arXiv subjects

Gianluca Sarri

Publications and source records attributed to Gianluca Sarri.

14 recordsLinked to original sources

arXiv2026

Observation of quantum effects on radiation reaction in strong fields

Radiation reaction, the force experienced by an accelerated charge due to radiation emission, has long been the subject of extensive theoretical and experimental research. Experimental verification of a quantum, strong-field description of radiation reaction is fundamentally important, and has wide-ranging implications for astrophysics, laser-driven particle acceleration, next-generation particle colliders and inverse-Compton photon sources for medical and industrial applications. However, the difficulty of accessing regimes where strong field and quantum effects dominate inhibited previous efforts to observe quantum radiation reaction in charged particle dynamics with high significance. We report the first high significance (> 5σ) observation of strong-field radiation reaction on electron spectra where quantum effects are substantial. We obtain the first, quantitative, strong evidence favouring the quantum-continuous and quantum-stochastic models over the classical model; the quantum models perform comparably. The lower electron energy losses predicted by the quantum models accounts for their improved performance. Model comparison was performed using a novel Bayesian framework which has widespread utility for laser-particle collision experiments, including those utilising conventional accelerators, where some collision parameters cannot be measured directly.

hep-ph↗

arXiv2025

Neural network-based deconvolution for GeV-Scale Gamma-Ray Spectroscopy

High-energy gamma-ray spectroscopy is crucial for studying and advancing the application of high-energy photons in areas like strong-field physics, high-energy-density science, and laboratory astrophysics. However, high-energy gamma-ray spectroscopy in the multi-MeV to GeV range faces significant challenges in precise spectral reconstruction. This study presents a machine learning-based inversion approach that combines a spectrometer design with advanced deconvolution algorithms. We develop a gamma-ray spectrometer optimized through Monte Carlo simulations for maximum positron yield and minimal noise. A two-stage neural network framework is proposed based on the structure of the spectrometer: a denoising autoencoder suppresses statistical noise in measured positron spectra, while a U-Net architecture solves the ill-posed inverse problem to reconstruct incident gamma spectra. This approach establishes a new methodology for gamma-ray diagnostics in strong-field QED experiments and high-energy photon sources.

physics.ins-det↗

arXiv2025

Design Initiative for a 10 TeV pCM Wakefield Collider

This document outlines a community-driven Design Study for a 10 TeV pCM Wakefield Accelerator Collider. The 2020 ESPP Report emphasized the need for Advanced Accelerator R\&D, and the 2023 P5 Report calls for the ``delivery of an end-to-end design concept, including cost scales, with self-consistent parameters throughout." This Design Study leverages recent experimental and theoretical progress resulting from a global R\&D program in order to deliver a unified, 10 TeV Wakefield Collider concept. Wakefield Accelerators provide ultra-high accelerating gradients which enables an upgrade path that will extend the reach of Linear Colliders beyond the electroweak scale. Here, we describe the organization of the Design Study including timeline and deliverables, and we detail the requirements and challenges on the path to a 10 TeV Wakefield Collider.

physics.acc-ph↗

arXiv2024

Optimizing laser coupling, matter heating, and particle acceleration from solids using multiplexed ultraintense lasers

Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology limitations. Here, we investigate how to optimize their coupling with solid targets. Experimentally, we show that overlapping two intense lasers in a mirror-like configuration onto a solid with a large preplasma can greatly improve the generation of hot electrons at the target front and ion acceleration at the target backside. The underlying mechanisms are analyzed through multidimensional particle-in-cell simulations, revealing that the self-induced magnetic fields driven by the two laser beams at the target front are susceptible to reconnection, which is one possible mechanism to boost electron energization. In addition, the resistive magnetic field generated during the transport of the hot electrons in the target bulk tends to improve their collimation. Our simulations also indicate that such effects can be further enhanced by overlapping more than two laser beams.

physics.plasm-ph↗

arXiv2021

Conceptual Design Report for the LUXE Experiment

This Conceptual Design Report describes LUXE (Laser Und XFEL Experiment), an experimental campaign that aims to combine the high-quality and high-energy electron beam of the European XFEL with a powerful laser to explore the uncharted terrain of quantum electrodynamics characterised by both high energy and high intensity. We will reach this hitherto inaccessible regime of quantum physics by analysing high-energy electron-photon and photon-photon interactions in the extreme environment provided by an intense laser focus. The physics background and its relevance are presented in the science case which in turn leads to, and justifies, the ensuing plan for all aspects of the experiment: Our choice of experimental parameters allows (i) effective field strengths to be probed at and beyond the Schwinger limit and (ii) a precision to be achieved that permits a detailed comparison of the measured data with calculations. In addition, the high photon flux predicted will enable a sensitive search for new physics beyond the Standard Model. The initial phase of the experiment will employ an existing 40 TW laser, whereas the second phase will utilise an upgraded laser power of 350 TW. All expectations regarding the performance of the experimental set-up as well as the expected physics results are based on detailed numerical simulations throughout.

hep-ex↗

arXiv2021

Ultra-short, MeV-scale laser-plasma positron source for positron annihilation lifetime spectroscopy

Sub-micron defects represent a well-known fundamental problem in manufacturing since they can significantly affect performance and lifetime of virtually any high-value component. Positron annihilation lifetime spectroscopy is arguably the only established method capable of detecting defects down to the sub-nanometer scale but, to date, it only works for surface studies, and with limited resolution. Here, we experimentally and numerically show that laser-driven systems can overcome these well-known limitations, by generating ultra-short positron beams with a kinetic energy tuneable from 500 keV up to 2 MeV and a number of positrons per shot in a 50 keV energy slice \color{black} of the order of $10^3$. Numerical simulations of the expected performance of a typical mJ-scale kHz laser demonstrate the possibility of generating MeV-scale narrow-band and ultra-short positron beams with a flux exceeding $10^5$ positrons/s, of interest for fast volumetric scanning of materials at high resolution.

physics.acc-ph↗

arXiv2020

Non-invasive characterisation of a laser-driven positron beam

We report on an indirect and non-invasive method to simultaneously characterise the energy-dependent emittance and source size of ultra-relativistic positron beams generated during the propagation of a laser-wakefield accelerated electron beam through a high-Z converter target. The strong correlation of the geometrical emittance of the positrons with that of the scattered electrons allows the former to be inferred, with high accuracy, from monitoring the latter. The technique has been tested in a proof-of-principle experiment where, for 100 MeV positrons, we infer geometrical emittances and source sizes of the order of $ε_{e^+} \approx$ 3 $μ$m and $D_{e^+} \approx$ 150 $μ$m, respectively. This is consistent with the numerically predicted possibility of achieving sub-$μ$m geometrical emittances and micron-scale source sizes at the GeV level.

physics.plasm-ph↗

arXiv2019

Plasma Wakefield Accelerator Research 2019 - 2040: A community-driven UK roadmap compiled by the Plasma Wakefield Accelerator Steering Committee (PWASC)

The acceleration gradients generated in a laser- or beam-driven plasma wakefield accelerator are typically three orders of magnitude greater than those produced by a conventional accelerator, and hence plasma accelerators can open a route to a new generation of very compact machines. In addition, plasma-based accelerators can generate beams with unique properties, such as tens of kiloamp peak currents, attosecond bunch duration, ultrahigh brightness and intrinsic particle beam-laser pulse synchronization. In this roadmap we review the status of plasma accelerator research in the UK. We outline potential applications, describe the research and development required to enable those applications, and discuss synergies with related areas of research. We also set-out the resources required to realise these ambitions and provide a timeline for advances in the key areas.

physics.acc-ph↗

arXiv2018

Laser-driven high-quality positron sources as possible injectors for plasma-based accelerators

The intrinsic constraints in the amplitude of the accelerating fields sustainable by radio-frequency accelerators demand for the pursuit of alternative and more compact acceleration schemes. Among these, plasma-based accelerators are arguably the most promising, thanks to the high-accelerating fields they can sustain, greatly exceeding the GeV/m. While plasma-based acceleration of electrons is now sufficiently mature for systematic studies in this direction, positron acceleration is still at its infancy, with limited projects currently undergoing to provide a viable test facility for further experiments. In this article, we propose a recently demonstrated laser-driven configuration as a relatively compact and inexpensive source of high-quality ultra-relativistic positrons for laser-driven and particle-driven plasma wakefield acceleration studies. Monte-Carlo simulations show that near-term high-intensity laser facilities can produce positron beams with high-current, femtosecond-scale duration, and sufficiently low normalised emittance at energies in the GeV range to be injected in further acceleration stages.

physics.plasm-ph↗

arXiv2016

Particle-in-cell simulation study of a lower-hybrid shock

The expansion of a magnetized high-pressure plasma into a low-pressure ambient medium is examined with particle-in-cell (PIC) simulations. The magnetic field points perpendicularly to the plasma's expansion direction and binary collisions between particles are absent. The expanding plasma steepens into a quasi-electrostatic shock that is sustained by the lower-hybrid (LH) wave. The ambipolar electric field points in the expansion direction and it induces together with the background magnetic field a fast E cross B drift of electrons. The drifting electrons modify the background magnetic field, resulting in its pile-up by the LH shock. The magnetic pressure gradient force accelerates the ambient ions ahead of the LH shock, reducing the relative velocity between the ambient plasma and the LH shock to about the phase speed of the shocked LH wave, transforming the LH shock into a nonlinear LH wave. The oscillations of the electrostatic potential have a larger amplitude and wavelength in the magnetized plasma than in an unmagnetized one with otherwise identical conditions. The energy loss to the drifting electrons leads to a noticable slowdown of the LH shock compared to that in an unmagnetized plasma.

physics.plasm-ph↗

arXiv2014

The evolution of a slow electrostatic shock into a plasma shock mediated by electrostatic turbulence

The collision of two plasma clouds at a speed that exceeds the ion acoustic speed can result in the formation of shocks. This phenomenon is observed not only in astrophysical scenarios such as the propagation of supernova remnant (SNR) blast shells into the interstellar medium, but also in laboratory-based laser-plasma experiments. These experiments and supporting simulations are thus seen as an attractive platform for the small-scale reproduction and study of astrophysical shocks in the laboratory. We model two plasma clouds, which consist of electrons and ions, with a 2D PIC simulation. The ion temperatures of both clouds differ by a factor of 10. Both clouds collide at a speed, which is realistic for laboratory studies and for SNR shocks in their late evolution phase like that of RCW86. A magnetic field, which is orthogonal to the simulation plane, has a strength that is comparable to that at SNR shocks. A forward shock forms between the overlap layer of both plasma clouds and the cloud with the cooler ions. A large-amplitude ion acoustic wave is observed between the overlap layer and the cloud with the hotter ions. It does not steepen into a reverse shock, because its speed is below the ion acoustic speed. A gradient of the magnetic field amplitude builds up close to the forward shock as it compresses the magnetic field. This gradient gives rise to an electron drift that is fast enough to trigger an instability. Electrostatic ion acoustic wave turbulence develops ahead of the shock. It widens its transition layer and thermalizes the ions, but the forward shock remains intact.

astro-ph.HE↗

arXiv2013

Modification of the formation of high-Mach number electrostatic shock-like structures by the ion acoustic instability

The formation of unmagnetized electrostatic shock-like structures with a high Mach number is examined with one- and two-dimensional particle-in-cell (PIC) simulations. The structures are generated through the collision of two identical plasma clouds, which consist of equally hot electrons and ions with a mass ratio of 250. The Mach number of the collision speed with respect to the initial ion acoustic speed of the plasma is set to 4.6. This high Mach number delays the formation of such structures by tens of inverse ion plasma frequencies. A pair of stable shock-like structures is observed after this time in the 1D simulation, which gradually evolve into electrostatic shocks. The ion acoustic instability, which can develop in the 2D simulation but not in the 1D one, competes with the nonlinear process that gives rise to these structures. The oblique ion acoustic waves fragment their electric field. The transition layer, across which the bulk of the ions change their speed, widens and their speed change is reduced. Double layer-shock hybrid structures develop.

physics.plasm-ph↗

arXiv2012

Simulation of relativistically colliding laser-generated electron flows

The plasma dynamics resulting from the simultaneous impact, of two equal, ultra-intense laser pulses, in two spatially separated spots, onto a dense target is studied via particle-in-cell (PIC) simulations. The simulations show that electrons accelerated to relativistic speeds, cross the target and exit at its rear surface. Most energetic electrons are bound to the rear surface by the ambipolar electric field and expand along it. Their current is closed by a return current in the target, and this current configuration generates strong surface magnetic fields. The two electron sheaths collide at the midplane between the laser impact points. The magnetic repulsion between the counter-streaming electron beams separates them along the surface normal direction, before they can thermalize through other beam instabilities. This magnetic repulsion is also the driving mechanism for the beam-Weibel (filamentation) instability, which is thought to be responsible for magnetic field growth close to the internal shocks of gamma-ray burst (GRB) jets. The relative strength of this repulsion compared to the competing electrostatic interactions, which is evidenced by the simulations, suggests that the filamentation instability can be examined in an experimental setting.

physics.plasm-ph↗

arXiv2012

Magnetic instability in a dilute circular rarefaction wave

The generation of a magnetic field in a circular rarefaction wave is examined in form of a 2D particle-in-cell (PIC) simulation. Electrons with a temperature of 32 keV are uniformly distributed within a cloud with a radius of 14.2 electron skin depths. They expand under their thermal pressure and carry with them the cold protons, which are initially concentrated in a hollow ring at the boundary of the electron cloud. The interior of the ring contains an immobile positive charge background that compensates for the electron charge. The protons expand in form of a circularly symmetric rarefaction wave and they extract energy from the electrons. A thermal anisotropy of the electrons develops and triggers through a Weibel-type instability the growth of TM waves within the plasma cloud, which acts as a wave guide. The changing cross section of this waveguide introduces a coupling between the TM wave and a TE wave and in-plane magnetic fields grow. The relevance of the simulation results to a previous experimental study of a laser-ablated wire is discussed.

physics.plasm-ph↗