Showing papers on "Relativistic plasma published in 1992"

A jet model for the gamma-ray emitting blazar 3C 279

Abstract: The physical conditions in the gamma-ray-emitting blazar 3C 279 are discussed. The requirement of transparency for gamma-rays, together with the observation of rapid variability, imply that the high-energy radiation is anisotropic. It is proposed that the gamma-rays are produced in a relativistic jet via the synchrotron self-Compton mechanism. The gamma-ray spectrum is the high-energy extension of the inverse Compton radiation responsible for the X-ray emission. It is softer than the X-ray spectrum, owing to upper cutoffs in the electron energy spectra along the jet. The same electrons are responsible for the low-frequency emission via synchrotron radiation. The expected correlation of variability at different frequencies is discussed. 38 refs.

Propagation and guiding of intense laser pulses in plasmas

Abstract: A two-dimensional, axisymmetric, relativistic fluid model describing the propagation of intense laser pulses in plasmas is formulated and numerically evaluated. Relativistic guiding is ineffective in preventing the diffractive spreading of short laser pulses and long pulses become modulated due to relativistic and wake-field effects. Laser pulses can be propagated over many Rayleigh lengths by use of a performed plasma density channel or by tailoring the pulse profile. Ultrahigh axial electric fields can be generated behind the laser pulse.

Self-focusing and Raman scattering of laser pulses in tenuous plasmas.

Abstract: The propagation of laser pulses of intensity which is large enough for relativistic self-focusing to occur is strongy affected by Raman instabilities. Both large and small angle scattering are important. The latter is the most severe since it couples with relativistic self-focusing leading the pulses to acquire significant axial and transverse structure in a time of the order of the self-focusing time. This prevents smooth self-focused pulses propagation for distances longer than the Rayleigh length except for pulse duration of the order of the plasma period.

Pair production in a strong wake field driven by an intense short laser pulse.

Abstract: A preliminary investigation is presented of electron-positron pair production by means of plasma electrons accelerated by relativistic velocities in a strong wake field. The propagation distance of the plasma wake field, which is determined by the depletion of the short laser pulse due to wake-field generation, is much larger than the pulse length. For this case, the total number of electron-positron pairs produced is independent of the plasma concentration. For achievable parameters of the laser pulse, the total number of pairs may be quite significant ([similar to]10[sup 6][ital Z2], where [ital Z] is the nuclear charge of the plasma ion).

Nonlinear 1D laser pulse solitons in a plasma

Abstract: A class of exact one-dimensional solutions for modulated light pulses coupled to electron plasma waves in a relativistic cold plasma is investigated. The solutions are in the form of isolated envelope solitons and the nonlinear relationship between their group velocity, amplitude, and frequency are discussed. Numerical results are presented for intense pulses propagating close to the velocity of light; such pulses are of great interest from the point of view of particle and photon accelerators.

Interaction of ultrahigh laser fields with beams and plasmas

Abstract: The nonlinear interaction of ultraintense laser pulses with electron beams and plasmas is rich in a wide variety of new phenomena. Advances in laser science have made possible compact terawatt lasers capable of generating subpicosecond pulses at ultrahigh powers (≥1 TW) and intensities (≥1018 W/cm2). These ultrahigh intensities result in highly relativistic nonlinear electron dynamics. This paper briefly addresses a number of phenomena including (i) laser excitation of large‐amplitude plasma waves (wake fields), (ii) relativistic optical guiding of laser pulses in plasmas, (iii) optical guiding by preformed plasma channels, (iv) laser frequency amplification by ionization fronts and plasma waves, (v) relativistic harmonic generation, (vi) stimulated backscattering from plasmas and electron beams, (vii) nonlinear Thomson scattering from plasmas and electron beams, and (viii) cooling of electron beams by intense lasers. Potential applications of these effects are also discussed.

Double layers, spiky solitary waves, and explosive modes of relativistic ion‐acoustic waves propagating in a plasma

Abstract: The fully relativistic ion fluid equations are presented. These equations are reduced to a mixed modified Korteweg–de Vries (MKdV) equation by using the reductive perturbation method. The high‐speed streaming ions and the negative cubic nonlinearity of the mixed MKdV equation give rise to the new nonlinear wave modes, that is, the compressive double layer, the spiky solitary wave, and the explosive solutions. The double layer and the spiky solitary wave are confined within the specified positive potential region, while the explosive solutions are confined within the region where the potential exceeds the maximum potential or the negative potential region. It is shown for the first time that the double‐layer thickness narrows as the ion temperature and the relativistic effects increase, that the potential drop of the double layer grows as the ion temperature increases, and that the amplitudes of the spiky solitary wave and the explosive solution grow as the ion temperature effect increases. This investigation relates to the evolution process of the nonlinear wave structure in which these three modes form the fine structure in space.

Relativistic plasma microwave electronics: Studies of high‐power plasma‐filled backward‐wave oscillators

Abstract: The area of relativistic plasma microwave electronics has only recently generated renewed interest. New experimental data are presented demonstrating that the presence of a low‐density background plasma in a relativistic backward‐wave oscillator leads to several beneficial effects, including (a) enhanced interaction efficiency (40%), (b) operation at very low and possibly zero guiding magnetic field, (c) tunability by controlling the plasma density, (d) high degree of spectral coherency, and (e) operation well above the vacuum limiting current.

Third-harmonic generation with ultrahigh-intensity laser pulses.

Abstract: When an intense, plane-polarized, laser pulse interacts with a plasma, the relativistic nonlinearities induce a third-harmonic polarization. A phase-locked growth of a third-harmonic wave can take place, but the difference between the nonlinear dispersion of the pump and driven waves leads to a rapid unlocking, resulting in a saturation. What become third-harmonic amplitude oscillations are identified here, and the nonlinear phase velocity and the renormalized electron mass due to plasmon screening are calculated. A simple phase-matching scheme, based on a resonant density modulation, is then proposed and analyzed.

X-ray studies of various shapes of electron-velocity distribution functions and of electron confinement affected by kilovolt-range electrostatic potentials

Abstract: Several types of x-ray diagnostics, such as x-ray energy spectrum analyses, x-ray absorption methods, and x-ray tomographic reconstructions using various types of x-ray detectors (i.e., a Si(Li), a pure Ge, a NaI(Tl), Si surface-barrier detectors, as well as microchannel plates) have been employed for obtaining various shapes of electron-velocity distribution functions as well as their spatial profiles: (i) a plateau-shaped electron-velocity distribution function in the plug region, supporting a scaling theory between thermal-barrier potentials and ion-confining potentials (Cohen's strong electron-cyclotron heating theory); (ii) mirror-trapped 60-keV relativistic Maxwellian electrons in the thermal-barrier region; and (iii) two-component Maxwellian electrons in the central cell have been observed in the tandem-mirror GAMMA 10. During experiments with thermal barriers, it has been observed that the bulk-electron temperature and its evolution with time in the central cell are quite different from the electron energy and its temporal evolution in the plug region. These differences as well as the different shape of the electron-velocity distribution function in each region have clearly demonstrated the existence of a thermal-isolation effect due to the thermal barriers between the central cell and the plug region. X-ray tomography data in these three regions have shown good axisymmetric radial profiles peaked on themore » magnetic axis; this axisymmetric shape is useful for reducing nonambipolar radial particle losses. Furthermore, the validity of the Pastukhov theory for electron-energy confinement that is enhanced due to the formation of thermal-barrier potentials has been demonstrated using the electron-energy balance analyses. These data have represented a good electron-energy confinement capability due to the formation of thermal barriers.« less

Suprathermal and relativistic electrons produced in laser–plasma interaction at 0.26, 0.53, and 1.05 μm laser wavelength

Abstract: Very energetic electrons produced in laser–plasma interactions at 0.26, 0.53, and 1.05 μm laser wavelength have been measured. The targets were 1.5 μm plastic foils and the laser intensity was around 1015 W/cm2. Detailed measurements of the electron distribution performed at a 0.26 μm laser wavelength exhibit an angular distribution strongly peaked along the laser axis at the highest energies (above 200 keV). Electrons up to 1.3 MeV have been observed in the 1.05 μm experiments. The hot temperatures inferred from the measured energy distributions are of the order of 100 keV in the 1.05 μm experiments, and 50 keV in the 0.53 μm/0.26 μm experiments. The experimental electron emission features are discussed with a special focus on the relation between the linear as well as the nonlinear electron plasma wave generation mechanisms and the maximum energy reached by an electron trapped in this wave.

Relativistic effects in plasma reflectometry

Abstract: The refractive indices and cutoff conditions for electromagnetic waves in plasmas are investigated for cold, hot and relativistic plasma models. Significant relativistic modifications of refractive indices and locations of cutoffs are found in regimes relevant for reflectometry in large Tokamaks. For X-mode it is demonstrated that these effects may shift the location of the reflecting layer by a significant fraction of the minor radius and that the cold model may lead to considerable underestimations of the density profile. Relativistic effects predicted for O-mode reflectometry are smaller than for X-mode, but not negligible. An algorithm for reconstruction of density profiles which allows a relativistic plasma model to be used is presented.

Emergence of new quasiparticles in quantum electrodynamics at finite temperature

Abstract: We study the spectrum of fermionic excitations in a hot relativistic electron plasma. Numerical analysis of the one-loop electron propagator shows the appearance of new quasiparticle modes, as already studied in the massless fermion limit, as the temperature is raised to exceed the electron mass $m$. We calculate the relevant spectral densities and show that one mode, whose splitting in energy from the original electron is of the order of $m$, moves as the temperature is raised towards higher frequency along with the electron while retaining a narrow width. We compare results derived in Feynman and Coulomb gauges. The role of the zero-temperature counterterms is discussed.

Sound waves in an electron-positron plasma

Abstract: By means of a kinetic description, we obtain the sound wave velocity in an electron-positron plasma at relativistic temperatures.

Three‐dimensional effects in the acceleration of test electrons in a relativistic electron plasma wave

Abstract: The acceleration of test electrons in a relativistic electron plasma wave is computed. The plasma wave is either due to the beating of two laser beams or constitutes the wake of an ultrashort laser pulse. The plasma wave geometry reflects the geometry of the laser. The electron beam has a finite emittance. The parameters of the calculation correspond to experiments now in progress. This 3D model is able to predict the corresponding electron spectrum.

Nonlinear relativistic interaction of an ultrashort laser pulse with a cold plasma

Abstract: The nonlinear, relativistic dynamics that results when intense (1018 W/cm2 and above) and ultrashort (one plasma period or shorter) laser pulse travels through a cold underdense plasma is investigated. Using a Lagrangian analysis of the plasma response, it can be demonstrated that the nonlinear wake, the collective dissipation, the nonlinear Compton losses, and the harmonic generation, are all determined by a finite set of integrated scalar quantities. This result holds for one‐dimensional, short pulses of arbitrary amplitude, shape, and polarization, so that these very short intense laser pulses in a plasma can be viewed essentially as a quasiparticle characterized by a small set of global parameters.

Electron-acoustic solitons in a weakly relativistic plasma

Abstract: Weakly relativistic electron-acoustic solitons are investigated in a two-electron-component plasma whose cool electrons form a relativistic beam. A general Korteweg-de Vries (KdV) equation is derived, in the small-|o| domain, for a plasma consisting of an arbitrary number of relativistically streaming fluid components and a hot Boltzmann component. This equation is then applied to the specific case of electron-acoustic waves. In addition, the fully nonlinear system of fluid and Poisson equations is integrated to yield electron-acoustic solitons of arbitrary amplitude. It is shown that relativistic beam effects on electron-acoustic solitons significantly increase the soliton amplitude beyond its non-relativistic value. For intermediate- to large-amplitude solitons, a finite cool-electron temperature is found to destroy the balance between nonlinearity and dispersion, yielding soliton break-up. Also, only rarefactive electronacoustic soliton solutions of our equations are found, even though the relativistic beam provides a positive contribution to the nonlinear coefficient of the KdV equation, describing relativistic, nonlinear electron-acoustic waves.

General-relativistic hydrodynamics of a collisionless plasma in a strong magnetic field.

Abstract: The closed set of general-relativistic hydrodynamical equations describing a strongly magnetized collisionless plasma with an anisotropic pressure tensor is derived Consideration is based on the ``3+1'' formulation of magnetohydrodynamics and the orthonormal tetrad technique The model is the further generalization of the theory of Chew, Goldberger, and Low [Proc R Soc London Ser A 236, 1204 (1954)] for the general-relativistic case In ultrarelativistic limit the equations of state are obtained, which differ noticeably from those known previously

Self-induced distributed feedback in plasma-filled Čerenkov free electron masers

Abstract: Two strong counterpropagating waves in the cavity of a plasma‐filled Cerenkov free electron maser modulate the density of the plasma electrons and ions. These density modulations induce periodic perturbations in the effective high‐frequency dielectric constant of the plasma. When the intensity of the waves is high, and the ions can move to reduce the charge separation, the modulations are saturated. The two waves are then coupled by a self‐induced distributed feedback. The distributed feedback is shown to resonantly enhance the gain of the Cerenkov amplifier. In the oscillator, the threshold gain is significantly reduced. Estimates of the oscillator efficiency show that the distributed feedback may enhance this efficiency to about eight times more than in a comparable vacuum Cerenkov oscillator.

Spiky Langmuir solitons in a dense ultrarelativistic electron–positron plasma

Abstract: Spiky and short‐duration Langmuir solitons are found to exist in an ultrarelativistic electron–positron plasma. Nonlinear Landau damping and pulsar radiation are discussed.

Relativistic Spin-One Boson Plasma

Abstract: We derive the polarization tensor for a system of charged spin-one bosons and antibosons in the case of no external magnetic field. This requires a thorough exposition of relativistic spin-one quantum mechanics, and thus we initially focus upon the Sakata-Taketani equation and its free-field solutions. We employ these results to evaluate the matrix elements required for the calculation of the polarization tensor, which itself is derived via the self-consistent random-phase approximation (RP A) method. It is from this tensor that we obtain the longitudinal and transverse dielectric response functions for this plasma. We evaluate these response functions at zero temperature, and exhibit the characteristic modes of oscillation. Finally, we discuss possible generalizations of this work, in particular to a finite-temperature plasma, and to one with an external magnetic field. In this paper, we present a study of the relativistic spin-one particle-antiparticle plasma, in the presence of no external magnetic field. The course of the investigation begins with a review of single particle theories of spin-one (vector) bosons, which we present in § 2 of this work. In § 3 of the paper, we present a detailed treatment of the six-component formalism for spin-one bosons, first developed by Sakata and Taketani/) which we then employ in our linear response theory calculations for the plasma. To our knowledge, this particular formalism is under-represented in the literature pertinent to spin-one bosons, and hence our exposition is an attempt to clarify its general features, and underscore its particular utility in work of the nature we have undertaken. The latter part of the paper (§§ 4 and 5) contains the linear response calculations proper. We set about deriving the polarization four-tensor, employing a method first· proposed by Harris,z) this being the self-consistent random-phase approximation (RPA) method. We then obtain the characteristic modes of oscillation of the plasma. At present, we concern ourselves solely with the plasma properties of the polari­ zation tensor, leaving a complete study of the vacuum modes of oscillation and their renormalization to a later paper, in which we also propose to introduce the presence of an external magnetic field. Employing our plane-wave solutions of the Sakata­ Taketani equation for the case of no external fields, we proceed to calculate the longitudinal and transverse dielectric response functions, which are obtained via the employment of the relationship between the covariant polarization four-tensor and the dielectric three-tensor. In the case of the longitudinal response function, we present the formal result which is valid for all temperatures, and we then evaluate the longitudinal and transverse response functions at zero temperature, from which we obtain the modes of oscillation. Our work follows on from that of Kowalenko, Frankel and Hines (KFH),3) who studied the spin-zero pair plasma by employing a self-consistent field method to find

Relativistic semiconductor plasma wave frequency up-converter

Abstract: A device that frequency up-shifts an impinging electromagnetic wave, facilitating signal pulse compression, consisting of a semiconductor block or waveguide with an optically-induced relativistic plasma wave which interacts with an applied or self generated electromagnetic signal.

A stability result for the relativistic Vlasov-Maxwell system

Abstract: We consider a space-periodic version of the relativistic Vlasov-Maxwell system describing a collisionless plasma consisting of electrons and positively charged ions. As our main result, we prove that certain spacially homogeneous stationary solutions are nonlinearly stable. To this end we also establish global existence of weak solutions to the corresponding initial value problem. Our investigation is motivated by a corresponding result for the Vlasov-Poisson system, cf. [1, 14].

Flute instability of an ion-focused slab electron beam in a broad plasma.

Abstract: An intense relativistic electron beam with an elongated cross section, propagating in the ion-focused regime through a broad, uniform, unmagnetized plasma, is shown to suffer a transverse flute instability. This instability arises from the electrostatic coupling between the beam and the plasma electrons at the ion-channel edge. The instability is found to be absolute and the asymptotic growth of the flute amplitude is computed in the ``frozen-field'' approximation and the large skin-depth limit. The minimum growth length is shown to be much less than the betatron period, with the consequence that focusing is rendered ineffective. It is further shown that growth is much reduced when the beam propagates through a narrow channel where the ion density greatly exceeds that of the surrounding plasma. In this limit, a modest spread in betatron frequency produces rapid saturation. The effect of plasma electron collisions is also considered. Results of beam breakup simulations are noted.

Relativistic plasma microwave electronics: studies of high power plasma filled backward wave oscillators

Abstract: Summary form only given, as follows. The area of relativistic plasma microwave electronics has recently generated renewed interest in the microwave and millimeter-wave device community. The authors have obtained experimental data demonstrating that the presence of a low-density background plasma in a relativistic backward wave oscillator leads to several beneficial effects, including enhanced interaction efficiency (40%), operation at very low and possibly zero guiding magnetic field, tunability by controlling the plasma density, a high degree of spectral purity, and operation well above the vacuum limiting current. >

Three-dimensional magnetic field configurations in relativistic magnetohydrodynamic outflows

Abstract: A class of steady 3D relativistic magnetohydrodynamic (RMHD) winds is constructed from a primary radial RMHD outflow of spherical symmetry. The energetic source for modifying the given radial wind is the Poynting flux into the outflowing plasma due to interaction of transverse flow and magnetic field at a reference sphere surrounding a central object. The energy flux associated with such three-dimensional transverse RMHD perturbations is conserved to the leading order of large radial distance r. Asymptotically, the radial magnetic field B0 varies as 1/r-squared while transverse field b approaches about 1/r such that b dominates B0 at large r. Furthermore, the nonlinear effect of transverse electric force due to charge separation acts against transverse magnetic force. Since magnetic field configurations and their strengths are crucial for a realistic modeling of synchrotron emissions, the class of three-dimensional RMHD winds described here provides an important basis for synchrotron calculations which can be used to probe the structures of extragalactic radio jets and supernova remnants. 28 refs.

Magnetohydrodynamics for electron-positron plasmas.

Abstract: An alternative system of magnetohydrodynamic equations for relativistically hot electron-positron plasmas is derived. The results should be useful for studying low-frequency wave motions as well as instabilities in astrophysical systems

Pair-creation collective modes in an electron gas.

Abstract: High-energy modes of oscillation in a zero-temperature relativistic eiectron gas in a strong background magnetic field are reported. The modes propagate parallel to the magnetic field and appear both in a longitudinal and in two transverse polarizations. The underlying mechanism is the binding between electrons near the Fermi surface and virtual positions, which is enhanced by the presence of the filled Fermi distribution, in a Cooper-pair-like phenomenon