102 research outputs found
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
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
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
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
Solar coronal heating by short-wavelength dispersive shear Alfvén waves
The electron heating of the solar coronal plasma has remained as one of the most important problems in solar physics. An explanation of the electron heating rests on the identification of the energy source and appropriate physical mechanisms via which the energy can be channelled to the electrons. Our objective here is to present an estimate for the electron heating rate in the presence of finite amplitude short-wavelength (in comparison with the ion gyroradius) dispersive shear Alfven (SWDSA) waves that propagate obliquely to the ambient magnetic field direction in the solar corona. Specifically, it is demonstrated that SWDSA waves can significantly contribute to the solar coronal electron heating via collisionless heating involving SWDSA wave-electron interactions
Nonlinear dynamics of large amplitude dust acoustic shocks and solitary pulses in dusty plasmas
We present a fully nonlinear theory for dust acoustic (DA) shocks and DA
solitary pulses in a strongly coupled dusty plasma, which have been recently
observed experimentally by Heinrich et al. [Phys. Rev. Lett. 103, 115002
(2009)], Teng et al. [Phys. Rev. Lett. 103, 245005 (2009)], and Bandyopadhyay
et al. [Phys. Rev. Lett. 101, 065006 (2008)]. For this purpose, we use a
generalized hydrodynamic model for the strongly coupled dust grains, accounting
for arbitrary large amplitude dust number density compressions and potential
distributions associated with fully nonlinear nonstationary DA waves.
Time-dependent numerical solutions of our nonlinear model compare favorably
well with the recent experimental works (mentioned above) that have reported
the formation of large amplitude non-stationary DA shocks and DA solitary
pulses in low-temperature dusty plasma discharges.Comment: 9 pages, 4 figures. To be published in Physical Review
Instability and dynamics of two nonlinearly coupled laser beams in a plasma
We investigate the nonlinear interaction between two laser beams in a plasma
in the weakly nonlinear and relativistic regime. The evolution of the laser
beams is governed by two nonlinear Schroedinger equations that are coupled with
the slow plasma density response. We study the growth rates of the Raman
forward and backward scattering instabilities as well of the Brillouin and
self-focusing/modulational instabilities. The nonlinear evolution of the
instabilities is investigated by means of direct simulations of the
time-dependent system of nonlinear equations.Comment: 18 pages, 8 figure
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