A kinetic equation describing the nonlinear evolution of intense electromagnetic pulses in electron-positron (e-p) plasmas is presented. The modulational instability is analyzed for a relativistically intense partially coherent pulse, and it is found that the modulational instability is inhibited by the spectral pulse broadening. A numerical study for the one-dimensional kinetic photon equation is presented. Computer simulations reveal a Fermi-Pasta-Ulam-like recurrence phenomena for localized broadband pulses. The results should be of importance in understanding the nonlinear propagation of broadband intense electromagnetic pulses in e-p plasmas in laser-plasma systems as well as in astrophysical plasma settings.
Particle-in-cell (PIC) simulation results of sustained acceleration of electron-positron (e+e-) plasmas by comoving electromagnetic (EM) pulses are presented. When a thin slab of overdense e+e- plasma is irradiated with linear-polarized ultra-intense short laser pulses from both sides, the pulses are transmitted when the plasma is compressed to thinner than ~ 2 relativistic skin depths. A fraction of the plasma is then captured and efficiently accelerated by self-induced JxB forces. For 1 micron laser and 1021Wcm-2 intensity, the maximum energy exceeds GeV in a picosecond.
In simulations of a 10PW laser striking a solid we demonstrate the possibility of producing a pure electron-positron plasma by the same processes as those thought to operate in high-energy astrophysical environments. A maximum positron density of 10^26/m^3 is achieved, seven orders of magnitude greater than achieved in previous experiments. Additionally, 35% of the laser energy is converted to a burst of gamma-rays of intensity 10^22W/cm^2, potentially the most intense gamma-ray source available in the laboratory. This absorption results in a strong feedback between both pair and gamma-ray pro…
We study the initial properties and positron annihilation within a small electron-positron plasma drop formed by intense laser pulse. Such QED cascade initiated plasma is, in general, far below the chemical (particle yield) equilibrium. We find that the available electrons and positrons equilibrate kinetically, yet despite relatively high particle density, the electron-positron annihilation is very slow, suggesting a rather long lifespan of the plasma drop.
Although several laser-plasma-based methods have been proposed for generating energetic electrons, positrons and γ-photons, manipulation of their microstructures is still challenging, and their angular momentum control has not yet been achieved. Here, we present and numerically demonstrate an all-optical scheme to generate bright GeV γ-photon and positron beams with controllable angular momentum by use of two counter-propagating circularly-polarized lasers in a near-critical-density plasma. The plasma acts as a "switching medium", where the trapped electrons first obtain angular momentum from …
Generation of ultrarelativistic polarized positrons during interaction of an ultrarelativistic electron beam with a counterpropagating two-color petawatt laser pulse is investigated theoretically. Our Monte Carlo simulation based on a semi-classical model, incorporates photon emissions and pair productions, using spin-resolved quantum probabilities in the local constant field approximation, and describes the polarization of electrons and positrons for the pair production and photon emission processes, as well as the classical spin precession in-between. The main reason of the polarization is s…
We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with length 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in $\leq$ 20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies ($\leq$ 20THz) and increase of the electromagnetic pulse energy in the high-frequency r…
Electron-positron pairs, produced in intense laser-solid interactions, are diagnosed using magnetic spectrometers with image plates, such as the National Ignition Facility (NIF) Electron Positron Proton Spectrometers (EPPS). Although modeling can help infer the quantitative value, the accuracy of the models needs to be verified to ensure measurement quality. The dispersion of low-energy electrons and positrons may be affected by fringe magnetic fields near the entrance of the EPPS. We have calibrated the EPPS with six electron beams from a Siemens Oncor linear accelerator (linac) ranging in en…
The effective interaction between two classical nonrelativistic electrons (positrons) in the presence of intense electromagnetic radiation (one and two waves) is theoretically studied. Small relativistic corrections are taking into account in the laboratory reference frame. The field of an intense wave forms the movement of particles in such a way that their trajectories are practically parallel for quite a long time, and in the perpendicular direction the particles shift slightly, approaching first and then moving away from each other. This result can be considered as an effective attraction …
The interaction of high energy electrons, positrons, and photons with intense laser pulses is studied in head-on collision geometry. It is shown that electrons and/or positrons undergo a cascade-type process involving multiple emissions of photons. These photons can consequently convert into electron-positron pairs. As a result charged particles quickly lose their energy developing an exponentially decaying energy distribution, which suppresses the emission of high energy photons, thus reducing the number of electron-positron pairs being generated. Therefore, this type of interaction suppresse…
Non-linear wave-driven processes in plasmas are normally described by either a monochromatic pump wave that couples to other monochromatic waves, or as a random phase wave coupling to other random phase waves. An alternative approach involves an incoherent, random or broadband pump coupling to monochromatic and/or coherent structures in the plasma. This approach can be implemented through the wave kinetic model. In this model, the incoming pump wave is described by either a bunch (for coherent waves) or a sea (for random phase waves) of quasi-particles. A particle-in-cell type code has been de…
This paper studies the interaction of laser-driven $γ$-photons and high energy charged particles with high-Z targets through Monte-Carlo simulations. The interacting particles are taken from particle-in-cell simulations of the interaction of a tightly-focused ultraintense laser pulse with a titanium target. Lead is chosen as the secondary high-Z target owing to its high cross section of the giant dipole resonance and electron-positron pair production. The results reveal an ultra-short ultra-relativistic collimated positron population and their energy spectra, angular distribution, and temporal…
The main purpose of this work is the investigation of the influence of electron-positron-ion on the electrostatic wakefields that are driven by intense, short electromagnetic wave packets in a three component unmagnetized plasma. The equations that describes the driven electrostatic wakefield are given in the form of system of nonlinear differential equations. The solution of that system was carried out numerically and the results are displayed graphically.
The mechanism of laser-driven relativistic pair-jet production qualitatively changes as laser intensity exceeds $I\gtrsim5\times10^{22}$ W/cm$^{2}$ because of the appearance of laser-induced strong-field QED processes. Here, we show that by exceeding this intensity additional physics operates and opens a new and efficient channel to convert laser photons into dense pair-jets -- the combination of nonlinear Compton scattering and the Bethe-Heitler process. This channel generates relativistic electron-positron jets more than three orders of magnitude denser than has so far been possible. We find…
The dynamics of an electron bunch irradiated by two focused colliding super-intense laser pulses and the resulting gamma and electron-positron production are studied. Due to attractors of electron dynamics in a standing wave created by colliding pulses the photon emission and pair production, in general, are more efficient with linearly polarized pulses than with circularly polarized ones. The dependence of the key parameters on the laser intensity and wavelength allows to identify the conditions for the cascade development and gamma-electron-positron plasma creation.
We consider a situation in when the interaction of relativistically intense EM waves with an isotropic electron positron plasma takes place, i.e.,we consider short pulse lasers with intensity up to 1021 W/cm2, in which the photon density is of the order of 1030cm3 and the strength of electric field E = 10^9 statvolt/cm. Such a situation is possible in astrophysical and laboratory plasma which are subject to intense laser radiation, thus leading to non thermal equilibrium field radiations. Such interaction of the super-strong laser radiation with an isotropic pair plasma leads to the generation…
Relativistic positron beams are required for fundamental research in nonlinear strong field QED, plasma physics, and laboratory astrophysics. Positrons are difficult to create and manipulate due to their short lifetime, and their energy gain is limited by the accelerator size in conventional facilities. Alternative compact accelerator concepts in plasmas are becoming more and more mature for electrons, but positron generation and acceleration remain an outstanding challenge. Here we propose a new setup where we can generate, inject and accelerate them in a single stage during the propagation o…
The expansion dynamics of hot electron-positron-photon plasma droplets is dealt with within relativistic hydrodynamics. Such droplets, envisaged to be created in future experiments by irradiating thin foils with counter-propagating ultra-intense laser beams, are sources of flashes of gamma radiation. Warm electron-positron plasma droplets may be identified and characterized by a broadened 511 keV line.
The production of a highly-polarized positron beam via nonlinear Breit-Wheeler processes during the interaction of an ultraintense circularly polarized laser pulse with a longitudinally spin-polarized ultrarelativistic electron beam is investigated theoretically. A new Monte Carlo method employing fully spin-resolved quantum probabilities is developed under the local constant field approximation to include three-dimensional polarizations effects in strong laser fields. The produced positrons are longitudinally polarized through polarization transferred from the polarized electrons by the mediu…
Dense quantum plasmas are ubiquitous in planetary interiors and in compact astrophysical objects, in semiconductors and micro-mechanical systems, as well as in the next generation intense laser-solid density plasma interaction experiments and in quantum x-ray free-electron lasers. In contrast to classical plasmas, one encounters extremely high plasma number density and low temperature in quantum plasmas. The latter are composed of electrons, positrons and holes, which are degenerate. Positrons (holes) have the same (slightly different) mass as electrons, but opposite charge. The degenerate cha…
Plasma wakefield acceleration in the nonlinear blowout regime has been shown to provide high acceleration gradients and high energy transfer efficiency while maintaining great beam quality for electron acceleration. In contrast, research on positron acceleration in this regime is still in a preliminary stage. We find that an on-axis electron filament can be self-consistently formed and maintained by loading an intense positron beam at the back of the electron beam driven blowout cavity. Via an analytic model and fully nonlinear simulations, we show this coaxial electron filament not only can f…
Ultra-intense lasers are expected to produce, in near future, relativistic electron-positron plasma droplets. Considering the local photon production rate in complete leading order in quantum electrodynamics (QED), we point out that these droplets are interesting sources of gamma ray flashes
We consider interaction of a high-energy electron beam with two counterpropagating femtosecond laser pulses. Nonlinear Compton scattering and electron-positron pair production by the emitted photons result in development of an electromagnetic "shower-type" cascade, which however collapses rather quickly due to energy losses by secondary particles. Nevertheless, the laser field accelerates the low-energy electrons and positrons trapped in the focal region, thus giving rise to development of electromagnetic cascade of another type ("avalanche-type"). This effect of cascade collapse and revival c…
Polarized quantum effects in countable signals from intense laser - electron beam interactions
National Institute for Fusion Science（国立核聚变科学研究所）；Graduate School of Advanced Science and Engineering, Hiroshima University（广岛大学先进理工学研究科）；Nagasaki Institute of Applied Science（长崎应用科学研究所）
Showers of $γ$-rays and positrons are produced when a high-energy electron beam collides with a super-intense laser pulse. We present scaling laws for the electron beam energy loss, the $γ$-ray spectrum, and the positron yield and energy that are valid in the non-linear, radiation-reaction--dominated regime. As an application we demonstrate that by employing the collision of a $>$GeV electron beam with a laser pulse of intensity $>5\times10^{21}\,\text{Wcm}^{-2}$, today's high-intensity laser facilities are capable of producing $O(10^4)$ positrons per shot via light-by-light scattering.
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-intens…
The dynamics of electrons in counter-propagating, circularly polarized laser beams are shown to exhibit attractors whose ability to trap particles depends on the ratio of the beam intensities and a single parameter describing radiation reaction. Analytical expressions are found for the underlying limit cycles and the parameter range in which they are stable. In high-intensity optical pulses, where radiation reaction strongly modifies the trajectories, the production of collimated gamma-rays and the initiation of non-linear cascades of electron-positron pairs can be optimized by a suitable choi…
The injection of electrons into a laser wakefield accelerator (LWFA) is observed to generate an intense coherent ultra-broadband and ultrashort pulse radiation flash, consistent with the acceleration of electrons from rest to nearly the speed of light in a distance < ~ 1 $μ$m. The flash is sufficiently bright to induce large nonlinear refractive index shifts in optical materials; we estimate a source brightness temperature of ~$10^{18}$ K. We present measurements of the flash spectra, coherence, pulse duration, polarization and angular distribution, providing a detailed picture of electron inj…
The existence of the dust acoustic wave (DAW) in a strongly magnetized electron-positron (pair)-dust plasma is demonstrated. In the DAW, the restoring force comes from the pressure of inertialess electrons and positrons, and the dust mass provides the inertia. The waves could be of interest in astrophysical settings such as the supernovae and pulsars, as well as in cluster explosions by intense laser beams in laboratory plasmas.
Self-organized positron reorienting and pinching mechanism for the experimental detection of the linear Breit-Wheeler process
York Plasma Institute, Department of Physics, University of York（约克大学等离子体研究所）；GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa（里斯本大学高等技术学院等离子体与核聚变研究所）；Department of Mechanical and Aerospace Engineering, University of California San Diego（加州大学圣地亚哥分校机械与航空航天工程系）；General Atomics（通用原子能公司）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）
The ability of an intense laser pulse to propagate in a classically over-critical plasma through the phenomenon of relativistic transparency is shown to facilitate the generation of strong plasma magnetic fields. Particle-in-cell simulations demonstrate that these fields significantly enhance the radiation rates of the laser-irradiated electrons, and furthermore they collimate the emission so that a directed and dense beam of multi-MeV gamma-rays is achievable. This capability can be exploited for electron-positron pair production via the linear Breit-Wheeler process by colliding two such dens…
It is generally believed that relativistically underdense plasma is transparent for intense laser radiation. However, particle-in-cell simulations reveal abnormal laser field absorption above the intensity threshold about~$3 \times 10^{24}~\mathrm{W}\,\mathrm{cm}^{-2}$ for the wavelength of $1~μ\mathrm{m}$. Above the threshold, the further increase of the laser intensity doesn't lead to the increase of 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 elect…
Next generation of ultra-intense laser facilities will lead to novel physical conditions ruled by collective and quantum electrodynamics effects, such as synchrotron-like emission of high-energy photons and electron-positron pair generation. In view of the future experiments performed in this regime, the latter processes have been implemented into the particle-in-cell code CALDER.
The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves (QIAWs) obliquely to an external magnetic field is reported in a quantum electron-positron-ion (e-p-i) plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter $H$ associated with the Bohm potential and the positron to electron density ratio $δ$. The profiles may, however, steepen initially and reach a steady state with…
We report simulation results of pair production by ultra-intense lasers irradiating a gold target using the GEANT4 Monte-Carlo code. Certain experimental features of the positron and electron energy spectra are reproduced, as well as trends with regard to target thickness and hot electron temperature Te. For Te in the range 5-10 MeV, the optimal target thickness for pair production is found to be about 3 mm. Further Monte-Carlo simulations may aid in the optimization of laser-driven positron sources.
It is conjectured that all perturbative approaches to quantum electrodynamics (QED) break down in the collision of a high-energy electron beam with an intense laser, when the laser fields are boosted to `supercritical' strengths far greater than the critical field of QED. As field strengths increase toward this regime, cascades of photon emission and electron-positron pair creation are expected, as well as the onset of substantial radiative corrections. Here we identify the important role played by the collision angle in mitigating energy losses to photon emission that would otherwise prevent …
When a photon collides with a laser pulse, an electron-positron pair can be produced via the nonlinear Breit-Wheeler process. A simulation framework has been developed to calculate this process, which is based on a ponderomotive approach that includes strong-field quantum electrodynamical effects via the locally monochromatic approximation (LMA). Here we compare simulation predictions for a variety of observables, in different physical regimes, with numerical evaluation of exact analytical results from theory. For the case of a focussed laser background, we also compare simulation with a high-…
Twisted Laguerre-Gaussian lasers, with orbital angular momentum and characterised by doughnut shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high gradient positron acceleration. The production of ultrahigh intensity twisted laser pulses …
Direct production of electron--positron pairs in two photon collisions, the Breit--Wheeler process, is one of the basic processes in the Universe. However, it has never been observed in laboratory because of absence of the intense gamma-ray sources. Laser induced synchrotron sources emission may open for the first time a way to observe this process. A feasibility of an experimental set--up using a MeV photon source is studied in this paper. We compare several $γ$--ray sources, estimate the expected number of electron--positron pairs and competing processes by using numerical simulations includ…
We perform particle-in-cell simulations to elucidate the microphysics of relativistic weakly magnetized shocks loaded with electron-positron pairs. Various external magnetizations $σ\lesssim 10^{-4}$ and pair-loading factors $Z_\pm \lesssim 10$ are studied, where $Z_\pm$ is the number of loaded electrons and positrons per ion. We find the following. (1) The shock becomes mediated by the ion Larmor gyration in the mean field when $σ$ exceeds a critical value $σ_{\rm L}$ that decreases with $Z_\pm$. At $σ\lesssimσ_{\rm L}$ the shock is mediated by particle scattering in the self-generated microt…
The laser interaction with an electron-positron-ion mixed plasma is studied, from the perspective of the associated high-order harmonic generation. For an idealized mixed plasma which is assumed with a sharp plasma-vacuum interface and uniform density distribution, when it is irradiated by a weakly relativistic laser pulse, well-defined signals at harmonics of the plasma frequency in the harmonic spectrum are observed. These characteristic signals are attributed to the inverse two-plasmon decay of the counterpropagating monochromatic plasma waves which are excited by the energetic electrons an…
The advent of Petawatt-class laser systems allows generating electro-magnetic fields of unprecedented strength in a controlled environment, driving increasingly more efforts to probe yet unobserved processes through their interaction with the quantum vacuum. Still, the lowest intensity scale governing these effects lies orders of magnitude beyond foreseen capabilities, so that such endeavor is expected to remain extremely challenging. In recent years, however, plasma mirrors have emerged as a promising bridge across this gap, by enabling the conversion of intense infrared laser pulses into coh…
A model for the excitation of a non-linear ion-wake mode by a train of plasma electron oscillations in the non-linear time-asymmetric regime is developed using analytical theory and particle-in-cell based computational solutions. The ion-wake is shown to be a driven non-linear ion-acoustic wave in the form of a cylindrical ion-soliton. The near-void and radially-outwards propagating ion-wake channel of a few plasma skin-depth radius, is explored for application to "Crunch-in" regime of positron acceleration. The coupling from the electron wakefield mode to the ion-mode dictates the long-term e…
