L. O. Silva

Instituto Técnico y Cultural, Santa Clara de Portugal, Michoacán, Mexico

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Publications (284)725.94 Total impact

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    ABSTRACT: An emissivity formula is derived using the generalised Fermi-Weizacker-Williams method of virtual photons which accounts for the recoil the charged particle experiences as it emits radiation. It is found that through this derivation the formula obtained by Sokolov et al using QED perturbation theory is recovered. The corrected emissivity formula is applied to nonlinear Thomson scattering scenarios in the transition from the classical to the quantum regime, for small values of the nonlinear quantum parameter \chi. Good agreement is found between this method and a QED probabilistic approach for scenarios where both are valid. In addition, signatures of the quantum corrections are identified and explored.
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    ABSTRACT: The microphysics of relativistic collisionless sheared flows is investigated in a configuration consisting of a globally neutral, relativistic $e^-e^+$ beam streaming through a hollow plasma/dielectric channel. We show through multidimensional PIC simulations that this scenario excites the Mushroom instability (MI), a transverse shear instability on the electron-scale, when there is no overlap (no contact) between the $e^-e^+$ beam and the walls of the hollow plasma channel. The onset of the MI leads to the conversion of the beam's kinetic energy into magnetic (and electric) field energy, effectively slowing down a globally neutral body in the absence of contact. The collisionless shear physics explored in this configuration may operate in astrophysical environments, particularly in highly relativistic and supersonic settings where macroscopic shear processes are stable.
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    ABSTRACT: In this paper we show a plausible mechanism that could lead to the formation of the Dark Lanes in Lunar Swirls, and the electromagnetic shielding of the lunar surface that results in the preservation of the white colour of the lunar regolith. We present the results of a fully self-consistent 2 and 3 dimensional particle-in-cell simulations of mini-magnetospheres that form above the lunar surface and show that they are consistent with the formation of `lunar swirls' such as the archetypal formation Reiner Gamma. The simulations show how the microphysics of the deflection/shielding of plasma operates from a kinetic-scale cavity, and show that this interaction leads to a footprint with sharp features that could be the mechanism behind the generation of `dark lanes'. The physics of mini-magnetospheres is described and shown to be controlled by space-charge fields arising due to the magnetized electrons and unmagnetized ions. A comparison between model and observation is shown for a number of key plasma parameters.
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    E. P. Alves · T. Grismayer · R. A. Fonseca · L. O. Silva
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    ABSTRACT: Electron-scale surface waves are shown to be unstable in the transverse plane of a shear flow in an initially unmagnetized plasma, unlike in the (magneto)hydrodynamics case. It is found that these unstable modes have a higher growth rate than the closely related electron-scale Kelvin-Helmholtz instability in relativistic shears. Multidimensional particle-in-cell simulations verify the analytic results and further reveal the emergence of mushroom-like electron density structures in the nonlinear phase of the instability, similar to those observed in the Rayleigh Taylor instability despite the great disparity in scales and different underlying physics. Macroscopic ($\gg c/\omega_{pe}$) fields are shown to be generated by these microscopic shear instabilities, which are relevant for particle acceleration, radiation emission and to seed MHD processes at long time-scales.
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    ABSTRACT: Electron-positron pair plasmas represent a unique state of matter, whereby there exists an intrinsic and complete symmetry between negatively charged (matter) and positively charged (antimatter) particles. These plasmas play a fundamental role in the dynamics of ultra-massive astrophysical objects and are believed to be associated with the emission of ultra-bright gamma-ray bursts. Despite extensive theoretical modelling, our knowledge of this state of matter is still speculative, owing to the extreme difficulty in recreating neutral matter-antimatter plasmas in the laboratory. Here we show that, by using a compact laser-driven setup, ion-free electron-positron plasmas with unique characteristics can be produced. Their charge neutrality (same amount of matter and antimatter), high-density and small divergence finally open up the possibility of studying electron-positron plasmas in controlled laboratory experiments.
    Nature Communications 04/2015; 6:6747. DOI:10.1038/ncomms7747 · 10.74 Impact Factor
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    ABSTRACT: The spatial-temporal evolution of the purely transverse current filamentation instability is analyzed by deriving a single partial differential equation for the instability and obtaining the analytical solutions for the spatially and temporally growing current filament mode. When the beam front always encounters fresh plasma, our analysis shows that the instability grows spatially from the beam front to the back up to a certain critical beam length; then the instability acquires a purely temporal growth. This critical beam length increases linearly with time and in the non-relativistic regime it is proportional to the beam velocity. In the relativistic regime the critical length is inversely proportional to the cube of the beam Lorentz factor $\gamma_{0b}$. Thus, in the ultra-relativistic regime the instability immediately acquires a purely temporal growth all over the beam. The analytical results are in good agreement with multidimensional particle-in-cell simulations performed with OSIRIS. Relevance of current study to recent and future experiments on fireball beams is also addressed.
    New Journal of Physics 03/2015; 17(4). DOI:10.1088/1367-2630/17/4/043049 · 3.67 Impact Factor
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    ABSTRACT: The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms, including instabilities, dynamo effects and ultra-high energy particle flows through gas, plasma and interstellar-media. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each operates can be reconciled by scaling parameters that enable to recreate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles can strongly magnetize the boundary between the plasma and the non-ionized gas to magnetic fields up to 10-100 Tesla (micro Tesla in astrophysical conditions). The physics is observed from the first time-resolved large scale magnetic field measurements obtained in a laser wakefield accelerator. Particle-in-cell simulations capturing the global plasma and field dynamics over the full plasma length confirm the experimental measurements. These results open new paths for the exploration and modelling of ultra high energy particle driven magnetic field generation in the laboratory.
    Nature Physics 03/2015; 11(5). DOI:10.1038/nphys3303 · 20.60 Impact Factor
  • M Vranic · J L Martins · J Vieira · R A Fonseca · L O Silva
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    ABSTRACT: Using full-scale 3D particle-in-cell simulations we show that the radiation reaction dominated regime can be reached in an all-optical configuration through the collision of a ∼1 GeV laser wakefield accelerated electron bunch with a counterpropagating laser pulse. In this configuration the radiation reaction significantly reduces the energy of the particle bunch, thus providing clear experimental signatures for the process with currently available lasers. We also show that the transition between the classical and quantum radiation reaction could be investigated in the same configuration with laser intensities of 10^{23} W/cm^{2}.
    Physical Review Letters 09/2014; 113(13):134801. · 7.51 Impact Factor
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    J. Vieira · R. A. Fonseca · W. B. Mori · L. O. Silva
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    ABSTRACT: We explore the role of the background plasma ion motion in self-modulated plasma wakefield accelerators. We employ J. Dawson's plasma sheet model to derive expressions for the transverse plasma electric field and ponderomotive force in the narrow bunch limit. We use these results to determine the on-set of the ion dynamics, and demonstrate that the ion motion could occur in self-modulated plasma wakefield accelerators. Simulations show the motion of the plasma ions can lead to the early suppression of the self-modulation instability and of the accelerating fields. The background plasma ion motion can nevertheless be fully mitigated by using plasmas with heavier plasmas.
    Physics of Plasmas 09/2014; 21(5). DOI:10.1063/1.4876620 · 2.25 Impact Factor
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    A. Stockem · T. Grismayer · R. A. Fonseca · L. O. Silva
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    ABSTRACT: A new magnetic field generation mechanism in electrostatic shocks is found, which can produce fields with magnetic energy density as high as 0.01 of the kinetic energy density of the flows on time scales $ \tilde \, 10^4 \, {\omega}_{pe}^{-1}$. Electron trapping during the shock formation process creates a strong temperature anisotropy in the distribution function, giving rise to the pure Weibel instability. The generated magnetic field is well-confined to the downstream region of the electrostatic shock. The shock formation process is not modified and the features of the shock front responsible for ion acceleration, which are currently probed in laser-plasma laboratory experiments, are maintained. However, such a strong magnetic field determines the particle trajectories downstream and has the potential to modify the signatures of the collisionless shock.
    Physical Review Letters 08/2014; 113(10). DOI:10.1103/PhysRevLett.113.105002 · 7.51 Impact Factor
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    ABSTRACT: It is shown that co-linear injection of electrons or positrons into the wakefield of the self-modulating particle beam is possible and ensures high energy gain. The witness beam must co-propagate with the tail part of the driver, since the plasma wave phase velocity there can exceed the light velocity, which is necessary for efficient acceleration. If the witness beam is many wakefield periods long, then the trapped charge is limited by beam loading effects. The initial trapping is better for positrons, but at the acceleration stage a considerable fraction of positrons is lost from the wave. For efficient trapping of electrons, the plasma boundary must be sharp, with the density transition region shorter than several centimeters. Positrons are not susceptible to the initial plasma density gradient.
    Physics of Plasmas 08/2014; 21(12). DOI:10.1063/1.4904365 · 2.25 Impact Factor
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    J Vieira · L D Amorim · Y Fang · W B Mori · P Muggli · L O Silva
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    ABSTRACT: We study the evolution of the self-modulation instability for bunches with finite rise times. Using particle-in-cell simulations we show that, unlike with long bunches with sharp rise times, there are large variations of the wake amplitude and phase velocity with finite rise time bunches. These results show that bunches with sharp rise times are important to seed the self-modulation instability and to ensure stable acceleration.
    Plasma Physics and Controlled Fusion 07/2014; 56(8):084014. DOI:10.1088/0741-3335/56/8/084014 · 2.39 Impact Factor
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    ABSTRACT: Raman and Brillouin amplification of laser pulses in plasma have been shown to produce picosecond pulses of petawatt power. In previous studies, filamentation of the probe pulse has been identified as the biggest threat to the amplification process, especially for Brillouin amplification, which employs the highest plasma densities. Therefore it has been proposed to perform Brillouin scattering at densities below $n_{cr}/4$ to reduce the influence of filamentation. However, parastic Raman scattering can become a problem at such densities, contrary to densities above $n_{cr}/4$, where it is suppressed. In this paper, we investigate the influence of parasitic Raman scattering on Brillouin amplification at densities below $n_{cr}/4$. We expose the specific problems posed by both Raman backward and forward scattering, and how both types of scattering can be mitigated, leading to an increased performance of the Brillouin amplification process.
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    ABSTRACT: We preform hybrid simulations of super Alfvenic quasi-parallel shock, driven by a Coronal Mass Ejection (CME), propagating in the Outer Coronal or Solar Wind at distances of between 3 to 6 solar radii. The hybrid treatment of the problem enable the study of the shock propagation on the ion time scale, preserving ion kinetics and allowing for a self consistent treatment of the shock propagation and particle acceleration. The CME plasma drags the embedded magnetic field lines stretching from the sun, and propagates out into interplanetary space at a greater velocity than the in-situ solar wind, driving the shock, and producing very energetic particles. Our results show electromagnetic Alfven waves are generated at the shock front. The waves propagate upstream of the shock and are produced by the counter streaming ions of the solar wind plasma being reflected at the shock. A significant fraction of the particles are accelerated in two distinct phases: first, particles drift from the shock and are accelerated in the upstream region and, second, particles arriving at the shock get trapped, and are accelerated at the shock front. A fraction of the particles diffused back to the shock, which is consistent with the Fermi acceleration mechanism.
    The Astrophysical Journal 06/2014; 792(1). DOI:10.1088/0004-637X/792/1/9 · 6.28 Impact Factor
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    X. Davoine · F. Fiúza · R. A. Fonseca · W. B. Mori · L. O. Silva
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    ABSTRACT: In this paper, we determine the electron beam quality requirements to obtain exponential radiation amplification in the ion-channel laser, where a relativistic electron beam wiggles in a focusing ion-channel that can be created in a wakefield accelerator. The beam energy and wiggler parameter spreads should be limited. Those spread limits are functions of the Pierce parameter, which is calculated here without neglecting the radiation diffraction. Two dimensional and three dimensional simulations of the self-consistent ion-channel laser confirm our theoretical predictions.
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Publication Stats

3k Citations
725.94 Total Impact Points

Institutions

  • 1997–2015
    • Instituto Técnico y Cultural
      Santa Clara de Portugal, Michoacán, Mexico
  • 2008–2014
    • University of Lisbon
      Lisboa, Lisbon, Portugal
  • 2013
    • University of Nevada, Reno
      • Department of Physics
      Reno, Nevada, United States
  • 2009–2013
    • Instituto Superior de Contabilidade e Administração de Lisboa
      Lisboa, Lisbon, Portugal
  • 1998–2012
    • University of California, Los Angeles
      • • Department of Electrical Engineering
      • • Department of Physics and Astronomy
      Los Angeles, California, United States
  • 2011
    • ISCTE-Instituto Universitário de Lisboa
      Lisboa, Lisbon, Portugal
  • 2003–2011
    • Technical University of Lisbon
      • • Institute for Plasma Research and Nuclear Fusion (IPFN)
      • • Centro de Fisica dos Plasmas
      Lisboa, Lisbon, Portugal
  • 2010
    • Iowa State University
      • Department of Physics and Astronomy
      Ames, Iowa, United States
  • 2007
    • ISG | Business & Economics School
      Lisboa, Lisbon, Portugal
  • 2006–2007
    • University of Strathclyde
      • Department of Physics
      Glasgow, Scotland, United Kingdom
  • 1998–2004
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany