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) l
imits of the radiation reaction are considered. For the constant accelerating force, we show that the amplitude of the oscillations of the QED parameter $chi$ in the radiation-dominated regime reaches the equilibrium value determined only by the magnitude of the accelerating field, while the averaged over betatron oscillations radiation reaction force saturates at the value smaller than the accelerating force and thus is incapable of preventing infinite 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 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).
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 equation 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 a significant role in future lepton colliders with high-current particle beams.
We propose a new method for analytical self-consistent description of the excitation of a strongly nonlinear wakefield (a bubble) excited by an electron bunch. This method makes it possible to calculate the shape of the bubble and the distribution of
the electric field in it based only on the properties of the driver, without relying on any additional parameters. The analytical results are verified by particle-in-cell simulations and show good correspondence. A complete analytical solution for cylindrical drivers and scaling laws for the properties of the bubble and other plasma accelerator parameters depending on the bunch charge and length are derived.
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 inc
ludes 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.
Three-dimensional particle-in-cell simulations show that the periodic solid-state structures irradiated by intense ($sim 10^{19}$ W/cm${}^2$) laser pulses can generate collimated electron bunches with energies up to 30 MeV (and acceleration gradient
of $11.5$ GeV/cm), if the microstructure period is equal to the laser wavelength. A one-dimensional model of piecewise acceleration in the microstructure is proposed and it is in a good agreement with the results of numerical simulations. It shows that the acceleration process for relativistic electrons can be theoretically infinite. In the simulations, the optimal target parameters (the width of the microstructure elements and the microstructure period) are determined. The explored parameters can be used for proof-of-principle experiments demonstrating an ultrahigh gradient acceleration by a number of identical and mutually coherent laser pulses [A. Pukhov et al., Eur. Phys. J. Spec. Top. 223, 1197 (2014)].
The photon emission by an ultrarelativistic charged particle in extremely strong magnetic field is analyzed, with vacuum polarization and photon recoil taken into account. The vacuum polarization is treated phenomenologically via refractive index. Th
e photon emission occurs in the synergic (cooperative) synchrotron-Cherenkov process [J. Schwinger, W. Tsai and T. Erber, Annals of Physics, 96 303 (1976)] which is similar to the synchrotron emission rather than to the Cherenkov one. For electrons, the effect of the vacuum polarization on the emission spectrum is not evident even beyond the probable onset of non-perturbative quantum electrodynamics (QED). However, the effect of the vacuum polarization on the emission spectrum can be observable for muons already at $gamma B / B_S approx 30$, with $gamma$ 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.
An improved formula is proposed for field ionization rate covering tunnel and barrier suppression regime. In contrast to the previous formula obtained recently in [I. Yu. Kostyukov and A. A. Golovanov, Phys. Rev. A 98, 043407 (2018)], it more accurat
ely describes the transitional regime (between the tunnel regime and the barrier suppression regime). In the proposed approximation, the rate is mainly governed by two parameters: by the atom ionization potentials and by the external electric field, which makes it perfectly suitable for particle-in-cell (PIC) codes dedicated to modeling of intense laser-matter interactions.
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.
A formula for the ionization rate in extremely intense electromagnetic field is proposed and used for numerical study of QED (quantum-electrodynamical) cascades in noble gases in the field of two counter-propagating laser pulses. It is shown that the
number of the electron-positron pairs produced in the cascade increases with the atomic number of the gas where the gas density is taken to be reversely proportional to the atomic number. While the most electrons produced in the laser pulse front are expelled by the ponderomotive force from region occupied by the strong laser field there is a small portion of the electrons staying in the laser field for a long time until the instance when the laser field is strong enough for cascading. This mechanism is relevant for all gases. For high-$Z$ gases there is an additional mechanism associated with the ionization of inner shells at the the instance when the laser field is strong enough for cascading. The role of both mechanisms for cascade initiation is revealed.
