Plasma physics governs the area of interactions between charged particles. As 99% of the visible universe is in a plasma state, it is an important topic in astronomy and space physics, where we already at an altitude of 60 km reach the plasma environment surrounding our planet in the form of the ionosphere. The search for fusion, the source of power for the sun, as well as industrial use have been the main topics for earth bound plasma reasurch. A plasma is composed of charged particles which interact by the electromagnetic force. In the kinetic description, via the Vlasov-Maxwell equations, the system is described in terms of probability distribution functions for each particle species, expressed in terms of particles position and velocity. The particles interact via self-consistent fields as determined by Maxwell's equations. For understanding the complex behaviour of the system, we need numerical solvers. These come in two flavours, Lagrangian methods, dealing with the moving around of synthetic particles, and Eulerian methods, which solve the set of partial differential, Vlasov and Maxwell equations. To perform the computations within reasonable time, we need to distribute our calculations on multiple machines, i.e. parallel programming, with the best possible matching between our computational needs and the need of splitting algorithms to adapt to our processing environment. Paper I studies electron and ion beams within a Lagrangian and fluid model and compare the results with experimental observations. This is continued with studies of a full kinetic system, using an Eulerian solver, for a closer look at electron-ion interactions in relation to ionospheric observations, (Papers II and IV). To improve the performance of the Eulerian solver it was parallelised (Paper III). The thesis is ending with the possibility to observe ultrahigh energy neutrinos from an orbiting satellite by using the Moon's surface as a detector Paper V.

Cette thèse porte sur l’étude théorique du transport d’un faisceau intense d’électrons relativistes dans une cible solide. Dans la première partie nous présentons les interprétations théoriques d’une partie des résultats d’une campagne d’expérience portant sur la production et le transport d’électrons relativistes dans une cible d’aluminium. Nous y démontrons la prédominance des e?ets collectifs sur les e?ets collisionels dans la première dizaine de microns de propagation grâce à des modèles de transports déjà existant au début de cette thèse. Ces modèles deviennent insu?sants dans le cas du transport de faisceau dans un isolant. Aussi, dans la deuxième partie, nous présentons un modèle de propagation du faisceau d’électrons relativistes dans un diélectrique incluant l’e?et de l’ionisation de la cible par le faisceau. Nous y quanti?ons les pertes d’énergies des électrons en fonction des paramètres du faisceau et du milieu environnant, et nous démontrons l’existence d’un régime de propagation pour lequel les électrons du plasma ne sont pas à l’équilibre thermodynamique local avec les ions. Ces résultats ont été comparés et con?rmés avec un code cinétique qui prend en compte l’ionisation par champ électrique et par collisions entre les électrons du plasma et les ions. Nous avons examiné la stabilité du faisceau et montré que ce dernier pouvait exciter deux types d’instabilités transverses sur des longueurs de propagation de l’ordre de 30 à 300 µm en fonction de la taille de la perturbation. / This PhD thesis is a theoretical study of high-current relativistic electron beam transport through solid targets. In the ?rst part, we present an interpretation of a part of experimental results of laser– produced electron beam transport in aluminium foil targets. We have estimated the fast electron beam characteristics and we demonstrated that the collective e?ects dominate the transport in the ?rst tens of µm of propagation. These quantitative estimates were done with the transport models already existing at the beginning of this thesis. These models are no longer su?cient in the case a fast electron beam propagation in insulator targets. Thus, in the second part, we have developed a propagation model of the beam that includes the e?ects of electric ?eld ionization and the collisional ionization by the plasma electrons. We present estimates of the electron energy loss induced by the target ionization, and we discuss its dependence on the beam and target parameters. In the case of a relatively low fast electron density, we demonstrated that the beam creates a plasma where the electons are not in a local thermodynamic equilibrium with ions. We have examined the beam stability and we demonstrated that transverse instabilities can be excited by the relativistic electron beam over the propagation distances of 30 - 300 µm depending on the perturbation wavelength.