Spectrum Of Plasma Waves Research Articles

Electron kinetic effects in back-stimulated Raman scattering bursts driven by broadband laser pulses

We examine electron kinetic effects in broadband-laser-driven back-stimulated Raman scattering (BSRS) bursts using particle-in-cell simulations. These bursts occur during the nonlinear stage, causing reflectivity spikes and generating large numbers of hot electrons. Long-duration simulations are performed to observe burst events, and a simplified model is developed to eliminate the interference of the broadband laser’s random intensity fluctuations. Using the simplified model, we isolate and characterize the spectrum of electron plasma waves. The spectrum changes from a sideband structure to a turbulence-like structure during the burst. A significant asymmetry in the spectrum is observed. This asymmetry is amplified and transferred to electron phase space by high-intensity broadband laser pulses, leading to violent vortex-merging and generation of hot electrons. The proportion of hot electrons increases from 6.76% to 14.7% during a single violent burst event. We demonstrate that kinetic effects profoundly influence the BSRS evolution driven by broadband lasers.

Toward streaked collective Thomson scattering measurements on an extreme ultraviolet plasma light source

We show through forward modeling calculations that streaked collective Thomson scattering measurements are feasible on laser-produced tin plasmas generated under conditions relevant for extreme ultraviolet lithography. Using a 532 nm probe laser beam, the feasibility of simultaneous measurements of electron plasma wave (EPW) and ion acoustic wave (IAW) spectra is investigated. Absolute photon counts for laser scattering off both waves are calculated. Probe laser electron heating and bremsstrahlung background radiation effects are accounted for. While a large spatiotemporal region can be successfully probed based on the IAW feature, only one measurement location can be accessed through the EPW as a result of the low signal to noise ratio. A portable/traveling tabletop system is proposed.

Inferring Jovian Electron Densities Using Plasma Wave Spectra Obtained by the Juno/Waves Instrument

AbstractThe Waves instrument onboard the Juno spacecraft has plasma wave‐measuring capabilities using a single electric dipole antenna and a uniaxial magnetic search coil. Together, these simultaneously measure electric and magnetic field spectral densities in the frequency range 50 Hz–20 kHz, above which only electric field spectral densities are measured up to 41 MHz. A major objective of the Juno mission is to explore Jupiter's high‐latitude magnetosphere and ionosphere. One of the key contributions of the Waves instrument is the determination of electron densities from plasma wave spectra. Given the very high magnetic field strengths near Juno's perijove passes, established techniques cannot be utilized to infer electron densities since such highly magnetized space plasma conditions have not previously been met in planetary missions. By revisiting theoretical treatments of plasma waves, we describe a novel method to determine electron densities from plasma wave spectra that is unique to the near‐Jupiter region. In the absence of the commonly observed upper hybrid resonance frequency in high‐density space plasmas (e.g., the vicinities of Io, Ganymede, Enceladus, and the near‐Earth environment), we achieve this by identifying emission cutoffs at the lower hybrid frequency and electron plasma frequency. Further, we discuss the development of the process and tools for identifying and digitizing appropriate resonance and cutoff frequencies.

The High‐Latitude Extension of Jupiter's Io Torus: Electron Densities Measured by Juno Waves

AbstractWe present Jovian electron densities measured by the Juno Waves instrument at high‐latitudes (with magnetic latitudes of on magnetic field lines threading the Io torus and plasma sheet (with M‐shells of ) using the first 29 orbits of the Juno mission. We infer electron densities from characteristic frequency cutoffs and resonances in plasma wave spectra. Often more than one of the characteristic frequencies of the plasma can be identified, whose consistency provides credibility to the plasma density estimates. The majority of density measurements are on magnetic field lines threading the Io torus and intersecting Jupiter's ionosphere between Io's M‐shell and the auroral main oval, but there is evidence of density dropouts near and poleward of the auroral oval, which may be important in auroral particle acceleration. Sharp density gradients are found near field lines mapping to the inner edge of the Io torus M‐shells. These observations demonstrate the extension of elevated Io torus densities along field lines to higher latitudes.

Discovery of Two-Dimensional Electromagnetic Plasma Waves

We report the experimental discovery of "superluminal" electromagnetic 2D plasma waves in the electromagnetic response of a high-quality GaAs/AlGaAs two-dimensional electron system on a dielectric substrate. We measure the plasma wave spectrum on samples with different electron density. It is established that, at large two-dimensional densities, there is a strong hybridization between the plasma and the Fabry-Perot light modes. In the presence of a perpendicular magnetic field, the plasma resonance is shown to split into two modes, each corresponding to a particular sense of circular polarization. Experimental results are found to be in good agreement with the theory.

Raman three-wave interaction in partially spin polarized plasma

By employing the separate spin evolution-quantum hydrodynamic model (SSE-QHD), the nonlinear growth rate of the parametric decay instability is studied via the Raman scattering process of three-wave coupling. SSE-QHD equations are solved for the pump wave (O-mode), sideband Shear Alfvén wave, and the electron plasma perturbations. It is observed that the spectrum of the electron plasma waves is modified due to newly generated spin dependent waves which contribute in the coupling process. The nonlinear growth rate as a result of three wave coupling is plotted for different sets of parameters and conditions. It is also observed that the growth rate is suppressed due to the spin effects. Shifting of diamagnetic behavior of plasma to paramagnetic behavior is noticed.

Electron densities inferred from plasma wave spectra obtained by the Waves instrument on Van Allen Probes.

The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum.

Externally driven plasmaspheric ULF waves observed by the Van Allen Probes

AbstractWe analyze data acquired by the Van Allen Probes on 8 November 2012, during a period of extended low geomagnetic activity, to gain new insight into plasmaspheric ultralow frequency (ULF) waves. The waves exhibited strong spectral power in the 5–40 mHz band and included multiharmonic toroidal waves visible up to the eleventh harmonic, unprecedented in the plasmasphere. During this wave activity, the interplanetary magnetic field cone angle was small, suggesting that the waves were driven by broadband compressional ULF waves originating in the foreshock region. This source mechanism is supported by the tailward propagation of the compressional magnetic field perturbations at a phase velocity of a few hundred kilometers per second that is determined by the cross‐phase analysis of data from the two spacecraft. We also find that the coherence and phase delay of the azimuthal components of the magnetic field from the two spacecraft strongly depend on the radial separation of the spacecraft and attribute this feature to field line resonance effects. Finally, using the observed toroidal wave frequencies, we estimate the plasma mass density for L = 2.6–5.8. By comparing the mass density with the electron number density that is estimated from the spectrum of plasma waves, we infer that the plasma was dominated by H+ ions and was distributed uniformly along the magnetic field lines. The electron density is higher than the prediction of saturated plasmasphere models, and this “super saturated” plasmasphere and the uniform ion distribution are consistent with the low geomagnetic activity that prevailed.

Modulational stability of electron plasma wave spectra

Analytical models for weakly nonlinear electron plasma waves are considered in order to obtain dynamic equations for the space-time evolution of their local power spectra. The model contains the wave kinetic equation as a limiting case for slow, long wavelength modulations. It is demonstrated that a finite spectral width in wavenumbers has a stabilizing effect on the modulational instability. The results invite a simple heuristic relation between the spectral width and the root-mean-square amplitude of stable stationary turbulent Langmuir wave spectra. A non-local average dispersion relation is derived as a limiting form by using the formalism developed for the spectral dynamics.

Study of the Plasma Turbulence Dynamics by Measurements of Diagnostic Stimulated Electromagnetic Emission. I. Experimental Results

We consider the possibilities of studying the evolution of the plasma wave spectrum and artificial striations of the plasma density at different altitudes of the disturbed ionospheric region modified by high-power HF radio waves from the SURA heating facility based on measurements of the dynamic characteristics of diagnostic stimulated electromagnetic emission.

Hydrodynamic electron transport and nonlinear waves in graphene

We derive the system of hydrodynamic equations governing the collective motion of massless fermions in graphene. The obtained equations demonstrate the lack of Galilean- and Lorentz invariance, and contain a variety of nonlinear terms due to quasi-relativistic nature of carriers. Using those equations, we show the possibility of soliton formation in electron plasma of gated graphene. The quasi-relativistic effects set an upper limit for soliton amplitude, which marks graphene out of conventional semiconductors. The lack of Galilean and Lorentz invariance of hydrodynamic equations is revealed in spectra of plasma waves in the presence of steady flow, which no longer obey the relations of Doppler shift. The possibility of plasma wave excitation by direct current in graphene channels is also discussed.

Neutrino oscillations in a turbulent plasma

A new model for the joint neutrino flavor and plasma oscillations is introduced, in terms of the dynamics of the neutrino flavor polarization vector in a plasma background. Fundamental solutions are found for both time-invariant and time-dependent media, considering slow and fast variations of the electron plasma density. The model is shown to be described by a generalized Hamiltonian formalism. In the case of a broad spectrum of electron plasma waves, a statistical approach indicates the shift of both equilibrium value and frequency oscillation of flavor coherence, due to the existence of a turbulent plasma background.

Anomalously Hot Electrons due to Rescatter of Stimulated Raman Scattering in the Kinetic Regime

Using particle-in-cell simulations, we examine hot electron generation from electron plasma waves excited by stimulated Raman scattering and rescattering in the kinetic regime where the wave number times the Debye length (kλ(D)) is >/~0.3 for backscatter. We find that for laser and plasma conditions of possible relevance to experiments at the National Ignition Facility, anomalously energetic electrons can be produced through the interaction of a discrete spectrum of plasma waves generated from stimulated Raman scattering (back and forward scatter), rescatter, and the Langmuir decay of the rescatter-generated plasma waves. Electrons are bootstrapped in energy as they propagate into plasma waves with progressively higher phase velocities.

Frequency drift of Saturn chorus emission compared to nonlinear theory

The fine structure of nonlinear drifting‐frequency chorus is observed at Saturn by the Cassini Radio and Plasma Wave Investigation. During a high‐inclination orbit in which Cassini is at near‐constant L‐shell within about 10° of the magnetic equator, moderately intense nonlinear chorus is observed. Cassini observed a region of intense chorus and large bandwidth a few degrees on either side of the magnetic equator, with lower intensities and bandwidths observed nearest the magnetic equator. Using the observed plasma wave spectra and electron phase space distribution, we have measured plasma parameters within or near the chorus generation region and evaluated the theoretical value of the frequency sweep rate, ∂f/∂t, based on the nonlinear wave growth theory of Omura et al. and the backward wave oscillator theory of Trakhtengerts. Both theories produce rates that are within a factor of 2 of the observed values, but the nonlinear wave growth theory values are closer to the observations for the cases examined. The work presented is consistent with nonlinear theory in the generation of chorus, but also reveals a distinct region of weaker or linear chorus growth nearest to the magnetic equator at Saturn.

Multi-dimensional PIC-simulations of parametric instabilities for shock-ignition conditions

Laser-plasma interaction is investigated for conditions relevant for the shock-ignition (SI) scheme of inertial confinement fusion using two-dimensional particle-in-cell (PIC) simulations of an intense laser beam propagating in a hot, large-scale, non-uniform plasma. The temporal evolution and interdependence of Raman- (SRS), and Brillouin- (SBS), side/backscattering as well as Two-Plasmon-Decay (TPD) are studied. TPD is developing in concomitance with SRS creating a broad spectrum of plasma waves near the quarter-critical density. They are rapidly saturated due to plasma cavitation within a few picoseconds. The hot electron spectrum created by SRS and TPD is relatively soft, limited to energies below one hundred keV. 1. SHOCK-IGNITION AND THE IMPORTANCE OF LASER-PLASMA INTERACTION The shock-ignition scheme (1) is based on an energy redistribution of the available energy: the laser pulse inducing compression of the pellet has lower intensity than in the original direct-drive scheme, followed by a second, intense laser pulse (∼ 100ps) which creates an intense short shock that combined with the rebound of the first shock allows the creation of a hot spot. The intensity of the second pulse is up to 10 times higher than the standard ones, and the laser will propagate in a hot (few keV), long, inhomogeneous plasma. For laser plasma-interaction kinetic effects will be dominant. A first estimate on the importance of laser plasma interaction comes from evaluating the local growth rate for parametric instabilities. As a consequence, even though the proposed intensities for the shock pulse are high, Io 2 = 10 15...16 Wm 2 /cm 2 at 3 o, Stimulated Raman Scattering (SRS) was not expected to be a great danger since the pulse propagates in a hot plasma of 3...5keV and the excited electron plasma waves by SRS are in a strongly damped regime. Some concern could come from the fact that a regime of inflationary SRS (2) was predicted, but the main worry was expected to originate from strong Stimulated Brillouin Scattering (SBS) developing along the whole density profile. 1D-simulation investigating this ansatz showed unexpected results (3): after an initial phase SBS is suppressed by absolute SRS and cavitation at nc/4 and subsequent cascade at nc/16. As a result laser absorption is by collective effects and cavitation appears as a dominant mechanism. 2D-simulations confirm some of these results, but show a richer physics (4, 5). Plasma parameters and profiles are motivated by CHIC hydro-simulations of the HiPER target as considered in the 1D-simulations (3). The simulation set up is as follows: the size of the plasma is 160 m × 103 m; Te = 5keV,Ti = 1keV; the density varies from n = 0.04nc to n = 0.4nc, it has exponential profile with scale length Ln = 186 o ≈ 60 m, followed

Mode crossing effects at electron beam–plasma interaction and related phenomena

Mode crossing points are shown to play an important role in interpreting the spatio-temporal plasma wave spectra from satellite and laboratory measurements. Here, the Langmuir wave near the electron plasma frequency is considered and from linear dispersion curve analysis it may cross the whistler wave, the L-wave or the electron-acoustic mode depending on plasma conditions. An essential parameter is the electron cyclotron frequency to plasma frequency ratio, G = Ωe/ωe. The crossing point exists for wave propagation slightly oblique to a background magnetic field and we find that for a broad spectrum of waves excited by an instability, via an energetic beam or background plasma temperature anisotropy, the maximum amplitude of the wave activity appears at the crossing points which can be well separated from the region of maximum linear growth. Within this process the saturated waves act as an ‘antenna’ for other wave modes in the same wave number range. Linear and kinetic simulation analysis are used to demonstrate the frequency splitting at mode crossing points in two relevant examples; unmagnetized beam–plasma instability with Langmuir and electron-acoustic mode crossing in the presence of electron plateau distribution, and beam-excited Langmuir waves in overdense (G < 1) and underdense plasmas (G > 1) with background magnetic field. It is shown that the appearance of amplitude modulations associated with double-peak spectra of the electric field is directly related to the frequency splitting and coupling at mode crossing points. The importance of transitions between quasi-longitudinal wave modes at oblique propagation to transverse modes for the interpretation of beam–plasma interaction phenomena, such as type III radiation, and laboratory experiments is discussed.

On the theory of a Cherenkov relativistic plasma emitter with a coaxial electrodynamic system

A plasma microwave amplifier based on a relativistic electron beam in an electrodynamic system in the form of a coaxial waveguide with a thin tubular plasma in a strong external magnetic field has been considered. Dispersion relations for determining the spectra of plasma and beam waves in the coaxial waveguide, as well as the general dispersion relation describing beam-plasma interaction, have been obtained in the linear approximation. The frequency dependences of the spatial growth rates for different plasma radii and different plasma frequencies, as well as the characteristic frequencies of the plasma amplifier, have been obtained by numerically and analytically solving the dispersion relations. The parameters of the plasma amplifier and generator with the coaxial electrodynamic system have been estimated for their experimental implementation.

Bulk plasma waves in a randomly inhomogeneous conductor

The modification of the spectrum and damping of bulk plasma waves due to three-dimensional random inhomogeneities of the density of a degenerate electron gas in a conductor have been investigated using the averaged Green’s function method. The dependences of the frequency and damping of the averaged plasma waves, as well as the position ν m and width Δν of the peak of the imaginary part of the Fourier trans-form of the averaged Green’s function, on the wave vector k have been determined in the self-consistent approximation, which makes it possible to take into account multiple scattering of plasma waves by inhomogeneities. It has been found that, in the long-wavelength region of the spectrum, the decrease revealed in the frequency of the plasma waves is caused by the inhomogeneities, which agrees qualitatively with the behavior of the position of the peak ν m . In the range of large values of the correlation length of inhomogeneities and small values of k, the damping of the plasma waves tends to zero, whereas the width of the peak Δν remains finite, which is due to the nonuniform broadening. A comparison with the data of numerical calculations has been performed.

Magnetoplasma waves on the surface of a semiconductor nanotube with a superlattice

The spectra of plasma waves in the electron gas on the surface of a semiconductor nanotube with a superlattice in a parallel magnetic field have been studied using the random phase approximation. The frequencies of the long-wave intra- and inter-band magnetoplasmons in a degenerate electron gas are calculated in quantum and quasiclassical limits. If a large number of the electron levels associated with the orbital motion of electrons is filled, the magnetoplasmon frequencies exhibit the oscillations similar to the de Haas–van Alphen oscillations upon variation of nanotube parameters and the Aharonov–Bohm oscillations upon variation of the magnetic flux through the nanotube cross-section. The oscillation characteristics are determined by the ratio of the Fermi energy to the miniband width. For large values of the ratio, the beating pattern appears in the magnetoplasmon frequency dependence on the nanotube parameters. These oscillations are not present if the ratio is sufficiently small.

Colloquium: Nonlinear collective interactions in quantum plasmas with degenerate electron fluids

The current understanding of some important nonlinear collective processes in quantum plasmas with degenerate electrons is presented. After reviewing the basic properties of quantum plasmas, we present model equations (e.g. the quantum hydrodynamic and effective nonlinear Schr\"odinger-Poisson equations) that describe collective nonlinear phenomena at nanoscales. The effects of the electron degeneracy arise due to Heisenberg's uncertainty principle and Pauli's exclusion principle for overlapping electron wavefunctions that result in tunneling of electrons and the electron degeneracy pressure. Since electrons are Fermions (spin-1/2), there also appears an electron spin current and a spin force acting on electrons due to the Bohr magnetization. The quantum effects produce new aspects of electrostatic (ES) and electromagnetic (EM) waves in a quantum plasma that are summarized in here. Furthermore, we discuss nonlinear features of ES ion waves and electron plasma oscillations (ESOs), as well as the trapping of intense EM waves in quantum electron density cavities. Specifically, simulation studies of the coupled nonlinear Schr\"odinger (NLS) and Poisson equations reveal the formation and dynamics of localized ES structures at nanoscales in a quantum plasma. We also discuss the effect of an external magnetic field on the plasma wave spectra and develop quantum magnetohydrodynamic (Q-MHD) equations. The results are useful for understanding numerous collective phenomena in quantum plasmas, such as those in compact astrophysical objects, in plasma-assisted nanotechnology, and in the next-generation of intense laser-solid density plasma interaction experiments.