1,534 research outputs found
Particle-in-Cell simulations of electron spin effects in plasmas
We have here developed a particle-in-cell code accounting for the magnetic
dipole force and for the magnetization currents associated with the electron
spin. The electrons is divided into spin-up and spin-down populations relative
to the magnetic field, where the magnetic dipole force acts in opposite
directions for the two species. To validate the code, we have studied the
wakefield generation by an electromagnetic pulse propagating parallel to an
external magnetic field. The properties of the generated wakefield is shown to
be in good quantitative agreement with previous theoretical results.
Generalizations of the code to account for more quantum effects is discussedComment: 5 pages, 6 figure
Spin induced nonlinearities in the electron MHD regime
We consider the influence of the electron spin on the nonlinear propagation
of whistler waves. For this purpose a recently developed electron two-fluid
model, where the spin up- and down populations are treated as different fluids,
is adapted to the electron MHD regime. We then derive a nonlinear Schrodinger
equation for whistler waves, and compare the coefficients of nonlinearity with
and without spin effects. The relative importance of spin effects depend on the
plasma density and temperature as well as the external magnetic field strength
and the wave frequency. The significance of our results to various plasmas are
discussed.Comment: 5 page
Generation of wakefields by whistlers in spin quantum magnetoplasmas
The excitation of electrostatic wakefields in a magnetized spin quantum
plasma by the classical as well as the spin-induced ponderomotive force (CPF
and SPF, respectively) due to whistler waves is reported. The nonlinear
dynamics of the whistlers and the wakefields is shown to be governed by a
coupled set of nonlinear Schr\"{o}dinger (NLS) and driven Boussinesq-like
equations. It is found that the quantum force associated with the Bohm
potential introduces two characteristic length scales, which lead to the
excitation of multiple wakefields in a strongly magnetized dense plasma (with a
typical magnetic field strength T and particle density
m), where the SPF strongly dominates over the CPF.
In other regimes, namely T and
m, where the SPF is comparable to the CPF, a plasma wakefield can also
be excited self-consistently with one characteristic length scale. Numerical
results reveal that the wakefield amplitude is enhanced by the quantum
tunneling effect, however it is lowered by the external magnetic field. Under
appropriate conditions, the wakefields can maintain high coherence over
multiple plasma wavelengths and thereby accelerate electrons to extremely high
energies. The results could be useful for particle acceleration at short
scales, i.e. at nano- and micrometer scales, in magnetized dense plasmas where
the driver is the whistler wave instead of a laser or a particle beam.Comment: 8 pages, 2 figures; Revised version to appear in Physics of Plasmas
(Dec. 2010 issue
Nonlinear wave interaction and spin models in the MHD regime
Here we consider the influence on the electron spin in the MHD regime.
Recently developed models which include spin-velocity correlations are taken as
a starting point. A theoretical argument is presented, suggesting that in the
MHD regime a single fluid electron model with spin correlations is equivalent
to a model with spin-up and spin-down electrons constituting different fluids,
but where the spin-velocity correlations are omitted. Three wave interaction of
2 shear Alfven waves and a compressional Alfven wave is then taken as a model
problem to evaluate the asserted equivalence. The theoretical argument turns
out to be supported, as the predictions of the two models agree completely.
Furthermore, the three wave coupling coefficients obey the Manley-Rowe
relations, which give further support to the soundness of the models and the
validity of the assumptions made in the derivation. Finally we point out that
the proposed two-fluid model can be incorporated in standard Particle-In-Cell
schemes with only minor modifications.Comment: 8 page
Nonlinear Interactions Between Gravitational Radiation and Modified Alfven Modes in Astrophysical Dusty Plasmas
We present an investigation of nonlinear interactions between Gravitational
Radiation and modified Alfv\'{e}n modes in astrophysical dusty plasmas.
Assuming that stationary charged dust grains form neutralizing background in an
electron-ion-dust plasma, we obtain the three wave coupling coefficients, and
calculate the growth rates for parametrically coupled gravitational radiation
and modified Alfv\'{e}n-Rao modes. The threshold value of the gravitational
wave amplitude associated with convective stabilization is particularly small
if the gravitational frequency is close to twice the modified Alfv\'en
wave-frequency. The implication of our results to astrophysical dusty plasmas
is discussed.Comment: A few typos corrected. Published in Phys. Rev.
Resonant interaction between gravitational waves, electromagnetic waves and plasma flows
In magnetized plasmas gravitational and electromagnetic waves may interact
coherently and exchange energy between themselves and with plasma flows. We
derive the wave interaction equations for these processes in the case of waves
propagating perpendicular or parallel to the plasma background magnetic field.
In the latter case, the electromagnetic waves are taken to be circularly
polarized waves of arbitrary amplitude. We allow for a background drift flow of
the plasma components which increases the number of possible evolution
scenarios. The interaction equations are solved analytically and the
characteristic time scales for conversion between gravitational and
electromagnetic waves are found. In particular, it is shown that in the
presence of a drift flow there are explosive instabilities resulting in the
generation of gravitational and electromagnetic waves. Conversely, we show that
energetic waves can interact to accelerate particles and thereby \emph{produce}
a drift flow. The relevance of these results for astrophysical and cosmological
plasmas is discussed.Comment: 12 pages, 1 figure, typos corrected and numerical example adde
Circularly polarized modes in magnetized spin plasmas
The influence of the intrinsic spin of electrons on the propagation of
circularly polarized waves in a magnetized plasma is considered. New eigenmodes
are identified, one of which propagates below the electron cyclotron frequency,
one above the spin-precession frequency, and another close to the
spin-precession frequency.\ The latter corresponds to the spin modes in
ferromagnets under certain conditions. In the nonrelativistic motion of
electrons, the spin effects become noticeable even when the external magnetic
field is below the quantum critical\ magnetic field strength, i.e.,
and the electron density
satisfies m. The importance of electron
spin (paramagnetic) resonance (ESR) for plasma diagnostics is discussed.Comment: 10 page
New Quantum Limits in Plasmonic Devices
Surface plasmon polaritons (SPPs) have recently been recognized as an
important future technique for microelectronics. Such SPPs have been studied
using classical theory. However, current state-of-the-art experiments are
rapidly approaching nanoscales, and quantum effects can then become important.
Here we study the properties of quantum SPPs at the interface between an
electron quantum plasma and a dielectric material. It is shown that the effect
of quantum broadening of the transition layer is most important. In particular,
the damping of SPPs does not vanish even in the absence of collisional
dissipation, thus posing a fundamental size limit for plasmonic devices.
Consequences and applications of our results are pointed out.Comment: 5 pages, 2 figures, to appear in Europhysics Letter
Graviton mediated photon-photon scattering in general relativity
In this paper we consider photon-photon scattering due to self-induced
gravitational perturbations on a Minkowski background. We focus on four-wave
interaction between plane waves with weakly space and time dependent
amplitudes, since interaction involving a fewer number of waves is excluded by
energy-momentum conservation. The Einstein-Maxwell system is solved
perturbatively to third order in the field amplitudes and the coupling
coefficients are found for arbitrary polarizations in the center of mass
system. Comparisons with calculations based on quantum field theoretical
methods are made, and the small discrepances are explained.Comment: 5 pages, 3 figure
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