Towards realistic simulations of QED cascades: non-ideal laser and electron seeding effects

A number of analytical and numerical studies has been performed to investigate the onset and the development of QED cascades in the collision of two counterpropagating laser pulses as a function of the laser intensity. However, it has been recently demonstrated [M. Tamburini et al., Sci. Rep. 7, 5694 (2017)] that the onset of QED cascades is also strongly influenced by the structure of the laser pulses, such as the laser pulse waist radius. Here we investigate how QED cascades are affected by: (a) the laser pulse duration, (b) the presence of a relative delay for the peak of the laser pulses to reach the focus, (c) the existence of a mismatch between the laser focal axis of the two laser pulses. This is especially important as, in realistic laboratory conditions, fluctuations may arise in the temporal and point stability of the lasers.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in Physics of Plasma

Radiation reaction effects in superintense laser-plasma interaction

At the extremely high laser intensities expected in next generation experiments, electrons can become ultrarelativistic within a fraction of wave period experiencing superstrong accelerations therefore emitting large amounts of electromagnetic radiation. The Radiation Reaction (RR) force basically describes the back action on a single electron by its self-generated electromagnetic fields and it may significantly affect the dynamics at the extreme intensities expected in the foreseen laser-plasma interaction regimes. In the present thesis, we present the results of our multi-dimensional Particle-In-Cell (PIC) simulations at ultra-high intensities showing the RR ability to reduce the electron heating and to increase both the electron and the ion bunching. Our approach is based on the Landau-Lifshitz equation of motion for electrons which is free from known problems of other approaches such as, e.g., runaway solutions. A detailed study of polarization effects at ultra-high intensities is also presented

Giant collimated gamma-ray flashes

Bright sources of high energy electromagnetic radiation are widely employed in fundamental research as well as in industry and medicine. This steadily growing interest motivated the construction of several facilities aiming at the realisation of sources of intense X- and gamma-ray pulses. To date, free electron lasers and synchrotrons provide intense sources of photons with energies up to 10-100 keV. Facilities under construction based on incoherent Compton back scattering of an optical laser pulse off an electron beam are expected to yield photon beams with energy up to 19.5 MeV and peak brilliance in the range 10$^{20}$-10$^{23}$ photons s$^{-1}$ mrad$^{-2}$ mm$^{-2}$ per 0.1% bandwidth. Here, we demonstrate a novel mechanism based on the strongly amplified synchrotron emission which occurs when a sufficiently dense electron beam interacts with a millimetre thickness solid target. For electron beam densities exceeding approximately 3\times10^{19}\text{ cm^{-3}} filamentation instability occurs with the self-generation of 10$^{7}$-10$^{8}$ gauss magnetic fields where the electrons of the beam are trapped. This results into a giant amplification of synchrotron emission with the production of collimated gamma-ray pulses with peak brilliance above $10^{25}$ photons s$^{-1}$ mrad$^{-2}$ mm$^{-2}$ per 0.1% bandwidth and photon energies ranging from 200 keV up to several hundreds MeV. These findings pave the way to compact, high-repetition-rate (kHz) sources of short (30 fs), collimated (mrad) and high flux ($>10^{12}$ photons/s) gamma-ray pulses.Comment: Full-text access to a view-only version of the published paper by the following SharedIt link: https://rdcu.be/LGtC This is part of the Springer Nature Content Sharing Initiative (https://www.springernature.com/gp/researchers/sharedit). Enhanced PDF features such as annotation tools, one-click supplements, citation file exports and article metrics are freely availabl

Polarized laser-wakefield-accelerated kiloampere electron beams

High-flux polarized particle beams are of critical importance for the investigation of spin-dependent processes, such as in searches of physics beyond the Standard Model, as well as for scrutinizing the structure of solids and surfaces in material science. Here we demonstrate that kiloampere polarized electron beams can be produced via laser-wakefield acceleration from a gas target. A simple theoretical model for determining the electron beam polarization is presented and supported with self-consistent three-dimensional particle-in-cell simulations that incorporate the spin dynamics. By appropriately choosing the laser and gas parameters, we show that the depolarization of electrons induced by the laser-wakefield-acceleration process can be as low as 10%. Compared to currently available sources of polarized electron beams, the flux is increased by four orders of magnitude.Comment: 6 pages, 3 figure

Laser-pulse-shape control of seeded QED cascades

QED cascades are complex avalanche processes of hard photon emission and electron-positron pair creation driven by ultra-strong electromagnetic fields. They play a fundamental role in astrophysical environments such as a pulsars' magnetosphere, rendering an earth-based implementation with intense lasers attractive. In the literature, QED cascades were also predicted to limit the attainable intensity in a set-up of colliding laser beams in a tenuous gas such as the residual gas of a vacuum chamber, therefore severely hindering experiments at extreme field intensities. Here, we demonstrate that the onset of QED cascades may be either prevented even at intensities around 10^{26}\text{ W/cm^{2}} with tightly focused laser pulses and low-$Z$ gases, or facilitated at intensities below 10^{24}\text{ W/cm^{2}} with enlarged laser focal areas or high-$Z$ gases. These findings pave the way for the control of novel experiments such as the generation of pure electron-positron-photon plasmas from laser energy, and for probing QED in the extreme-intensity regime where the quantum vacuum becomes unstable.Comment: 11 pages, 3 figures, 1 tabl

SFQEDtoolkit: a high-performance library for the accurate modeling of strong-field QED processes in PIC and Monte Carlo codes

Strong-field quantum electrodynamics (SFQED) processes are central in determining the dynamics of particles and plasmas in extreme electromagnetic fields such as those present in the vicinity of compact astrophysical objects or generated with ultraintense lasers. SFQEDtoolkit is an open source library designed to allow users for a straightforward implementation of SFQED processes in existing particle-in-cell (PIC) and Monte Carlo codes. Through advanced function approximation techniques, high-energy photon emission and electron-positron pair creation probability rates and energy distributions are calculated within the locally-constant-field approximation (LCFA) as well as with more advanced models [Phys. Rev. A 99, 022125 (2019)]. SFQEDtoolkit is designed to provide users with high-performance and high-accuracy, and neat examples showing its usage are provided. In the near future, SFQEDtoolkit will be enriched to model the angular distribution of the generated particles, i.e., beyond the commonly employed collinear emission approximation, as well as to model spin and polarization dependent SFQED processes. Notably, the generality and flexibility of the presented function approximation approach makes it suitable to be employed in other areas of physics, chemistry and computer science.Comment: Published open access in Computer Physics Communications under CC BY 4.0. SFQEDtoolkit can be used as a black box, in which case the user can directly refer to "Appendix A. User guide". The repository with the associated open-source code is available on github https://github.com/QuantumPlasma/SFQEDtoolki

Efficient High-Energy Photon Production in the Supercritical QED Regime

When dense high-energy lepton bunches collide, the beam particles can experience rest-frame electromagnetic fields which greatly exceed the QED critical one. Here it is demonstrated that beamstrahlung efficiently converts lepton energy to high-energy photons in this so-called supercritical QED regime, as the single-photon emission spectrum exhibits a pronounced peak close to the initial lepton energy. It is also shown that the observation of this high-energy peak in the photon spectrum requires one to mitigate multiple photon emissions during the interaction. Otherwise, the photon recoil induces strong correlations between subsequent emissions which soften the photon spectrum and suppress the peak. The high-energy peak in the photon spectrum constitutes a unique observable of photon emission in the supercritical QED regime, and provides decisive advantages for the realization of an efficient multi-TeV laserless gamma-gamma collider based on electron-electron collisions.Comment: 11 pages, 4 figures. Published version is Open Acces

Inflammation du verbe vivre di W. Mouawad: quando l'Aldilà riaccende la Vita. La mia proposta di traduzione

La traduzione teatrale è un campo d’indagine e di lavoro abbastanza recente nella storia della traduzione, avendo attirato l’interesse degli studiosi e dei traduttori da a malapena un secolo. Affascinante e poliedrica, la traduzione di opere teatrali richiede ai traduttori competenze aggiuntive rispetto agli altri tipi di traduzione: fondamentale, in particolare, è la capacità di adottare i punti di vista dei numerosi e variegati ruoli (attori, scenografi, drammaturghi, ...) che gravitano attorno a un prodotto artistico dalla duplice natura, scritta e orale. L’obiettivo di questa tesi è illustrare i procedimenti e le scelte traduttive che ho dovuto adottare per tradurre dal francese verso l’italiano l’opera teatrale Inflammation du verbe vivre (2015) del drammaturgo libanese Wajdi Mouawad (Deyr el-Qamar, 1968), in vista del suo successivo adattamento sotto forma di sopratitoli per la compagnia teatrale ravennate Teatro delle Albe, compagnia che ha deciso di presentare per la prima volta in Italia questa pièce di formazione tanto psichico-personale quanto etico-sociale. Tramite l’analisi della traduzione del titolo, dei tempi verbali delle parti narrate al passato e della restituzione di giochi di suoni e citazioni, è possibile notare come la traduzione di un’opera teatrale non è un procedimento lineare e immediato. Bensì, presuppone una profonda elasticità mentale, per entrare nel testo, scomporlo, trasformarlo e infine renderlo fruibile per un pubblico culturalmente differente da quello di partenza