99 research outputs found
Simulation study of the interaction between large-amplitude HF radio waves and the ionosphere
The time evolution of a large-amplitude electromagnetic (EM) wave injected
vertically into the overhead ionosphere is studied numerically. The EM wave has
a carrier frequency of 5 MHz and is modulated as a Gaussian pulse with a width
of approximately 0.1 milliseconds and a vacuum amplitude of 1.5 V/m at 50 km.
This is a fair representation of a modulated radio wave transmitted from a
typical high-power HF broadcast station on the ground. The pulse is propagated
through the neutral atmosphere to the critical points of the ionosphere, where
the L-O and R-X modes are reflected, and back to the neutral atmosphere. We
observe mode conversion of the L-O mode to electrostatic waves, as well as
harmonic generation at the turning points of both the R-X and L-O modes, where
their amplitudes rise to several times the original ones. The study has
relevance for ionospheric interaction experiments in combination with
ground-based and satellite or rocket observations.Comment: 6 pages, 7 figure
Conservation laws for the Maxwell-Dirac equations with a dual Ohm's law
Using a general theorem on conservation laws for arbitrary differential
equations proved by Ibragimov, we have derived conservation laws for Dirac's
symmetrized Maxwell-Lorentz equations under the assumption that both the
electric and magnetic charges obey linear conductivity laws (dual Ohm's law).
We find that this linear system allows for conservation laws which are
non-local in time
Neutrino orbital angular momentum in a plasma vortex
It is shown that an electron-neutrino beam, propagating in a background
plasma, can be decomposed into orbital momentum (OAM) states, similar to the
OAM photon states. Coupling between different OAM neutrino states, in the
presence of a plasma vortex, is considered. We show that plasma vorticity can
be transfered to the neutrino beam, which is relevant to the understanding of
the neutrino sources in astrophysics. Observation of neutrino OAM states could
eventually become possible.Comment: 4 pages. Submitted to Phys. Lett.
Zakharov simulation study of spectral features of on-demand Langmuir turbulence in an inhomogeneous plasma
We have performed a simulation study of Langmuir turbulence in the Earth's
ionosphere by means of a Zakharov model with parameters relevant for the F
layer. The model includes dissipative terms to model collisions and Landau
damping of the electrons and ions, and a linear density profile, which models
the ionospheric plasma inhomogeneity whose length scale is of the order 10--100
km. The injection of energy into the system is modeled by a constant source
term in the Zakharov equation. Langmuir turbulence is excited ``on-demand'' in
controlled ionospheric modification experiments where the energy is provided by
an HF radio beam injected into the overhead ionospheric plasma. The ensuing
turbulence can be studied with radars and in the form of secondary radiation
recorded by ground-based receivers. We have analyzed spectral signatures of the
turbulence for different sets of parameters and different altitudes relative to
the turning point of the linear Langmuir mode where the Langmuir frequency
equals the local plasma frequency. By a parametric analysis, we have derived a
simple scaling law, which links the spectral width of the turbulent frequency
spectrum to the physical parameters in the ionosphere. The scaling law provides
a quantitative relation between the physical parameters (temperatures, electron
number density, ionospheric length scale, etc.) and the observed frequency
spectrum. This law may be useful for interpreting experimental results.Comment: 7 pages, 8 figure
Linear and angular momentum of electromagnetic fields generated by an arbitrary distribution of charge and current densities at rest
Starting from Stratton-Panofsky-Phillips-Jefimenko equations for the electric
and magnetic fields generated by completely arbitrary charge and current
density distributions at rest, we derive far-zone approximations for the
fields, containing all components, dominant as well as sub-dominant. Using
these approximate formulas, we derive general formulas for the total
electromagnetic linear momentum and angular momentum, valid at large distances
from arbitrary, non-moving charge and current sources.Comment: Six pages, one figure. Errors correcte
Photon Orbital Angular Momentum and Mass in a Plasma Vortex
We analyse the Anderson-Higgs mechanism of photon mass acquisition in a
plasma and study the contribution to the mass from the orbital angular momentum
acquired by a beam of photons when it crosses a spatially structured charge
distribution. To this end we apply Proca-Maxwell equations in a static plasma
with a particular spatial distribution of free charges, notably a plasma
vortex, that is able to impose orbital angular momentum (OAM) onto light. In
addition to the mass acquisition of the conventional Anderson-Higgs mechanism,
we find that the photon acquires an additional mass from the OAM and that this
mass reduces the Proca photon mass.Comment: Four pages, no figures. Error corrections, improved notation, refined
derivation
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