We propose and detail a multi-step analytical procedure, based on an improved fully relativistic plane model for Laser Wake Field Acceleration, to tailor the initial density of a cold diluted plasma to the laser pulse profile, so as to control the spacetime localization and features of wave-breakings of the plasma wave and maximize the early stage acceleration of small bunches of electrons self-injected by the first wave-breaking at the density down-ramp. We find an excellent agreement with the results of 1D Particle In Cell simulations obtained with the same input data.

We present a numerical study on a structured plasma target to simultaneously improve the energy spread and divergence of a laser-driven very high energy electron (VHEE) beam designed for VHEE-radiotherapy (RT) application. The main concept to obtain such an enhanced quality beam is to localize the injection, acceleration, and extraction of the electrons by tailoring the plasma target density profile. The injection space is truncated by spatially confining the ionization-injection dopant, while the rest of the target is filled with He atoms. In order to reduce the emittance growth during the bunch extraction, an optimized density downramp profile is adopted. By using a 100 TW class Ti:Sa laser system and an ionization-injection scheme in the blow-out regime, a relatively high charge (>= 120 pC) beam with mean energy >= 200 MeV, rms energy spread <= 6%, and normalized emittance epsilon(nx) < 4 mm mrad can be obtained. This combination of bunch specification enables an efficient transport and focusing of the particles, thus making the beam of particular interest for VHEE-RT.

Laser wakefield accelerators are on the way to provide GeV scale high-brightness electron beams for multidisciplinary applications. In the present work, electron bunches are studied in the framework of a Free-Electron Laser driven by an accelerator in the Resonant Multi-Pulse Ionisation framework. The transport to the undulator is provided by a matched beam focusing with marginal beam quality degradation. Finally, using the CRESCO/ENEAGRID High Performance Computing infrastructure, 3D time-dependent simulations of the produced radiation show that about 10^10 photons with central wavelength of 0.15 nm will be delivered with the electron bunches under consideration.

Ultra-low emittance and length-tuneable electron beams can be obtained with the Laser Wake Field Acceleration (LWFA) by employing advanced ionization injection techniques, such as the Two-Color and the Resonant Multi-Pulse Ionization injection (ReMPI) schemes. There, a tightly focused, short wavelength (ionization) pulse extracts electrons from a selected inner shell of a dopant, allowing them to be longitudinally compressed and trapped in the wakefield excited by a different (driver) pulse. In this work we demonstrate, by means of analytical results and Particle In Cell simulations, that 340 as long electron beams with 2.3 GeV energy, 6.1 pC charge, 0.15 % projected energy spread, 60 nm normalised emittance, and projected 6D-Brightness in excess of [Formula: see text] can be generated with a  200 TW Ti:Sa laser system. The beam slice analysis reveals its potentialities for driving a few-spikes attosecond X-ray Free Electron Laser. Furthermore, the ultra-high projected quality, and the extreme shortness of the beams make them ideal candidates for the generation of attosecond and quasi-monochromatic γ photons beams through Thomson/Compton backscattering, or for the injection in subsequent plasma wakefield structures so as to reach TeV energies from staged LWFA.

We introduce a scheme aiming at the generation of quasi-monochromatic carbon ion bunches from laser-solid interaction. The proposed scheme is an extension of the "peeler" acceleration originally proposed for proton acceleration, which involves irradiating the narrow (sub-micrometer) side of a tape target. This results in the generation of a surface plasma wave and the subsequent acceleration of a proton bunch with high peak energy, quasi-monochromaticity, low energy bandwidth, and low divergence by the electrostatic field induced at the target rear. Up to now, the higher-Z (e.g., carbon) ion bunches obtained with the peeler scheme have been found to exhibit an exponentially decaying thermal-like energy spectrum. To achieve a low energy bandwidth, we place a mass-limited carbon structure at the rear of the target. Using 3D particle-in-cell simulations, we show that a quasi-monochromatic carbon bunch can indeed be obtained. With a multi-PW laser pulse, 10(8) carbon ions with peak energy similar to 110 MeV/u and with a divergence of 20 degrees in the vertical plane and similar to 1 degrees in the horizontal plane can be generated. The quasi-monochromaticity, together with the low duration of the beam and in combination with the versatility of high-power laser facilities, should make this scheme attractive for practical applications such as heavy ion cancer therapy and higher-resolution diagnostics of extreme plasma states. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Abstract The state-of-the-art ultrashort, few-cycle laser pulses recently have entered the regime of the 100 TW-class power and at 10 Hz repetition rate. We explore the potential of such pulses for efficient electron acceleration. The numerical modelling predicts that hundreds-MeV, nC-class electron bunches can be generated, transferring up to 58% of the laser pulse energy into electrons above 15 MeV. Furthermore, we exploit such electron bunches for the generation of a secondary source of hard X-ray Bremsstrahlung in a high-Z converter. The results suggest that up to 30% of the laser energy can be transformed into hard X-rays with energy above 10 keV. Such an exceptionally high conversion efficiency is achieved through increased laser-to-electron conversion due to the short duration of the laser pulse and the high energy of the accelerated electrons, where radiation losses in the converter significantly outweigh collisional losses. This Bremsstrahlung emitter could function as a generator of tertiary particles, including neutrons released through photonuclear reactions.

High-quality ionization injection methods for wakefield acceleration driven by lasers or charged beams (LWFA/PWFA) can be optimized so as to generate high-brightness electron beams with tuneable duration in the attosecond range. We present a model of the minimum bunch duration obtainable with low-emittance ionization injection schemes by spotting the roles of the ionization pulse duration, of the wakefield longitudinal shape and of the delay of the ionization pulse position with respect to the node of the accelerating field. The model is tested for the resonant multi-pulse ionization injection (ReMPI) scheme, showing that bunches having a length of about 300 as can be obtained with an ionization pulse having a duration of 30 fs FWHM.

Electron plasma waves can be efficiently excited by a resonant train of ultrashort pulses, spatially separated by a plasma wavelength. Generating a pulse train from a single amplified ultrashort pulse may be challenging when dealing with large beams. Here we discuss a pulse splitting technique using a simple delay mask that can be adapted to large diameter petawatt beams. We show via detailed numerical simulations that unique signatures of electrons accelerated by a resonantly excited wakefield can be obtained from realistic focused double-pulse trains obtained from a single-region delay mask.

We numerically show that laser-wakefield accelerated electron beams obtained using a PetaWatt-scale laser system can produce high-flux sources of relativistic muons that are suitable for radiographic applications. Scalings of muon energy and flux with the properties of the wakefield electron beams are presented. Applying these results to the expected performance of the 10-PW class laser at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) demonstrates that ultra-high power laser facilities currently in the commissioning phase can generate ultra-relativistic muon beams with more than 10(4) muons per shot reaching the detector plane. Simple magnetic beamlines are shown to be effective in separating the muons from noise, allowing for their detection using, for example, silicon-based detectors. It is shown that a laser facility like the one at ELI-NP can produce high-fidelity and spatially resolved muon radiographs of enclosed strategically sensitive materials in a matter of minutes.

Abstract After the introduction of the ionization-injection scheme in laser wake field acceleration and of related high-quality electron beam generation methods, such as two-color and resonant multi-pulse ionization injection (ReMPI), the theory of thermal emittance has been used to predict the beam normalized emittance obtainable with those schemes. We recast and extend such a theory, including both higher order terms in the polynomial laser field expansion and non-polynomial corrections due to the onset of saturation effects on a single cycle. Also, a very accurate model for predicting the cycle-averaged distribution of the extracted electrons, including saturation and multi-process events, is proposed and tested. We show that our theory is very accurate for the selected processes of ${\mathrm{Kr}}^{8^{+}\to {10}^{+}}$ and ${\mathrm{Ar}}^{8^{+}\to {10}^{+}}$ , resulting in a maximum error below 1%, even in a deep-saturation regime. The accurate prediction of the beam phase-space can be implemented, for example, in laser-envelope or hybrid particle-in-cell (PIC)/fluid codes, to correctly mimic the cycle-averaged momentum distribution without the need for resolving the intra-cycle dynamics. We introduce further spatial averaging, obtaining expressions for the whole-beam emittance fitting with simulations in a saturated regime, too. Finally, a PIC simulation for a laser wakefield acceleration injector in the ReMPI configuration is discussed.

Figure 20.1 was not correct in the published article. The original article has been corrected. The published apologizes for the inconvenience.

The direct use of so-called Very High Energy Electrons for radiotherapy is currently deserving a renewed and growing attention. This is mostly due to the recent emergence of the so-called FLASH effect in radiobiology [1], consisting in a surprising reduction of adverse effects on healthy tissue by ionizing radiation when dose delivery occurs at very high average dose rates (greater than a few tens of Gy/s). In order for a real clinical translation of this new protocol in the clinical practice, the development of novel kind of ionizing radiation sources featuring such very high dose rates, which are basically hindered by the relatively low Bremsstrahlung conversion efficiency in current machines, is considered as an essential step. With this respect, laser-driven accelerators of Very High Energy Electron (VHEE) beams, with energy in the range 100-250 MeV, are regarded as one of the most promising tool [2]. Furthermore, both early studies, dating back to 1990s, and more recent works suggest that an improved dose deposition pattern can be expected from electron beams, as compared to photon beams, when the very high energy region is reached. In this talk, we report on a recent experiment aimed at assessing dose deposition for deep seated tumors using advanced irradiation schemes, typical of current radiotherapy protocols, with an existing laser-driven VHEE source [3]. In particular, our measurements showed control of localized dose deposition and modulation, suitable to target a volume at depths in the range from 5 to 10 cm with mm resolution. Based on this experimental findings and on further numerical simulations, we also discuss the features and potentialities of laser-driven VHEE sources for radiobiology experiments aimed at deepening the understanding of the mechanisms underpinning the FLASH effect. The main requirements and the perspectives for a longer term translation of an electron-based radiotherapy into the real clinical practice will be also addressed. [1] M.-C. Vozenin et al., Biological Benefits of Ultra-high Dose Rate FLASH Radiotherapy: Sleeping Beauty Awoken, Clin. Oncol. 31 (2019), 407 [2] A. Giulietti (Eds), Laser-Driven Particle Acceleration Towards Radiobiology and Medicine, Springer (2016) [3] L. Labate et al., Toward an effective use of laser‐driven very high energy electrons for radiotherapy: Feasibility assessment of multi‐field and intensity modulation irradiation schemes, Sci. Rep. 10 (2020), 17307

The interaction of ultraintense laser pulses with solids is largely affected by the plasma gradient at the vacuum-solid interface, which modifies the absorption and ultimately, controls the energy distribution function of heated electrons. A micrometer scale-length plasma has been predicted to yield a significant enhancement of the energy and weight of the fast electron population and to play a major role in laser-driven proton acceleration with thin foils. We report on recent experimental results on proton acceleration from laser interaction with foil targets at ultra-relativistic intensities. We show a three-fold increase of the proton cut-off energy when a micrometer scale-length pre-plasma is introduced by irradiation with a low energy femtosecond pre-pulse. Our realistic numerical simulations agree with the observed gain of the proton cut-off energy and confirm the role of stochastic heating of fast electrons in the enhancement of the accelerating sheath field.

The interaction of ultraintense laser pulses with solids is largely affected by the plasma gradient at the vacuum-solid interface, which modifies the absorption and ultimately, controls the energy distribution function of heated electrons. A micrometer scale-length plasma has been predicted to yield a significant enhancement of the energy and weight of the fast electron population and to play a major role in laser-driven proton acceleration with thin foils. We report on recent experimental results on proton acceleration from laser interaction with foil targets at ultra-relativistic intensities. We show a threefold increase of the proton cut-off energy when a micrometer scale-length pre-plasma is introduced by irradiation with a low energy femtosecond pre-pulse. Our realistic numerical simulations agree with the observed gain of the proton cut-off energy and confirm the role of stochastic heating of fast electrons in the enhancement of the accelerating sheath field.

Trains of femtosecond pulses generated by a delay mask are considered for application to laser driven acceleration of particles. Here we show the results of numerical simulations and a preliminary experimental characterization of a two-pulse configuration.

This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science - through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8-10 years.

From plasma-wakefield acceleration as a physics experiment toward a plasma-based accelerator as a user facility, the beam physics issues remaining to be solved are still numerous. Providing beams with high energy, charge, and quality simultaneously, not only within the plasma but also at the user doorstep itself, is the main concern. Despite its tremendous efficiency in particle acceleration, the wakefield displays a complex 3D profile which, associated to the beam-loading field induced by the accelerated beam itself, makes the acceleration of high charge to high energy often incompatible with high beam quality. Beam extraction from the plasma without quality degradation for a transfer either to the next plasma stage or to the user application is another difficulty to consider. This article presents the substantial studies carried out and the different innovative methods employed for tackling all these different issues. Efforts focused on achieving the challenging beam parameters targeted by the EuPRAXIA accelerator facility project. The lessons learned at the end of these in-depth simulations and optimizations are highlighted. The sensitivity to different error sources is also estimated to point out the critical components of such an accelerator. Finally, the needs in terms of laser and plasma parameters are provided.

We report on recent experimental results on proton acceleration from laser interaction with foil targets at ultra-relativistic intensities. We show a three-fold increase in the proton cut-off energy when a micrometer scale-length pre-plasma is introduced by irradiation with a low energy femtosecond pre-pulse. The foil target is sufficiently thick to prevent disruption of the sheath field at the rear surface by the shock launched by the pre-pulse. Measurements are compared with accurate, numerical hydrodynamic and Particle-In-Cell simulations where the role of the finite plasma scale-length at the laser-target interface is taken into account and the role of stochastic heating in enhancing fast electron production is discussed.