The matter/antimatter asymmetry is one of the greatest mysteries in modern physics. In fact, the observable universe’s lack of antimatter poses a considerable problem for physicists, especially because the Standard Model predicts that the Big Bang should have produced identical amounts of matter and antimatter. The deviations observed experimentally in the production of matter with respect to antimatter, both in the leptonic and the hadronic sectors, are still insufficient to account for the matter’s domination of the universe. Therefore, one possible explanation for the discrepancy is that antimatter could interact differently than matter with gravity, resulting in a violation of the (Weak) Equivalence Principle. The Equivalence Principle, one of the pillars of general relativity, postulates that the gravitational charge of antimatter should be equal to its inertial mass, as it is for matter. However, some physics beyond the Standard Model (BSM) theories admit a difference in the gravitational properties of matter and antimatter [8]. Measuring antimatter’s gravitational force is a challenging task, both because of its scarcity and the complexities involved in trapping and handling antimatter particles. Indirect limits based on astronomical data have been posed [9], and lately, indirect measurements have progressed significantly [10]. Nonetheless, these indirect methods depend on theoretical models involving additional hypotheses: therefore they cannot be as conclusive as direct measurements. To date, the only direct measurement of the matter-antimatter gravitational interaction is from ALPHA [11]: while eliminating the possibility of “pure-repulsion”, its precision still lacks towards what is considered theoretically intriguing. This PhD thesis has been developed in the context of the AE ̄gIS experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy), which aims at measuring directly the acceleration exerted on antimatter by the gravitational field of the Earth and potentially by other gravity-like interactions. Specifically, antihydrogen has been selected as the test particle, as it is the simplest system of a neutral antimatter that can be synthesized1. To perform such a measurement, the methodology chosen is to create a pulsed beam of antihydrogen atoms, well defined in time, and let it pass through the grids of a moir ́e deflectometer [13] while accelerating because of the influence of the Earth’s gravitational field. By the pattern created by the particles passing through the grids, the displacement due to gravity can be determined. For the formation of antihydrogen, AE ̄gIS relies on the charge-exchange reaction between a positronium atom (Ps) (which is the bound state of an electron and a positron) and an antiproton: in the reaction, the electron is swapped with the antiproton, and the antihydrogen atom is thus formed. The AE ̄gIS experiment is located at the European Organisation for Nuclear Research (CERN), in the Antimatter Factory (AD, from Antiproton Decelerator). The AD is the sole source of bunched trappable antiprotons in the world: they are a key ingredient for the formation of antihydrogen. The AE ̄gIS experimental apparatus consists of multiple subsystems linked together, used in different combinations depending on the experiment’s needs (e.g. antihydrogen formation instead of positronium cooling). The principal piece of hardware is the main vacuum chamber, hosting the cryostat, the magnets system and the traps. The magnet system divides the traps into two zones, one at 5T and one at 1 T: in the first region, the capture trap is present, with electrodes tunable in the ±200V range and three dedicated electrodes going up to 15 kV, and it is used to capture the antiprotons coming from the decelerators, after being moderated by a material degrader. The high magnetic field is used to provide stronger radial confinement to the more energetic particles and to ensure a more efficient ̄p cooling via electron sympathetic cooling (which is proportional to B2). In the 1T region, instead, is present the formation trap: here the cold antiprotons are transferred from the capture trap, and the antihydrogen production takes place. A lower magnetic field ensures a higher rate of formation: in fact, the antihydrogen charge-exchange cross-section is proportional to the fourth power of the Rydberg level of the positronium involved (σ ̄H ∝ n4 Ps). But the maximum Rydberg level achievable by Ps is limited by the magnetic field, since it is bounded by the motional Stark effect induced field ionisation (nmax ∝ B−1/4) [14]. Therefore, a lower magnetic field in the formation region can enhance greatly the production rate of antihydrogen. To the main vacuum chamber, the positrons line is connected, which is used to inject positrons in the formation trap, to form the positronium atoms needed for the ̄H formation. It consists of a 22Na source emitting e+, moderated by a solid Neon moderator and stored in a Surko trap. To form positronium, a bunch of positrons are extracted and collided into the e+→Ps converter, consisting of a nanochanneled porous silica plate. A series of two lasers, then, is used to excite the so-formed Ps from the ground state to a high Rydberg state (1S →3 P → 17÷32). The cloud of Ps then expands towards the ̄p plasma, and ̄H formation can take place. The number of antihydrogens thus created is determined by observing, using the scintillators posed around the cryostat, the difference in annihilation rates arising when both positrons, antiprotons, and lasers are present, in opposition to the lack of (at least) one of them. AE ̄gIS successfully produced cold antihydrogen in pulsed mode in 2018 [15], marking the end of its Phase 1. The formation rate was determined to be approximately 0.05 ̄Hper decelerator cycle, which lasts ∼ 110 s. This result showed that to arrive at a gravity measurement with a precision in the order of 1 %, antihydrogen formation needs to be improved significantly: in order to gather enough statistical data, a rate of approximately 1 ÷ 10 ̄H per decelerator cycle is necessary, which is more than two orders of magnitude greater than what was obtained in Phase 1. A substantial reduction in temperature is also required, from the previously reached level of around 400K to a few tenths of kelvin. Therefore, AE ̄gIS entered in 2019 (together with CERN LS2), its Phase 2 (which is going to last until CERN LS3, in 2025), with four goals: the two just aforementioned aims (2-3 order of magnitude higher rate and one order of magnitude colder ̄H, with respect to Phase 1), together with the formation of a forward-boosted beam of antihydrogen, and the development of a moir ́e deflectometer prototype for inertial measurement. To achieve these objectives, major upgrades of the apparatus have been deemed necessary, starting from the formation scheme. The Ps target has been positioned on the axis of the trap, to illuminate the ̄p plasma collinearly, and not perpendicularly as before: this has raised the maximum Ps Rydberg level from ∼ 19 to above 32 by reducing the Ps ionisation due to the motional Stark effect (nmax Ps ∝ θ−1/4 Ps|B). The updated formation scheme necessitated a redesign of the formation trap, which was built and installed in 2022. Additionally, the e+→Ps target has been optimised by fine-tuning the morphology of the nano-channel, so to increase up to five times the efficiency of positronium generation. In the context of the upgrades to the AE ̄gIS apparatus, my main contribution has been the development of the new control system controlling the entire experiment. In fact, AE ̄gIS has been operated using multiple independent control systems for each subsystem, coordinating them by a grown-up program and by the manual labour of multiple experts simultaneously. This already resulted demanding from the scientists at the end of Phase 1, when antihydrogen production was successfully attempted. But with the introduction, in 2021, of ELENA (Extra Low Energy viii Antiproton ring) [16], the modality of antiprotons delivery changed from 8 h daily shifts to continuous cycles: keeping the experiment up day and night would have become completely unfeasible with the previous system, ultimately leading to beam time loss and team overwork. Therefore, it was decided to completely rewrite the control system, creating a distributed system with stability and automation as the main targets. The new control system is called CIRCUS (Computer Interface for Reliably Controlling, in an Unsupervised manner, Scientific experiments) [1], whose main component is the TALOS framework (Total Automation of Labview Operations for Science) [2]. TALOS creates an environment where all individual control programs are subdivided into atomic modules, called MicroServices, which are integrated into a single, coordinated, distributed system: these features are the base that enables the complete automation of experimental procedures since high-level decisions often rely on parameters residing on multiple computers. TALOS is built upon the distributed system architecture provided by the Actor Model [17], which facilitates the modular structure. In particular, it is realised by dividing the code into standalone units, called MicroServices, each with a precise scope and function, which operate in parallel, communicating through non-blocking messages, to ensure complete asynchronous functionality. The unification of the distributed system is realised by a common process, called Guardian, an instance of which is executing on each machine. Every Guardian monitors the status of the other Guardian in the experiment’s computer network and oversees the local MicroServices, thanks to a series of three distributed watchdog systems. This system ensures that no component becoming unresponsive can pass unnoticed: it significantly strengthens the reliability and safety of the system, ultimately leading to unsupervised operation for extended periods. Furthermore, the automation of the system was augmented by the introduction of an optimiser, that leverages the feedback given by the online analysis of the data acquired, to autonomously find the best parameters that optimise a series of predefined observable CIRCUS, per se, is experiment-agnostic, being general enough to be usable by other experiments than AE ̄gIS, in particular nuclear, atomic and quantum ones. Therefore, to be able to adopt it in AE ̄gIS, I also coded the majority of the MicroServices necessary to manage most of the detectors and actuators, plus the interface with the decelerators and the data acquisition interface, among others. The implementation of CIRCUS would not have been possible without upgrading the control electronics from the previous custom-made hardware (with a very limiting software interface) to a new one based on ARTIQ/Sinara [18], an open hardware & software ecosystem expressly created for quantum physics experiment. The hardware modularity has enabled progressive migration and guarantees future-proofness; its ns synchronisation (internal and w.r.t. an external clock) capability has further improved the timing accuracy of the apparatus. Conversely, the programming interface done in ARTIQ, a Python-based real-time language, has greatly simplified the generation of experimental procedures, enabling both a library-based approach (which minimises debugging time and code duplication) and the integration with TALOS, to ensure the automation of the full system. In this respect, during this thesis, I contributed to the installation and integration of the Sinara hardware, and I wrote part of the libraries used to operate it and, in particular, to interface the FPGA seamlessly with the CIRCUS control system. During the three antiprotons campaigns (2021, 2022, 2023) that occurred during the development of this thesis, the system was tested with the particles, and the various operations needed to form antihydrogen were re-developed using the new control system. In this thesis, the physics motivations that brought these procedures to the form that we found most performant, which is also presented, are explained. The main operations tested and optimised are: antiprotons capture, trap closure time optimisation, antiproton beam alignment, traps voltage reshape, electrons loading, ̄p sympathetic cooling, ̄p plasma compression with rotating-wall technique, electrons removal before antiprotons transfer, antiprotons transfer and recapture in the formation trap, ̄p ballistic transfer to the formation trap, electrons recycling, antiprotons partial recycling, positronium formation optimisation, laser synchronisation for Ps excitation, antihydrogen formation. ix Chapter 0. Abstract These operations were implemented sequentially, by consolidating each one before passing to the subsequent one. A key ingredient was the extensive use of custom libraries for the Python code of the various experiments: every time an atomic operation was tested and optimised, it was defined as a function in the AE ̄gIS libraries, so to be able to recall it in all the subsequent operations scripts. This greatly facilitated the development, since the new code was progressively added to the already consolidated one, minimising code duplication, script proliferation, and debugging time. To guide the success and performance of the operations, two detectors were mainly used: the scintillating slabs surrounding the main apparatus, acquired via photomultipliers (PMTs) and digitised, and a combination of a multichannel plate (MCP), a phosphor screen and a camera, placed downstream with respect to the formation trap. The firsts are fundamental to monitoring and understanding the lifetime and the quality of the operations with the antiprotons, by understanding the time and position of the various annihilations. The second is mainly used to understand radial plasma profiles and to perform time-of-flight (ToF) analyses. In the end, to determine the formation rate of antihydrogen with the new apparatus, I took part in the data analysis, by developing one of the three parallel analyses that have been performed. One analysis, analogue to the one already performed in 2018, used the scintillators counts to discriminate the difference in ̄p annihilation profiles in case that both ̄p, positrons and laser were employed together, or that one of them was missing: by the difference, ̄H production can be inferred. My data analysis, instead, used different techniques to look at the MCP data to understand not only the formation rate but also, by comparison with the scintillators’ data, the possible forward-boosted antihydrogen formation. The images were algorithmically selected, background corrected, and binarised; then, clusters were extracted. A Bayesian test was finally performed between runs where ̄H production was attempted, versus runs where it was suppressed by omitting one of the lasers. The analyses hint toward a successful production of antihydrogen with the upgraded apparatus, at a higher rate than the one seen at the end of Phase 1: nevertheless, it has been difficult to determine the direction of production with the MCP analyses, and deeper analyses and/or more data is needed to fully conclude. Overall, the work accomplished during this PhD thesis has been fundamental to achieving the formation of antihydrogen using the ballistic antiprotons transfer, which leads to the creation of a forward-boosted beam of neutral antihydrogen. This is an important milestone towards measuring directly the gravitational interaction between matter and antimatter, which could lead to a confirmation of the WEP on antimatter or could find a violation and, so, hint at new physics.

Synthesis and capture of antihydrogen in controlled laboratory conditions will enable precise studies of neutral antimatter. The work presented deals with some of the physics pertinent to manipulating charged antiparticles in order to create neutral antimatter, and may be applicable to other scenarios of plasma confinement and charged particle interaction. The topics covered include the electrostatic confinement of a reflecting ion beam and the transverse confinement of an ion beam in a purely electrostatic configuration; the charge sign effect on the Coulomb logarithm for a two component (e.g., antihydrogen) plasma in a Penning trap as well as the collisional scattering for binary Coulomb interactions that are cut off at a distance different than the Debye length; and the formation of magnetobound positronium and protonium.

L’expérience GBAR propose de mesurer, au CERN, l’accélération de la pesanteur terrestre sur l’antimatière grâce à des atomes froids (neV) d’antihydrogène soumis à une chute libre. Ceux-ci sont obtenus en refroidissant d’abord des ions positifs d’antihydrogène, obtenus grâce à deux réactions consécutives se produisant lors de la collision d’un faisceau d’antiprotons avec un nuage dense de positronium.Le travail de thèse porte sur l'étude de ces réactions dans le but d’optimiser la production des ions d’antihydrogène. Pour cela, les sections efficaces des deux réactions ont été calculées dans le cadre d’un modèle de théorie des perturbations (Continuum Distorted Wave – Final State) pour des antiprotons ayant une énergie comprise entre 0 et 30 keV ; différents états excités du positronium ont été examinés. Ces sections efficaces ont ensuite été intégrées à une simulation de la zone d’interaction entre positronium et antiprotons afin de définir les paramètres expérimentaux optimaux pour GBAR. Les résultats suggèrent d’utiliser les états 2P, 3D ou, dans une moindre mesure, 1S du positronium, respectivement pour des antiprotons de 2, moins de 1 ou 6 keV. L’importance de compresser les impulsions temporelles d’antiprotons est soulignée ; le positronium devra être confiné dans un tube de 20 mm de long pour 1 mm de diamètre.Un laser en impulsion à 410 nm permettant d’exciter la transition à deux photons vers l’état 3D du positronium avait déjà été proposé. Son principe repose sur le doublage en fréquence d’un laser titane-saphir à 820 nm. Le dernier volet de la thèse fut dédié à la réalisation de ce laser, qui délivre des impulsions courtes (9 ns) de 4 mJ à 820 nm. / The future CERN experiment called GBAR intends to measure the gravitational acceleration of antimatter on Earth using cold (neV) antihydrogen atoms undergoing a free fall. The experiment scheme first needs to cool antihydrogen positive ions, obtained thanks to two consecutive reactions occurring when an antiproton beam collides with a dense positronium cloud.The present thesis studies these two reactions in order to optimise the production of the anti-ions. The total cross sections of both reactions have been computed in the framework of a perturbation theory model (Continuum Distorted Wave – Final State), in the range 0 to 30 keV antiproton kinetic energy; several excited states of positronium have been investigated. These cross sections have then been integrated to a simulation of the interaction zone where antiprotons collide with positronium; the aim is to find the optimal experimental parameters for GBAR. The results suggest that the 2P, 3D or, to a lower extend, 1S states of positronium should be used, respectively with 2, less than 1 or 6 keV antiprotons. The importance of using short pulses of antiprotons has been underlined; the positronium will have to be confined in a tube of 20 mm length and 1 mm diameter.In the prospect of exciting the 1S-3D two-photon transition in positronium at 410 nm, a pulsed laser system had already been designed. It consists in the frequency doubling of an 820 nm pulsed titanium-sapphire laser. The last part of the thesis has been dedicated to the realisation of this laser system, which delivers short pulses (9 ns) of 4 mJ energy at 820 nm.

AEGIS (Antimatter Experiment, Gravity, Interferometry and Spectroscopy) isan experiment under development at CERN which will measure earth's gravitationalforce on antimatter. This will be done by creating a horizontal pulsedbeam of low energy antihydrogen, an atom consisting of an antiproton anda positron. The experiment will measure the vertical de ection of the beamthrough which it is possible to calculate the gravitational constant for antimatter.To characterise the production process in the current state of the experimentit is necessary to develop an imaging detector for single excited hydrogenatoms. This thesis covers the design phase of that detector and includes studiesand tests of detector components. Following literature studies, tests and havingdiscarded several potential designs, a baseline design was chosen. The suggesteddetector will contain a set of ionising rings followed by an electron multiplyingmicrochannel plate, a light emitting phosphor screen, a lens system and nallya CCD camera for readout. The detector will be able to detect single hydrogenatoms, measure their time of ight as well as being able to image electronplasmas and measure the time of ight of the initial particles in such a plasma.Tests were made to determine the behaviour of microchannel plates at the lowtemperatures used in the experiment. Especially, the resistance and multiplicationfactor of the microchannel plates have been measured at temperaturesdown to 14 K. / AEGIS

AEgIS is an experiment at CERN where the goal is to directly measure the gravitational force on antimatter by producing antihydrogen. The antihydrogen will be produced by a charge exchange reaction using laser excited positronium and cold antiprotons. Having a well-characterized positron plasma with at least 108 positrons and knowing how it can be controlled is essential for the positronium production. This thesis is based on the goals of AEgIS experiment and describes the positron plasma manipulations being used in AEgIS in order to achieve the required plasma properties for the experiment. The positron system is made up by a source, a Surko trap and a Penning-Malmberg trap. This system was first optimized to increase the number of positrons. The plasma was then moved to the main traps of the experiment where it was systematically characterized in terms of lifetime, cooling efficiency and compression. Positron plasma compression in time, trapping and cooling was tested for the first time in AEgIS using a buncher and Penning-Malmberg traps respectively. In this thesis, it is shown that a compression of more than 50 % in time of the positron cloud using a buncher can be achieved. It is also shown that trapping and cooling with an efficiency of nearly 100 % in the main traps using a “V” shaped potential trap was successful. On top of that, the lifetime inside this “V” shaped potential trap was observed to be longer than 30 minutes.

L’expérience GBAR repose sur la production d’ions antihydrogène positifs dans le but de mesurer l’accélération gravitationnelle à laquelle est soumise l’antimatière au repos. Le projet ANTION, sous-projet de GBAR, a pour but la production de ces ions d’antimatière. Il vise également à mesurer la section efficace de production d’antihydrogène dans les collisions d’antiprotons sur des atomes de positronium, ainsi que les sections efficaces correspondantes avec la matière, de production d’hydrogène et de l’ion hydrogène négatif. Ces expériences reposent sur la formation d’un nuage très dense de positronium, et nécessitent donc une grande quantité de positons qui seront implantés sur un matériau convertisseur de positons en positronium. Cette thèse décrit la construction d’un piège à “buffer gas” à trois étages, destiné à piéger et accumuler des positons pour le projet ANTION. L’association d’un piège de Penning avec une source basée sur un Linac constitue un montage expérimental unique. Le piège a été construit et optimisé, et est maintenant pleinement opérationnel. Les protocoles de piégeage ont été étudiés et les effets du gaz tampon et du gaz de refroidissement sur le taux de piégeage et la durée de vie des positons ont été quantifiés. Afin de faciliter la mesure de la section efficace de production de l’hydrogène, une simulation avec GEANT4 a été mise au point. Elle décrit l’évolution temporelle et spatiale des atomes d’ortho-positronium dans la cavité où aura lieu la production d’hydrogène. On estime que 2.7 atomes d’hydrogène sont produits pour des proton de 6 keV d’énergie incidente, en utilisant les sections efficaces calculées avec le modèle “Coulomb-Born Approximation”, et 1.6 atomes d’hydrogène pour des protons de 10 keV, si l’on utilise la méthode “two-center convergent close-coupling”. Les simulations permettent également d’estimer le bruit de fond associé aux positons et à l’annihilation du para-positronium. Cette étude amène à proposer une modification permettant d’augmenter le nombre d’atomes de positronium dans la cavité. En parallèle, une étude a porté sur l’efficacité de modération de positons d’une couche épitaxiale de carbure de silicium 4H-SiC. Une efficacité de modération de 65% a été mesurée pour des positons implantés avec une énergie de l’ordre du kilo- électronvolt. Ce résultat intéresse les expériences de physique utilisant des positons lents, car il permet d’améliorer la luminosité de faisceaux de positons; dans le cas de GBAR cela permettrait d’augmenter l’efficacité de piégeage des positons. / The GBAR experiment relies on the production of antihydrogen positive ions to achieve its goal of measuring the gravitational acceleration of antimatter at rest. The ANTION project, included in the GBAR enterprise, is responsible for the production of these antimatter ions. Moreover, it also aims to measure the cross section of antihydrogen production throughout the collision of antiprotons and positronium atoms, as well as the matter cross sections of hydrogen and the hydrogen negative ion. These experiments imply the formation of a very dense positronium cloud, thus a large amount of positrons will be implanted on a positron/positronium converter material. This thesis reports the construction of a three stage buffer gas trap with the goal of trapping and accumulating positrons for the ANTION project. The combination of the Penning-type trap with a LINAC source constitutes a unique experimental setup. The trap was commissioned and optimized and is now fully operational. Trapping protocols were studied and the effect of the buffer and cooling gases on the positron trapping rate and lifetime was assessed. In order to assist the cross section measurement of hydrogen, a GEANT4 simulation was developed. It evaluates the time and spatial evolution of the ortho-positronium atoms in a cavity, where hydrogen production will take place. It was estimated that 2.7 hydrogen atoms are produced for proton impact energy of ∼ 6 keV, according to the cross sections computed with the Coulomb-Born Approximation model, and 1.6 hydrogen atoms for a proton impact energy of ∼ 10 keV, according to the two-center convergent close-coupling method. The simulations also allow the estimation of the background associated with the positron and para-positronium decay. In addition, a suggestion is proposed to increase the number of positronium atoms in the cavity. In parallel, the positron moderation efficiency of a commercially available 4H-SiC epitaxial layer was studied. A 65% moderation efficiency was observed for kiloelectronvolt implanted positrons. This result can be of interest to slow positron physics experiments by improving the brightness of positron beams, and in particular to GBAR as it can potentially increase the efficiency of positron trapping.

Depuis les années 1975, les atomes de Rydberg sont étudiés et maintenant utilisés en information quantique pour leurs propriétés particulières d’interaction. Cependant, ces objets physiques peuvent se retrouver impliqués dans différentes autres applications, où leurs caractéristiques remarquables en font de parfaits outils. Dans ce mémoire, nous nous intéresserons à deux applications distinctes faisant intervenir des atomes de Rydberg de césium. Tout d’abord, nous verrons comment utiliser de tels atomes pour produire une source d’électrons monocinétiques, grâce au mécanisme d’ionisation singulier de ce type d’atomes à une valeur précise de champ électrique dépendante du niveau d’excitation. Les électrons ainsi produits sont ensuite extraits et leur dispersion en énergie mesurée. On montrera notamment de façon théorique et d’après les premières mesures expérimentales réalisées pendant la thèse, que l’on peut espérer obtenir une dispersion en énergie des électrons produits par cette technique de l’ordre du meV, résolution jamais atteinte à ce jour. Ce type de source devient aujourd’hui un outil indispensable pour accéder à la mise au point et l’étude de nouveaux matériaux par contrôle de réactions chimiques à l’échelle moléculaire, et à la cartographie des phonons. Dans un second temps, nous verrons qu’il est possible de désexciter un nuage d’atomes de Rydberg de niveaux variés grâce à une source externe dans le domaine térahertz. Ce projet s’inscrit dans le cadre des expériences d’étude de l’antimatière menées actuellement au CERN, qui visent à élucider le mystère de l’asymétrie matière/antimatière. Les méthodes actuelles de production de l’antihydrogène, forment des nuages de ces anti-atomes dans différents états de Rydberg. Pour les étudier, il est alors nécessaire de désexciter le plus d’atomes d’antihydrogène possible vers le niveau fondamental. Nous présenterons la méthode envisagée, ainsi que les résultats obtenus expérimentalement sur un dispositif créé pendant la thèse pour montrer la faisabilité de la technique. Ces premiers résultats montrent qu’il est possible d’accélérer la désexcitation d’un atome de Rydberg sur un état très élevé grâce à une lampe se comportant comme un corps noir. Nous détaillerons les améliorations envisagées, en particulier pour adapter le spectre des fréquences THz à utiliser et empêcher la photoionisation des atomes, par des filtres ou par le façonnage spectral via l’utilisation d’un photomixer. / Since 1975, Rydberg atoms have been studied and now used in quantum information for their particular interaction properties. However, these physical objects can be involved in various other applications, where their remarkable characteristics make them perfect tools. In this paper, we will focus on two distinct applications involving cesium Rydberg atoms. First, we will see how to use such atoms to produce a source of monocinetic electrons, thanks to the singular ionization mechanism of this type of atoms at a precise value of electric field dependent on the excitation level. The electrons thus produced are then extracted and their energy dispersion measured. Theoretically and according to the first experimental measurements made during the thesis, we will show that we can hope an energy dispersion of the electrons produced by this meV technique, a resolution never reached before. Today, this type of source is becoming an indispensable tool for the development and study of new materials by molecular scale chemical reaction control and for phonon mapping. In a second step, we will see that it is possible to de-energize a cloud of Rydberg atoms of various levels thanks to an external source in the tera-hertz domain. This project is part of the ongoing anti-matter experiments at CERN, which aim to unravel the mystery of the matter/anti-matter asymmetry. The current methods of production of antihydrogen, forms clouds of these anti-atoms in different Rydberg states. To study them, it is then necessary to de-energize as many antihydrogen atoms as possible to the fundamental level. We will present the method envisaged, as well as the results obtained experimentally on a device created during the thesis to show the feasibility of the technique. These first results show that it is possible to accelerate the deenergization of a Rydberg atom on a very high state thanks to a lamp behaving like a black body. We will detail the improvements envisaged, in particular to adapt the spectrum of the THz frequencies to use and prevent the photoionization of atoms, by filters or by spectral shaping via the use of a photomixer.

The production and control of antihydrogen at very low temperatures provided a key tool to test the validity for the antimaterial of the fundamental principles of the interactions of nature such as the weak principle of equivalence (WEP), and CPT symmetry (Charge, Parity, and Time reversal). The work presented in this dissertation studies the collisions of electrons and positrons in strong magnetic fields that generate magnetobound positronium (positron-electron system temporarily bound due to the presence of a magnetic field) and its possible role in the generation of antihydrogen.

The ALPHA experiment at CERN is an ongoing project which tests fundamental symmetries between matter and antimatter by producing and trapping antihydrogen atoms in order to perform precision spectroscopic measurements. A logical next step is to form the antihydrogen molecular ion (consisting of one positron and two antiprotons). This system possesses net charge, and can therefore be trapped electrostatically, making repeated measurements possible. Moreover it has been suggested that the molecule has the potential to allow for higher-precision comparisons with ordinary matter than have been attained with the atom. Since both momentum and energy have to be conserved in a collision, a simple collision process between an antihydrogen atom (“Hbar”) and an antiproton (“pbar”) does not suffice in order to form the molecular ion. However it is possible, upon mixing of the two species, for a pbar colliding with an Hbar in the ground electronic state to form a metastable molecular state (i.e., a resonance) which is weakly coupled to a stable molecular state (i.e., a bound state) via spontaneous quadrupole transition. During the time a metastable ion exists, a second pbar can happen to undergo a Coulomb collision with the metastable molecular ion. The quadrupole electrostatic interaction with this secondary antiproton acts as a time-dependent perturbation on the molecular system which can strengthen the coupling between resonance and bound state. Hence a collision with a secondary pbar can induce a transition to a bound state whereby the excess energy is carried off by the secondary pbar. This work aims to determine the efficiency of the process just described. On the theoretical side, the following is done: a study is conducted on the topic of resonance scattering as it relates to the problem in consideration; building on this study a generalized time-dependent perturbation theory is constructed which is valid for transitions to and from resonant states as well as bound states. On the numerical side: the effective potential for pbar-Hbar scattering in the ground electronic state is obtained numerically within the adiabatic approximation; the energies and lifetimes of the resonant states of the molecular ion are estimated; a temperature-dependent rate coefficient is obtained for the process described which, in order to obtain a proper rate, needs to be multiplied by the square of the density of the antiproton plasma and by the number of antihydrogen atoms. It is concluded that at current capacity for trapping and storage of pbar and Hbar the process examined is not competitive with respect to other formation routes which have been proposed for the molecular ion.

Comparisons between measurements of the ground-state hyperfine structure and gravitational acceleration of hydrogen and antihydrogen could provide a test of fundamental physical theories such as CPT (charge conjugation, parity, time-reversal) and gravitational symmetries. Currently, antihydrogen traps are based on Malmberg-Penning traps. The number of antiprotons in Malmberg-Penning traps with sufficiently low energy to be suitable for trappable antihydrogen production may be reduced by the electrostatic space charge of the positrons and/or collisions among antiprotons. Alternative trap designs may be needed for future antihydrogen experiments. A computational tool is developed to simulate charged particle motion in customizable magnetic fields generated by combinations of current loops and current lines. The tool is used to examine charged particle confinement in two systems consisting of dual, levitated current loops. The loops are coaxial and arranged to produce a magnetic null curve. Conditions leading to confinement in the system are quantified and confinement modes near the null curve and encircling one or both loops are identified. Furthermore, the tool is used to examine and quantify charged particle motion parallel to the null curve in the large radius limit of the dual, levitated current loops. An alternative to new trap designs is to identify the effects of the positron space in existing traps and to find modes of operation where the space charge is beneficial. Techniques are developed to apply the Boltzmann density relation along curved magnetic field lines. Equilibrium electrostatic potential profiles for a positron plasma are computed by solving Poisson's equation using a finite-difference method. Equilibria are computed in a model Penning trap with an axially varying magnetic field. Also, equilibria are computed for a positron plasma in a model of the ALPHA trap. Electric potential wells are found to form self-consistently. The technique is expanded to compute equilibria for a two-species plasma with an antiproton plasma confined by the positron space charge. The two-species equilibria are used to estimate timescales associated with three-body recombination, losses due to collisions between antiprotons, and temperature equilibration. An equilibrium where the three-body recombination rate is the smallest is identified.