Quantum electrodynamics (QED) cascade arising in a superposition of incident multipetawatt laser pulse and its reflection from a solid target were studied numerically and analytically.

The potential feasibility is demonstrated of observing self-sustaining electromagnetic cascades at the XCELS facility with a random phase difference of radiation pulses in different channels for a total power of 36 PW.

We study the dynamics of an electron wave packet in a strong constant crossed electromagnetic field with account for radiative corrections due to interaction of the electron with the vacuum fluctuations. We evaluate a wave packet composed of the solutions to the Dyson-Schwinger equation, which describes electron propagation without emission of real photons. Spacetime dependence of the wave packet is obtained analytically for a short time interval, the more restricted from above the wider is the packet in momentum space. The radiative corrections alter the electron wavefunction, resulting in particular in a damping of the wave packet. The expectation value of the Dirac spin operator also gets modified.

It is generally believed that relativistically underdense plasmas are transparent for intense laser radiation. However, particle-in-cell simulations reveal abnormal laser field absorption above the intensity threshold of about 3×1024 Wcm−2 for the wavelength of 1 μm. Above the threshold, the further increase in the laser intensity does not lead to an increase in the propagation distance. The simulations take into account emission of hard photons and subsequent pair photoproduction in the laser field. These effects lead to onset of a self-sustained quantum electromagnetic cascade and to formation of dense electron–positron (e+e−) plasma right inside the laser field. The plasma absorbs the laser field efficiently, which ensures the plasma opacity. The role of a weak longitudinal electron–ion electric field in the cascade growth is discussed.

A system of reduced equations is proposed for electron motion in the strongly radiation-dominated regime for an arbitrary electromagnetic field configuration. The approach developed here is used to analyze various scenarios of electron dynamics in this regime: motion in rotating electric and magnetic fields and longitudinal acceleration in a plane wave and in a plasma wakefield. The results obtained show that this approach is able to describe features of electron dynamics that are essential in certain scenarios, but cannot be captured in the framework of the original radiation-free approximation [Samsonov et al., Phys. Rev. A 98, 053858 (2018) and A. Gonoskov and M. Marklund, Phys. Plasmas 25, 093109 (2018)]. The results are verified by numerical integration of the nonreduced equations of motion with account taken of radiation reaction in both semiclassical and fully quantum cases.

We study electron acceleration in a plasma wakefield under the influence of the radiation-reaction force caused by the transverse betatron oscillations of the electron in the wakefield. Both the classical and the strong quantum-electrodynamic (QED) limits of the continuous radiation reaction are considered. For the constant accelerating force, we show that the amplitude of the oscillations of the QED parameter χ in the radiation-dominated regime reaches an equilibrium value determined only by the magnitude of the accelerating field, while the averaged over betatron oscillations radiation reaction force saturates at a value smaller than the accelerating force and thus is incapable of stopping acceleration. We find the parameters of the electron bunch and the plasma accelerator for which reaching such a regime is possible. We also study effects of the dephasing and the corresponding change of the accelerating force over the course of acceleration and conclude that the radiation-dominated regime is realized both in cases of single-stage acceleration with slow dephasing (usually corresponding to bunch-driven plasma accelerators) and multi-stage acceleration with fast dephasing (corresponding to the use of laser-driven accelerators).

One can find the electron energy spectrum by measuring (with a scintillating screen) the angular distribution of the electrons which pass through a magnetic field. However, two electron beams with different spectra can yield almost the same image on the scintillating screen, because non-zero angular dispersion of the electron beams before the magnet brings a blur to the scintillating screen images. A simple and steady procedure is proposed which reconstructs the electron spectrum correctly down to some threshold scale Δɛ and gives low level of artificial defects. It is shown that the bumps in the spectrum of the energy scale less or about Δɛ cannot be reconstructed correctly by any procedure.

The radiation reaction (beamstrahlung) effect on particle dynamics during interaction of oppositely charged beams is studied. It is shown that the beam focusing can be strongly enhanced due to beamstrahlung. An approximate analytical solution of the motion equations including the radiation reaction force is derived. The disruption parameter is calculated for classical and quantum regime of beamstrahlung. The analytical model is verified by QED-PIC simulations. The model for head-on collision of long beams undergoing a number of betatron oscillation during interaction is also developed. It is demonstrated that the beamstrahlung-enhanced disruption effect can play an important role in future lepton colliders with high-current particle beams.

Using machine-learning methods based on self-organising Kohonen maps, the results of numerical simulation of the acceleration of electrons during the interaction of high-power laser radiation with plasma are analysed and classified. The particle-in-cell (PIC) method is used to simulate the interaction in a wide range of parameters (laser intensity and plasma concentration). For each set of parameters, the spectrum of accelerated electrons is found, based on which the charge, average energy, and relative energy spread of accelerated electrons are calculated. Using the obtained values as input parameters of the map, the classification of various acceleration regimes is performed. The developed scheme can be used to identify the optimal acceleration regimes under more realistic conditions, considering a larger number of parameters.

We consider the effect of electron–positron pair production on the generation of a quasi-stationary magnetic field in the interaction of an ultra-intense circularly polarised laser pulse with a thick plasma target. Full-scale three-dimensional numerical simulations by the particle-in-cell method performed taking into account quantum electrodynamic effects indicates a qualitative change in the generation of the magnetic field at a laser radiation intensity I ≳ 1024 W cm−2, which gives rise to a macroscopic number of electron–positron pairs. In this case, the amplitude of the magnetic field increases with an increase in the radiation intensity, whereas the amplitude of the magnetic field is hardly intensity-dependent when the effect of electron–positron pair production is neglected.

Development of the self-sustained quantum-electrodynamical (QED) cascade in a single strong laser pulse is studied analytically and numerically. The hydrodynamical approach is used to construct the analytical model of the cascade evolution, which includes the key features of the cascade observed in 3D QED particle-in-cell (QED-PIC) simulations such as the magnetic field predominance in the cascade plasma and laser energy absorption. The equations of the model are derived in the closed form and are solved numerically. Direct comparison between the solutions of the model equations and 3D QED-PIC simulations shows that our model is able to describe the complex nonlinear process of the cascade development qualitatively well. The various regimes of the interaction based on the intensity of the laser pulse are revealed in both the solutions of the model equations and the results of the QED-PIC simulations.

Photon emission by an ultrarelativistic charged particle in extremely strong magnetic field is analyzed, with vacuum polarization and photon recoil taken into account. Vacuum polarization is treated phenomenologically via refractive index. The photon emission occurs in the synergic (cooperative) synchrotron–Cherenkov process [J Schwinger et al 1976 Annals of Physics 96 303] which is similar to the synchrotron emission rather than to the Cherenkov one. For electrons, the effect of vacuum polarization on the emission spectrum is not evident at least below the probable onset of non-perturbative quantum electrodynamics (QED). However, the effect of vacuum polarization on the emission spectrum can be observable for muons already at γB / B S ≈ 30, with γ the muon Lorentz factor, B the magnetic field strength and B S the critical QED field. Nevertheless, vacuum polarization leads to only 10% enhancement of the maximum of the radiation spectrum.

In the laser-electron beam head-on interaction electron energy can decrease due to radiation reaction, i.e. emission of photons. For 10-100 fs laser pulses and for the laser field strength up to the pair photoproduction threshold, it is shown that one can calculate the resulting electron and photon spectra as if the electron beam travels through a constant magnetic field. The strength of this constant field and the interaction time are found as functions of the laser field amplitude and duration. Using of constant field approximation can make a theoretical analysis of stochasticity of the radiation reaction much more simple in comparison with the case of alternating laser field, also, it allows one to get electron and photon spectra much cheaper numerically than by particle in-cell simulations.

The use of rectangular-shaped microstructures at the front surface of a solid target is shown to improve gamma-ray generation by 2–3 orders of magnitude, compared to the case of a planar target, when irradiated by laser pulses with an intensity of 1.13 × 1022 W cm−2. Also, it is observed that the laser energy absorption rate increases more than 10 times, up to 57%. The analysis of the simulation results suggests that in the case of relatively narrow microstructure elements, the gamma-ray generation mechanism is similar to that in the case of laser pulse normally incident onto a planar target, but with differences in the electron trajectories. The optimal dimensions of rectangular-shaped microstructured target have been found with the help of 3D particle-in-cell simulations.

The vast majority of QED results are obtained in relatively weak fields and so in the framework of perturbation theory. However, forthcoming laser facilities providing extremely high fields can be used to enter not-yet-studied regimes. Here, a scheme is proposed that might be used to reach a supercritical regime of radiation reaction or even the fully non-perturbative regime of quantum electrodynamics. The scheme considers the collision of a 100 GeV-class electron beam with a counterpropagating ultraintense electromagnetic pulse. To reach these supercritical regimes, it is unavoidable to use a pulse with ultrashort duration. Using two-dimensional particle-in-cell simulations, it is therefore shown how one can convert a next-generation optical laser to an ultraintense (I ≈ 2.9 × 1024 Wcm−2) attosecond (duration ≈ 150 as) pulse. It is shown that if the perturbation theory persists in extreme fields, the spectrum of secondary particles can be found semi-analytically. In contrast, a comparison with experimental data may allow differentiating the contribution of high-order radiative corrections if the perturbation theory breaks.

It is demonstrated by three-dimensional quantum electrodynamics — particle-in-cell (QED-PIC) simulations that vacuum breakdown wave in the form of QED cascade front can propagate in an extremely intense plane electromagnetic wave. The result disproves the statement that the self-sustained cascading is not possible in a plane wave configuration. In the simulations the cascade is initiated during laser-foil interaction in the light sail regime. As a result, a constantly growing electron-positron plasma cushion is formed between the foil and laser radiation. The cushion plasma efficiently absorbs the laser energy and decouples the radiation from the moving foil thereby interrupting the ion acceleration. The models describing propagation of the cascade front and electrodynamics of the cushion plasma are presented and their predictions are in a qualitative agreement with the results of numerical simulations.

Typical extremely intense laser-matter interactions include ionization, plasma production and generation of secondary particles. Modern laser systems are able to generate short and intense laser pulses ionizing matter in the poorly explored barrier-suppression regime. The classical and quantum models of barrier-suppression ionization are proposed and a simple formula of the ionization rate both for the tunnel and the barrier-suppression regimes is derived. After ionization free electrons move in extremely intense laser field in radiation-dominated regime when the radiation losses strongly affect electron dynamics. We show that the electron trajectories in this regime become close to some asymptotic trajectories where the radiation losses are minimal. The particle velocity of the asymptotic trajectory is completely determined by the local and instant EM field. At high laser intensity the laser-matter interaction can be accompanied by the avalanche-like production of electron-positron plasma via QED cascading. We demonstrate that QED cascade can develop even in a plane electromagnetic wave. The cascade front propagates as vacuum breakdown waves which is similar an avalanche breakdown at a gas discharge developing via ionization waves. The cascading makes the radiation pressure acceleration inefficient at extremely high intensities. QED cascades may also develop because of Weibel instability in two counterstreaming hot relativistic plasma flows. If the plasma flows are dense, fast, and hot enough, the overall energy of the synchrotron photons can be much higher than the energy of the generated electromagnetic fields. Furthermore, a sizable number of positrons can be produced due to the pair photoproduction in the generated magnetic field. We propose a rough criterion to judge copious pair production and considerable synchrotron losses. By means of this criterion, we conclude that the incoherent synchrotron emission and the pair production during the Weibel instability can have implications for the collapsar model of gamma-ray bursts.

It is demonstrated by QED-PIC (particle-in-cell) simulations that self-sustained QED cascades can efficiently develop in a plane wave of extremely high intensity which is believed not suitable for cascading. In the simulations, the cascade starts in the light sail regime of laser-foil interaction. As a result, a constantly growing electron-positron pair plasma `cushionu0027 is formed in front of the foil. Then the cushion starts to absorb the laser energy and decouples the laser radiation from the moving foil thereby interrupting the ion acceleration. Nevertheless, the cascade continues to develop. The models describing the cushion front dynamics and the cushion electrodynamics are presented and their predictions are in a qualitative agreement with the numerical simulations.

In the present work, a scheme is proposed that can be used to probe the fully non-perturbative regime of quantum electrodynamics. The scheme considers the collision of a 100 GeV-class electron beam with a counterpropagating ultraintense electromagnetic pulse. To reduce the radiative losses by the electrons, it is unavoidable to use a pulse with ultrashort duration. Therefore, in two-dimensional particle-in-cell simulations, it is shown how one can convert a next-generation optical laser to an ultraintense ($Iapprox 2.9times 10^{24}$ Wcm$^{-2}$) attosecond (duration $approx$ 150 as) pulse. It is shown that the contribution of high-order radiative corrections can be differentiated from the background in the particle spectra generated in the interaction.

We study electron motion in electromagnetic (EM) fields in the radiation-dominated regime. It is shown that the electron trajectories become close to some asymptotic trajectories in the strong field limit. The description of the electron dynamics by this asymptotic trajectories significantly differs from the ponderomotive description that is barely applicable in the radiation-dominated regime. The particle velocity on the asymptotic trajectory is completely determined by the local and instant EM field. The general properties of the asymptotic trajectories are discussed. In most of standing EM waves (including identical tightly-focused counter-propagating beams) the asymptotic trajectories are periodic with the period of the wave field. Furthermore, for a certain model of the laser beam we show that the asymptotic trajectories are periodic in the reference frame moving along the beam with its group velocity that may explain the effect of the radiation-reaction trapping.