Dense Electron-positron Plasma Research Articles

Towards critical and supercritical electromagnetic fields

Abstract The availability of ever stronger, laser-generated electromagnetic fields underpins continuing progress in the study and application of nonlinear phenomena in basic physical systems, ranging from molecules and atoms to relativistic plasmas and quantum electrodynamics. This raises the question: how far will we be able to go with future lasers? One exciting prospect is the attainment of field strengths approaching the Schwinger critical field ${E}_{\mathrm{cr}}$ in the laboratory frame, such that the field invariant ${E}^2-{c}^2{B}^2>{E}_{\mathrm{cr}}^2$ is reached. The feasibility of doing so has been questioned, on the basis that cascade generation of dense electron–positron plasma would inevitably lead to absorption or screening of the incident light. Here we discuss the potential for future lasers to overcome such obstacles, by combining the concept of multiple colliding laser pulses with that of frequency upshifting via a tailored laser–plasma interaction. This compresses the electromagnetic field energy into a region of nanometre size and attosecond duration, which increases the field magnitude at fixed power but also suppresses pair cascades. Our results indicate that laser facilities with peak power of tens of PW could be capable of reaching ${E}_{\mathrm{cr}}$ . Such a scenario opens up prospects for the experimental investigation of phenomena previously considered to occur only in the most extreme environments in the universe.

Dense positrons and γ-rays generation by lasers interacting with convex target

We use quantum electrodynamics particle-in-cell simulation to study the generation of dense electron–positron plasma and strong γ-ray bursts in counter-propagating laser beam interactions with two different solid targets, i.e. planar (type I) and convex (type II). We find that type II limits fast electron flow most effectively. while the photon density is increased by about an order of magnitude and energy by approx. 10%–20% compared with those in type I target. γ-photon source with an ultrahigh peak brilliance of 2 × 1025 photons/s/mm2/mrad2/0.1% BW is generated by nonlinear Compton scattering process. Furthermore, use of type II target increases the positron density and energy by 3 times and 32% respectively, compared with those in type I target. In addition, the conversion efficiencies of total laser energy to γ-rays and positrons of type II are improved by 13.2% and 9.86% compared with type I. Such improvements in conversion efficiency and positron density are envisaged to have practical applications in experimental field.

Efficient ion acceleration and dense electron–positron plasma creation in ultra-high intensity laser-solid interactions

The radiation pressure of next generation ultra-high intensity (>1023 W cm−2) lasers could efficiently accelerate ions to GeV energies. However, nonlinear quantum-electrodynamic effects play an important role in the interaction of these laser pulses with matter. Here we show that these effects may lead to the production of an extremely dense (∼1024 cm−3) pair-plasma which absorbs the laser pulse consequently reducing the accelerated ion energy and laser to ion conversion efficiency by up to 30%–50% and 50%–65%, respectively. Thus we identify the regimes of laser-matter interaction, where either ions are efficiently accelerated to high energy or dense pair-plasmas are produced as a guide for future experiments.

Dense electron-positron plasmas and gamma-ray bursts generation by counter-propagating quantum electrodynamics-strong laser interaction with solid targets

We use quantum electrodynamics (QED) particle-in-cell simulations to investigate and compare the generation of dense electron-positron plasmas and intense γ-ray bursts in the case of counter-propagating laser solid interaction (two-side irradiation) and single laser solid interaction (one-side irradiation). In the case of counter-propagating linearly polarized laser pulses irradiating a thin aluminum foil with each pulse peak power of 12.5 PW (I = 4 × 1023 W/cm2), we calculate that about 20% of the laser energy is converted into a burst of γ-rays with flux exceeding 1014 s.−1 This would be one of the most intense γ-ray sources among those currently available in laboratories. The γ-ray conversion efficiency in the case of two-side irradiation is three times higher than in the case of one-side irradiation using a single 12.5 PW laser. Dense electron-positron plasma with a maximum density of 6 × 1027 m−3 are generated simultaneously during the two-side irradiation which is eightfold denser compared to the one-side irradiation. The enhancement of the effects in the case of counter-propagating lasers are the results of the symmetrical compression of the foil target and the formation of electric potential and standing wave around the target. Realizing experimentally the proposed counter-propagating QED-strong laser-solid interaction to produce dense electron-positron pairs and prolific γ-rays will be made possible by the Extreme Light Infrastructure-Nuclear Physics facility under construction.

Nonlinear Electromagnetic Waves in a Degenerate Electron-Positron Plasma

Using the reductive perturbation technique (RPT), the nonlinear propagation of magnetosonic soli- tary waves in an ultracold, degenerate (extremely dense) electron-positron (EP) plasma (containing ultracold, degen- erate electron, and positron fluids) is investigated. The set of basic equations is reduced to a Korteweg-de Vries (KdV) equation for the lowest-order perturbed magnetic field and to a KdV type equation for the higher-order perturbed mag- netic field. The solutions of these evolution equations are obtained. For better accuracy and searching on new fea- tures, the new solutions are analyzed numerically based on compact objects (white dwarf) parameters. It is found that

Dense electron-positron plasmas and bursts of gamma-rays from laser-generated quantum electrodynamic plasmas

In simulations of a 12.5 PW laser (focussed intensity I=4×1023Wcm−2) striking a solid aluminum target, 10% of the laser energy is converted to gamma-rays. A dense electron-positron plasma is generated with a maximum density of 1026m−3, seven orders of magnitude denser than pure e− e+ plasmas generated with 1PW lasers. When the laser power is increased to 320 PW (I=1025Wcm−2), 40% of the laser energy is converted to gamma-ray photons and 10% to electron-positron pairs. In both cases, there is strong feedback between the QED emission processes and the plasma physics, the defining feature of the new “QED-plasma” regime reached in these interactions.

Coherent nonlinear structures in dense electron—positron plasma

It is shown that rarefactive-type double layer structures exist in ultradense electron—positron plasma. For this purpose, an extended Korteweg de Vries equation is derived and solved analytically in the low amplitude limit by employing the appropriate fluid equations. A strong influence of quantum degeneracy pressure of electrons and positrons, quantum diffraction effects and concentration of background positive ions on double layer is noticed. It is also pointed out that the amplitude and steepness of the double layer increases with an increase in ion concentration or ion charge number. The results are examined numerically for some interesting cases of dense plasmas with illustrations.

On the pulse-width statistics in radio pulsars - III. Importance of the conal profile components

This work is a continuation of two previous papers of a series, in which we examined the pulse-width statistics of normal radio pulsars. In the first paper, we compiled the largest ever data base of pulsars with interpulses in their mean profiles. In the second one, we confirmed the existence of the lower boundary in the scatter plot of core component pulse-widths versus the pulsar period W50 ∼ 2.°5 P−0.5, first discovered by Rankin using a much smaller number of interpulse cases. In this paper, we show that the same lower boundary also exists for the conal profile components. Rankin proposed a very simple method of estimation of the pulsar inclination angle based on comparing the width W50 of its core component with the period-dependent value of the lower boundary. We claim that this method can be extended to conal components as well. To explain the existence of the lower boundary, Rankin proposed that the core emission originates at or near the polar cap surface. We demonstrated clearly that no coherent pulsar radio emission can originate at altitudes lower than 10 stellar radii, irrespective of the actual mechanism of coherence. We argue that the lower boundary reflects the narrowest angular structures that can be distinguished in the average pulsar beam. These structures represent the core and the conal components in mean pulsar profiles. The P−0.5 dependence follows from the dipolar nature of the magnetic field lines in the radio emission region, while the numerical factor of about 2.°5 reflects the curvature radius of a non-dipolar surface magnetic field in the partially screened gap above the polar cap, where dense electron–positron plasma is created. Both the core and conal emission should originate at altitudes of about 50 stellar radii in a typical pulsar, with a possibility that the core beam is emitted at slightly lower heights than the conal ones.

A Blast of Gamma Rays and Positrons

The next generation of ultrahigh energy lasers will be able to produce extremely dense electron-positron plasmas and intense bursts of gamma rays, according to simulations, and both will lead to new types of experiments.

Nonlinear electromagnetic perturbations in a degenerate ultrarelativistic electron-positron plasma

Nonlinear propagation of fast and slow magnetosonic perturbation modes in an ultrarelativistic, ultracold, degenerate (extremely dense) electron positron (EP) plasma (containing ultrarelativistic, ultracold, degenerate electron and positron fluids) has been investigated by the reductive perturbation method. The Alfvén wave velocity is modified due to the presence of the enthalpy correction in the fluid equations of motion. The degenerate EP plasma system (under consideration) supports the Korteweg-de Vries (KdV) solitons, which are associated with either fast or slow magnetosonic perturbation modes. It is found that the ultrarelativistic model leads to compressive (rarefactive) electromagnetic solitons corresponding to the fast (slow) wave mode. There are certain critical angles, θ(c), at which no soliton solution is found corresponding to the fast wave mode. For the slow mode, the magnetic-field intensity affects both the soliton amplitude and width. It is also illustrated that the basic features of the electromagnetic solitary structures, which are found to exist in such a degenerate EP plasma, are significantly modified by the effects of enthalpy correction, electron and positron degeneracy, magnetic-field strength, and the relativistic effect. The applications of the results in a pair-plasma medium, which occurs in many astrophysical objects (e.g., pulsars, white dwarfs, and neutron stars) are briefly discussed.

Acoustic double layer structures in dense magnetized electron-positron-ion plasmas

The acoustic double layer structures are studied using quantum hydrodynamic model in dense magnetized electron-positron-ion plasmas. The extended Korteweg-de Vries is derived using reductive perturbation method. It is found that increase in the ion concentration in dense magnetized electron-positron plasmas increases the amplitude as well as the steepness of the double layer structure. However, increase in the magnetic field strength and decrease in the obliqueness of the nonlinear acoustic wave enhances only the steepness of the double layer structures. The numerical results have also been shown by using the data of the outer layer regions of white dwarfs given in the literature.

Influence of photon-neutrino processes on the cooling of a magnetar

The photon-neutrino processes $\gamma e^{\pm} \to e^{\pm} \nu \bar \nu$, $\gamma \to \nu \bar \nu$ and $\gamma \gamma \to \nu \bar \nu$ are investigated in the presence of a strongly magnetized and dense electron-positron plasma. The amplitudes of the reactions $\gamma e^{\pm} \to e^{\pm} \nu \bar \nu$ and $\gamma \gamma \to \nu \bar \nu$ are obtained. In the case of a cold degenerate plasma contributions of the considering processes to neutrino emissivity are calculated. It is shown that contribution of the process $\gamma \gamma \to \nu \bar \nu$ to neutrino emissivity is supressed in comparision with the contributions of the processes $\gamma e^{\pm} \to e^{\pm} \nu \bar \nu$ and $\gamma \to \nu \bar \nu$. The constraint on the magnetic field strength in the magnetar outer crust is obtained.

Neutrino (antineutrino) effective charge in a magnetized electron–positron plasma

Using dynamical techniques of the plasma physics, the neutrino (antineutrino) effective charge in a magnetized dense electron–positron plasma is determined here. It shown that its value, which is determined by the plasma collective processes, depends mainly on the propagation direction of plasma waves and neutrinos against the external magnetic field direction. The direction dependence of the effective charge occurs due to the fact that the magnetic field breaks the plasma isotropy. The present theory gives a unified picture of the problem which is valid for an external magnetic field below the Landau–Schwinger critical value. Comparison with some of the results from the quantum field theory has been made.

Electroweak interactions between intense neutrino beams and dense electron-positron magnetoplasmas

The electroweak coupling between intense neutrino beams and strongly degenerate relativistic dense electron-positron magnetoplasmas is considered. The intense neutrino bursts interact with the plasma due to the weak Fermi interaction force, and their dynamics is governed by a kinetic equation. Our objective here is to develop a kinetic equation for a degenerate neutrino gas and to use that equation to derive relativistic magnetohydrodynamic equations. The latter are useful for studying numerous collective processes when intense neutrino beams nonlinearly interact with degenerate, relativistic, dense electron-positron plasmas in strong magnetic fields. If the number densities of the plasma particles are of the order of 1033 cm-3, the pair plasma becomes ultra-relativistic, which strongly affects the potential energy of the weak Fermi interaction. The new system of equations allows several neutrino-driven streaming instabilities involving new types of relativistic Alfven-like waves. The relevance of our investigation to the early universe and supernova explosions is discussed.

Relativistic Plasma Physics. Relativistic Electron-Positron Pair Plasmas.

Electron-positron plasmas are believed to exist around the center of galaxy and compact stars. This relativistic electron-positron pair plasma has special features different from normal plasmas. The equilibrium conditions are given to solve the rate equation for pair creations and pair annihilation. The limit of temperature exists around 15 MeV under the condition that electron-positron plasma stays in equilibrium. In addition to the astrophysical plasmas, the dense electron-positron plasmas are produced by ultra-intense lasers in alaboratory.The studies of the relativistic electron-positron plasmas become important subjects in both astrophysics and laboratory plasma physics.

Review of physics and applications of relativistic plasmas driven by ultra-intense lasers

As tabletop lasers continue to reach record levels of peak power, the interaction of light with matter has crossed a new threshold, in which plasma electrons at the laser focus oscillate at relativistic velocities. The highest forces ever exerted by light have been used to accelerate beams of electrons and protons to energies of a million volts in distances of only microns. Not only is this acceleration gradient up to a thousand times greater than in radio-frequency-based sources, but the transverse emittance of the particle beams is comparable or lower. Additionally, laser-based accelerators have been demonstrated to work at a repetition rate of 10 Hz, an improvement of a factor of 1000 over their best performance of just a couple of years ago. Anticipated improvements in energy spread may allow these novel compact laser-based radiation sources to be useful someday for cancer radiotherapy and as injectors into conventional accelerators, which are critical tools for x-ray and nuclear physics research. They might also be used as a spark to ignite controlled thermonuclear fusion. The ultrashort pulse duration of these particle bursts and the x rays they can produce, hold great promise as well to resolve chemical, biological or physical reactions on ultrafast (femtosecond) time scales and on the spatial scale of atoms. Even laser-accelerated protons are soon expected to become relativistic. The dense electron–positron plasmas and vast array of nuclear reactions predicted to occur in this case might even help bring astrophysical phenomena down to Earth, into university laboratories. This paper reviews the many recent advances in this emerging discipline, called high-field science.

Spontaneous magnetization of dense neutron matter and electron-positron plasma

It is shown that dense degenerate neutron gas can undergo transition to a magnetically ordered state, and this one is a phase transition of the second order. It is also shown that the occurrence of the spontaneous magnetization explains the characteristic value of the neutron star (pulsar) density and magnetic field. The problem of the occurrence of spontaneous magnetization in dense electron-positron plasma is studied also.

Relativistic Electron-Positron Gamma Ray Laser

The prerequisite for an efficient electron-positron gamma ray laser, which is the rapid formation o f a dense electron-positron plasma in a time shorter than the time for pair annihilation, is ideally fulfilled in a relativistic electron-positron superpinch. Because the cross section for annihilation decreases quadratically with the center o f mass energy, the time requirements otherwise imposed, are greatly relaxed. A relativistic electron-positron pinch can collapse under a complete population inversion into a very dense state possessing the form o f a long filament, just as it is required for a gamma ray laser. The gamma ray energies are the total center of mass energies, which can be much larger than the electron-positron rest mass energies.