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Classical and quantum description of plasma and radiation in strong fields

Abstract : With the advent of the new generation of petawatt lasers, it will become more and more important in the near future to study strong-field QED. As previously mentioned, it can either serve as a new nonperturbative regime for physics beyond the standard model, allow to understand extreme astro-physics events (such as magnetars), or even become a dominant effect in laser-plasma interaction.However, in all these cases, the system under consideration is not a single particle as usually consid-ered in pure SFQED works, but will be a collection of such particles (either electron/photon beams or pair plasmas etc.). It will therefore be important to understand how the behavior of single particles affect the overall state of the system, and in particular the shape of its electron distribution function and of its radiated spectrum. This is what this work is focused on. The manuscript is organized as fol-lows In chapter 2, we introduce the basis of classical electrodynamics and derive all the results and notations that will be useful in the rest of this thesis. We explain why any accelerated charge radiates an electromagnetic field and compute the spectrum radiated by an ultrarelativistic electron. We show that it follows the well-know synchrotron spectrum. When the energy radiated by the electron is no longer negligible, the emitted radiation will counteract on the trajectory of the particle itself. This is the so-called radiation reaction. We derive the Lorentz-Abraham-Dirac (LAD) equation, that describes the motion of an electron, taking into account radiation reaction (RR). We show that this equation presents unphysical solutions and deduce the Landau-Lifshitz (LL) equation, that we will use to describe RR in the classical regime in the rest of this work. We then consider the solution of the LL equation in simplified fields such as plane-waves or constant uniform magnetic fields. The classical radiation dominated regime (CRDR) is described and the limit of validity of the classical description analyzed. Chapter 3 : when the electron quantum parameter is of the order of unity, emitted photons can have an energy close to that of the emitting electron. In this case, radiation reaction can no longer be treated classically. In this chapter, we present the basis of quantum electrodynamics (QED), which is the framework in which such quantum effects can be computed. We derive the Volkov states that take into account exactly the nonperturbative coupling between the electron and the strong background field. These fields are used in the so-called Furry picture in order to compute the different QED pro-cesses such as the nonlinear Compton scattering or the nonlinear Breit-Wheeler process. The cross-sections for these two processes are then analyzed. Chapter 4 : so far, the description of radiation concerned only single particles. Here we introduce the Vlasov equation that describes the evolution of the function distribution of a set a particles. We then see how to modify this equation in order to take into account classical and quantum RR. The numeri-cal resolution of this equation, together with Maxwell's equations is then described, in particular through the well-known PIC loop. We describe how to modify this classical PIC loop in order to in-clude classical and quantum RR, in particular through the use of a Monte-Carlo module. Chapter 5 : we present the state of the art on RR in our community and a brief introduction to the sec-ond part of this thesis where most of the original results are reported. Chapter 6 : after a brief reminder of the Landau-Lifshitz (LL) equation, which describes radiation re-action (RR) in classical electrodynamics (CED) as a deterministic force in the particle momentum equation, we recall the emission properties of a quantum radiating electron. We then turn our attention to the linear Boltzmann equation which is at the center of the kinetic description of RR explored in this thesis [...]
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  • HAL Id : tel-03714678, version 1

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Fabien Niel. Classical and quantum description of plasma and radiation in strong fields. Plasma Physics [physics.plasm-ph]. Sorbonne Université, 2018. English. ⟨NNT : 2018SORUS624⟩. ⟨tel-03714678⟩

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