La mise en œuvre de nouvelles formulations d’électrolytes adaptées à des électrodes positives à haut potentiel pour batterie lithium-ion est un défi majeur pour des systèmes à haute densité d’énergie. Afin d’obtenir une stabilité en oxydation supérieure à 5 V vs. Li+/Li, différents solvants (dinitriles, lactones, phosphates) ont été analysés. Nous avons montré par voltampérométrie cyclique que des électrolytes contenant du sébaconitrile sont stables jusqu’à 5,3 V vs. Li+/Li sur LiCoPO4. Toutefois, les résultats obtenus par impédance électrochimique et spectroscopie photoélectronique X ont révélé la présence d’une nouvelle interface à l’électrode positive issue de la dégradation de l’électrolyte. Bien que cette dégradation limite la cyclabilité, une optimisation de l’interface formée pourrait s’avérer un atout du point de vue de la sûreté du système grâce à une protection de l’électrode positive. / Implementation of new electrolyte formulations adapted to high potential positive electrodes for lithium-ion battery is a key challenge for high energy density systems. In order to obtain stability in oxidation greater than 5 V vs. Li+/Li, various solvents (dinitriles, lactones, phosphates) were analyzed. We have shown by cyclic voltammetry that electrolytes containing sebaconitrile are stable up to 5.3 V vs. Li+/Li on LiCoPO4. Nonetheless, the results obtained by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy revealed the presence of a new interface onto the positive electrode due to electrolyte degradation. Even though this degradation limits the cycle ability, optimization of the formed interface could be an asset in view of the system safety through the protection of the positive electrode.

In this study, quantum chemical methods have been used to study two isomers of the proposed high energy density material N8. It has been suggested as a green substitute for conventional solid rocket fuel. Several techniques were used to study the barrier height towards decomposition along reaction path of four N8 isomers. The potential energy surfaces around the transition states of two of the isomers were further investigated. Results show that the bond length of the isomers may have been overestimated, and one of the isomers has a lower barrier and may have a more complicated reaction route. Furthermore, there is a rather large difference in barrier height between calculations at the CCSD and CCSD(T) levels of theory / I den här studien har kvantkemiska beräkningsmetoder använts för att studera två isomerer av N8. På grund av sitt höga energiinnehåll har N8 föreslagits som ett grönt alternativ till konventionellt fast racketbränsle. Flera tekniker har använts för att studera barriären för nedbrytning utefter reaktionskoordinaten för fyra N8-isomerer. Potentialytan runt aktiveringstillståndet för två av isomererna studerades närmare. Resultaten visar att bindningslängden hos isomererna kan ha överskattats och en av isomererna har en lägre barriär samt kan ha en mer komplicerad reaktionsväg. Vidare är det en tämligen stor skillnad i aktiveringsenergi mellan CCSD- och CCSD(T)- nivåerna.

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Laser-driven plasma accelerators can produce high-energy, high peak current ion beams by irradiating solid materials with ultra-intense laser pulses. This innovative concept attracts a lot of attention for various multidisciplinary applications as a compact and energy-efficient alternative to conventional accelerators. The maturation of plasma accelerators from complex physics experiments to turnkey particle sources for practical applications necessitates breakthroughs in the generated beam parameters, their robustness and scalability to higher repetition rates and efficiencies. This thesis investigates viable optimisation strategies for enhancing ion acceleration from thin foil targets in ultra-intense laser-plasma interactions. The influence of the detailed laser pulse parameters on plasma-based ion acceleration has been systematically investigated in a series of experiments carried out on two state-of-the-art high-power laser systems. A central aspect of this work is the establishment and integration of laser diagnostics and operational techniques to advance control of the interaction conditions for maximum acceleration performance. Meticulous efforts in continuously monitoring and enhancing the temporal intensity contrast of the laser system, enabled to optimise ion acceleration in two different regimes, each offering unique perspectives for applications. Using the widely established target-normal sheath acceleration (TNSA) scheme and adjusting the temporal shape of the laser pulse accordingly, proton energies up to 70 MeV were reliably obtained over many months of operation. Asymmetric laser pulses, deviating significantly from the standard conditions of an ideally compressed pulse, resulted in the highest particle numbers and an average energy gain ≥ 37 %. This beam quality enhancement is demonstrated across a broad range of parameters, including thickness and material of the target, laser energy and temporal intensity contrast. To overcome the energy scaling limitations of TNSA, the second part of the thesis focuses on an advanced acceleration scheme occurring in the relativistically induced transparency (RIT) regime. The combination of thin foil targets with precisely matched temporal contrast conditions of the laser enabled a transition of the initially opaque targets to transparency upon main pulse arrival. Laser-driven proton acceleration to a record energy of 150 MeV is experimentally demonstrated using only 22 J of laser energy on target. The low-divergent high-energy component of the accelerated beam is spatially and spectrally well separated from a lower energetic TNSA component. Start-to-end simulations validate these results and elucidate the role of preceding laser light in pre-expanding the target along with the detailed acceleration dynamics during the main pulse interaction. The ultrashort pulse duration of the laser facilitates a rapid succession of multiple known acceleration regimes to cascade efficiently at the onset of RIT, leading to the observed beam parameters and enabling ion acceleration to unprecedented energies. The discussed acceleration scheme was successfully replicated at two different laser facilities and for different temporal contrast levels. The results demonstrate the robustness of this scenario and that the optimum target thickness decreases with improved laser contrast due to reduced pre-expansion. Target transparency was found to identify the best-performance shots within the acquired data sets, making it a suitable feedback parameter for automated laser and target optimisation to enhance stability of plasma accelerators in the future. Overall, the obtained results and described optimisation strategies of this thesis may become the guiding step for the further development of laser-driven ion accelerators.:1 Introduction 1.1 Motivation 1.2 Thesis outline 2 Fundamentals of laser-matter interactions 2.1 Plasma 2.1.1 Plasma properties 2.1.2 Dispersion relation of a plasma 2.1.3 Laser propagation in a plasma 2.2 Laser-matter interactions 2.2.1 Ionisation processes 2.2.2 Electron dynamics in the laser field 2.2.3 Ponderomotive force 2.2.4 Plasma heating processes 2.3 Laser-driven ion acceleration mechanisms 2.3.1 Target normal sheath acceleration 2.3.2 Radiation pressure acceleration 2.3.3 Acceleration in the relativistically induced transparency regime 3 Methodology for high-power laser experiments 3.1 High-power lasers 3.1.1 High-power laser techniques 3.1.2 Temporal contrast of high-power laser systems 3.1.3 DRACO laser system 3.1.4 J-KAREN-P laser system 3.2 Experimental Area 3.2.1 Short-f chamber at HZDR 3.2.2 Short-f chamber at KPSI 3.3 Targets 3.4 Optical diagnostic 3.4.1 Transmitted and reflected laser light 3.4.2 Spectral phase measurements 3.5 Particle diagnostic 3.5.1 Thomson parabola spectrometer 3.5.2 Time of flight measurements 3.5.3 Spatial proton beam profiler 3.5.4 Radiochromic films 3.5.5 Nuclear activation measurements 4 Optimisation of sheath acceleration for high-quality proton beams 4.1 Introduction 4.2 Temporal contrast at experimental environment 4.3 Plasma mirror 4.3.1 Plasma mirror implementation at DRACO-PW 4.3.2 Plasma mirror characterisation at DRACO-PW 4.4 Temporal pulse shaping by spectral phase modification 4.4.1 Theory on temporal pulse shaping 4.4.2 Experimental realisation and results 4.5 Proton acceleration under optimised temporal contrast conditions 4.6 Experimental results 4.7 Discussion on numerical simulations 4.8 Conclusions 5 Enhanced ion acceleration in the relativistic transparency regime 5.1 Introduction 5.2 Experimental setup using the J-KAREN-P laser 5.3 Experimental results 5.4 Laser-induced breakdown and target pre-expansion 5.5 Elucidating ion acceleration in the relativistically induced transparency regime 5.5.1 Details on simulation methodology 5.5.2 Simulation results 5.6 Acceleration in the RIT regime for modified temporal contrast 5.6.1 Experimental setup using the DRACO-PW laser 5.6.2 Experimental results using the DRACO-PW laser 5.6.3 Simulation results for modified temporal contrast 5.7 Conclusions 6 Ion acceleration beyond the 100 MeV frontier from cascading acceleration schemes 6.1 Introduction 6.2 Experimental setup 6.3 Experimental results 6.3.1 Analysis of acceleration performance 6.3.2 Spatial proton beam profile 6.3.3 Nuclear activation measurement 6.3.4 Scaling of maximum proton energy 6.4 Numerical simulations 6.4.1 Simulation setup 6.4.2 Simulation results & discussion 6.5 Conclusions 7 Summary and outlook Appendix References

Ce travail de thèse suit l'apparition récente de ces nouvelles sources intenses et courtes de rayonnement dans la gamme X/XUV que sont les lasers X/XUV à électrons libres (XFEL). Contrairement aux sources optiques qui déposent principalement leur énergie via les électrons libres, les photons X/XUV déposent leur énergie dans la matière par la photoionisation de couches internes avec éjection de photo-électrons, suivie par l'éjection d'électrons Auger et d'électrons de recombinaison à trois corps dans la distribution d'électrons libres. Le chauffage se fait donc par l'intermédiaire de la structure atomique. La forte intensité des XFELs permet de faire jusqu'à un trou par atome dans un solide produisant ainsi, sur une échelle femtoseconde, un état exotique fortement hors-équilibre appelé solide creux. Cet état exotique instable se désexcite via un ensemble de processus atomiques élémentaires. Nous nous sommes intéressés dans cette thèse au développement d'outils permettant de calculer la cinétique des populations atomiques, couplée à la cinétique des électrons libres, pendant la transition à densité ionique constante, de solide à plasma dense en passant par l'état de solide creux, induit par le rayonnement XFEL irradiant une cible solide. Tout le défi ici a été de calculer cette cinétique couplée hors-équilibre entre ces états de la matière de nature très différente. Pour répondre a ce défi nous avons développé deux modèles cinétiques d'interaction XFELsolide, pour lesquels la description d'un solide comme un plasma froid dégénéré nous a permis d'utiliser une même approche plasma pendant l'ensemble de la transition du solide au plasma. L'ensemble de la physique atomique HETL d'intérêt ayant lieu à densité du solide, bien avant la détente de la matière, nous avons développé deux codes associés à ces modèles pour une utilisation à densité ionique constante. Pour aborder l'étude nous nous sommes d'abord concentrés sur la cinétique des électrons liés en supposant une distribution d'électrons libres à l'équilibre (ce qui suppose une thermalisation instantanée des électrons libres). Dans le cadre de l'approche de plasma dense étendue jusqu'au solide, nous avons développé un modèle collisionnel-radiatif généralisé. Cette généralisation passe par l'identification d'un lien entre état solide et plasma au niveau des processus atomiques élémentaires. Le code développé à partir de ce modèle nous a permis d'étudier des résultats expérimentaux et ainsi d'améliorer notre description des effets de densités dans les plasmas denses. Dans une seconde partie nous avons ajouté à l'étude la cinétique des électrons libres en considérant une distribution d'électrons libres hors-équilibre. Le code associé, basé sur la discrétisation de cette distribution et son couplage avec les états liés, nous a permis d'étudier le rôle des processus atomiques élémentaires dans la thermalisation de la distribution d'électrons libres. / This work follows the recent development of the free electron lasers in the X-ray and XUV-ray range (XFEL). Unlike optical sources that deposit their energy via the free electrons, the X/XUV photons deposit their energy directly via photoionization of inner shell electrons with the ejection of photo-electrons, followed by the ejection of Auger electrons and three body recombination electrons in the free electron distribution. The matter is thus heated via the atomic structure. The high XFEL intensity allows one to make up to one hole per atom in a solid, thus producing, on a femtosecond time scale, an exotic state, highly out of equilibrium, called hollow cristal. This unstable exotic state deexcite via a set of elementary atomic processes. In this work we were interested in the development of tools to calculate the atomic population kinetics, coupled to the free electron kinetics, during the transition at constant ionic density, from solid to dense plasma, induced by an XFEL irradiating a solid target. The goal here was to calculate this out of equilibrium coupled kinetics between states of matter having a very different nature. To address this problem we have developed two kinetics models of XFEL interaction with solids. In both these models the description of the solid as a cold degenerated plasma allowed us to use the same plasma approach during all the solid-plasma transition. Considering the fact that all the atomic physics takes place at solid density, way before the matter relaxation, we have developed two codes, associated with these two models, for a use at constant ionic density. To approach this study, we first focused on the bound electron kinetics assuming a free electron distribution at equilibrium (i.e. hypothesis of instantaneous thermalization of the free electrons). In the framework of the dense plasma approach extended up to the solid state, we have developed a generalized collisional radiative model. This generalization goes through the identification of a link between the solid state and the plasma state for the elementary atomic processes. The code associated with this model allowed us to study experimental results and to improve our description of the density effects in dense plasmas. In a second part the free electron kinetics is included in the model with a free electron distribution out of thermodynamic equilibrium. The associated code, based on the discretization of this distribution and its coupling with bound atomic states allowed us to study the role of the atomic elementary processes in the free electron distribution thermalization.

To enable future environmentally friendly access to space by means of solid rocket propulsion a viable replacement to the hazardous ammonium perchlorate oxidizer is needed. Ammonium dinitramide (ADN) is one of few such compounds currently known. Unfortunately compatibility issues with many polymer binder systems and unexplained solid-state behavior have thus far hampered the development of ADN-based propellants. Chapters one, two and three offer a general introduction to the thesis, and into relevant aspects of quantum chemistry and polymer chemistry. Chapter four of this thesis presents extensive quantum chemical and spectroscopic studies that explain much of ADN’s anomalous reactivity, solid-state behavior and thermal stability. Polarization of surface dinitramide anions has been identified as the main reason for the decreased stability of solid ADN, and theoretical models have been developed to explain and predict the solid-state stability of general dinitramide salts. Experimental decomposition characteristics for ADN, such as activation energy and decomposition products, have been explained for different physical conditions. The reactivity of ADN towards many chemical groups is explained by ammonium-mediated conjugate addition reactions. It is predicted that ADN can be stabilized by changing the surface chemistry with additives, for example by using hydrogen bond donors, and by trapping radical intermediates using suitable amine-functionalities. Chapter five presents several conceptual green energetic materials (GEMs), including different pentazolate derivatives, which have been subjected to thorough theoretical studies. One of these, trinitramide (TNA), has been synthesized and characterized by vibrational and nuclear magnetic resonance spectroscopy. Finally, chapter six covers the synthesis of several polymeric materials based on polyoxetanes, which have been tested for compatibility with ADN. Successful formation of polymer matrices based on the ADN-compatible polyglycidyl azide polymer (GAP) has been demonstrated using a novel type of macromolecular curing agent. In light of these results further work towards ADN-propellants is strongly encouraged. / QC 20101103

Diagnosing the temperatures and densities of plasmas is critical to the understanding of a wide variety of phenomena. Everything from equations of state for warm dense matter (WDM) found in Jovian planets and inertial confinement fusion (ICF) to turbulent and dissipative processes in laser-produced plasmas, rely on accurate and precise measurements of temperature and density. This work presents improvements on two distinct techniques for measuring temperatures and densities in plasmas: x-ray Thomson scattering (XRTS), and Langmuir probes (LPs). At the OMEGA laser facility, experiments on warm dense matter were performed by firing lasers at an ablator foil and driving a planar shock into cryogenically cooled liquid deuterium. XRTS in the collective scattering regime was implemented to probe the matter, measuring densities of n_e ~ 4.3 x 10²³ cm^-3, temperatures of T_e ~ 12 eV and ionizations of Z ~ 1.0. Through an extension to XRTS theory for inhomogeneous systems, it was possible to extract an additional parameter, the length scale of the shock, whose value of ? ~ 1.33 nm was consistent with the predicted mean free path, and therefore the thickness of the shock. A unique triple Langmuir probe prototype was designed and tested at the Gregori group's lab at the University of Oxford. This probe was designed for a high temporal resolution of ~ 200 MHz for probing laser-produced shocks. The probes were used to measure the shock formed from ablating carbon rods in an argon gas fill. The probe yielded plasma parameters of n_e ~ 1.0 x 10¹⁷ cm^-3 , and T^e ~ 1.5 eV, consistent with measurements from interferometry and emission spectroscopy.

The recent development of free-electron lasers operating at XUV and X-ray wavelengths are proving vital for the exploration of matter in extreme conditions. The ultra-short pulse length and high peak brightness these light sources provide, combined with a tunable X-ray wavelength range, makes them ideally suited both for creating high energy density samples and for their subsequent study. In this thesis I describe the work done on the XUV free-electron laser FLASH in Hamburg, aimed at creating homogeneous samples of warm dense matter through the process of volumetric XUV photo-absorption, and the theoretical work undertaken to understand the process of high-intensity laser-matter interactions. As a first step, we have successfully demonstrated intensities above 10¹⁷ Wcm-2 at a wavelength of 13.5 nm, by focusing the FEL beam to micron and sub-micron spot sizes by means of a multilayer-coated off-axis parabolic mirror. Using these record high intensities, we have demonstrated for the first time saturable absorption in the XUV. The effect was observed in aluminium and magnesium samples and is due to the bleaching of a core-state absorption channel by the intense radiation field. This result has major implications for the creation of homogeneous high energy density systems, as a saturable absorption channel allows for a more homogeneous heating mechanism than previously thought possible. Further, we have conducted soft X-ray emission spectroscopy measurements which have delivered a wealth of information on the highly photo-excited system under irradiation, immediately after the excitation pulse, yet before the system evolves into the warm dense matter state. Such strongly photo-excited samples have also been studied theoretically, by means of density functional theory coupled to molecular dynamics calculations, yielding detailed electronic structure information. The use of emission spectroscopy as a probe for solid-density and finite-temperature systems is discussed in light of these results. Theoretical efforts have further been made in the study of the free-free absorption of aluminium as the system evolves from the solid state to warm dense matter. We predict an absorption peak in temperature as the system heats and forms a dense plasma. The physical significance of this effect is discussed in terms of intense light-matter interactions on both femtosecond and picosecond time-scales.

In der vorliegenden Arbeit wird die Darstellung neuer organischer Polyazide dokumentiert, die durch einfache nucleophile Substitution mittels NaN3 dargestellt werden können. Organische Azide mit der Formel RN3 können sich unter Stickstoff-Abspaltung in exothermen, teilweise explosionsartigen Reaktionen zersetzen. Sie sind daher prinzipiell als energiereiche Materialien (HEDM) für entsprechende Anwendungen geeignet. Die als Treibladungsmaterialien potentiell geeignetsten, handhabungssicheren, dendritischen Polyazide werden unter anderem mittels Thermogravimetrie und Differenzkalorimetrie analysiert. In einer neuen Synthesemethode können die wenig bekannten Heteroazidomethane aus Tris(azidomethyl)amin erzeugt werden. Von besonderem Interesse ist dabei die Synthese neuartiger Azidohalogenmethane. Diese können durch analytische Gas-Chromatographie charakterisiert und mittels präparativer Gas-Chromatographie isoliert werden. Durch die 1,3-dipolare Cycloaddition mit Cyclooctin konnten einige Heteroazidomethane zu Triazolen abgefangen und so einer Einkristall-Röntgen-Strukturanalyse zugeführt werden. Als letztes in der homologen Reihe der Azidomethane noch fehlendes Azid konnte Tetraazidomethan synthetisiert werden. Das Perazidomethan besitzt mit 93.3% den für organische Azide höchstmöglichen Stickstoffgehalt. Seine Existenz wurde bislang lediglich durch molekültheoretische Berechnungen nahegelegt. Die Synthese dieses homoleptischen Kohlenstoffazides gelang durch die Behandlung von Trichloracetonitril mit Natriumazid. Es ließ sich durch präparative GC als extrem explosive, farblose Flüssigkeit isolieren. Mit Hilfe der analytischen GC konnten sowohl der Siedepunkt als auch die Polarität von C(N3)4 abgeschätzt werden. C(N3)4 wird desweiteren durch IR, MS, 13C-NMR und 15N-NMR-Spektroskopie sowie durch Einkristall-Röntgen-Strukturanalysen seiner Abfangprodukte mit Cyclooctin charakterisiert. Mit Wasser zeigt C(N3)4 eine quantitative Hydrolyse unter Bildung von Carbonyldiazid. Durch Austauschprozesse mit Na15N3 konnte die mögliche Dissoziation von C(N3)4 nachgewiesen werden. Reaktionen von C(N3)4 mit Phosphinen führen zu Cyanamidderivaten, mit Norbornen sowie Norbornadien wurden über vielstufige Reaktionsmechanismen Aminotetraazole erhalten.

<div>For decades, the response of high-energy (HE) density materials at extreme conditions of pressure and temperature from strong insults like burning or impact have been studied in depth by the shock community. Shock physicists aim to develop a fundamental understanding for coupled chemical and physical processes across orders of magnitude spatial and temporal regimes. In order to succeed, this requires extensive collaboration between experiments and simulations, ranging from the electronic to the engineering scales. The end goals would be to develop predictive multiscale models capable of explaining ignition and initiation of HE systems and composites. The collected works in this thesis detail my contributions to the field of HE materials, specifically addressing the chemical reactivity at the atomistic level using reactive molecular dynamics (MD) simulations.</div><div><div>Through this endeavor, we aim to develop a critical understanding for the decomposition processes of HE materials. We begin with a validation the reactive force field, ReaxFF, by addressing the very strong anisotropic shock sensitivity in 2,2-Bis[(nitrooxy)methyl]propane-1,3-diyl dinitrate (PETN) through direct comparison of time-evolved spectra between experiments and simulations. Such strong orientation dependence is thought to relate to the initial decomposition events. Therefore we compare spectra at three different shock pressures, where we observe similar timescales for the disappearance of the NO2 symmetric and antisymmetric stretch modes. A more detailed chemical species analysis indicates that the NO2 molecular species could be considered the primary intermediate which initiates the decomposition process. Furthermore, these results suggest that the combination of explicit MD simulations and ultrafast spectroscopy will be key to the development of a detailed understanding of chemistry at extreme conditions.</div></div><div><div>Following the validation study, we further our understanding of reactivity in HE systems by investigating the differences in kinetics between an ordered and disordered system. It has been shown that shocked material is often severely strained, causing a loss in crystalline order. This in turn results in the disordered materials, such as amorphous solids, having</div><div>faster reactivity due to their higher internal energy and/or lower thermal conductivity. Our results indicate that extra energy is required to break the long-range order in bulk crystalline systems, thus resulting in slower decomposition rates. Further analyses of thermal hotspots point towards slightly faster chemical propagation in the amorphous samples due to lower thermal conductivity. These results provide an understanding for how molecular disorder can be attributed to increased reactivity.</div></div><div><div>After developing an understanding for the initial decomposition processes of HE materials, we turn our attention to a growing interest in the community which is the developing reduced order chemistry models for use in multiscale efforts. Many schemes report mechanisms that are obtained from experiments, which can have large error bars depending on the apparatus and/or extraction technique, or from gas phase simulations, which may not be relevant at shock conditions. To circumvent these issues, we develop a coarse-grained chemical kinetics model from all-atom reactive MD simulations by taking advantage of an unsupervised dimensionality reduction machine learning technique called non-negative matrix factorization. Doing so allows us to represent the overall decomposition chemistry as latent concentrations akin to reactants, intermediates, and products, which we then use to extract kinetics parameters and heats of reaction. These values are implemented into a continuum model, where we could simulate the criticality of thermal hotspots at regimes beyond the reach of MD, as well as verify how uncertainties in the parameters vary as a function of hotspot sizes.</div></div><div><div>Finally, we close with significant progress made towards on-going and future work, where we address two of the most challenging ideas in the field of HE materials: 1) developing definitive chemistry models at extreme conditions, and 2) improving coarse-grained descriptions for multiscale modeling.</div></div>