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Modélisation de sources X générées par interaction laser-plasma en régime relativiste

Abstract : When an ultra-short ultra-intense laser impulsion propagates through a low density gas jet, a plasma is created and a bunch of electrons can be accelerated through laser wakefield acceleration to Gev energies in only a few centimetres. Those accelerated electrons then emit what is called Betatron radiation: a highly focused X-ray source with extremely good spatial and temporal properties, which has a lot of possible applications including ultra-high resolution imaging.In this thesis, we investigate possible improvements to one of the main numerical tools used to simulate those phenomenons: the Particle-In-Cell codes (CALDER). We have especially studied a numerical artefact called the numerical Cherenkov radiation, that occurs when relativistic particles move at speeds aproaching the speed of light in a vaccuum.We show that this artefact has a negative impact on the behaviour of the accelerated electron beam, especially on its transverse motion, which leads to important errors on the betatron radiation calculated using PIC simulations.We then introduce a new approach to mitigate the impact of this numerical Cherenkov radiation on laser wakefield acceleration simulation with a simple modification of the electromagnetic field interpolation method used in PIC codes. The results obtained with this new technique show a meaningful improvement on the electron motion wich becomes close to the theoretically expected behaviour.We then explore other possible applications for this new technique, notably improving the modelization of betatron sources, vacuum laser acceleration or direct laser acceleration.The improvement of the computation of the particles transverse motion thanks to this new method leads to more accurate results but also enables us to study physical phenomenon with subtle effects that would otherwise be hidden among the numerical noise of the simulation.
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https://tel.archives-ouvertes.fr/tel-03086213
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Submitted on : Tuesday, December 22, 2020 - 1:23:07 PM
Last modification on : Friday, December 3, 2021 - 11:34:04 AM

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  • HAL Id : tel-03086213, version 1

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Citation

Pierre-Louis Bourgeois. Modélisation de sources X générées par interaction laser-plasma en régime relativiste. Physique des plasmas [physics.plasm-ph]. Institut Polytechnique de Paris, 2020. Français. ⟨NNT : 2020IPPAX073⟩. ⟨tel-03086213⟩

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