Showing 1–11 of 11 results for author: Babjak, R

Microcoulomb-level electron beam and multi-Joule hard X-rays driven by a high-efficiency laser-plasma accelerator

Authors: B. Mahieu, L. Ribotte, W. Cayzac, G. Boutoux, R. Parreault, J. Gastineau, E. Lamoine, F. Audo, R. Babjak, D. Batani, N. Blanchot, J. L. Bourgade, M. Brochier, T. Caillaud, P. Canel, S. Cavaro, C. Chappuis, S. Debesset, R. Diaz, E. D Humieres, W. Duchastenier, R. du Jeu, A. Duval, B. Etchessahar, M. Ferri , et al. (16 additional authors not shown)

Abstract: We report on the production of ultrahigh-charge relativistic electron beams and the development of a laser-wakefield acceleration platform at the LMJ facility. Making use of the kilojoule-class, sub-picosecond PETAL laser pulse focused onto a supersonic helium gas jet, electron beams carrying a total charge beyond 1 $μ$C were generated, with energies up to $\sim$500 MeV. Given the ps-scale laser p… ▽ More We report on the production of ultrahigh-charge relativistic electron beams and the development of a laser-wakefield acceleration platform at the LMJ facility. Making use of the kilojoule-class, sub-picosecond PETAL laser pulse focused onto a supersonic helium gas jet, electron beams carrying a total charge beyond 1 $μ$C were generated, with energies up to $\sim$500 MeV. Given the ps-scale laser pulse duration, an on-target intensity approaching $10^{19}~\mathrm{W/cm^2}$, and a plasma density reaching 2% of the critical density, electron energisation arises from a combination of self-modulated laser wakefield acceleration (SMLWFA) and direct laser acceleration (DLA). The resulting electron spectrum exhibits a Maxwellian-like distribution, characteristic of this mixed SMLWFA/DLA regime. The total energy carried by the electron beam is estimated to be up to 17 J, within a sub-ps duration. A broadband Joule-level photon beam was also produced by Bremsstrahlung, demonstrating the potential for future applications. Experimental results are supported by start-to-end numerical simulations, including 3-D particle-in-cell and Monte-Carlo particle transport calculations. These findings pave the way for applications requiring high-charge electron beams, including the generation of high-power secondary radiation or particle sources. The use of these beams to probe matter in high-energy density states driven by the nanosecond-duration LMJ beams represents another promising avenue. △ Less

Submitted 18 August, 2026; v1 submitted 17 August, 2026; originally announced August 2026.

Report on the Advanced Linear Collider Study Group (ALEGRO) Workshop 2026

Authors: L. Verra, P. Muggli, B. Cross, E. Adli, R. Babjak, T. Barklow, F. Bencivenga, C. Benedetti, C. Benedetti, M. Buscher, S. S. Bulanov, A. Caldwell, G. Chen, O. Chubenko, R. D'Arcy, S. Diederichs, K. Downham, J. Farmer, M. Ferrario, A. Ferran Pousa, A. Formenti, M. Fuchs, S. Gessner, L. Giannessi, Z. Gong , et al. (37 additional authors not shown)

Abstract: The 7th ALEGRO workshop, hosted by INFN Frascati National Laboratories from 3rd to 5th March 2026, brought together the international Advanced Novel Accelerators (ANA) community to discuss the role of advanced wakefield accelerators (AWA) in particle and high-energy physics. Organized under the ICFA-ANA panel, the workshop highlighted recent progress in plasma- and structure-based wakefield accele… ▽ More The 7th ALEGRO workshop, hosted by INFN Frascati National Laboratories from 3rd to 5th March 2026, brought together the international Advanced Novel Accelerators (ANA) community to discuss the role of advanced wakefield accelerators (AWA) in particle and high-energy physics. Organized under the ICFA-ANA panel, the workshop highlighted recent progress in plasma- and structure-based wakefield acceleration and strengthened international collaboration toward future energy-frontier colliders. A major focus was the ongoing 10 TeV linear collider design study, launched in 2025 following the US P5 recommendations. A dedicated session covered accelerator concepts, enabling technologies, and the associated physics case, while recognizing that future priorities will depend on the outcome of the European Strategy for Particle Physics Update. The workshop also reviewed nearer-term applications of advanced accelerators, including fixed-target experiments, injectors for future colliders and light sources, plasma-based Higgs factory concepts, and proton-driven plasma wakefield acceleration. Beyond high-energy physics, sessions covered free-electron lasers, synchrotron light sources, and strong-field QED. Recent demonstrations of FEL lasing with plasma-accelerated electron beams highlighted significant progress in beam quality and accelerator performance. Operational challenges for reliable user facilities, including high-availability laser and electron-beam systems, were discussed alongside the growing role of artificial intelligence and machine learning for accelerator optimization and control. This report summarizes the workshop discussions and conclusions from the chairs, together with short contributions from the presenters, providing an overview of the current status and future prospects of advanced wakefield accelerators. △ Less

Submitted 10 July, 2026; originally announced July 2026.

Single-laser scheme for reaching strong field QED regime via direct laser acceleration

Authors: Robert Babjak, Marija Vranic

Abstract: We investigate a single-laser scheme for reaching the strong-field QED regime based on direct laser acceleration (DLA) of electrons followed by their head-on collision with the same laser pulse reflected from an overdense foil. In this configuration, electrons are first accelerated inside an underdense plasma by a relativistic laser pulse and subsequently interact with the reflected laser field, e… ▽ More We investigate a single-laser scheme for reaching the strong-field QED regime based on direct laser acceleration (DLA) of electrons followed by their head-on collision with the same laser pulse reflected from an overdense foil. In this configuration, electrons are first accelerated inside an underdense plasma by a relativistic laser pulse and subsequently interact with the reflected laser field, emitting high-energy photons via nonlinear Compton scattering which decay into electron-positron pairs through the nonlinear Breit-Wheeler process. Using analytical scalings supported by quasi-3D particle-in-cell simulations including QED effects, we demonstrate that a laser pulse with power as low as 2 PW is sufficient to reach the quantum regime characterized by $χ_e> 1$ . For higher powers, we observe a rapid nonlinear increase in the number of generated positrons, reaching more than 2 nC for a 10 PW laser pulse with energy of approximately 1.1 kJ. A semi-analytical model is employed to estimate the positron yield, showing good agreement with simulation results. We further study the influence of laser depletion and the positioning of the reflecting foil on the efficiency of pair production. The presented scheme provides an experimentally feasible platform for probing strong-field QED effects using currently available multi-petawatt laser systems. △ Less

Submitted 21 January, 2026; originally announced January 2026.

Comments: 33 pages, 10 figures

Betatron radiation emitted during the direct laser acceleration of electrons in underdense plasmas

Authors: Robert Babjak, Marija Vranic

Abstract: Relativistic laser pulses can accelerate electrons up to energies of several GeV during the interaction with gaseous targets through the direct laser acceleration (DLA) mechanism. While the electrons are accelerated to high energies, they oscillate transversely to the laser propagation direction, emitting radiation. We demonstrate using particle-in-cell (PIC) simulations that the high accelerated… ▽ More Relativistic laser pulses can accelerate electrons up to energies of several GeV during the interaction with gaseous targets through the direct laser acceleration (DLA) mechanism. While the electrons are accelerated to high energies, they oscillate transversely to the laser propagation direction, emitting radiation. We demonstrate using particle-in-cell (PIC) simulations that the high accelerated electron charge enables DLA sources to emit $\sim 10^{10}~\rm{photons}/0.1\%\rm{BW}$ at energies of hundreds MeV when interacting with multi-petawatt laser pulses. We provide an analytical estimate of the expected critical frequency for the DLA betatron spectrum which is in strong agreement with PIC simulations. We also show that using gas jets of low density ($\sim 10^{19}~\rm{cm^{-3}}$) is beneficial for the brightness of the source, since low plasma density produces collimated radiation. If the laser pulse is focused to an optimal spot size that results in the highest cut-off energies, conversion efficiency from laser to radiation can reach up to a few percent, which makes the DLA a promising high-brilliance source of gamma-ray radiation. △ Less

Submitted 10 February, 2025; originally announced February 2025.

Comments: 29 pages, 7 figures, submitted to PPCF

Improved Bethe-Heitler positron creation and retention by combining direct laser acceleration and solid target interaction within a gas jet

Authors: Lucas I. Iñigo Gamiz, Robert Babjak, Bertrand Martinez, Marija Vranić

Abstract: The next generation of Petawatt-class lasers presents the opportunity to study positron production and acceleration experimentally, in an all-optical setting. Several configurations were proposed to produce and accelerate positrons in a single laser stage. However, these configurations have yielded limited positron beam quality and low particle count. This paper presents methods for improving the… ▽ More The next generation of Petawatt-class lasers presents the opportunity to study positron production and acceleration experimentally, in an all-optical setting. Several configurations were proposed to produce and accelerate positrons in a single laser stage. However, these configurations have yielded limited positron beam quality and low particle count. This paper presents methods for improving the injection and retention of positrons obtained via Bethe-Heitler pair production and accelerated using direct laser acceleration (DLA) in a plasma channel. The work first introduces a semi-analytical model which predicts laser energy depletion in this highly nonlinear regime. We demonstrate through PIC simulations that accelerated electrons can induce charge inversion within the channel, leading to positron trapping and acceleration. We investigate how laser focusing position, channel wall density, target foil position and target thickness influence positron creation and retention. Our configuration can achieve an 8-fold increase in positron retention compared to previous studies and a higher number of positrons produced overall. This work establishes a robust, single-stage approach for obtaining positron beams, opening new avenues for experiments with Petawatt-class lasers and potential applications in electron-positron collisions and QED cascades. △ Less

Submitted 26 November, 2024; originally announced November 2024.

Direct laser acceleration in varying plasma density profiles

Authors: Robert Babjak, Bertrand Martinez, Miroslav Krus, Marija Vranic

Abstract: Direct laser acceleration has proven to be an efficient source of high-charge electron bunches and high brilliance X-rays. However, an analytical description of the acceleration in the interaction with varying plasma density targets is still missing. Here, we provide an analytical estimate of the maximum energies that electrons can achieve in such a case. We demonstrate that the maximum energy dep… ▽ More Direct laser acceleration has proven to be an efficient source of high-charge electron bunches and high brilliance X-rays. However, an analytical description of the acceleration in the interaction with varying plasma density targets is still missing. Here, we provide an analytical estimate of the maximum energies that electrons can achieve in such a case. We demonstrate that the maximum energy depends on the local electron properties at the moment when the electron fulfills the resonant condition at the beginning of the acceleration. This knowledge enables density shaping for various purposes. One application is to decrease the required acceleration distance which has important implications for multi-petawatt laser experiments, where strong laser depletion could play a crucial role. Another use for density tailoring is to achieve acceleration beyond the radiation reaction limit. We derive the energy scaling law that is valid for arbitrary density profile that varies slowly compared with the betatron period. Our results can be applied to electron heating in exponential preplasma of thin foils, ablating plasma plumes, or gas jets with long-scale ramp-up. △ Less

Submitted 15 June, 2024; originally announced June 2024.

Direct Laser Acceleration of Bethe-Heitler positrons in laser-channel interactions

Authors: Bertrand Martinez, Robert Babjak, Marija Vranic

Abstract: Positron creation and acceleration is one of the major challenges for constructing future lepton colliders. On the one hand, conventional technology can provide a solution, but at a prohibitive cost and scale. On the other hand, alternative, reduced-scale ideas for positron beam generation could bring this dream closer to reality. Here we propose a novel plasma-based positron acceleration method u… ▽ More Positron creation and acceleration is one of the major challenges for constructing future lepton colliders. On the one hand, conventional technology can provide a solution, but at a prohibitive cost and scale. On the other hand, alternative, reduced-scale ideas for positron beam generation could bring this dream closer to reality. Here we propose a novel plasma-based positron acceleration method using a powerful laser propagating through a dense and narrow plasma channel. A large amount of electrons is injected within the channel during laser propagation. This electron loading creates static fields in the plasma, enabling positrons to be guided transversely while they directly gain energy from the laser field itself. Within this context, we present a theoretical model to describe how the laser injects the electrons and estimate the beam-loaded effective electron density. We validate our theoretical predictions through Quasi-3D PIC simulations and demonstrate the robustness of this guiding and direct laser acceleration process for positrons. Our approach could pave the way for testing this new positron acceleration scheme at ELI-Beamlines, showcasing unprecedentedly high average energy gain rate of a few TeV/m. The fireball jet produced contains GeV-level electrons, positrons, and x-rays, opening the path towards potential laboratory astrophysics experiments using these beams. △ Less

Submitted 31 May, 2024; originally announced May 2024.

Direct laser acceleration: A model for the electron injection from the walls of a cylindrical guiding structure

Authors: P. Valenta, D. Maslarova, R. Babjak, B. Martinez, S. V. Bulanov, M. Vranic

Abstract: We use analytical methods and particle-in-cell simulation to investigate the origin of electrons accelerated by the process of direct laser acceleration driven by high-power laser pulses in preformed narrow cylindrical plasma channels. The simulation shows that the majority of accelerated electrons are originally located along the interface between the channel wall and the channel interior. The an… ▽ More We use analytical methods and particle-in-cell simulation to investigate the origin of electrons accelerated by the process of direct laser acceleration driven by high-power laser pulses in preformed narrow cylindrical plasma channels. The simulation shows that the majority of accelerated electrons are originally located along the interface between the channel wall and the channel interior. The analytical model based on the electron hydrodynamics illustrates the underlying physical mechanism of the release of electrons from the channel wall when irradiated by an intense laser, the subsequent electron dynamics, and the corresponding evolution of the channel density profile. The quantitative predictions of the total charge of released electrons and the average electron density inside the channel are validated by comparison with the simulation results. △ Less

Submitted 28 May, 2024; v1 submitted 22 February, 2024; originally announced February 2024.

Comments: 10 pages, 9 figures

Journal ref: Phys. Rev. E 109, 065204 (2024)

The Influence of Laser Focusing Conditions on the Direct Laser Acceleration of Electrons

Authors: H. Tang, K. Tangtartharakul, R. Babjak, I-L. Yeh, F. Albert, H. Chen, P. T. Campbell, Y. Ma, P. M. Nilson, B. K. Russell, J. L. Shaw, A. G. R. Thomas, M. Vranic, A. V. Arefiev, L. Willingale

Abstract: Direct Laser Acceleration (DLA) of electrons during a high-energy, picosecond laser interaction with an underdense plasma has been demonstrated to be substantially enhanced by controlling the laser focusing geometry. Experiments using the OMEGA EP facility measured electrons accelerated to maximum energies exceeding 120 times the ponderomotive energy under certain laser focusing, pulse energy, and… ▽ More Direct Laser Acceleration (DLA) of electrons during a high-energy, picosecond laser interaction with an underdense plasma has been demonstrated to be substantially enhanced by controlling the laser focusing geometry. Experiments using the OMEGA EP facility measured electrons accelerated to maximum energies exceeding 120 times the ponderomotive energy under certain laser focusing, pulse energy, and plasma density conditions. Two-dimensional particle-in-cell simulations show that the laser focusing conditions alter the laser field evolution, channel fields generation, and electron oscillation, all of which contribute to the final electron energies. The optimal laser focusing condition occurs when the transverse oscillation amplitude of the accelerated electron in the channel fields matches the laser beam width, resulting in efficient energy gain. Through this observation, a simple model was developed to calculate the optimal laser focal spot size in more general conditions and is validated by experimental data. △ Less

Submitted 12 February, 2024; originally announced February 2024.

Comments: 14 pages, 6 figures

Direct laser acceleration in underdense plasmas with multi-PW lasers: a path to high-charge, GeV-class electron bunches

Authors: R. Babjak, L. Willingale, A. Arefiev, M. Vranic

Abstract: The direct laser acceleration (DLA) of electrons in underdense plasmas can provide 100s of nC of electrons accelerated to near-GeV energies using currently available lasers. Here we demonstrate the key role of electron transverse displacement in the acceleration and use it to analytically predict the expected maximum electron energies. The energy scaling is shown to be in agreement with full-scale… ▽ More The direct laser acceleration (DLA) of electrons in underdense plasmas can provide 100s of nC of electrons accelerated to near-GeV energies using currently available lasers. Here we demonstrate the key role of electron transverse displacement in the acceleration and use it to analytically predict the expected maximum electron energies. The energy scaling is shown to be in agreement with full-scale quasi-3D particle-in-cell (PIC) simulations of a laser pulse propagating through a preformed guiding channel and can be directly used for optimizing DLA in near-future laser facilities. The strategy towards optimizing DLA through matched laser focusing is presented for a wide range of plasma densities paired with current and near-future laser technology. Electron energies in excess of 10 GeV are accessible for lasers at $I\sim 10^{21}~\mathrm{W/cm^2}$. △ Less

Submitted 7 March, 2024; v1 submitted 20 April, 2023; originally announced April 2023.

Comments: Accepted for publication in PRL

The role of standing wave in the generation of hot electrons by femtosecond laser beams incident on dense ionized target

Authors: Robert Babjak, Jan Psikal

Abstract: We demonstrate the differences in hot electron absorption mechanisms dominant in the interaction of femtosecond laser pulse with intensities 1e18 W/cm2 and 1e21 W/cm2 on fully ionized target with steep density profile and preplasma with moderate scale length (3 microns). We show that acceleration of each electron starts at the moment when magnetic component of standing electromagnetic wave changes… ▽ More We demonstrate the differences in hot electron absorption mechanisms dominant in the interaction of femtosecond laser pulse with intensities 1e18 W/cm2 and 1e21 W/cm2 on fully ionized target with steep density profile and preplasma with moderate scale length (3 microns). We show that acceleration of each electron starts at the moment when magnetic component of standing electromagnetic wave changes its polarity in regime without preplasma. In the presence of preplasma the stochastic heating is the dominant absorption mechanism along with the longitudinal electric field. It is observed, that wave's energy is absorbed only if standing wave is already created at the position of electron during the interaction with the pulse with intensity 1e18 W/cm2. In the case with intensity 1e21 W/cm2, part of electrons is pre-accelerated in front of the target before the reflection and following stochastic heating. The presence of preplasma results in electron temperatures close to or even exceeding ponderomotive scaling. At higher intensity, the re-injection of electrons previously repelled by incident wave's ponderomotive force into high-field regions is allowed if standing wave is created. △ Less

Submitted 13 January, 2021; originally announced January 2021.

Comments: 29 pages, 17 figures