159 research outputs found
Giga-Gauss scale quasistatic magnetic field generation in an 'escargot' target
A simple setup for the generation of ultra-intense quasistatic magnetic
fields, based on the generation of electron currents with a predefined geometry
in a curved 'escargot' target, is proposed and analysed. Particle-In-Cell
simulations and qualitative estimates show that giga-Gauss scale magnetic
fields may be achieved with existent laser facilities. The described mechanism
of the strong magnetic field generation may be useful in a wide range of
applications, from laboratory astrophysics to magnetized ICF schemes.Comment: Submitted to PRL. arXiv admin note: text overlap with arXiv:1409.524
X-ray amplification from a Raman Free Electron Laser
accepted for publication in Phys. Rev. Lett. 03/11/2012We demonstrate that a mm-scale free electron laser can operate in the X-ray range, in the interaction between a moderately relativistic electron bunch, and a transverse high intensity optical lattice. The corrugated light-induced ponderomotive potential acts simultaneously as a guide and as a low-frequency wiggler, triggering stimulated Raman scattering. The gain law in the small signal regime is derived in a fluid approach, and confirmed from Particle-In-Cell simulations. We describe the nature of bunching, and discuss the saturation properties. The resulting all-optical Raman X-ray laser opens perspectives for ultra-compact coherent light sources up to the hard X-ray range
γ-ray generation enhancement by the charge separation field in laser-target interaction in the radiation dominated regime
A new source of radiation can be created with a laser pulse of intensity 1023W/cm2 interacting with a slightly overdense plasma. Collective effects driven by the electrostatic field significantly enhance the synchrotron radiation. They impact on the laser energy repartition leading to a specific emission but also constitute a crucial element for the intense radiation production. They allow electrons to be accelerated over a length up to 10 laser wavelengths favoring emission of an intense radiation. It is shown that charge separation field depends on the ion mass and target thickness but also on laser polarization. These phenomena are studied with an one dimensional relativistic particle-in-cell code accounting for the classical radiation reaction force
Fluctuating lattice Boltzmann
The lattice Boltzmann algorithm efficiently simulates the Navier Stokes
equation of isothermal fluid flow, but ignores thermal fluctuations of the
fluid, important in mesoscopic flows. We show how to adapt the algorithm to
include noise, satisfying a fluctuation-dissipation theorem (FDT) directly at
lattice level: this gives correct fluctuations for mass and momentum densities,
and for stresses, at all wavevectors . Unlike previous work, which recovers
FDT only as , our algorithm offers full statistical mechanical
consistency in mesoscale simulations of, e.g., fluctuating colloidal
hydrodynamics.Comment: 7 pages, 3 figures, to appear in Europhysics Letter
Symmetry-breaking and chaos in electron transport in semiconductor superlattices
We study the motion of electrons in a single miniband of a semiconductor
superlattice driven by THz electric field polarized along the growth direction.
We work in the semiclassical balance-equation model, including different
elastic and inelastic scattering rates, and incorporating the self-consistent
electric field generated by electron motion. We explore regions of complex
dynamics, which can include chaotic behaviour and symmetry-breaking. We
estimate the magnitudes of dc current and dc voltage that spontaneously appear
in regions of broken-symmetry for parameters characteristic of modern
semiconductor superlattices. This work complements PRL 80(1998)2669 [
cond-mat/9709026 ].Comment: 4 pages, 3 figures, RevTEX, EPS
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The properties of tagged lattice fluids: II. Velocity correlation functions
We report preliminary measurements of the velocity autocorrelation function for a tagged particle in a lattice gas. These measurements agree with the Boltzmann-level theory. The Green-Kubo integration of these measurements agrees with theoretical predictions for the diffusion coefficient. To within the error bars of the simulations (3 /times/ 10/sup /minus/3/) we observe no long-time tails. 9 refs., 1 fig., 1 tab
The analysis on the single particle model of CDW
Gruner put forward a single particle model of charge-density wave, which is a
typical nonlinear differential equation, and also a mathematical model of
pendulum. This Letter analyzes the solution of equation by the rotated vector
fields theory, providing the relation between the applied field E and the
periodic solution, and the conclusion that the critical value of E for the
periodic solution is fixed in the over-damped situation. With these
conclusions, it derives the formulae of nonlinear conductivity, narrow-band
noise, which are consistent with the empirical ones given by Fleming.Comment: This is a version with a physics focus, the part with a mathematical
focus is submitted at arXiv:0807.328
Rheology of Lamellar Liquid Crystals in Two and Three Dimensions: A Simulation Study
We present large scale computer simulations of the nonlinear bulk rheology of
lamellar phases (smectic liquid crystals) at moderate to large values of the
shear rate (Peclet numbers 10-100), in both two and three dimensions. In two
dimensions we find that modest shear rates align the system and stabilise an
almost regular lamellar phase, but high shear rates induce the nucleation and
proliferation of defects, which in steady state is balanced by the annihilation
of defects of opposite sign. The critical shear rate at onset of this second
regime is controlled by thermodynamic and kinetic parameters; we offer a
scaling analysis that relates the critical shear rate to a critical "capillary
number" involving those variables. Within the defect proliferation regime, the
defects may be partially annealed by slowly decreasing the applied shear rate;
this causes marked memory effects, and history-dependent rheology. Simulations
in three dimensions show instead shear-induced ordering even at the highest
shear rates studied here. This suggests that the critical shear rate shifts
markedly upward on increasing dimensionality. This may in part reflect the
reduced constraints on defect motion, allowing them to find and annihilate each
other more easily. Residual edge defects in the 3D aligned state mostly point
along the flow velocity, an orientation impossible in two dimensions.Comment: 18 pages, 12 figure
Lattice Boltzmann Equation: Failure or Success?
The lattice Boltzmann equation (LBE) is a microscopically-inspired method
designed to solve macroscopic fluid dynamics problems. As a such, it lives at
the interface between the microscopic (molecular) and macroscopic (continuum)
worlds, hopefully capturing the best of the two. In this paper we shall discuss
whether or not, after almost a decade since its inception, LBE has lived up to
the initial expectations. Open problems and future research developments are
also briefly outlined
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