108 research outputs found
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
Laser ion acceleration using a solid target coupled with a low density layer
We investigate by particle-in-cell simulations in two and three dimensions
the laser-plasma interaction and the proton acceleration in multilayer targets
where a low density "near-critical" layer of a few micron thickness is added on
the illuminated side of a thin, high density layer. This target design can be
obtained by depositing a "foam" layer on a thin metallic foil. The presence of
the near-critical plasma strongly increases both the conversion efficiency and
the energy of electrons and leads to enhanced acceleration of proton from a
rear side layer via the Target Normal Sheath Acceleration mechanism. The
electrons of the foam are strongly accelerated in the forward direction and
propagate on the rear side of the target building up a high electric field with
a relatively flat longitudinal profile. In these conditions the maximum proton
energy is up to three times higher than in the case of the bare solid target.Comment: 9 pages, 11 figures. Submitted to Physical Review
Simulation of the laser-plasma acceleration for the PLASMONX project with the PIC code ALaDyn
In this paper we will briefly introduce laser–plasma acceleration for electrons and present some numerical simulations. The simulations have been performed to find a suitable working point for one of the test experiments of the INFN–CNR PLASMONX project. FLAME (Frascati laser for acceleration and multidisciplinary experiments), a 300 TW Ti:Sa laser, is being installed and commissioned at Laboratori Nazionali di Frascati (LFN). The first pilot experiment SITE (self-injection test experiment) is planned for this year (2010). The simulations have been run using a fully self-consistent particle-in-cell code AlaDyn (Acceleration by LAser and DYNamics of charged particles) developed and maintained at the Department of Physics at the University of Bologna within the PLAMSONX project
Polarization Dependence of Bulk Ion Acceleration from Ultrathin Foils Irradiated by High-Intensity Ultrashort Laser Pulses
The acceleration of ions from ultrathin (10-100 nm) carbon foils has been investigated using intense (∼ 6 x1020 Wcm-2), ultrashort (45 fs) laser pulses, highlighting a strong dependence of the ion beam parameters on the laser polarization, with circularly polarized (CP) pulses producing the highest energies for both protons and carbons (25-30 MeV/nucleon); carbon ion energies obtained employing CP pulses were signicantly higher (∼2.5 times) than for irradiations employing linearly polarized (LP) pulses. Particle-in-cell simulations indicate that Radiation Pressure Acceleration becomes the dominant mechanism for the thinnest targets and CP pulses
Evidence of resonant surface wave excitation in the relativistic regime through measurements of proton acceleration from grating targets
The interaction of laser pulses with thin grating targets, having a periodic
groove at the irradiated surface, has been experimentally investigated.
Ultrahigh contrast () pulses allowed to demonstrate an enhanced
laser-target coupling for the first time in the relativistic regime of
ultra-high intensity >10^{19} \mbox{W/cm}^{2}. A maximum increase by a factor
of 2.5 of the cut-off energy of protons produced by Target Normal Sheath
Acceleration has been observed with respect to plane targets, around the
incidence angle expected for resonant excitation of surface waves. A
significant enhancement is also observed for small angles of incidence, out of
resonance.Comment: 5 pages, 5 figures, 2nd version implements final correction
Relativistic surface plasmon enhanced harmonic generation from gratings
The role of relativistic surface plasmons (SPs) in high order harmonic emission from laser-irradiated grating targets has been investigated by means of particle-in-cell simulations. SP excitation drives a strong enhancement of the intensity of harmonics, particularly in the direction close to the surface tangent. The SP-driven enhancement overlaps with the angular separation of harmonics generated by the grating, which is beneficial for applications requiring monochromatic extreme ultraviolet (XUV) pulses
Extreme Ultraviolet Beam Enhancement by Relativistic Surface Plasmons
The emission of high-order harmonics in the extreme ultraviolet range from the interaction of a short, intense laser pulse with a grating target is investigated experimentally. When resonantly exciting a surface plasmon, both the intensity and the highest order observed for the harmonic emission along the grating surface increase with respect to a flat target. Harmonics are obtained when a suitable density gradient is preformed at the target surface, demonstrating the possibility to manipulate the grating profile on a nanometric scale without preventing the surface plasmon excitation. In support of this, the harmonic emission is spatiotemporally correlated to the acceleration of multi-MeV electron bunches along the grating surface. Particle-in-cell simulations reproduce the experimental results and give insight on the mechanism of high harmonic generation in the presence of surface plasmons
Evaluation of tsunamigenic hazard through numerical modeling from seismic and non-seismic sources in the Crotone offshore (Calabria, Southern Italy)
Tsunamis in the Mediterranean Sea can be considered among the major sources of hazard, both for the extension of the area that can be involved by the water impact and for the closeness of potential sources to the coast, which reduces dramatically the alert and evacuation time. Moreover, landslides, as other non-seismic tsunami sources, are often characterized by a lack of precursors (such as seismic shaking), a reason for which the ensuing waves are sometimes called “surprise tsunamis”
Development of foam-based layered targets for laser-driven ion beam production
We report on the development of foam-based double-layer targets (DLTs) for laser-driven ion acceleration. Foam layers with a density of a few mg cm-3 and controlled thickness in the 8-36 μm range were grown on μm-thick Al foils by pulsed laser deposition (PLD). The DLTs were experimentally investigated by varying the pulse intensity, laser polarisation and target properties. Comparing DLTs with simple Al foils, we observed a systematic enhancement of the maximum and average energies and number of accelerated ions. Maximum energies up to 30 MeV for protons and 130 MeV for C6+ ions were detected. Dedicated three-dimensional particle-in-cell (3D-PIC) simulations were performed considering both uniform and cluster-assembled foams to interpret the effect of the foam nanostructure on the acceleration process
Extensive study of electron acceleration by relativistic surface plasmons
The excitation of surface plasmons with ultra-intense (I ∼ 5 × 1019W/cm2), high contrast (∼1012) laser pulses on periodically modulated solid targets has been recently demonstrated to produce collimated bunches of energetic electrons along the target surface [Fedeli et al., Phys. Rev. Lett. 116, 015001 (2016)]. Here, we report an extensive experimental and numerical study aimed to a complete characterization of the acceleration mechanism, demonstrating its robustness and promising characteristics for an electron source. By comparing different grating structures, we identify the relevant parameters to optimize the acceleration and obtain bunches of ∼650 pC of charge at several MeV of energy with blazed gratings
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