1,697 research outputs found
Spin quantum plasmas - new aspects of collective dynamics
Quantum plasmas is a rapidly expanding field of research, with applications
ranging from nanoelectronics, nanoscale devices and ultracold plasmas, to
inertial confinement fusion and astrophysics. Here we give a short systematic
overview of quantum plasmas. In particular, we analyze the collective effects
due to spin using fluid models. The introduction of an intrinsic magnetization
due to the plasma electron (or positron) spin properties in the
magnetohydrodynamic limit is discussed. Finally, a discussion of the theory and
examples of applications is given.Comment: 17 pages, short review concerning quantum plasmas, to appear in the
Proceedings of the 2007 ICTP Summer College on Plasma Physics, Trieste 30
July - 24 August, 200
Nonlinear Breit-Wheeler pair creation with bremsstrahlung rays
Electron-positron pairs are produced through the Breit-Wheeler process when
energetic photons traverse electromagnetic fields of sufficient strength. Here
we consider a possible experimental geometry for observation of pair creation
in the highly nonlinear regime, in which bremsstrahlung of an ultrarelativistic
electron beam in a high- target is used to produce rays that
collide with a counterpropagating laser pulse. We show how the target thickness
may be chosen to optimize the yield of Breit-Wheeler positrons, and verify our
analytical predictions with simulations of the cascade in the material and in
the laser pulse. The electron beam energy and laser intensity required are well
within the capability of today's high-intensity laser facilities.Comment: 12 pages, 5 figure
On the contribution of exchange interactions to the Vlasov equation
Exchange effects play an important role in determining the equilibrium
properties of dense matter systems, as well as for magnetic phenomena. There
exists an extensive literature concerning, e.g., the effects of exchange
interactions on the equation of state of dense matter. Here, a generalization
of the Vlasov equation to include exchange effects is presented allowing for
electromagnetic mean fields, thus incorporating some of the dynamic effects due
to the exchange interactions. Treating the exchange term perturbatively, the
correction to classical Langmuir waves in plasmas is found, and the results are
compared with previous work. It is noted that the relative importance of
exchange effects scales similarly with density and temperature as particle
dispersive effects, but that the overall magnitude is sensitive to the details
of the specific problem. The implications of our results are discussed.Comment: 9 page
Photon acceleration in vacuum
A new process associated with the nonlinear optical properties of the
electromagnetic vacuum, as predicted by quantum electrodynamics, is described.
This can be called photon acceleration in vacuum, and corresponds to the
frequency shift that takes place when a given test photon interacts with an
intense beam of background radiation.Comment: 10 pages, 2 figures, version to appear in Phys. Lett.
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
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
A Scalar Wigner Theory for Polarized Light in Nonlinear Kerr Media
A scalar Wigner distribution function for describing polarized light is
proposed in analogy with the treatment of spin variables in quantum kinetic
theory. The formalism is applied to the propagation of circularly polarized
light in nonlinear Kerr media and an extended phase space evolution equation is
derived along with invariant quantities. We further consider modulation
instability as well as the extension to partially coherent fields.Comment: 6 page
Ferromagnetic behavior in magnetized plasmas
We consider a low-temperature plasma within a newly developed MHD Fluid
model. In addition to the standard terms, the electron spin, quantum particle
dispersion and degeneracy effects are included. It turns out that the electron
spin properties can give rise to Ferromagnetic behavior in certain regimes. If
additional conditions are fulfilled, a homogenous magnetized plasma can even be
unstable. This happen in the low-temperature high-density regime, when the
magnetic properties associated with the spin can overcome the stabilizing
effects of the thermal and Fermi pressure, to cause a Jeans like instability.Comment: 4 pages, 1 figur
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