arXiv subjects

Andrea Macchi

Publications and source records attributed to Andrea Macchi.

At least 19 recordsLinked to original sources

arXiv2019

Basics of Laser-Plasma Interaction: a Selection of Topics

A short, tutorial introduction to some basic concepts of laser-plasma interactions at ultra-high intensities is given. The selected topics include a) elements of the relativistic dynamics of an electron in electromagnetic fields, including the ponderomotive force and classical radiation friction; b) the "relativistic" nonlinear optical transparency and self-focusing; c) the moving mirror concept and its application to light sail acceleration and high harmonic generation, with a note on related instabilities; d) some specific phenomena related to the absorption of energy, kinetic momentum and angular momentum from the laser light.

physics.plasm-ph↗

arXiv2019

Momentum Absorption and Magnetic Field Generation by Obliquely Incident Light

The partial reflection of an electromagnetic (EM) wave from a medium leads to absorption of momentum in the direction perpendicular to the surface (the standard radiation pressure) {and, for oblique incidence on a partially reflecting medium}, also in the parallel direction. This latter component drives a transverse current and a slowly growing, quasi-static magnetic field in the evanescence ``skin'' layer. Through a simple model we illustrate how EM momentum is transfered to ions and estimate the value of the magnetic field which may be of the order of the driving EM wave field, i.e. up to several hundreds of megagauss for high intensity laser-solid interactions.

physics.optics↗

arXiv2018

Extensive study of electron acceleration by relativistic surface plasmons

The excitation of surface plasmons with ultra-intense ($I\sim 5\times 10^{19}$ W/cm$^2$), high contrast ($\sim 10^{12}$) 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, 5001 (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 $\sim 650$ pC of charge at several MeV of energy with blazed gratings.

physics.plasm-ph↗

arXiv2017

A Review of Laser-Plasma Ion Acceleration

An overview of research on laser-plasma based acceleration of ions is given. The experimental state of the art is summarized and recent progress is discussed. The basic acceleration processes are briefly reviewed with an outlook on hybrid mechanisms and novel concepts. Finally, we put focus on the development of engineered targets for enhanced acceleration and of all-optical methods for beam post-acceleration and control.

physics.plasm-ph↗

arXiv2017

Few-cycle Surface Plasmon Polariton Generation by Rotating Wavefront Pulses

A concept for the efficient generation of surface plasmon polaritons (SPPs) with a duration of very few cycles is presented. The scheme is based on grating coupling and laser pulses with wavefront rotation (WFR), so that the resonance condition for SPP excitation is satisfied only for a time window shorter than the driving pulse. The feasibility and robustness of the technique is investigated by means of simulations with realistic parameters. In optimal conditions, we find that a $29.5$~fs pulse with $800$~nm wavelength can excite a $3.8$~fs SPP ($\sim 1.4$ laser cycles) with a peak field amplitude $2.7$ times the peak value for the laser pulse.

physics.optics↗

arXiv2017

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 XUV pulses.

physics.plasm-ph↗

arXiv2017

Radiation Pressure Driven Ion Weibel Instability and Collisionless Shocks

The Weibel instability from counterstreaming plasma flows is a basic process highly relevant for collisionless shock formation in astrophysics. In this Letter we investigate, via two- and three- dimensional simulations, suitable configurations for laboratory investigations of the ion Weibel instability (IWI) driven by a fast quasi-neutral plasma flow launched into the target via the radiation pressure of an ultra-high-intensity (UHI) laser pulse ('Hole-Boring' process). The use of S-polarized light at oblique incidence is found to be an optimal configuration for driving IWI, as it prevents the development of surface rippling observed at normal incidence, that would lead to strong electron heating and favors competing instabilities. Conditions for the evolution of IWI into a collisionless shock are also investigated.

physics.plasm-ph↗

arXiv2016

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.

physics.plasm-ph↗

arXiv2015

Electron acceleration by relativistic surface plasmons in laser-grating interaction

The generation of energetic electron bunches by the interaction of a short, ultra-intense ($I>10^{19} \textrm{W/cm}^2$) laser pulse with "grating" targets has been investigated in a regime of ultra-high pulse-to-prepulse contrast ($10^{12}$). For incidence angles close to the resonant condition for Surface Plasmon (SP) excitation, a strong electron emission was observed within a narrow cone along the target surface, with energies exceeding 10 MeV. 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 SPs and for their role in driving the acceleration process. Besides the possible applications of the scheme as a compact, ultra-short source of MeV electrons, these results are a step forward the development of high field plasmonics.

physics.plasm-ph↗

arXiv2015

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.

cs.DC↗

arXiv2014

High Energy Gain in Three-Dimensional Simulations of Light Sail Acceleration

The dynamics of radiation pressure acceleration in the relativistic light sail regime are analysed by means of large scale, three-dimensional (3D) particle-in-cell simulations. Differently to other mechanisms, the 3D dynamics leads to faster and higher energy gain than in 1D or 2D geometry. This effect is caused by the local decrease of the target density due to transverse expansion leading to a "lighter sail". However, the rarefaction of the target leads to an earlier transition to transparency limiting the energy gain. A transverse instability leads to a structured and inhomogeneous ion distribution.

physics.plasm-ph↗

arXiv2014

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.

physics.plasm-ph↗

arXiv2014

Theory of Light Sail Acceleration by Intense Lasers: an Overview

A short overview of the theory of acceleration of thin foils driven by the radiation pressure of superintense lasers is presented. A simple criterion for radiation pressure dominance at intensities around $5 \times 10^{20} \mbox{W cm}^{-2}$ is given, and the possibility for fast energy gain in the relativistic regime is discussed.

physics.plasm-ph↗

arXiv2013

Ion acceleration by superintense laser-plasma interaction

Ion acceleration driven by superintense laser pulses is attracting an impressive and steadily increasing effort. Motivations can be found in the potential for a number of foreseen applications and in the perspective to investigate novel regimes as far as available laser intensities will be increasing. Experiments have demonstrated in a wide range of laser and target parameters the generation of multi-MeV proton and ion beams with unique properties such as ultrashort duration, high brilliance and low emittance. In this paper we give an overview of the state-of-the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives. We describe the main features observed in the experiments, the observed scaling with laser and plasma parameters and the main models used both to interpret experimental data and to suggest new research directions.

physics.plasm-ph↗

arXiv2012

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.

physics.plasm-ph↗

arXiv2012

Toy model of the "fountain effect" for magnetic field generation in intense laser-solid interactions

A very simple "geometrical" model of a fountain is analyzed to evaluate the net flow on the ground resulting from the superposition of the source and the falling streams. On this basis we suggest a scaling for the magnetic field generated at the rear surface of high-intensity laser-irradiated solid targets due to the "fountain effect" related to fast electrons escaping in vacuum.

physics.plasm-ph↗

arXiv2011

Solitary versus Shock Wave Acceleration in Laser-Plasma Interactions

The excitation of nonlinear electrostatic waves, such as shock and solitons, by ultraintense laser interaction with overdense plasmas and related ion acceleration are investigated by numerical simulations. Stability of solitons and formation of shock waves is strongly dependent on the velocity distribution of ions. Monoenergetic components in ion spectra are produced by "pulsed" reflection from solitary waves. Possible relevance to recent experiments on "shock acceleration" is discussed.

physics.plasm-ph↗

arXiv2010

Radiation Reaction Effects on Electron Nonlinear Dynamics and Ion Acceleration in Laser-solid Interaction

Radiation Reaction (RR) effects in the interaction of an ultra-intense laser pulse with a thin plasma foil are investigated analytically and by two-dimensional (2D3P) Particle-In-Cell (PIC) simulations. It is found that the radiation reaction force leads to a significant electron cooling and to an increased spatial bunching of both electrons and ions. A fully relativistic kinetic equation including RR effects is discussed and it is shown that RR leads to a contraction of the available phase space volume. The results of our PIC simulations are in qualitative agreement with the predictions of the kinetic theory.

physics.plasm-ph↗