Three-dimensional (3D) particle-in-cell (PIC) simulations are used to
investigate the interaction of ultrahigh intensity lasers ($> 10^{20}$
W/cm$^{-2}$) with matter at overcritical densities. Intense laser pulses are
shown to penetrate up to relativistic critical density levels and to be
strongly self-focused during this process. The heat flux of the accelerated
electrons is observed to have an annular structure when the laser is tightly
focused, showing that a large fraction of fast electrons is accelerated at an
angle. These results shed light into the multi-dimensional effects present in
laser-plasma interactions of relevance to fast ignition of fusion targets and
laser-driven ion acceleration in plasmas.Comment: 2 pages, 1 figur

Fiuza, F.

Fonseca, R. A.

May, J.

Mori, W. B.

Silva, L. O.

Tonge, J.

English

arXiv

WOS:000299683400282 (Nº de Acesso Web of Science)Three-dimensional particle-in-cell simulations are used to investigate the interaction of ultrahigh-intensity lasers (>;1020 W/cm-2) with matter at overcritical densities. Intense laser pulses are shown to penetrate up to relativistic critical density levels and to be strongly self-focused during this process. The heat flux of the accelerated electrons is observed to have an annular structure when the laser is tightly focused, showing that a large fraction of fast electrons is accelerated at an angle. These results shed light into the multidimensional effects present in laser-plasma interactions of relevance to fast ignition of fusion targets and laser-driven ion acceleration in plasmas

Repositório Institucional do ISCTE-IUL

arXiv:1205.3120v1  [physics.plasm-ph]  14 May 20121Three-dimensional simulations of laser-plasmainteractions at ultrahigh intensitiesFrederico Fiu´za, Ricardo A. Fonseca, Luı´s O. Silva, John Tonge, Joshua May, and Warren B. MoriAbstract—Three-dimensional (3D) particle-in-cell (PIC) sim-ulations are used to investigate the interaction of ultrahighintensity lasers (> 1020 W/cm−2) with matter at overcriticaldensities. Intense laser pulses are shown to penetrate up torelativistic critical density levels and to be strongly self-focusedduring this process. The heat flux of the accelerated electronsis observed to have an annular structure when the laser istightly focused, showing that a large fraction of fast electronsis accelerated at an angle. These results shed light into themulti-dimensional effects present in laser-plasma interactions ofrelevance to fast ignition of fusion targets and laser-driven ionacceleration in plasmas.Index Terms—Intense lasers, fast ignition, plasma-based accel-erators, three-dimensional particle-in-cell simulations.THE interaction of ultraintense laser pulses with matter hasopened the way to the exploration of highly nonlinearphysical regimes of interest for many applications such asfast ignition of fusion targets [1], [2] or compact plasmabased accelerators [3], [4]. In many of these scenarios, thelaser frequency is lower than the plasma frequency of theionized target (overcritical target) and therefore the lasercannot penetrate deep into the plasma, being reflected and/orabsorbed.The detailed study of laser absorption is crucial in order tounderstand the generation of fast electrons in these regimes.However, overcritical targets are difficult to probe experi-mentally and therefore many experimental results rely onparticle-in-cell (PIC) simulations in order to better understandlaser absorption and fast electron acceleration. Most of thesimulation studies are limited to one-dimensional (1D) [5]and two-dimensional (2D) [6] simulations, due to the needto resolve the fine temporal and spacial scales of plasmas atvery high densities.In this paper we present 3D OSIRIS [7] simulations of theinteraction of ultraintense laser pulses with overcritical targetsin order to study some of the multi-dimensional features ofF. Fiuza and L. O. Silva are with the GoLP/Instituto de Plasmas eFusa˜o Nuclear - Laborato´rio Associado, Instituto Superior Te´cnico, 1049-001Lisboa, Portugal (e-mail: frederico.fiuza@ist.utl.pt; luis.silva@ist.utl.pt).R. A. Fonseca is with the GoLP/Instituto de Plasmas e Fusa˜o Nuclear -Laborato´rio Associado, Instituto Superior Te´cnico, 1049-001 Lisboa, Portugaland also with the Departamento Cieˆncias e Tecnologias da Informac¸a˜o,Instituto Superior de Cieˆncias do Trabalho e da Empresa, 1649-026 Lisboa,Portugal.J. Tonge, J. May, and W. B. Mori are with the University of California atLos Angeles, Los Angeles, CA 90095 USA.This work was supported by Fundac¸a˜o para a Cieˆncia e Tecnologia (Por-tugal) through the Grants PTDC/FIS/66823/2006 and SFRH/BD/38952/2007,by PRACE through the project PRA030, by the European Community (HiPERproject EC FP7 no. 211737), by the NSF under Grant Nos. PHY-0078508 andPHY-0904039, and by the DOE under Contract Nos. DE-FG03-09NA22569,and under the Fusion Science Center for Matter Under Extreme Conditions.particle acceleration/laser absorption in these regimes. We usea laser pulse with an intensity of 2×1020 W/cm−2 (normalizedvector potential a0 = 12), central wavelength λ0 = 1 µm,focused to a spot size of 5 µm at the target front. Thepulse has a gaussian transverse profile and a flat-top temporalprofile with 60 fs gaussian rise time. The target consists ofa deuterium plasma with a density gradient going from thecritical density, nc, to 50 nc, scale length Lg = 2.5 µm,followed by a 30 µm region at 50 nc. The simulation boxhas a size of 50 × 30 × 30 µm3, which is resolved with1416 × 848 × 848 cells, and is run up to 500 fs. Each cellhas 8 electrons and 8 ions for a total of ∼ 15 billion particles.Fig. 1 illustrates the interaction of the laser pulse with theovercritical target after 400 fs of propagation as well as themain features of the fast electron population that is generatedduring the interaction. The laser pulse is observed to penetratethe target up to > 15 nc due to relativistic effects and tobe continuously self-focused during this process down to aspot size of ∼ 1 µm. This penetration density is consistentwith the relativistic critical density, γnc, which is ∼ 12 ncfor the initial pulse intensity. The plasma electron density ishighly distorted during the interaction. Close to the criticallayer, the density is highly modulated at the laser wavelength,and at higher densities it is expelled forming a channel. Theelectron heat flux in the forward direction is shown to exhibitan annular structure, indicating that, due to the tight focus ofthe laser, most of fast electrons are accelerated at an angle,which is consistent with experimental observations of annularpatterns at the back of a solid target after being hit by anultraintense laser pulse [8]. The plasma electron kinetic energyis maximum at the tip of the laser pulse where considerableelectron acceleration occurs.In conclusion, we have presented 3D simulations of theinteraction of ultrahigh intensity laser pulses with overcriticaltargets. Our results illustrate the importance of a detailedmulti-dimensional analysis in order to understand laser absorp-tion and the dynamics of fast electrons, which can be relevantin several scenarios, such as fast ignition of fusion targets andion acceleration in laser-solid interactions.ACKNOWLEDGMENTThe simulations presented in this paper were performed atthe Intrepid supercomputer (ANL) and at the Ju¨gene super-computer (Ju¨lich, Germany).REFERENCES[1] M. Tabak et al, ”Ignition and high gain with ultrapowerful lasers,” Phys.Plasmas, vol. 1, no. 5, pp. 1626-1634, May 1994.2Fig. 1. Interaction of an ultrahigh intensity laser pulse with an overcritical plasma slab. (top-left) The laser pulse (red-blue) hits a deuterium plasma (green)from the left-hand-side of the simulation box, accelerating electrons (spheres colored by energy from 0 to 15 MeV: blue-yellow-red). (top-right) Laser (red-blue) penetration and self-focusing in the overcritical plasma. The different isosurfaces (green) correspond to different plasma densities: nc (left plane), 5nc (middle plane), and 15 nc (right plane). (bottom-left) Electron heat-flux (violet-blue-green-red) generated by the strong laser (red-blue). The projectionscorrespond to the heat flux in the different simulation planes, illustrating the generation of an annular pattern in the laser propagation direction. (bottom-right)Plasma electron kinetic energy density (violet-blue-green-red) when hit by the laser pulse (red-blue). The projections correspond to the kinetic energy densityin the different simulation planes.[2] R. Kodama et al, ”Fast heating of ultrahigh-density plasma as a steptowards laser fusion ignition,” Nature, vol. 412, pp. 798-802, Aug. 2002.[3] T. Tajima and J. M. Dawson, ”Laser electron accelerator,” Phys. Rev.Lett., vol. 43, pp. 267-270, Jul. 1979.[4] V. Malka et al, ”Principles and applications of compact laser-plasmaaccelerators,” Nat. Phys., vol. 4, pp. 447-453, Jun. 2008.[5] A. J. Kemp, Y. Sentoku, and M. Tabak, ”Hot-electron energy couplingin ultraintense laser-matter interaction,” Phys. Rev. Lett., vol. 101, no.7, p. 075004, Aug. 2008.[6] J. Tonge et al, ”A simulation study of fast ignition with ultrahighintensity lasers,” Phys. Plasmas, vol. 16, no. 5, p. 056311, May 2009.[7] R. A. Fonseca et al, ”OSIRIS: A Three-Dimensional, Fully RelativisticParticle in Cell Code for Modeling Plasma Based Accelerators,” Lect.Notes Comp. Sci., vol. 2331, pp. 342-351, 2002.[8] P. A. Norreys et al, ”Observation of annular electron beam transport inmulti-TeraWatt laser-solid interaction,” Plasma Phys. Control. Fusion,vol. 48, no. 2, pp. L11-L22, Feb. 2006.

IEEE Transactions on Plasma Science

Three-dimensional simulations of laser-plasma interactions at ultrahigh intensities

Frederico Fiuza

Ricardo A. Fonseca

Luís O. Silva

John Tonge

Joshua May

Warren B. Mori

Crossref

Three-Dimensional Simulations of Laser–Plasma Interactions at Ultrahigh Intensities

Three-dimensional simulations of laser-plasma interactions at ultrahigh
  intensities

Three-dimensional simulations of laser-plasma interactions at ultrahigh intensities

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