81 research outputs found
Enhanced Tuneable Rotatory Power in a Rotating Plasma
The gyrotropic properties of a rotating magnetized plasma are derived
analytically. Mechanical rotation leads to a new cutoff for wave propagation
along the magnetic field and polarization rotation above this cutoff is the sum
of the classical magneto-optical Faraday effect and the mechanico-optical
polarization drag. Exploiting the very large effective group index near the
cutoff, we expose here, for the first time, that polarization drag can be
larger than Faraday rotation at GHz frequency. The rotation leads to
weak absorption while allowing direct frequency control, demonstrating the
unique potential of rotating plasmas for non-reciprocal elements. The very
large rotation frequency of a dense non-neutral plasma could enable
unprecedented gyrotropy in the THz regime.Comment: 6 pages, 3 figures, to be published in Phys. Rev.
Rotating Alfv\'en waves in rotating plasmas
Angular momentum coupling between a rotating magnetized plasma and torsional
Alfv\'en waves carrying orbital angular momentum (OAM) is examined. It is not
only demonstrated that rotation is the source of Fresnel-Faraday rotation - or
orbital Faraday rotation effects - for OAM carrying Alfv\'en waves, but also
that angular momentum from an OAM carrying Alfv\'en wave can be transferred to
a rotating plasma through the inverse process. For the direct process, the
transverse structure angular rotation frequency is derived by considering the
dispersion relation for modes with opposite OAM content. For the inverse
process, the torque exerted on the plasma is derived as a function of wave and
plasma parameters.Comment: 14 pages, 3 figure
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Nonlinear relativistic interaction of an ultrashort laser pulse with a cold plasma
We investigate the nonlinear, relativistic dynamics that result when intense (10{sup 18}W/cm{sup 2} and above) and ultrashort (one plasma period or shorter) laser pulse travels through a cold underdense plasma. Using a Lagrangian analysis of the plasma response, it can be demonstrated that the nonlinear wake, the collective dissipation, the nonlinear Compton losses, and the harmonic generation, are all determined by a finite set of integrated scalar quantities. This result holds for one-dimensional, short pulses of arbitrary amplitude, shape, and polarization, so that these very short intense laser pulses in a plasma can be viewed essentially as a quasiparticle characterized by a small set of global parameters
Massive, Long-Lived Electrostatic Potentials in a Rotating Mirror Plasma
Hot plasma is highly conductive in the direction parallel to a magnetic
field. This often means that the electrical potential will be nearly constant
along any given field line. When this is the case, the cross-field voltage
drops in open-field-line magnetic confinement devices are limited by the
tolerances of the solid materials wherever the field lines impinge on the
plasma-facing components. To circumvent this voltage limitation, it is proposed
to arrange large voltage drops in the interior of a device, but coexisting with
much smaller drops on the boundaries. To avoid prohibitively large dissipation
requires both preventing substantial drift-flow shear within flux surfaces and
preventing large parallel electric fields from driving large parallel currents.
It is demonstrated here that both requirements can be met simultaneously, which
opens up the possibility for magnetized plasma tolerating steady-state voltage
drops far larger than what might be tolerated in material media.Comment: 9 pages, 3 figure
Angular momentum evolution in laser-plasma accelerators
The transverse properties of an electron beam are characterized by two
quantities, the emittance which indicates the electron beam extend in the phase
space and the angular momentum which allows for non-planar electron
trajectories. Whereas the emittance of electron beams produced in laser- plasma
accelerator has been measured in several experiments, their angular momentum
has been scarcely studied. It was demonstrated that electrons in laser-plasma
accelerator carry some angular momentum, but its origin was not established.
Here we identify one source of angular momentum growth and we present
experimental results showing that the angular momentum content evolves during
the acceleration
Elementary excitations in homogeneous neutron star matter
We study the collective density modes which can affect neutron-star
thermodynamics in the baryonic density range between nuclear saturation
() and . In this region, the expected constituents of
neutron-star matter are mainly neutrons, protons and electrons ( matter),
under the constraint of beta equilibrium. The elementary excitations of this
medium are studied in the RPA framework. We emphasize the effect of
Coulomb interaction, in particular the electron screening of the proton plasmon
mode. For the treatment of the nuclear interaction, we compare two modern
Skyrme forces and a microscopic approach. The importance of the nucleon
effective mass is observed.Comment: misprint corrected in Eq. (1
Nonlinear Radiation Pressure and Stochasticity in Ultraintense Laser Fields
The radiation force on a single electron in an ultraintense plane wave () is calculated and shown to be proportional to in the
high- limit for arbitrary waveform and polarization. The cyclotron motion of
an electron in a constant magnetic field and an ultraintense plane wave is
numerically found to be quasiperiodic even in the high- limit if the
magnetic field is not too strong, as suggested by previous analytical work. A
strong magnetic field causes highly chaotic electron motion and the boundary of
the highly chaotic region of parameter space is determined numerically.
Applications to experiments and astrophysics are briefly discussed.Comment: 5 pages, 4 figures; uses RevTex, epsf macros. Corrected, expanded
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Two-color interferometer for the study of laser filamentation triggered electric discharges in air
International audienceWe present a space and time resolved interferometric plasma diagnostic for use on plasmas where neutral-bound electron contribution to the refractive index cannot be neglected. By recording simultaneously the plasma optical index at 532 and 1064 nm, we are able to extract independently the neutral and free electron density profiles. We report a phase resolution of 30 mrad, corresponding to a maximum resolution on the order of 4 × 10 22 m −3 for the electron density, and of 10 24 m −3 for the neutral density. The interferometer is demonstrated on centimeter-scale sparks triggered by laser filamentation in air with typical currents of a few tens of A
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