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 figure
The electron trapping in the “bubble” regime of laser-plasma interaction as proposed by Pukhov and Meyer-ter-Vehn [A. Pukhov and J. Meyer-ter-Vehn, Appl. Phys. B 74, 355 (2002)] is studied. In this regime the laser pulse generates a solitary plasma electron cavity: the bubble. It is free from the cold plasma electrons and runs with nearly light velocity. The present work discusses the form of the bubble and the spatial distribution of electromagnetic fields within the cavity. We extend the one-dimensional electron capture theory to the three-dimensional case. It is shown that the bubble can trap plasma electrons. The trapping condition is derived and the trapping cross section is estimated. Electron motion in the self-generated electron bunch is investigated. Estimates for the maximum of electron bunch energy and the bunch density are provided.
Recently, much attention has been attracted to the problem of limitations on the attainable intensity of high power lasers [A. M. Fedotov et al., Phys. Rev. Lett. 105, 080402 (2010)]. The laser energy can be absorbed by electron-positron pair plasma produced from a seed by a strong laser field via the development of the electromagnetic cascades. The numerical model for a 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 a not extremely high laser intensity I ∼ 10(24) W/cm(2) achievable in the near future.
Recently much attention has being attracted to the problem of limitations on the attainable intensity of high power lasers [A.M. Fedotov et al. Phys. Rev. Lett. 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 selfgenerated overdense electron-positron pair plasma is demonstrated. It is shown that the absorption becomes important for not extremely high laser intensity I ∼ 10 24 W/cm 2 achievable in the nearest future.PACS numbers: 12.20. Ds,41.75.Jv,42.50.Ct Due to an impressive progress in laser technology, laser pulses with peak intensity of nearly 2 × 10 22 W/cm 2 are now available in the laboratory [1]. When the matter is irradiated by so intense laser pulses ultrarelativistic dense plasma can be produced. Besides of fundamental interest, such plasma is an efficient source of particles and radiation with extreme parameters that opens bright perspectives in development of advanced particle accelerators [2], next generation of radiation sources [3,4], laboratory modeling of astrophysics phenomena [5], etc. Even higher laser intensities can be achieved with the coming large laser facilities like ELI (Extreme Light Infrastructure) [6] or HiPER (High Power laser Energy Research facility) [7]. At such intensity the radiation reaction and quantum electrodynamics (QED) effects become important [8][9][10][11][12][13].One of the QED effects, which has recently attracted much attention, is the electron-positron pair plasma (EPPP) creation in a strong laser field [11,12]. The plasma can be produced via avalanche-like electromagnetic cascades: the seed charged particles are accelerated in the laser field, then they emit energetic photons, the photons by turn decay in the laser field and create electron-positron pairs. The arising electrons and positrons are accelerated in the laser field and produce new generation of the photons and pairs. It is predicted [12] that an essential part of the laser energy is spent on EPPP production and heating. This can limit the attainable intensity of high power lasers. That prediction was derived using simple estimates, therefore self-consistent treatment based on the first principles is needed.The collective dynamics of EPPP in strong laser field is a very complex phenomenon and numerical modeling becomes important to explore EPPP. Up to now the numerical models for collective QED effects in strong laser field have been not self-consistent. One approach in numerical modeling is focused on plasma dynamics and neglects the QED processes like pair production in the laser field. It is typically based on particle-in-cell (PIC) methods and uses equation for particle motion with radiation reaction forces taken into account [13]. The second one is based on Monte Carlo (MC) algorithm for photon emission and electron-positro...
X-ray generation by relativistic electrons in an ion channel is studied. The emission process is analyzed in the regime of high harmonic generation when the plasma wiggler strength is large. Like for the conventional free electron laser, the synchrotron-like broadband spectrum is generated in this regime. An asymptotic expression for the radiation spectrum of the spontaneous emission is derived. The radiation spectrum emitted from an axisymmetric monoenergetic electron beam is analyzed. The stimulated emission in the ion channel is studied and the gain of the ion-channel synchrotron-radiation laser is calculated. It is shown that the use of laser-produced ion channels leads to a much higher power of x-ray radiation than the one in a self-generated channel. In addition, the mean photon energy, the number of emitted photons and the brilliance of the photon beam increase dramatically. Three-dimensional particle-in-cell simulations of a 25-GeV electron bunch propagating in a laser-produced ion channel are made. Several GeV γ-quants are produced in a good agreement with the analytical results.
We present an analytical model for electron self-injection in a nonlinear, multidimensional plasma wave excited by a short laser pulse in the bubble regime or by a short electron beam in the blowout regime. In these regimes, which are typical for electron acceleration, 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 particle-in-cell simulations.
We show that a laser wake field in the "bubble" regime [Appl. Phys. B 74, 355 (2002)]], works as a compact high-brightness source of x-rays. The self-trapped relativistic 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 good agreement with analytical results. The energy conversion is efficient, leading to a significant stopping of the electron bunch over 5 mm interaction distance.
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