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Electromagnetic cascades attract a lot of attention as an important QED effect that will reveal itself in various electromagnetic field configurations at ultrahigh intensities. We study cascade dynamics in rotating electric field analytically and numerically. The kinetic equations for the electron-positron plasma and gamma-quanta are formulated. The scaling laws are derived and analyzed. For the cascades arising far above the threshold the dependence of the cascade parameters on the field frequency is derived. The spectra of high-energy cascade particles are calculated. The analytical results are verified by numerical simulations., Comment: 14 pages, 10 figures

We present the results of kinetic modelling of quantum effects in laser-beam interaction. In the developed numerical model, electron-positron pair production by hard photons, hard photon emission and the electromagnetic fields generated by the created charged particles are taken into account. Interaction of a relativistic electron beam with a strong laser pulse is analyzed. It is shown that the quantum effects can be important even for moderately intense laser pulses when the number of emitted photons by single electron is not large. Electron-positron pair plasma production in extremely-intense laser field via development of electromagnetic cascades is also studied. The simulation results confirm the prediction of strong laser field absorption in the self-generated electron-positron plasma. It is shown that the self-generated electron-positron plasma can be an efficient source of energetic gamma-quanta., Comment: Submitted to Nuclear Instruments and Methods in Physics Research A

Recently much attention has being attracted to the problem of limitations on the attainable intensity of high power lasers [A.M. Fedotov {\it et al.} Phys. Rev. Lett. \textbf{105}, 080402 (2010)]. The laser energy can be absorbed by electron-positron pair plasma produced from a seed by strong laser field via development of the electromagnetic cascades. The numerical model for self-consistent study of electron-positron pair plasma dynamics is developed. Strong absorption of the laser energy in self-generated overdense electron-positron pair plasma is demonstrated. It is shown that the absorption becomes important for not extremely high laser intensity $I \sim 10^{24}$ W/cm$^2$ achievable in the nearest future., Comment: 5 figures

The results of Monte-Carlo simulations of electron-positron-photon cascades initiated by slow electrons in circularly polarized fields of ultra-high strength are presented and discussed. Our results confirm previous qualitative estimations [A.M. Fedotov, et al., PRL 105, 080402 (2010)] of the formation of cascades. This sort of cascades has revealed the new property of the restoration of energy and dynamical quantum parameter due to the acceleration of electrons and positrons by the field and may become a dominating feature of laser-matter interactions at ultra-high intensities. Our approach incorporates radiation friction acting on individual electrons and positrons., Comment: 13 pages, 10 figures

We study the cusp configuration of pre-seeded magnetic field for laser-driven flux-compression. The proposed configuration provides better particle confinement than that in Ref. [O.V. Gotchev et al., Journal of Fusion Energy 27 (2008) 25-31.] thereby leading to better magnetic insulation of hot fusion plasma. We develop the model that takes into account (i) magnetized target implosion, (ii) magnetic flux compression; (iii) particle losses from magnetic trap. The key parameter governing the process is the ratio of the implosion time to the particle loss time., Comment: Paper for 36th EPS Conference on Plasma Physics June 29 - July 3, 2009, Sofia, Bulgaria

We present an analytical model for electron self-injection in nonlinear, multidimensional plasma wave excited by short laser pulse in the bubble regime or by short electron beam in the blowout regime. In this regimes, which are typical for electron acceleration in the last experiments, the laser radiation pressure or the electron beam charge pushes out background plasma electrons forming a plasma cavity - bubble - with a huge ion charge. The plasma electrons can be trapped in the bubble and accelerated by the plasma wakefields up to very high energies. The model predicts the condition for electron trapping and the trapping cross section in terms of the bubble radius and the bubble velocity. The obtained results are in a good agreement with results of 3D PIC simulations.

We show that both the maximum energy gain and the accelerated beam quality can be efficiently controlled by the plasma density profile. Choosing a proper density gradient one can uplift the dephasing limitation. When a periodic wake field is exploited, the phase synchronism between the bunch of relativistic particles and the plasma wave can be maintained over extended distances due to the plasma density gradient. Putting electrons into the $n-$th wake period behind the driving laser pulse, the maximum energy gain is increased by the factor $2\pi n$ over that in the case of uniform plasma. The acceleration is limited then by laser depletion rather than by dephasing. Further, we show that the natural energy spread of the particle bunch acquired at the acceleration stage can be effectively removed by a matched deceleration stage, where a larger plasma density is used.

We investigate the dynamics of a relativistic electron in a strongly nonlinear plasma wave in terms of classical mechanics by taking into account the action of the radiative reaction force. The two limiting cases are considered. In the first case where the energy of the accelerated electrons is low, the electron makes many betatron oscillations during the acceleration. In the second case where the energy of the accelerated electrons is high, the betatron oscillation period is longer than the electron residence time in the accelerating phase. We show that the force of radiative friction can severely limit the rate of electron acceleration in a plasma accelerator., Comment: 17 pages, 5 figures

Radiation spectrum of extreme relativistic electrons and a probability of electron-positron pair production by energetic photons in a strong plasma wakefield are derived in the framework of a semiclassical approach. It is shown that that the radiation losses of the relativistic electron in the plasma wakefield scale as $ \propto \epsilon ^{2 / 3}$ in the quantum limit when the energy of the radiated photon becomes close to the electron energy, $\epsilon $. The quantum effects will play a key role in future plasma-based accelerators operating at ultrahigh energy of the electrons., Comment: 10 pages, 2 figures

The Bubble regime of electron acceleration in ultra-relativistic laser plasma is considered. It has been shown that the bubble can produce ultra-short dense bunches of electrons with quasi-monoenergetic energy spectra. The first experiment in this regime done at LOA has confirmed the peaked electron spectrum (J. Faure, et al., {\it submitted}, 2004). The generated electron bunch may have density an order of magnitude higher than that of the background plasma. The bubble is able to guide the laser pulse over many Rayleigh lengths, thus no preformed plasma channel is needed for high-energy particle acceleration in the bubble regime. In the present work we discuss a simple analytical model for the bubble fields as well as the scaling laws., Comment: accepted for publication in Plasma Physics and Controlled Fusion, 2004

Using three-dimensional particle-in-cell simulations we show that a strongly nonlinear plasma wave excited by an ultrahigh intensity laser pulse works as a compact high-brightness source of X-ray radiation. It has been recently suggested by A. Pukhov and J. Meyer-ter-Vehn, Appl. Phys. B \textbf{74}, 355 (2002), that in a strongly nonlinear regime the plasma wave transforms to a ``bubble'', which is almost free from background electrons. Inside the bubble, a dense bunch of relativistic electrons is produced. These accelerated electrons make betatron oscillations in the transverse fields of the bubble and emit a bright broadband X-ray radiation with a maximum about 50 keV. The emission is confined to a small angle of about 0.1 rad. In addition, we make simulations of X-ray generation by an external 28.5-GeV electron bunch injected into the bubble. $\gamma$-quanta with up to GeV energies are observed in the simulation in a good agreement with analytical results. The energy conversion is efficient, leading to a significant stopping of the electron bunch over 5 mm interaction distance., Comment: submitted to PRL

Spontaneous and stimulated emission of an electron in the ion channel is studied. The emission processes are studied in the regime of high harmonic generation when the parameter of plasma wiggler strength is large. Like for conventional free electron laser, a synchrotron-like broadband spectrum is generated in this regime. The asymptotic expression for the radiation spectrum of the spontaneous emission is derived. The radiation spectrum emitted from axisymmetric monoenergetic electron beam is analyzed. The gain of ion-channel synchrotron-radiation laser is calculated. Use of laser-produced ion channel for efficient X-ray generation is discussed., Comment: 15 pages, 6 figures, 1 table