arXiv subjects

Sébastien Corde

Publications and source records attributed to Sébastien Corde.

10 recordsLinked to original sources

arXiv2026

Multi-GeV Electron Combs from a Plasma Wakefield Accelerator

Plasma accelerators now produce GeV-class electron beams with brightness and stability sufficient to drive free-electron lasers. Beyond this, they possess a unique yet largely unexplored capability: shaping the phase space of the beam in situ during injection, on femtosecond or shorter timescales. Here we demonstrate this capability by generating a multi-GeV electron comb comprising more than ten microbunches simultaneously separated in both energy and time. Periodic pinching of the drive beam inside its self-excited plasma wake sequentially injects microbunches via ionization of embedded helium atoms at successive betatron oscillations, while the gently varying plasma density maps each bunchlet to a distinct wake phase, compressing electrons trapped over a ~17 cm region into a comb only micrometers long. Individual microbunches exhibit percent-level energy spreads, energy spacing up to ten percent, and contain several picocoulomb charge. The percent-level spreads and parabolic energy-spacing trend provide experimental evidence for sub-femtosecond microbunch durations and few-femtosecond separations as revealed by beam-loading analysis and confirmed by particle-in-cell simulations. This work demonstrates femtosecond, in-situ phase-space shaping in plasma accelerators, paving the way for electron beams with tailored energy-time structure.

physics.acc-ph↗

arXiv2026

Initial Performance of the E320 Tracker

Our recent study discussed the prospects for measuring single positrons produced in electron-laser collisions via the nonlinear Breit-Wheeler deep-tunneling process in the SLAC Experiment 320 at the FACET-II RF LINAC. In this work, we demonstrate how a tracking detector, that is a scaled-down version of the one discussed in the prospective simulation study, enables the measurement. This prototype detector, installed in Aug 2024, is built out of five layers of single ALPIDE chips. The data are taken from several standalone runs completed in Nov 2024 and Feb 2025. We use positrons generated through conversion of Bremsstrahlung photons as a proxy to the nonlinear Breit-Wheeler process. These positrons are produced by the beam electrons in a thin Beryllium foil close to the experiment's interaction point. The tracking approach used in this initial work is based on a Hough-Transform seeding algorithm followed by a straight line fit confined to the detector volume. Even with this relatively simple approach, we are able to measure a signal rate of $(1.20\pm0.06_{stat.}\pm0.56_{syst.})\times10^{-1}$ positrons per shot. This signal rate is comparable to the nonlinear Breit-Wheeler rate expected in the main experiment. Notably, the measurement is achieved under an extreme, unprecedented background hit density of ~1.7/mm$^2$, unlike the main experiment, where at least a twice lower density is expected. This large background is mostly due to secondary particles produced when the large flux of Bremsstrahlung photons interacts with the material of the beamline elements. When the foil is retracted, the false-positive signal rate is shown to be four orders of magnitude smaller than the signal rate. We further show that the high spatial tracking resolution of ~5 micron allows to characterize the positrons' spectra. The results are compared to simulations, which are found to be compatible with the data.

hep-ex↗

arXiv2026

Strong-field focusing of high-energy particles in beam-multifoil collisions

Extreme beams of charged particles and photons, reaching ultrahigh densities or producing intense gamma-ray bursts, are central to accelerator physics, laboratory astrophysics, and strong-field quantum electrodynamics research. Yet their generation is hindered by conventional focusing methods at multi-GeV energies that rely on massive magnetic assemblies, limiting compactness and attainable density. Here we report the first experimental observation of a fundamentally new focusing mechanism, in which a high-energy charged-particle beam is focused by its own magnetic field reflected from a stack of thin metallic foils via near-field coherent-transition-radiation. The experiment, performed at SLAC's FACET-II facility, reveals strong, cumulative focusing across a broad range of beam configurations, enabled by the delivered 10 GeV, 1 nC, 10 Hz electron beam. The measurements closely agree with predictions from an analytical model and particle-in-cell simulations. These results demonstrate that multifoil focusing is a remarkably straightforward, self-aligned approach to the generation of ultrahigh density beams, opening a path to explore unprecedented regimes of beam-matter interaction and high-energy radiation.

physics.acc-ph↗

arXiv2024

Self-triggered strong-field QED collisions in laser-plasma interaction

Exploring quantum electrodynamics in the most extreme conditions, where electron-positron pairs can emerge in the presence of a strong background field, is now becoming possible in Compton collisions between ultraintense lasers and energetic electrons. In the strong-field regime, the colliding electron emits $γ$ rays that decay into pairs in the strong laser field. While the combination of conventional accelerators and lasers of sufficient power poses significant challenges, laser-plasma accelerators offer a promising alternative for producing the required multi-GeV electron beams. To overcome the complexities of colliding these beams with another ultraintense laser pulse, we propose a novel scheme in which a single laser pulse both accelerates the electrons and collides with them after self-focusing in a dedicated plasma section and reflecting off a plasma mirror. The laser intensity boost in the plasma allows the quantum interaction parameter to be greatly increased. Using full-scale numerical simulations, we demonstrate that a single 100 J laser pulse can achieve a deep quantum regime with electric fields in the electron rest frame as high as $χ_e\sim 5$ times the Schwinger critical field, resulting in the production of about 40 pC of positrons.

physics.plasm-ph↗

arXiv2024

Channeling Acceleration in Crystals and Nanostructures and Studies of Solid Plasmas: New Opportunities

Plasma wakefield acceleration (PWFA) has shown illustrious progress and resulted in an impressive demonstration of tens of GeV particle acceleration in meter-long single structures. To reach even higher energies in the 1 TeV to 10 TeV range, a promising scheme is channeling acceleration in solid-density plasmas within crystals or nanostructures. The E336 experiment studies the beam-nanotarget interaction with the highly compressed electron bunches available at the FACET-II accelerator. These studies furthermore involve an in-depth research on dynamics of beam-plasma instabilities in ultra-dense plasma, its development and suppression in structured media like carbon nanotubes and crystals, and its potential use to transversely modulate the electron bunch.

physics.acc-ph↗

arXiv2023

Beam current from downramp injection in electron-driven plasma wakefields

We study the stability of plasma wake wave and the properties of density-downramp injection in an electron-driven plasma accelerator. In this accelerator type, a short high-current electron bunch (generated by a conventional accelerator or a laser-wakefield acceleration stage) drives a strongly nonlinear plasma wake wave (blowout), and accelerated electrons are injected into it using a sharp density transition which leads to the elongation of the wake. The accelerating structure remains highly stable until the moment some electrons of the driver reach almost zero energy, which corresponds to the best interaction length for optimal driver-to-plasma energy transfer efficiency. For a particular driver, this efficiency can be optimized by choosing appropriate plasma density. Studying the dependence of the current of the injected bunch on driver and plasma parameters, we show that it does not depend on the density downramp length as long as the condition for trapping is satisfied. Most importantly, we find that the current of the injected bunch primarily depends on just one parameter which combines both the properties of the driver (its current and duration) and the plasma density.

physics.plasm-ph↗

arXiv2022

High average gradient in a laser-gated multistage plasma wakefield accelerator

Plasma wakefield accelerators driven by particle beams are capable of providing accelerating gradient several orders of magnitude higher than currently used radio-frequency technology, which could reduce the length of particle accelerators, with drastic influence on the development of future colliders at TeV energies and the minimization of x-ray free-electron lasers. Since inter-plasma components and distances are among the biggest contributors to the total accelerator length, the design of staged plasma accelerators is one of the most important outstanding questions in order to render this technology instrumental. Here, we present a novel concept to optimize inter-plasma distances in a staged beam-driven plasma accelerator by drive-beam coupling in the temporal domain and gating the accelerator via a femtosecond ionization laser.

physics.acc-ph↗

arXiv2021

Extremely Dense Gamma-Ray Pulses in Electron Beam-Multifoil Collisions

Sources of high-energy photons have important applications in almost all areas of research. However, the photon flux and intensity of existing sources is strongly limited for photon energies above a few hundred keV. Here we show that a high-current ultrarelativistic electron beam interacting with multiple submicrometer-thick conducting foils can undergo strong self-focusing accompanied by efficient emission of gamma-ray synchrotron photons. Physically, self-focusing and high-energy photon emission originate from the beam interaction with the near-field transition radiation accompanying the beam-foil collision. This near field radiation is of amplitude comparable with the beam self-field, and can be strong enough that a single emitted photon can carry away a significant fraction of the emitting electron energy. After beam collision with multiple foils, femtosecond collimated electron and photon beams with number density exceeding that of a solid are obtained. The relative simplicity, unique properties, and high efficiency of this gamma-ray source open up new opportunities for both applied and fundamental research including laserless investigations of strong-field QED processes with a single electron beam.

physics.plasm-ph↗

arXiv2020

Generation of terawatt, attosecond pulses from relativistic transition radiation

When a fs duration and hundreds of kA peak current electron beam traverses the vacuum and high-density plasma interface a new process, that we call relativistic transition radiation (R-TR) generates an intense $\sim100$ as pulse containing $\sim$ TW power of coherent VUV radiation accompanied by several smaller fs duration satellite pulses. This pulse inherits the radial polarization of the incident beam field and has a ring intensity distribution. This R-TR is emitted when the beam density is comparable to the plasma density and the spot size much larger than the plasma skin depth. Physically, it arises from the return current or backward relativistic motion of electrons starting just inside the plasma that Doppler up-shifts the emitted photons. The number of R-TR pulses is determined by the number of groups of plasma electrons that originate at different depths within the first plasma wake period and emit coherently before phase mixing.

physics.plasm-ph↗

arXiv2017

High-brilliance betatron gamma-ray source powered by laser-accelerated electrons

Recent progress in laser-driven plasma acceleration now enables the acceleration of electrons to several gigaelectronvolts. Taking advantage of these novel accelerators, ultra-short, compact and spatially coherent X-ray sources called betatron radiation have been developed and applied to high-resolution imaging. However, the scope of the betatron sources is limited by a low energy efficiency and a photon energy in the 10's of kiloelectronvolt range, which for example prohibits the use of these sources for probing dense matter. Here, based on three-dimensional particle-in-cell simulations, we propose an original hybrid scheme that combines a low-density laser-driven plasma accelerator with a high-density beam-driven plasma radiator, and thereby considerably increases the photon energy and the radiated energy of the betatron source. The energy efficiency is also greatly improved, with about 1% of the laser energy transferred to the radiation, and the gamma-ray photon energy exceeds the megaelectronvolt range when using a 15 J laser pulse. This high-brilliance hybrid betatron source opens the way to a wide range of applications requiring MeV photons, such as the production of medical isotopes with photo-nuclear reactions, radiography of dense objects in the defense or industrial domains and imaging in nuclear physics.

physics.plasm-ph↗