Counterstreaming Plasmas Research Articles

Temperature measurements of electrostatic shocks in laser-produced counter-streaming plasmas

Collisionless shocks in counter-streaming plasmas, created by the high-power laser system Gekko XII HIPER, are investigated. The shock structure and density are measured by optical diagnostics such as shadowgraphy, interferometry, and streaked interferometry. The plasma density and temperature are estimated from self-emission measurements with visible light by streaked optical pyrometer and gated optical imager. Brightness temperatures are calculated considering the efficiency of the detectors, and electron temperatures are estimated.

THE INFLUENCE OF THE MASS RATIO ON THE ACCELERATION OF PARTICLES BY FILAMENTATION INSTABILITIES

Almost all sources of high energy particles and photons are associated with jet phenomena. Prominent sources of such highly relativistic outflows are pulsar winds and Active Galactic Nuclei. The current understanding of these jets assumes diluted plasmas which are best described as kinetic phenomena. In this kinetic description particle acceleration to ultra-relativistic speeds can occur in completely unmagnetized and neutral plasmas through insetting effects of instabilities. Even though the morphology and nature of particle spectra are understood to a certain extent, the composition of the jets is not known yet. While Poynting-flux dominated jets are certainly composed of electron-positron plasmas, the understanding of the governing physics in AGN jets is mostly unclear. In this article we investigate how the constituting elements of an electron-positron-proton plasma behave differently under the variation of the fundamental mass-ratio m_p/m_e. We studied initially unmagnetized counterstreaming plasmas using fully relativistic three-dimensional particle-in-cell simulations to investigate the influence of the mass-ratio on particle acceleration and magnetic field generation in electron-positron-proton plasmas. We covered a range of mass-ratios m_p/m_e between 1 and 100 with a particle number composition of n_{p^+}/n_{e^+} of 1 in one stream, only protons are injected in the other, whereas electrons are present in both to guarantee charge neutrality in the simulation box. We find that with increasing proton mass the instability takes longer to develop and for mass-ratios > 20 the particles seem to be accelerated in two phases which can be accounted to the individual instabilities of the different species. This means that for high mass ratios the coupling between electrons/positrons and the heavier protons, which occurs in low mass-ratios, disappears.

Jet formation in counterstreaming plasmas produced by high-power laser beams

We report the experimental results of a plasma jet formation in counterstreaming plasmas created by irradiating a double CH-plane target with a high-power laser system. The time evolution of the jet collimation was obtained over several shots, each shot taking a shadowgraphy image at a different timing. Since no jet formation was observed when a single CH-plane target was irradiated, the presence of the counterstreaming plasma, as an ambient plasma, is essential to the jet plasma collimation.

Collisionless shock generation by a high-power laser

We report the experimental generation of an electrostatic collisionless shock in counter-streaming plasmas without an external magnetic field. The collisionless counter-streaming plasmas were created by a high-power laser. The expansion of plasmas was measured with interferometry and shadowgraphy. Large density jump was observed in both diagnostics. The density jump is the collisionless shock because the width of this jump is much shorter than the ion-ion mean-free-path calculated from flow velocities and densities. Particle-in-cell simulations suggest the formation of the electrostatic collisionless shock in the counter-streaming plasmas. In our experiment, considering the shock width, the observed shock is the electrostatic shock.

Laboratory experiment to study collisionless shock

We report the experimental results of collisionless shock formation in counterstreaming plasmas produced by a high-power laser system. The experiment was performed with Gekko XII HIPER laser system at the Institute of Laser Engineering. In order to model collisionless shocks in the universe, supersonic counterstreaming plasma flows were generated using a CH double-plane target. By using the self-emission measurements, we observed the emission increase toward the shock through the downstream. We also observed the density jump associated with the emission increase. The width of the transition region is shorter than the ion-ion mean-free-path calculated from the measured plasma velocity and density.

Modelling the steady state spectral energy distribution of the BL-Lac Object PKS 2155-30.4 using a selfconsistent SSC model

In this paper we present a fully selfconsistent SSC model with particle acceleration due to shock and stochastic acceleration (Fermi-I and Fermi-II-Processes respectively) to model the quiescent spectral energy distribution (SED) observed from PKS 2155. The simultaneous August/September 2008 multiwavelength data of H.E.S.S., Fermi, RXTE, SWIFT and ATOM give new constraints to the high-energy peak in the SED concerning its curvature. We find that, in our model, a monoenergetic injection of electrons at $\gamma_0 = 910$ into the model region, which are accelerated by Fermi-I- and Fermi-II-processes while suffering synchrotron and inverse Compton losses, finally leads to the observed SED of PKS 2155-30.4 shown in H.E.S.S. and Fermi-LAT collaborations (2009). In contrast to other SSC models our parameters arise from the jet's microphysics and the spectrum is evolving selfconsistently from diffusion and acceleration. The $\gamma_0$-factor can be interpreted as two counterstreaming plasmas due to the motion of the blob at a bulk factor of $\Gamma = 58$ and opposed moving upstream electrons at moderate Lorentz factors with an average of $\gamma_u \approx 8$.

Counterstreaming magnetized plasmas with kappa distributions – II. Perpendicular wave propagation

The analysis of the stability and the dispersion properties of a counterstreaming plasma system with kappa distributions are extended here with the investigation of perpendicular instabilities. Purely growing filamentation (Weibel-like) modes propagating perpendicular to the background magnetic field can be excited in streaming plasmas with or without an excess of parallel temperature. In this case, however, the effect of suprathermal tails of kappa populations is opposite to that obtained for parallel waves: the growth rates can be higher and the instability faster than for Maxwellian plasmas. The unstable wavenumbers also extend to a markedly larger broadband making this instability more likely to occur in space plasmas with anisotropic distributions of kappa-type. The filamentation instability of counterstreaming magnetized plasmas could provide a plausible mechanism for the origin of two-dimensional transverse magnetic fluctuations detected at different altitudes in the solar wind.

JET FORMATION IN COUNTERSTREAMING COLLISIONLESS PLASMAS

Plasma jet formation was observed in counterstreaming plasmas in a laboratory experiment. In order to model an ambient plasma of astrophysical jets, the counterstreaming plasmas were created by irradiating a double CH-plane target with a high-power laser system. Since the mean free paths of the ions in terms of the counterstreaming motion were larger than the scale length of the experiment, the two-stream interaction of the plasmas was essentially collisionless. The time evolution of the jet collimation was obtained over several shots with different timing by shadowgraphy. When a single CH-plane target was irradiated, no jet collimation was observed. The counterstreaming plasma as an ambient plasma is essential for the jet plasma to collimate.

Self-excited plasmon polaritons in counterstreaming quantum plasmas

The effect of counterstreaming on the quantum plasmon-polariton excitation is examined. For this purpose, the dispersion relation describing a counterstreaming quantum plasma system has been derived. Solutions are displayed numerically and analyzed for different values of the quantum parameters and the streaming electrons. It is found that the quantum effects and the two-stream instability are relevant for the self-consistently excited surface plasmon polaritons.

26pYF-7 高出力レーザーを用いた対向プラズマ流による無衝突衝撃波生成実験(プラズマ宇宙物理(相対論的宇宙プラズマ),領域2,プラズマ基礎・プラズマ科学・核融合プラズマ・プラズマ宇宙物理)

26pYF-7 高出力レーザーを用いた対向プラズマ流による無衝突衝撃波生成実験(プラズマ宇宙物理(相対論的宇宙プラズマ),領域2,プラズマ基礎・プラズマ科学・核融合プラズマ・プラズマ宇宙物理)

A comparative study of the filamentation and Weibel instabilities and their cumulative effect. II. Weakly relativistic beams

AbstractCounterstreaming plasma systems with intrinsic temperature anisotropies are unstable against the excitation of Weibel-type instabilities, namely, filamentation and Weibel instabilities, and their cumulative effect. Here, the analysis is extended to counterstreaming plasmas with weakly relativistic bulk velocities, while the thermal velocities are still considered to be non-relativistic. Such plasma systems are relevant for fusion plasma experiments and the more violent astrophysical phenomena, such as jets in gamma-ray burst sources. Simple analytical forms of the dispersion relations are derived in the limit of a small transverse temperature or a large temperature anisotropy of the beams. The aperiodic growing solutions are plotted systematically for the representative cases chosen in Paper I (Lazar et al. 2009 J. Plasma Phys. 75, in press). In the limit of slow non-relativistic plasma flows, the numerical solutions fit well with those obtained in Paper I, but for weakly relativistic streams an important deviation is found.

Erratum: “Self-excited surface plasmon-polaritons at the interface of counterstreaming plasmas” [Phys. Plasmas 16, 052102 (2009)

First Page

Resonant Weibel instability in counterstreaming plasmas with temperature anisotropies

AbstractThe Weibel instability, driven by a plasma temperature anisotropy, is non-resonant with plasma particles: it is purely growing in time, and does not oscillate. The effect of a counterstreaming plasma is examined. In a counterstreaming plasma with an excess of transverse temperature, the Weibel instability arises along the streaming direction. Here it is proved that for large wave-numbers the instability becomes resonant with a finite real (oscillation) frequency, ωr ≠ 0. When the plasma flows faster, with a bulk velocity larger than the parallel thermal velocity, the instability becomes dominantly resonant. This new feature of the Weibel instability can be relevant for astrophysical sources of non-thermal emissions and the stability of counterflowing plasma experiments.

Self-excited surface plasmon-polaritons at the interface of counterstreaming plasmas

Surface plasma modes are coupled electromagnetic/electrostatic (plasmon-polariton) excitations of free electrons near the vacuum-plasma or plasma-plasma interface. The surface plasmon-polariton propagates along the surface plane and decays on both sides of the boundary. The effect of counterstreaming on the surface plasmon-polariton excitation is examined. It is shown that the two-stream instability can excite self-consistently the surface modes at the interface of two counterstreaming plasmas. The dispersion relation is derived and the exact numerical solutions are plotted for comparison to the excitations of a nonstreaming plasma-plasma interface. Such plasma models are of interest in electronic signal transmission, as well as in astrophysical applications and in beam-plasma experiments.

COSMOLOGICAL EFFECTS OF WEIBEL-TYPE INSTABILITIES

New arguments are given here in favor of Weibel-type instabilities as one of the most plausible sources of the cosmological magnetic field. The Weibel instability has recently been proposed as one of the secondary mechanisms of relaxation for the large interpenetrating formations of galactic and intergalactic plasma. Here, these investigations are extended to counterstreaming plasmas which have, in addition, intrinsic temperature anisotropies, and where any form of the Weibel-type instability can be excited. This can be a simple filamentation instability due to the relative motion of counterstreaming plasmas, or a Weibel-like instability when it is generated by an excess of transverse temperature with respect to the streaming direction. But it can also be a cumulative filamentation/Weibel instability when the plasma is hotter along the streaming direction. Such plasma systems are relevant for the relative motions of filaments and sheets of galaxies, and are expected to exist at large scales and any age of our Universe. For such counterstreaming plasmas with internal temperature anisotropies, any Weibel-type instability mentioned before can become the primary wave relaxation mechanism of the plasma anisotropy, because it develops easily faster than the principal competitor, which is the two-stream electrostatic instability. The estimations made here for typical parameters of intergalactic plasmas, provide micro-Gauss levels of the magnetic field of Weibel type, which are consistent with magnetic field values, 10–7-10–5 G, derived from Faraday rotation measure of the linearly polarized emission of galactic or extragalactic sources.

A comparative study of the filamentation and Weibel instabilities and their cumulative effect. I. Non-relativistic theory

AbstractA comparative study of the electromagnetic instabilities in anisotropic unmagnetized plasmas is undertaken. The instabilities considered are the filamentation and Weibel instability, and their cumulative effect. Dispersion relations are derived and the growth rates are plotted systematically for the representative cases of non-relativistic counterstreaming plasmas with isotropic or anisotropic velocity distributions functions of Maxwellian type. The pure filamentation mode is attenuated by including an isotropic Maxwellian distribution function. Moreover, it is observed that counterstreaming plasmas can be fully stabilized by including bi-Maxellian distributions with a negative thermal anisotropy. This effect is relevant for fusion plasma experiments. Otherwise, for plasma streams with a positive anisotropy the filamentation and Weibel instabilities cumulate leading to a growth rate by orders of magnitude larger than that of a simple filamentation mode. This is noticeable for the quasistatic magnetic field generated in astrophysical sources, and which is expected to saturate at higher values and explain the non-thermal emission observed.

High-Mach number collisionless shock and photo-ionized non-LTE plasma for laboratory astrophysics with intense lasers

We propose that most of the collisionless shocks in the Universe, for example, supernova remnant shocks, are produced because of the magnetic field generated by Weibel instability and its nonlinear process. In order to verify and validate the computational result confirming this theory, we are carrying out model experiments with intense lasers. We are going to make a collisionless counter-streaming plasma with intense laser ablation based on the scaling law to laser plasma with the particle-in-cell simulation resulting in Weibel-mediated shock formation. Preliminary experimental data are shown. The photo-ionization and resultant non-LTE plasma physics are also very important subjects in astrophysics related to mainly compact objects, for example, black hole, neutron star and white dwarf. Planckian radiation with its temperature 80–100 eV has been produced in gold cavity with irradiation of intense lasers inside the cavity. The sample materials are irradiated by the radiation inside the cavity and absorption and self-emission spectra are observed and analyzed theoretically. It is demonstrated how the effect of non-LTE is essential to reproduce the experimental spectra with the use of a precision computational code.

Counterstreaming magnetized plasmas with kappa distributions - I. Parallel wave propagation

Non-thermal particle distributions of kappa type are frequently encountered in collisionless plasmas from space. The electromagnetic emissions coming from space are believed to originate in the counterstreaming structures of plasmas, which are ubiquitous in many astrophysical systems. Here, we investigate the dispersion properties and the stability of a counterstreaming plasma system with temperature anisotropies modelled by a bi-kappa distribution function. The numerical evaluation of parallel modes shows growth rates lower than those obtained for Maxwellian plasmas, with a strong dependence on the spectral index of the particle distribution function. If all other parameters are known, measuring the instability growth time can provide a possible tool for the determination of the spectral index κ.

Electromagnetic turbulence driven by the mixed mode instability

In continuation of a previous work, numerical results are presented, concerning relativistically counterstreaming plasmas. Here, the relativistic mixed mode instability evolves through and beyond the linear saturation, well into the nonlinear regime. Besides confirming earlier findings that wave power initially peaks on the mixed mode branch, it is observed that during late time evolution, wave power is transferred to other wave numbers. It is argued that the isotropization of power in wavenumber space may be a consequence of weak turbulence. Further, some modifications to the ideal weak turbulence limit is observed. Development of almost isotropic predominantly electrostatic—partially electromagnetic—turbulent spectra holds relevance when considering the spectral emission signatures of the plasma, namely, bremsstrahlung—partially magnetobremsstrahlung (synchrotron radiation and jitter radiation)—from relativistic shocks in astrophysical jets and from shocks in gamma-ray bursts and active galactic nuclei.

Cumulative effect of the Weibel-type instabilities in symmetric counterstreaming plasmas with kappa anisotropies

Counterstreaming plasma structures are ubiquitous in laboratory experiments and astrophysical systems, and they are investigated either to prevent unstable modes arising in beam-plasma experiments or to prove the existence of large scale magnetic fields in astrophysical objects. Filamentation instability arises in a counterstreaming plasma and is responsible for the magnetization of the plasma. A filamentationally unstable mode is described by assuming two symmetric counterstreaming plasmas, each with an isotropic Lorentzian (kappa) distribution. In this case, the filamentation instability growth rate can reach a maximum value markedly larger than that for a plasma with a Maxwellian distribution function. This behavior is opposite to what was observed for the Weibel instability growth rate in a bi-kappa plasma, which is always smaller than that obtained for a bi-Maxwellian plasma. The approach is further generalized for a counterstreaming plasma with a bi-kappa temperature anisotropy. In this case, the filamentation instability growth rate is enhanced by the Weibel effect when the plasma is hotter in the streaming direction, and the growth rate becomes even larger. These effects significantly improve the efficiency of the magnetic field generation, and provide further support for the potential role of the Weibel-type instabilities in the fast magnetization scenarios.