Numerical study of mode conversion between lower hybrid and whistler waves on short-scale density striations

We present a theoretical and numerical study of linear mode conversion of lower hybrid waves interacting with short-scale density striations in the Earth's ionosphere. The efficiency of the conversion process is investigated for different sets of parameters such as the angle of incidence, the wavelength of the lower hybrid wave, and the size of the striation. It is found that the most efficient whistler generation occurs at a critical angle of incidence where the whistler waves are driven resonantly along the density striations, and when the product of the striation width and the wave number of the lower hybrid wave is of the order unity. It is suggested that whistlers generated as a byproduct of upper hybrid F-region ionospheric heating can be observed on the ground and by satellites. The generated whistlers could be important for the precipitation of energetic electrons in the radiation belts

Nonlinear aspects of quantum plasma physics

Dense quantum plasmas are ubiquitous in planetary interiors and in compact astrophysical objects, in semiconductors and micro-mechanical systems, as well as in the next generation intense laser-solid density plasma interaction experiments and in quantum x-ray free-electron lasers. In contrast to classical plasmas, one encounters extremely high plasma number density and low temperature in quantum plasmas. The latter are composed of electrons, positrons and holes, which are degenerate. Positrons (holes) have the same (slightly different) mass as electrons, but opposite charge. The degenerate charged particles (electrons, positrons, holes) follow the Fermi-Dirac statistics. In quantum plasmas, there are new forces associated with i) quantum statistical electron and positron pressures, ii) electron and positron tunneling through the Bohm potential, and iii) electron and positron angular momentum spin. Inclusion of these quantum forces provides possibility of very high-frequency dispersive electrostatic and electromagnetic waves (e.g. in the hard x-ray and gamma rays regimes) having extremely short wavelengths. In this review paper, we present theoretical backgrounds for some important nonlinear aspects of wave-wave and wave-electron interactions in dense quantum plasmas. Specifically, we shall focus on nonlinear electrostatic electron and ion plasma waves, novel aspects of 3D quantum electron fluid turbulence, as well as nonlinearly coupled intense electromagnetic waves and localized plasma wave structures. Also discussed are the phase space kinetic structures and mechanisms that can generate quasi-stationary magnetic fields in dense quantum plasmas. The influence of the external magnetic field and the electron angular momentum spin on the electromagnetic wave dynamics is discussed.Comment: 42 pages, 20 figures, accepted for publication in Physics-Uspekh

Nonlinear propagation of broadband intense electromagnetic waves in an electron-positron plasma

A kinetic equation describing the nonlinear evolution of intense electromagnetic pulses in electron-positron (e-p) plasmas is presented. The modulational instability is analyzed for a relativistically intense partially coherent pulse, and it is found that the modulational instability is inhibited by the spectral pulse broadening. A numerical study for the one-dimensional kinetic photon equation is presented. Computer simulations reveal a Fermi-Pasta-Ulam-like recurrence phenomena for localized broadband pulses. The results should be of importance in understanding the nonlinear propagation of broadband intense electromagnetic pulses in e-p plasmas in laser-plasma systems as well as in astrophysical plasma settings.Comment: 16 pages, 5 figures, to appear in Phys. Plasma

The Intense Radiation Gas

We present a new dispersion relation for photons that are nonlinearly interacting with a radiation gas of arbitrary intensity due to photon-photon scattering. It is found that the photon phase velocity decreases with increasing radiation intensity, it and attains a minimum value in the limit of super-intense fields. By using Hamilton's ray equations, a self-consistent kinetic theory for interacting photons is formulated. The interaction between an electromagnetic pulse and the radiation gas is shown to produce pulse self-compression and nonlinear saturation. Implications of our new results are discussed.Comment: 7 pages, 1 figure, version to appear in Europhys. Let

Self-compression and catastrophic collapse of photon bullets in vacuum

Photon-photon scattering, due to photons interacting with virtual electron-positron pairs, is an intriguing deviation from classical electromagnetism predicted by quantum electrodynamics (QED). Apart from being of fundamental interest in itself, collisions between photons are believed to be of importance in the vicinity of magnetars, in the present generation intense lasers, and in intense laser-plasma/matter interactions; the latter recreating astrophysical conditions in the laboratory. We show that an intense photon pulse propagating through a radiation gas can self-focus, and under certain circumstances collapse. This is due to the response of the radiation background, creating a potential well in which the pulse gets trapped, giving rise to photonic solitary structures. When the radiation gas intensity has reached its peak values, the gas releases part of its energy into `photon wedges', similar to Cherenkov radiation. The results should be of importance for the present generation of intense lasers and for the understanding of localized gamma ray bursts in astrophysical environments. They could furthermore test the predictions of QED, and give means to create ultra-intense photonic pulses.Comment: 4 pages, 1 figur

Pitch angle scattering of relativistic electrons near EMIC resonances in diverging magnetic fields

A theoretical study of the propagation of left hand polarized shear Alfvén waves in spatially decreasing magnetic field geometries near the EMIC resonance, including the spectrum and amplitude of the mode converted EMIC waves and the pitch angle scattering of relativistic electrons transiting the resonant region, is presented. The objective of the paper is to motivate an experimental study of the subject using the UCLA LAPD chamber. The results are relevant in exploring the possibility that shear Alfvén waves strategically injected into the radiation belts using either ionospheric heating from ground based RF transmitters or injected by transmitters based on space platforms can enhance the precipitation rate of trapped relativistic electrons. Effects of multi-ionic composition are also investigated

Simulation study of magnetic holes at the Earth's collisionless bow shock

Recent observations by the Cluster and Double Star spacecraft at the Earth's bow shock have revealed localized magnetic field and density holes in the solar wind plasma. These structures are characterized by a local depletion of the magnetic field and the plasma density, and by a strong increase of the plasma temperature inside the magnetic and density cavities. Our objective here is to report results of a hybrid-Vlasov simulations of ion-Larmor-radius sized plasma density cavities with parameters that are representative of the high-beta solar wind plasma at the Earth's bow shock. We observe the asymmetric self-steepening and shock-formation of the cavity, and a strong localized temperature increase (by a factor of 5–7) of the plasma due to reflections and shock surfing of the ions against the collisionless shock. Temperature maxima are correlated with density minima, in agreement with Cluster observations. For oblique incidence of the solar wind, we observe efficient acceleration of ions along the magnetic field lines by the shock drift acceleration process

Nonlinear instability and dynamics of polaritons in quantum systems

We present analytical and simulation studies of the nonlinear instability and dynamics of an electron–hole/anti-electron (hereafter referred to as polaritons) system, which are common in ultra-small devices (semiconductors and micromechanical systems) as well as in dense astrophysical environments and the next generation intense laser–matter interaction experiments. Starting with three coupled nonlinear equations (two Schrödinger equations for interacting polaritons at quantum scales and the Poisson equation determining the electrostatic interactions and the associated charge separation effect), we demonstrate novel modulational instabilities and nonlinear polaritonic structures. It is suggested that the latter can transport information at quantum scales in high-density, ultracold quantum systems

The dynamics of electron and ion holes in a collisionless plasma

We present a review of recent analytical and numerical studies of the dynamics of electron and ion holes in a collisionless plasma. The new results are based on the class of analytic solutions which were found by Schamel more than three decades ago, and which here work as initial conditions to numerical simulations of the dynamics of ion and electron holes and their interaction with radiation and the background plasma. Our analytic and numerical studies reveal that ion holes in an electron-ion plasma can trap Langmuir waves, due the local electron density depletion associated with the negative ion hole potential. Since the scale-length of the ion holes are on a relatively small Debye scale, the trapped Langmuir waves are Landau damped. We also find that colliding ion holes accelerate electron streams by the negative ion hole potentials, and that these streams of electrons excite Langmuir waves due to a streaming instability. In our Vlasov simulation of two colliding ion holes, the holes survive the collision and after the collision, the electron distribution becomes flat-topped between the two ion holes due to the ion hole potentials which work as potential barriers for low-energy electrons. Our study of the dynamics between electron holes and the ion background reveals that standing electron holes can be accelerated by the self-created ion cavity owing to the positive electron hole potential. Vlasov simulations show that electron holes are repelled by ion density minima and attracted by ion density maxima. We also present an extension of Schamel's theory to relativistically hot plasmas, where the relativistic mass increase of the accelerated electrons have a dramatic effect on the electron hole, with an increase in the electron hole potential and in the width of the electron hole. A study of the interaction between electromagnetic waves with relativistic electron holes shows that electromagnetic waves can be both linearly and nonlinearly trapped in the electron hole, which widens further due to the relativistic mass increase and ponderomotive force in the oscillating electromagnetic field. The results of our simulations could be helpful to understand the nonlinear dynamics of electron and ion holes in space and laboratory plasmas