1,509 research outputs found
Two-surface wave decay: improved analytical theory and effects on electron acceleration
Two-surface wave decay (TSWD), i.e. the parametric excitation of electron
surface waves, was recently proposed as an absorption mechanism in the
interaction of ultrashort, intense laser pulses with solid targets. We present
an extension of the fluid theory of TSWD to a warm plasma which treats boundary
effects consistently. We also present test-particle simulations showing
localized enhancement of electron acceleration by TSWD fields; this effect
leads to a modulation of the current density entering into the target and may
seed current filamentation instabilities.Comment: 4 figures, submitted to Appl.Phys.B (special issue from HFSW X
conference, Biarritz, France, Oct 12-15 2003); slightly revised tex
Electric field dynamics and ion acceleration in the self-channeling of a superintense laser pulse
The dynamics of electric field generation and radial acceleration of ions by
a laser pulse of relativistic intensity propagating in an underdense plasma has
been investigated using an one-dimensional electrostatic, ponderomotive model
developed to interpret experimental measurements of electric fields [S. Kar et
al, New J. Phys. *9*, 402 (2007)]. Ions are spatially focused at the edge of
the charge-displacement channel, leading to hydrodynamical breaking, which in
turns causes the heating of electrons and an "echo" effect in the electric
field. The onset of complete electron depletion in the central region of the
channel leads to a smooth transition to a "Coulomb explosion" regime and a
saturation of ion acceleration.Comment: 9 pages, 7 figures, final revised version, to appear on Plasma Phys.
Contr. Fus., special issue on "Laser and Plasma Accelerators", scheduled for
February, 200
"Single-cycle" ionization effects in laser-matter interaction
We investigate numerically effects related to ``single-cycle'' ionization of
dense matter by an ultra-short laser pulse. The strongly non-adiabatic response
of electrons leads to generation of a megagauss steady magnetic field in
laser-solid interaction. By using two-beam interference, it is possible to
create periodic density structures able to trap light and to generate
relativistic ionization frontsComment: 12 pages, 6 figures, to be published in Laser and Particle Beam
Particle acceleration and radiation friction effects in the filamentation instability of pair plasmas
The evolution of the filamentation instability produced by two
counter-streaming pair plasmas is studied with particle-in-cell (PIC)
simulations in both one (1D) and two (2D) spatial dimensions. Radiation
friction effects on particles are taken into account. After an exponential
growth of both the magnetic field and the current density, a nonlinear
quasi-stationary phase sets up characterized by filaments of opposite currents.
During the nonlinear stage, a strong broadening of the particle energy spectrum
occurs accompanied by the formation of a peak at twice their initial energy. A
simple theory of the peak formation is presented. The presence of radiative
losses does not change the dynamics of the instability but affects the
structure of the particle spectra.Comment: 8 pages, 8 figures, submitted to MNRA
The original caliber of the carotid artery as a possible risk factor for complications of atherosclerosis.
The measurement of the calibers of the branches of the aortic arch: a statistical investigation of 430 living subjects using ultrasonic tomography.
The Importance of Nutrition in Hypertension
Arterial hypertension (AH) is considered to be one of the most relevant cardiovascular risk factors, and its wide prevalence in all age ranges makes it necessary to analyse all the possible causes and treatments. In this special issue, nutritional interventions are examined either as causes or as treatments of AH. [...]
Surface Oscillations in Overdense Plasmas Irradiated by Ultrashort Laser Pulses
The generation of electron surface oscillations in overdense plasmas
irradiated at normal incidence by an intense laser pulse is investigated.
Two-dimensional (2D) particle-in-cell simulations show a transition from a
planar, electrostatic oscillation at , with the laser
frequency, to a 2D electromagnetic oscillation at frequency and
wavevector . A new electron parametric instability, involving the
decay of a 1D electrostatic oscillation into two surface waves, is introduced
to explain the basic features of the 2D oscillations. This effect leads to the
rippling of the plasma surface within a few laser cycles, and is likely to have
a strong impact on laser interaction with solid targets.Comment: 9 pages (LaTeX, Revtex4), 4 GIF color figures, accepted for
publication in Phys. Rev. Let
Ion dynamics and coherent structure formation following laser pulse self-channeling
The propagation of a superintense laser pulse in an underdense, inhomogeneous
plasma has been studied numerically by two-dimensional particle-in-cell
simulations on a time scale extending up to several picoseconds. The effects of
the ion dynamics following the charge-displacement self-channeling of the laser
pulse have been addressed. Radial ion acceleration leads to the ``breaking'' of
the plasma channel walls, causing an inversion of the radial space-charge field
and the filamentation of the laser pulse. At later times a number of
long-lived, quasi-periodic field structures are observed and their dynamics is
characterized with high resolution. Inside the plasma channel, a pattern of
electric and magnetic fields resembling both soliton- and vortex-like
structures is observed.Comment: 10 pages, 5 figures (visit http://www.df.unipi.it/~macchi to download
a high-resolution version), to appear in Plasma Physics and Controlled Fusion
(Dec. 2007), special issue containing invited papers from the 34th EPS
Conference on Plasma Physics (Warsaw, July 2007
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