Papers by Ricardo Fonseca
Bulletin of the American Physical Society, Nov 15, 2011
The demonstration of fast-ignition (FI) inertial confinement fusion (ICF) requires the delivery o... more The demonstration of fast-ignition (FI) inertial confinement fusion (ICF) requires the delivery of 40 kJ-100 kJ of laser energy to the hot spot within 16 ps. In addition, third harmonic conversion to 351 nm is needed to optimize Iλ 2 to obtain the correct hot electron energy. High-energy picosecond petawatt beams at 351 nm are difficult to generate using conventional solid-state laser systems. Previous studies of Raman amplification concentrated on maximizing the intensity and power of femtosecond pulses [Trines et al., Nature Physics (2010)]. Here we present particle-in-cell simulations and analytic theory that confirm that Raman amplification of high-energy nanosecond pulses in plasma can generate petawatt peak power pulses of picosecond duration with high efficiency (up to 60%), even at 351 nm wavelength.
Bulletin of the American Physical Society, 2015
Plasma Physics and Controlled Fusion, 2021
Raman and Brillouin amplification of laser pulses in plasma have been shown to produce picosecond... more Raman and Brillouin amplification of laser pulses in plasma have been shown to produce picosecond pulses of petawatt power. In previous tudies, 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.
Plasma Physics and Controlled Fusion, 2017
AWAKE is a proton-driven plasma wakefield acceleration experiment. We show that the experimental ... more AWAKE is a proton-driven plasma wakefield acceleration experiment. We show that the experimental setup briefly described here is ready for systematic study of the seeded self-modulation of the 400 GeV proton bunch in the 10 m-long rubidium plasma with density adjustable from 1 to 10×10 14 cm −3. We show that the short laser pulse used for ionization of the rubidium vapor propagates all the way along the column, suggesting full ionization of the vapor. We show that ionization occurs along the proton bunch, at the laser time and that the plasma that follows affects the proton bunch.
Conference on Lasers and Electro-Optics, 2016
We identify a mechanism, based on Raman scattering, to endow near-infrared laser beams with high ... more We identify a mechanism, based on Raman scattering, to endow near-infrared laser beams with high orders of orbital angular momentum (OAM). In combination with high-harmonic generation, this could lead to very high OAM harmonics in the soft x-ray region.
Physics of Plasmas, 2010
ABSTRACT The modification of photon frequency shifting based on taking into account the nonlinear... more ABSTRACT The modification of photon frequency shifting based on taking into account the nonlinear quantum electrodynamics vacuum properties in plasma is studied. Motion equations of a laser field propagating in a plasma are derived from the Heisenberg–Euler Lagrangian density. It is found that besides the classical density perturbation of the plasma electrons, the energy density perturbation of the laser field will induce the frequency shifting via the ponderomotive force of the laser field on the vacuum. In addition it is shown that the electron density will be suppressed, which is attributed to a screening effect on the plasma electrons via the quantum vacuum polarization.
Bulletin of the American Physical Society, 2016
OSIRIS [1] is a state of the art, fully relativistic massively parallel particle in cell code, th... more OSIRIS [1] is a state of the art, fully relativistic massively parallel particle in cell code, that is widely used in kinetic plasma modeling for many astrophysical and laboratory scenarios, with a large worldwide user base. Over the years the code has been continuously improved, adding new features and algorithms, support for different computing hardware, and additional physics models, resulting in a large and complex code base with the inherent difficulties on maintenance and development. We report on the new version of the OSIRIS framework, focusing on the new structure of the code that leverages on the object oriented features of Fortran 2003, that are now widely supported by available compilers. Details on the new object-oriented structure, that allows for the encapsulation of specific features, and better collaboration between the development team, are given. We also focus on the new strategy for run-time selection of simulation mode, that allows for a single binary to be used...
Bulletin of the American Physical Society, 2018
media R. Trines1, H. Schmitz1, E.P. Alves2, F. Fiúza2, J. Vieira3, L.O. Silva3, R. Bingham1,4 1 C... more media R. Trines1, H. Schmitz1, E.P. Alves2, F. Fiúza2, J. Vieira3, L.O. Silva3, R. Bingham1,4 1 Central Laser Facility, STFC Rutherford Appleton Laboratory, Didcot, OX11 0QX, United Kingdom 2 SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA 3 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal 4 SUPA, Department of Physics, University of Strathclyde, Glasgow, G4 0NG, United Kingdom
Physical Review Accelerators and Beams, 2021
We present numerical simulations and experimental results of the self-modulation of a long proton... more We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported in [1]: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement.
Plasma Physics and Controlled Fusion, 2021
It is shown here that Brillouin amplification can be used to produce picosecond pulses of petawat... more It is shown here that Brillouin amplification can be used to produce picosecond pulses of petawatt power. Brillouin amplification is far more resilient to fluctuations in the laser and plasma parameters than Raman amplification, making it an attractive alternative to Raman amplification. Through analytic theory and multi-dimensional computer simulations, a novel, well-defined parameter regime has been found, distinct from that of Raman amplification, where pump-to-probe compression ratios of up to 100 and peak laser fluences over 1 kJ/cm 2 with 30% efficiency have been achieved. High pulse quality has been maintained through control of parasitic instabilities.
Plasma Physics and Controlled Fusion, 2015
The microphysics of relativistic collisionless sheared flows is investigated in a configuration c... more 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.
New Journal of Physics, 2015
The spatial-temporal evolution of the purely transverse current filamentation instability is anal... more 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 γ b 0. 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 the current study to recent and future experiments on fireball beams is also addressed.
2011 IEEE 33rd International Telecommunications Energy Conference (INTELEC), 2011
This paper presents an implementation of a solution for efficiently using supercapacitors to powe... more This paper presents an implementation of a solution for efficiently using supercapacitors to power mobile phones. This system achieves an increase in the autonomy of the device by maximizing the energy harnessed from the supercapacitors. Test results confirm the uplift in the device's autonomy by using a supercapacitor stacking scheme, when comparing with the use of a DCIDC voltage converter alone. A specific charging scheme for this solution is also prototyped, allowing ultrafast and incremental charges without affecting the scheme's operability.
2011 IEEE International Conference on Consumer Electronics -Berlin (ICCE-Berlin), 2011
This paper proposes a solution for using supercapacitors to power mobile phones. Based on a DC/DC... more This paper proposes a solution for using supercapacitors to power mobile phones. Based on a DC/DC voltage converter and a supercapacitor stacking scheme, this solution is designed to maximize the usable energy of the supercapacitors as well as the converter's performance, which is confirmed in simulation. A specific charging scheme for this design is also proposed and simulated, enabling fast and efficient charging of the mobile device.
The Astrophysical Journal, 2012
We investigate the acceleration of light particles in perpendicular shocks for plasmas consisting... more We investigate the acceleration of light particles in perpendicular shocks for plasmas consisting of a mixture of leptonic and hadronic particles. Starting from the full set of conservation equations for the mixed plasma constituents, we generalize the magnetohydrodynamical jump conditions for a multi-component plasma, including information about the specific adiabatic constants for the different species. The impact of deviations from the standard model of an ideal gas is compared in theory and particle-in-cell simulations, showing that the standard-MHD model is a good approximation. The simulations of shocks in electron-positron-ion plasmas are for the first time multi-dimensional, transverse effects are small in this configuration and 1D simulations are a good representation if the initial magnetization is chosen high. 1D runs with a mass ratio of 1836 are performed, which identify the Larmor frequency ω ci as the dominant frequency that determines the shock physics in mixed component plasmas. The maximum energy in the non-thermal tail of the particle spectra evolves in time according to a power-law ∝ t α with α in the range 1/3 < α < 1, depending on the initial parameters. A connection is made with transport theoretical models by Drury (1983) and Gargaté & Spitkovsky (2011), which predict an acceleration time ∝ γ and the theory for small wavelength scattering by Kirk & Reville (2010), which predicts a behavior rather as ∝ γ 2. Furthermore, we compare different magnetic field orientations with B 0 inside and out of the plane, observing qualitatively different particle spectra than in pure electron-ion shocks.
Physical Review Letters, 2005
The explosion dynamics of very large (10 6-10 7 atoms) deuterium clusters irradiated by ultrainte... more The explosion dynamics of very large (10 6-10 7 atoms) deuterium clusters irradiated by ultraintense laser pulses (I 10 18 W=cm 2) is analyzed self-consistently with one-to-one three-dimensional and twodimensional fully relativistic particle-in-cell simulations. Small-scale shock shells in the expanding ion cloud are observed. A technique to induce the formation of large shock shells inside a single cluster, increasing the probability of intracluster nuclear reactions, is proposed and demonstrated.
Computer Physics Communications, 2021
A customized finite-difference field solver for the particle-in-cell (PIC) algorithm that provide... more A customized finite-difference field solver for the particle-in-cell (PIC) algorithm that provides higher fidelity for wave-particle interactions in intense electromagnetic waves is presented. In many problems of interest, particles with relativistic energies interact with intense electromagnetic fields that have phase velocities near the speed of light. Numerical errors can arise due to (1) dispersion errors in the phase velocity of the wave, (2) the staggering in time between the electric and magnetic fields and between particle velocity and position and (3) errors in the time derivative in the momentum advance. Errors of the first two kinds are analyzed in detail. It is shown that by using field solvers with different k-space operators in Faraday's and Ampere's law, the dispersion errors and magnetic field time-staggering errors in the particle pusher can be simultaneously removed for electromagnetic waves moving primarily in a specific direction. The new algorithm was implemented into Osiris by using customized higherorder finite-difference operators. Schemes using the proposed solver in combination with different particle pushers are compared through PIC simulation. It is shown that the use of the new algorithm, together with an analytic particle pusher (assuming constant fields over a time step), can lead to accurate modeling of the motion of a single electron in an intense laser field with normalized vector potentials, eA/mc 2 , exceeding 10 4 for typical cell sizes and time steps.
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Papers by Ricardo Fonseca