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.
In this paper, we obtain the dispersion relation for the lower-hybrid oscillations/waves in a cold magnetized electron-positron-ion (e-p-i) plasma. It is found that the frequency of the lower-hybrid oscillations in an e-p-i plasma is approximate $1/\sqrt{3}$ times the frequency of lower-hybrid oscillations in an electron-ion (e-i) plasma, provided the plasma density is high, and the equilibrium densities of the positron and the ion are balanced. The present work may have some relevance for laboratory/astrophysical e-p-i plasmas.
Stimulated Brillouin backscattering of light is shown to be drastically enhanced in electron-positron plasmas, in contrast to the suppression of stimulated Raman scattering. A generalized theory of three-wave coupling between electromagnetic and plasma waves in two-species plasmas with arbitrary mass ratios, confirmed with a comprehensive set of particle-in-cell simulations, reveals violations of commonly-held assumptions about the behavior of electron-positron plasmas. Specifically, in the electron-positron limit three-wave parametric interaction between light and the plasma acoustic wave can…
We consider the separate spin evolution of electrons and positrons in electron-positron and electron-positron-ion plasmas. We consider oblique propagating longitudinal waves in this systems. We report presence of the spin-electron acoustic waves and their dispersion dependencies. In electron-positron plasmas, similarly to the electron-ion plasmas, we find one spin-electron acoustic wave (SEAW) at propagation parallel or perpendicular to the external field and two spin-electron acoustic waves at the oblique propagation. At the parallel or perpendicular propagation of the longitudinal waves in e…
Interchange drive and cross-field transport of density filaments in quasi-neutral inhomogeneously magnetized electron-positron plasmas is shown to be strongly reduced by the presence of minority ions. Two mechanisms are identified for the reduction in radial propagation and plasma transport: effective mass related inertia, and collisionality dependent Boltzmann spin-up of the filaments. Numerical results are obtained with a three-dimensional full-F multi-species gyrofluid model.
The non-linear evolution of spin-electron acoustic, positron-acoustic, and spin-electron-positron acoustic waves is considered. It is demonstrated that weakly nonlinear dynamics of each wave leads to the soliton formation. Altogether, we report on existence of three different solitons. The spin-electron acoustic soliton known for electron-ion plasmas is described for electron-positron-ion plasmas for the first time. The existence of the spin-electron-positron acoustic soliton is reported for the first time. The positron-acoustic soliton and the spin-electron-positron acoustic soliton arise as …
The gyrokinetic stability of electron-positron plasmas contaminated by ion (proton) admixture is studied in slab geometry. The appropriate dispersion relation is derived and solved. The ion-temperature-gradient driven instability, the electron-temperature-gradient driven instability, the universal mode, and the shear Alfven wave are considered. The contaminated plasma remains stable if the contamination degree is below some threshold, and it is found that the shear Alfven wave can be present in a contaminated plasma in cases where it is absent without ion contamination.
A novel approach for positron injection and acceleration in laser driven plasma wakefield is proposed. A theoretical model is developed and confirmed through PIC simulation. One ring-shaped beam and one co-axially propagating Gaussian beam drive wakefields in a preformed plasma volume filled with both electrons and positrons. The laser's ponderomotive force as well as the charge separation force in the front bucket of the first bubble are utilized to provide the transverse momenta of injected positrons and those positrons can be trapped by the focusing field and then accelerated by the wakefie…
Particle-in-cell (PIC) simulations of collisionless jets of electrons and positrons in an ambient electron-proton plasma have revealed an acceleration of positrons at the expense of electron kinetic energy. The dominant instability within the jet was a filamentation instability between electrons, protons and positrons. In this work we show that a filamentation instability, between an initially unmagnetized ambient electron-proton plasma at rest and a beam of pair plasma that moves through it at a non-relativistic speed, indeed results in preferential positron acceleration. Filaments form that …
High-energy positrons and bright γ-ray sources are unique both for fundamental research and practical applications. However, GeV electron-positron pair jets and γ-ray flashes are still hardly produced in laboratories. Here we demonstrate that, by irradiating two 10 PW-scale laser pulses onto a near-critical density plasma channel, highly-directional GeV electron-positron pairs and bright γ-ray beams can be efficiently generated. Three-dimensional particle-in-cell simulations show that GeV positron jets show high density (8*10^21/cm^3), attosecond duration (400 as) and a divergence angle of 14°…
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…
Relativistic laser wakefield acceleration is characterized by an unsurpassed accelerating gradient, which is very suitable for electron acceleration over short distances and could be a promising candidate for next-generation compact accelerators. However, using this technique for positron acceleration is still challenging because positively charged particles are naturally defocused in nonlinear wakefields. Here we propose and numerically demonstrate a scheme to accelerate an externally injected positron beam in a nonlinear laser wakefield in a regime where a tail wave is formed behind density …
Symmetric electron-positron plasmas in inhomogeneous magnetic fields are intrinsically subject to interchange instability and transport. Scaling relations for the propagation velocity of density blob perturbations relevant to transport in isothermal magnetically confined electron-positron plasmas are deduced, including damping effects when Debye lengths are large compared to Larmor radii. The relations are verified by nonlinear full-F gyrofluid computations. Results are in favour of sufficient magnetic confinement for planned electron-positron plasma experiments. The model is generalised to ot…
A precise theoretical investigation has been made on dust-acoustic (DA) waves (DAWs) in a four components dusty plasma medium having inertial warm adiabatic dust grains and inertialess $q$-distributed electrons as well as isothermal ions and positrons. The nonlinear and dispersive parameters of the nonlinear Schrödinger equation (NLSE), which develops by using reductive perturbations technique, have been used to recognize the stable and unstable parametric regions of the DAWs as well as associated DA rogue waves (DARWs) in the unstable parametric regime of the DAWs. The effects of the light po…
High-energy-density electron-positron pair plasma production and its dynamics in a thin foil illuminated by two counter-propagating laser pulses are investigated through multi-dimensional particle-in-cell simulations. We compare the production of electron-positron pairs and gamma-photons via quantum electrodynamics processes in the relativistic transparent and opaque regimes, and find that the target transparency can significantly enhance the electron-positron pair production due to the formation of stable standing wave (SW). An optimum foil density of 200 - 280 n_c (n_c is the laser critical …
The electrostatic stability of electron-positron plasmas is investigated in the point-dipole and Z-pinch limits of dipole geometry. The kinetic dispersion relation for sub-bounce-frequency instabilities is derived and solved. For the zero-Debye-length case, the stability diagram is found to exhibit singular behavior. However, when the Debye length is non-zero, a fluid mode appears, which resolves the observed singularity, and also demonstrates that both the temperature and density gradients can drive instability. It is concluded that a finite Debye length is necessary to determine the stabilit…
Nonlinear propagation of purely stationary large amplitude electromagnetic (EM) solitary waves in a magnetized electron-positron (EP) plasma is studied using a fully relativistic two-fluid hydrodynamic model which accounts for physical regimes of both weakly relativistic $(P\ll nmc^2)$ and ultrarelativistic $(P\gg nmc^2)$ random thermal energies. Here, $P$ is the thermal pressure, $n$ the number density and $m$ the mass of a particle, and $c$ is the speed of light in vacuum. Previous theory in the literature [Phys. Plasmas \textbf{11}, 3078 (2004)] is advanced and generalized by the relativist…
Thermodynamic properties of the electron-positron plasma (or gas) at high and very high temperatures are investigated. To achieve this goal we have derived a number of analytical formulas for the Fermi-Dirac distribution functions (or spectral functions) which can be applied to various Fermi gases in different cases. Almost all these formulas are represented in the form of series expansions. The coefficients in these expansions are the explicit and relatively simple functions of the $\fracμ{T}$ ratio, where $T$ is the temperature and $μ$ is the chemical potential of this Fermi system. Our new …
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…
A four component space plasma system (consisting of immobile positive ions, inertial cold positrons as well as hot electrons and positrons following Cairns' nonthermal distribution function is considered. The nonlinear propagation of the positron-acoustic (PA) waves, in which the inertia (restoring force) is provided by the cold positron species (nonthermal pressure of both hot electron and positron species) has been theoretically investigated by deriving the nonlinear Schrödinger (NLS) equation. It is found from the numerical analysis of this NLS equation that the space plasma system under co…
The nonlinear propagation of heavy-ion-acoustic (HIA) waves (HIAWs) in a four component multi-ion plasma (containing inertial heavy negative ions and light positive ions, as well as inertialess nonextensive electrons and positrons) has been theoretically investigated. The nonlinear Schrödinger (NLS) equation is derived by employing the reductive perturbation method. It is found that the NLS equation leads to the modulational instability (MI) of HIAWs, and to the formation of HIA rogue waves (HIARWs), which are due to the effects of nonlinearity and dispersion in the propagation of HIAWs. The c…
The propagation of arbitrary amplitude ion-acoustic (IA) solitary waves (SWs) is studied in unmagnetized, collisionless, homogeneous electron-positron-ion (e-p-i) plasmas with finite temperature degeneracy of both electrons and positrons. Starting from a set of fluid equations for classical ions and Fermi-Dirac distribution for degenerate electrons and positrons, a linear dispersion relation for IA waves is derived. It is seen that the wave dispersion is significantly modified due to the presence of positron species and the effects of finite temperature degeneracy of electrons and positrons. I…
Designing A Buildable Optimized Stellarator to Confine Electron-Positron Plasmas
Max-Planck-Institut für Plasmaphysik（德国马普等离子体物理研究所）；Plasma Science and Fusion Center, Massachusetts Institute of Technology（麻省理工学院等离子体科学与聚变中心）；Department of Physics, University of Wisconsin-Madison（威斯康星大学麦迪逊分校物理系）；SchulerTEC；Department of Mechanical Engineering, McGill University（麦吉尔大学机械工程系）
The dispersion properties of elliptically polarized electromagnetic (EM) waves in a magnetized electron-positron-pair (EP-pair) plasma are studied with the effects of particle dispersion associated with the Bohm potential, the Fermi degenerate pressure, and the exchange-correlation force. Two possible modes of the extraordinary or X wave, modified by these quantum effects, are identified and their propagation characteristics are investigated numerically. It is shown that the upper-hybrid frequency, and the cutoff and resonance frequencies are no longer constants but are dispersive due to these…
Sardar et al. [Phys. Plasmas 23, 073703 (2016)] have studied the stability of small amplitude dust ion acoustic solitary waves in a collisionless unmagnetized electron - positron - ion - dust plasma. They have derived a Kadomtsev Petviashvili (KP) equation to investigate the lowest - order stability of the solitary wave solution of the Korteweg-de Vries (KdV) equation for long-wavelength plane-wave transverse perturbation when the weak dependence of the spatial coordinates perpendicular to the direction of propagation of the wave is taken into account. In the present paper, we have extended th…
The modulational instability (MI) of the dust-acoustic waves (DAWs) in an electron-positron-ion-dust plasma (containing super-thermal electrons, positrons and ions along with negatively charged adiabatic dust grains) is investigated by the analysis of the nonlinear Schrödinger equation (NLSE). To derive the NLSE, the reductive perturbation method has been employed. Two different parametric regions for stable and unstable DAWs are observed. The presence of super-thermal electrons, positrons and ions significantly modifies both the stable and unstable regions. The critical wave number $k_c$ (at …
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 …
The linear gyrokinetic stability properties of magnetically confined electron-positron plasmas are investigated in the parameter regime most likely to be relevant for the first laboratory experiments involving such plasmas, where the density is small enough that collisions can be ignored and the Debye length substantially exceeds the gyroradius. Although the plasma beta is very small, electromagnetic effects are retained, but magnetic compressibility can be neglected. The work of a previous publication (Helander, 2014) is thus extended to include electromagnetic instabilities, which are of imp…
Plasma accelerators sustain extreme field gradients, and potentially enable future compact linear colliders. Although tremendous progress has been achieved in accelerating electron beams in a plasma accelerator, positron acceleration with collider-relevant parameters is challenging. A recently proposed positron acceleration scheme relying on the wake generated by an electron drive beam in a plasma column has been shown to be able to accelerate positron witness beams with low emittance and low energy spread. However, since this scheme relies on cylindrical symmetry, it is possibly prone to tran…
Following the idea of three wave resonant interactions of lower hybrid waves it is shown that quantum -modified lower hybrid (QLH) wave in electron positron ion plasma with spatial dispersion can decay into another QLH wave ( where electron and positrons are activated whereas ions remain in the background) and another ultra low frequency QULH (where ions are mobile). Quantum effects like Bohm potential, exchange correlation and Fermi pressure on the lower hybrid wave significantly reshaped the dispersion properties of lower hybrid waves. Later a set of nonlinear Zakharov equations have been de…
By means of hollow plasma, multiple proton bunches work well in driving nonlinear plasma wakefields and accelerate electrons to energy frontier with preserved beam quality. However, the acceleration of positrons is different because the accelerating structure is strongly charge dependent. There is a discrepancy between keeping a small normalized emittance and a small energy spread. This results from the conflict that the plasma electrons used to provide focusing to the multiple proton bunches dilute the positron bunch. By loading an extra electron bunch to repel the plasma electrons and meanwh…
Plasma-based accelerators sustain accelerating gradients which are several orders greater than obtained in conventional accelerators. Focusing of electron and positron beams by wakefield, excited in plasma, in electron-positron collider is very important. The focusing mechanism in the plasma, in which all electron bunches of a sequence are focused identically, has been proposed by authors earlier. The mechanism of focusing of a sequence of relativistic positron bunches in plasma, in which all positron bunches of sequence are focused identically and uniformly, has been investigated in this pape…
