Emittance-preserving acceleration of high-quality positron beams using warm plasma filaments

Preserving the quality of positron beams in plasma-based accelerators, where wakefields are generated in electron filaments, is challenging. These wakefields are characterized by transversely non-linear focusing fields and non-uniform accelerating fields. However, a nonzero plasma temperature linearizes the transverse wakefield within the central region of the electron filament. In this study, we employ 3D particle-in-cell simulations with mesh refinement to demonstrate that beams with emittances on the order of tens of nanometers are contained within the linearized region of the transverse wakefield. This enables emittance preservation to one percent, while positron beams with the same charge and micrometer emittances, which sample the non-linear part of the transverse wakefield, experience a relative emittance growth of ten percent. Additionally, we observe a significant reduction in the growth rate of the slice energy spread for the tens of nanometers emittance beams in comparison to the micrometer emittance beams. The utilization of warm plasmas in conjunction with low-emittance beams opens up new avenues for enhancing the beam quality across various plasma-based positron acceleration approaches.Comment: To be submitted as a proceedings for the 6th European Advanced Accelerator Concepts worksho

Laser and electron deflection from transverse asymmetries in laser-plasma accelerators.

We report on the deflection of laser pulses and accelerated electrons in a laser-plasma accelerator (LPA) by the effects of laser pulse front tilt and transverse density gradients. Asymmetry in the plasma index of refraction leads to laser steering, which can be due to a density gradient or spatiotemporal coupling of the laser pulse. The transverse forces from the skewed plasma wave can also lead to electron deflection relative to the laser. Quantitative models are proposed for both the laser and electron steering, which are confirmed by particle-in-cell simulations. Experiments with the BELLA Petawatt Laser are presented which show controllable 0.1-1 mrad laser and electron beam deflection from laser pulse front tilt. This has potential applications for electron beam pointing control, which is of paramount importance for LPA applications

Exascale and ML Models for Accelerator Simulations

Computational modeling is essential to the exploration and design of advanced particle accelerators. The modeling of laser-plasma acceleration and interaction can achieve predictive quality for experiments if adequate resolution, full geometry and physical effects are included. Here, we report on the significant evolution in fully relativistic full-3D modeling of conventional and advanced accelerators in the WarpX and ImpactX codes with the introduction of Exascale supercomputing and AI/ML models. We will cover the first PIC simulations on an Exascale machine, the need for and evolution of open standards, and based on our fully open community codes, the connection of time and space scales from plasma to conventional beamlines with data-driven machine-learning models

Modélisation de l’interaction d'une impulsion laser femtoseconde avec des plasmas sur-denses : de l’accélération d’électrons à la génération d’harmoniques

When a laser pulse with a relativistic intensity is focused onto a solid target, the material is instantly ionized and forms a plasma mirror, namely an overdense plasma with a short density gradient on its front side. During the laser pulse reflection, high harmonics are generated in the reflected pulse, and electrons can be accelerated out of the target. While the mechanisms for high harmonic generation are well-known, the acceleration of electrons remained unclear. Based on experimental results from two ultraintense femtosecond laser systems (the "Salle Noire" laser at LOA and the UHI100 laser at CEA), this theoretical and numerical thesis unravels the mechanisms for ejection and acceleration of electrons, following three research lines. First, using particle-in-cell numerical simulations, we identify the ejection mechanism occuring during every laser period at the plasma surface. In particular, the role of the fields inside the plasma is highlighted, and the scale length of the plasma density gradient is shown to be a key parameter. Second, after being ejected from the plasma surface, electrons can be accelerated by the laser fields in the reflected pulse. This so-called "vacuum laser acceleration" had not been studied extensively in experiments, the biggest hurdle being to inject electrons directly inside an ultraintense laser pulse. Plasma mirrors offer an answer to this question and serve as electron injectors. In this thesis, we develop a model to interpret experimental results obtained on the UHI100 laser at CEA. In particular, we show that these experiments lead to the first observation of vacuum laser acceleration of a high-charge (3 nC) electron beam to relativistic energies (10 MeV). Finally, high harmonic generation may occur via two mechanisms: coherent wake emission at low intensity and the relativistic oscillating mirror effect at high intensity. Comparing electron ejection with each of these mechanisms brought new insights into the nanoscale dynamics of the plasma surface.Lorsqu'une impulsion laser est focalisée à une intensité relativiste sur une cible solide, le matériau est instantanément ionisé et forme un miroir plasma, c'est-à-dire un plasma surdense présentant un court gradient de densité sur sa face avant. La réflexion de l'impulsion laser génère alors des harmoniques élevées dans l'impulsion réfléchie, et des électrons peuvent être accélérés hors de la cible. Si la génération d'harmoniques est bien comprise, l'accélération des électrons reste, à ce jour, mal expliquée. Basée sur des résultats expérimentaux obtenus sur deux lasers femtosecondes ultraintenses (le laser "Salle Noire" au LOA et le laser UHI100 au CEA), cette thèse théorique et numérique porte sur le mécanisme d'accélération des électrons en suivant trois axes de recherche. Premièrement, à l'aide de simulations numériques de type particle-in-cell, nous identifions le mécanisme d'éjection des électrons de la surface qui a lieu à l'échelle du cycle optique. En particulier, le rôle déterminant des champs à l'intérieur du plasma a été mis en évidence, et ce travail montre que la longueur caractéristique du gradient de densité est un paramètre fondamental de cette interaction. Deuxièmement, après l'éjection du plasma, les électrons peuvent être accélérés par les champs laser de l'impulsion réfléchie. Ce processus, appelé "accélération laser dans le vide", avait été peu étudié expérimentalement en raison de la difficulté d'injecter des électrons directement au centre d'une impulsion laser intense. Le miroir plasma constitue une solution à ce problème, servant d'injecteur à électrons. Grâce à un modèle présenté dans cette thèse, nous avons pu interpréter les résultats expérimentaux obtenus sur le laser UHI100 du CEA. En particulier, nous démontrons que ces expériences ont conduit pour la première fois à l'accélération dans le vide d'un faisceau d'électrons de charge élevée (3 nC) jusqu'à des énergies relativistes (10 MeV). Enfin, la génération d'harmoniques lors de cette interaction peut se produire suivant deux mécanismes : l'accélération cohérente de sillage à faible intensité et le miroir oscillant relativiste à haute intensité. La comparaison entre l'éjection d'électrons et chacun de ces mécanismes apporte de nouvelles informations sur la dynamique à l'échelle nanométrique de la surface plasma

Emittance preservation in advanced accelerators

Emittance is a beam quality that is vital for many future applications of advanced accelerators, such as compact free-electron lasers and linear colliders. In this paper, we review the challenges of preserving the transverse emittance during acceleration, both inside and outside accelerator stages. Sources of emittance growth range from space charge and instabilities caused by transverse wakefields, which can occur in any advanced accelerator scheme regardless of medium or driver type, to sources more specific to plasma accelerators, such as mismatching, misalignment, ion motion, Coulomb scattering, chromaticity between stages, and more

Emittance Preservation in Advanced Accelerators

Emittance is a beam quality that is vital for many future applications of advanced accelerators, such as compact free-electron lasers and linear colliders. In this paper, we review the challenges of preserving the transverse emittance during acceleration, both inside and outside accelerator stages. Sources of emittance growth range from space charge and instabilities caused by transverse wakefields, which can occur in any advanced accelerator scheme regardless of medium or driver type, to sources more specific to plasma accelerators, such as mismatching, misalignment, ion motion, Coulomb scattering, chromaticity between stages, and more

Emittance preservation in advanced accelerators

Emittance is a beam quality that is vital for many future applications of advanced accelerators, such as compact free-electron lasers and linear colliders. In this paper, we review the challenges of preserving the transverse emittance during acceleration, both inside and outside accelerator stages. Sources of emittance growth range from space charge and instabilities caused by transverse wakefields, which can occur in any advanced accelerator scheme regardless of medium or driver type, to sources more specific to plasma accelerators, such as mismatching, misalignment, ion motion, Coulomb scattering, chromaticity between stages, and more.Comment: 23 pages, 14 figures, prepared for ICFA Beam Dynamics Newsletter 8

Self-Stabilizing Positron Acceleration in a Plasma Column

Plasma accelerators sustain extreme  eld gradients and potentially enable future compact linear colliders. Although tremendous progress has been achieved in accelerating electron beams in a plasma accelerator, positron acceleration with collider-relevant parameters is challenging. The wake generated by an electron drive beam in a plasma column represents a promising candidate for positron acceleration owing to the ability to accelerate positron beams with low emittance and low energy spread. However, since this scheme relies on cylindrical symmetry, it is possibly prone to beam-break-up instabilities. In this Letter, we show that both the drive and the witness beams are subject to various damping mechanisms and therefore, this positron acceleration con guration is inherently stable. This enables stable, high-quality positron acceleration