05 Octobre – Thesis defense - Pilar Puyuelo Valdes

15 h Seminar room / CENBG (Gradignan)

Laser-driven ion acceleration with high-density gas-jet targets and application to elemental analysis.

In this joint thesis, performed between the French Institute CENBG (Bordeaux) and the Canadian Institute INRS (Varennes), laser driven ion acceleration and an application of the beams are studied. The first part, carried out at CENBG and on the PICO2000 laser facility of the LULI laboratory, studies both experimentally and using numerical particle-in-cell (PIC) simulations, the interaction of a high power infrared laser with a high density gas target. The second part, performed at ALLS laser facility of the EMT-INRS institute, investigates the utilization of laser generated beams for elementary analysis of various materials and artifacts. In this work, firstly the characteristics of the two lasers, the experimental configurations, and the different employed particle diagnostics (Thomson parabolas, radiochromic films, etc.) employed are introduced.
In the first part, a detailed study of the supersonic high density gas jets which have been used as targets at LULI is presented, from their conceptual design using fluid dynamics simulations, up to the characterization of their density profiles using Mach-Zehnder interferometry. Other optical methods such as strioscopy have been implemented to control the dynamics of the gas jet and thus define the optimal instant to perform the laser shot. The spectra obtained in different interaction conditions are presented, showing maximum energies of up to 6 MeV for protons and 16 MeV for Helium ions in the laser direction. Numerical simulations carried out with the PIC code PICLS are presented and used to discuss the different structures seen in the spectra and the underlying acceleration mechanisms.
The second part presents an experiment using laser based sources generated by the ALLS laser to perform a material analysis by the Particle-induced X-ray emission (PIXE) and X-ray fluorescence (XRF) techniques. Proton and X-ray beams produced by the interaction of the laser with Aluminum, Copper and Gold targets were used to make these analyzes. The relative importance of XRF or PIXE is studied depending on the nature of the particle production target. Several spectra obtained for different materials are presented and discussed. The dual contribution of both processes is analyzed and indicates that a combination improves the retrieval of constituents in materials and allows for volumetric analysis up to tens of microns on cm^2 large areas, up to a detection threshold of ppms.

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