17 research outputs found
Vlasov simulation of laser-driven shock acceleration and ion turbulence
We present a Vlasov, i.e. a kinetic Eulerian simulation study of nonlinear
collisionless ion-acoustic shocks and solitons excited by an intense laser
interacting with an overdense plasma. The use of the Vlasov code avoids
problems with low particle statistics and allows a validation of
particle-in-cell results. A simple original correction to the splitting method
for the numerical integration of the Vlasov equation has been implemented in
order to ensure the charge conservation in the relativistic regime. We show
that the ion distribution is affected by the development of a turbulence driven
by the relativistic "fast" electron bunches generated at the laser-plasma
interaction surface. This leads to the onset of ion reflection at the shock
front in an initially cold plasma where only soliton solutions without ion
reflection are expected to propagate. We give a simple analytic model to
describe the onset of the turbulence as a nonlinear coupling of the ion density
with the fast electron currents, taking the pulsed nature of the relativistic
electron bunches into account
Laser-Driven Rayleigh-Taylor Instability: Plasmonics Effects and Three-Dimensional Structures
The acceleration of dense targets driven by the radiation pressure of
high-intensity lasers leads to a Rayleigh-Taylor instability (RTI) with
rippling of the interaction surface. Using a simple model it is shown that the
self-consistent modulation of the radiation pressure caused by a sinusoidal
rippling affects substantially the wavevector spectrum of the RTI depending on
the laser polarization. The plasmonic enhancement of the local field when the
rippling period is close to a laser wavelength sets the dominant RTI scale. The
nonlinear evolution is investigated by three dimensional simulations, which
show the formation of stable structures with "wallpaper" symmetry.Comment: 5 pages, 5 figures. New version includes 2D and 3D simulations. More
details in the analytical calculation are given in the previous versio
Protons Acceleration by CO2 Laser Pulses and Perspectives for Medical Applications
In the present note we shall review the basic mechanisms for laser acceleration to present the related scaling laws and compare the results one expects from small (1 \u3bc) and large (10 \u3bc) wavelength pulses. Systematic 2D and 3D simulations were performed with the high order PICcodeALaDyn [Benedetti et al.(2008)] developedbytheuniversityofBolognatoprovide quantitative results in addition to the qualitative results of scaling laws. We shall also discuss the transport of a protons beam through an optical system.
The paper consists of six sections: after this introduction, in section 2 we recall the basic features and parameters of the laser beam, in section 3 the TNSA regime is reviewed, in section 4 the RPA regime is presented, in section 5 the acceleration on under-critical target is discussed, in section 6 we discuss the transport of the optically accelerated proton bunch, in section 7 we analyze the perspectives for therapy
Electron Acceleration by Relativistic Surface Plasmons in Laser-Grating Interaction
The generation of energetic electron bunches by the interaction of a short, ultraintense (I>1019 W/cm2) laser pulse with "grating" targets has been investigated in a regime of ultrahigh pulse-to-prepulse contrast (1012). For incidence angles close to the resonant condition for surface plasmon excitation, a strong electron emission was observed within a narrow cone along the target surface, with energy spectra peaking at 5-8 MeV and total charge of ∼100 pC. Both the energy and the number of emitted electrons were strongly enhanced with respect to simple flat targets. The experimental data are closely reproduced by three-dimensional particle-in-cell simulations, which provide evidence for the generation of relativistic surface plasmons and for their role in driving the acceleration process. Besides the possible applications of the scheme as a compact, ultrashort source of MeV electrons, these results are a step forward in the development of high-field plasmonics
Theoretical and numerical study of the laser-plasma ion acceleration
The laser driven ion acceleration is a burgeoning field of resarch
and is attracting a growing number of scientists since the first results reported in 2000 obtained
irradiating thin solid foils by high power laser pulses.
The growing interest is driven by the peculiar characteristics of the produced bunches,
the compactness of the whole accelerating system and the very short
accelerating length of this all-optical accelerators.
A fervent theoretical and experimental work has been done since then.
An important part of the theoretical study is done by means of numerical simulations and the most widely used
technique exploits PIC codes (“Particle In Cell'”).
In this thesis the PIC code AlaDyn, developed by our research group considering innovative
algorithms, is described. My work
has been devoted to the developement of the code and
the investigation of the laser driven ion acceleration
for different target configurations.
Two target configurations for the proton acceleration are
presented together with the results of the 2D and 3D numerical investigation.
One target configuration consists of a solid foil with a low density layer attached on the
irradiated side. The nearly critical plasma of the foam layer allows a very
high energy absorption by the target and an increase of the proton
energy up to a factor 3, when compared to the ``pure'' TNSA configuration.
The differences of the regime with respect to the standard TNSA are described
The case of nearly critical density targets has been investigated with
3D simulations. In this case the laser travels throughout the plasma
and exits on the rear side. During the propagation, the laser drills a channel
and induce a magnetic vortex that expanding on the rear side of the targer is source of a
very intense electric field. The protons of the plasma are
strongly accelerated up to energies of 100 MeV using a 200PW laser
Optimising PICCANTE - an Open Source Particle-in-Cell Code for Advanced Simulations on Tier-0 Systems
We present a detailed strong and weak scaling analysis of PICCANTE, an open
source, massively parallel, fully-relativistic Particle-In-Cell (PIC) code. PIC
codes are widely used in plasma physics and astrophysics to study the cases
where kinetic effects are relevant. PICCANTE is primarily developed to study
laser-plasma interaction. Within a PRACE Preparatory Access Project, various
revisions of different routines of the code have been analysed on the HPC
systems JUQUEEN at Juelich Supercomputing Centre (JSC), Germany, and FERMI at
CINECA, Italy, to improve scalability and I/O performance of the application.
The diagnostic tool Scalasca is used to identify suboptimal routines. Different
output strategies are discussed. The detailed strong and weak scaling behaviour
of the improved code are presented in comparison with the original version of
the code
piccante: 2016 with Poisson solver and quite start
Improved performance on some architecture thanks to unroll of some heavy function