density polymers, and the diagnosis of carbon composite materials impacted by an electric arc.
For objects with low absorption, such as low-density polymers, liquids or plasmas, conventional X-ray imaging, which provides contrast due to the absorption cross-sections variations, is insufficient. To complete absorption, it is possible to exploit the phase of X-rays, which provides better detection of inhomogeneities and interfaces. The method used here to measure the phase is the multilateral shearing interferometry (IDML). It uses a single two-dimensional checkerboard phase grating that generates a reference interference pattern on the detector. The introduction ofan object between the grating and the detector modifies the reference interference pattern, which is then analysed by Fourier transform to reconstruct the phase image. By requiring only a single phase grid and exhibiting minimal X-ray flux loss, this method has favourable intrinsic characteristics in terms of sensitivity, robustness, ease of alignment and versatility, for application to dynamic imaging.
Initially, the candidate will seek to dimension the imaging system. He/she will have to put in place a static methodology to prepare and optimise imaging under dynamic conditions, with the aim of achieving an image acquisition rate > 1 kHz, an exposure time of the order of µs and a spatial resolution range of between 30 and 300 µm. He/she will seek to find the best method for detecting X-rays at the desired rates: indirect detection using a scintillator that converts X-ray photons into visible photons, followed by detection using a high-speed camera, or direct detection using a matrix of pixelated semiconductors hybridised to an electronic chain. To achieve the objectives, he/she will use the CEA's imaging bench and the simulation codes developed at the CEA (CIVA software). He/she will then demonstrate the dynamic imaging of a PTR using X-ray sources that are at the cutting edge of technology (secondary laser emission source and liquid anode X-ray tube). Secondly, he/she will study the feasibility of extending the imaging system to very high rates (>100 kHz) and/or single-shot nanosecond flash.