Characterization methods for LMJ’s layered cryogenic targets

Inertial Fusion on the Laser Megajoule facilty requires to form a spherical DT layer at cryogenic temperature. A major topic of interest for fusion experiments is the characterization of the layer quality and thickness. The characterization will be done using two technics : optical shadowgraphy and X-ray phase contrast analysis. A cryostat developed by CEA is already available to work on future target designs and layer characterization.
The objectives of the PhD are to understand and model (theorically and numerically) the physics of the layer observation and to develop the characterization test bench in the cryostat’s environment and the image analysis for the 3D description of the layer.
The student will have to learn to use the cryostat, its command system and its simple actual characterization system. After a bibliography research, he will have to study the physics governing the characterization (multiple reflections, refractions, phase contrast, …) and develop the acquisition and image analysis system allowing the 3D description of the layer using images obtained during experiments with the cryostat. Lastly, the coupling between the command of the cryostat and the characterization will be developed. For all these developments, the student will have access to extensive bibliographical data and the expertise of the host team

Characterizations and modeling of metal tritide aging: application to palladium tritide

Using alternative energy sources such as fusion requires the storage and use of great amount of hydrogen.
This thesis work is about the storage of hydrogen isotopes by palladium hydrides at low equilibrium pressure.
This solid state storage, which ensures both safety and compactness, is particularly interesting for tritium, the radioactive isotope of hydrogen which decay produces helium-3. Helium-3 tends to form nanobubbles which modify the physico-chemical properties of palladium tritide. This phenomenon is called aging. When helium-3 concentration reaches a critical value it is released in the gas phase which can lead to an increase in the storage facility.
In order to better understand and predict the aging phenomenon, material which are aged under tritium during several years are characterized. Studying microstructure, nanobubbles architecture, chemical composition and mechanical behavior evolutions. The acquired data are then used as inputs and outputs of the aging mechanisms modeling.

Synthesis and post-synthesis treatments of ultra-light weight mesoporous metals obtained by plasma electrolysis for laser targets fabrication

For fundamental physics experiments conducted on the Megajoule Laser, the CEA must develop mesoporous metal materials with very low apparent density. Based on the discovery by CEA researchers of a new reactive mechanism between plasma and liquid, CEA has developed a unique electrolytic plasma synthesis process in the world. This technology converts thousands of flashes into as many metallic nano-filaments in seconds to form metals in the form of a nano-structured, ultra-light sponge.
The understanding of the physico-chemical mechanisms that govern the synthesis of these foams is crucial to optimize the properties of synthetic raw materials. A first part of the thesis will consist in continuing the studies already carried out and completing the innovative phenomenological model in the field of electrolytic plasmas.
In a second step, the influence of a heat treatment on the crystallization of these materials and their mechanical resistance will be conducted in order to optimize their subsequent shaping by laser or ultra-precision mechanical machining.