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B Vauzour,
J J Santos,
A Debayle,
S Hulin,
H-P Schlenvoigt,
X Vaisseau,
D Batani,
S D Baton,
J J Honrubia,
Ph Nicolaï, [......],
M Coury,
F Dorchies,
C Fourment,
E d'Humières,
L C Jarrot,
P McKenna,
Y J Rhee, V T Tikhonchuk,
L Volpe,
V Yahia
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ABSTRACT: We present experimental and numerical results on intense-laser-pulse-produced fast electron beams transport through aluminum samples, either solid or compressed and heated by laser-induced planar shock propagation. Thanks to absolute K_{α} yield measurements and its very good agreement with results from numerical simulations, we quantify the collisional and resistive fast electron stopping powers: for electron current densities of ≈8×10^{10} A/cm^{2} they reach 1.5 keV/μm and 0.8 keV/μm, respectively. For higher current densities up to 10^{12} A/cm^{2}, numerical simulations show resistive and collisional energy losses at comparable levels. Analytical estimations predict the resistive stopping power will be kept on the level of 1 keV/μm for electron current densities of 10^{14} A/cm^{2}, representative of the full-scale conditions in the fast ignition of inertially confined fusion targets.
Physical Review Letters 12/2012; 109(25):255002. · 7.37 Impact Factor
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ABSTRACT: We demonstrate that a mm-scale free-electron laser can operate in the x-ray range, in the interaction between a moderately relativistic electron bunch, and a transverse high intensity optical lattice. The corrugated light-induced ponderomotive potential acts simultaneously as a guide and as a low-frequency wiggler, triggering stimulated Raman scattering. The gain law in the small signal regime is derived in a fluid approach, and confirmed from particle-in-cell simulations. We describe the nature of bunching, and discuss the saturation properties. The resulting all-optical Raman x-ray laser opens perspectives for ultracompact coherent light sources up to the hard x-ray range.
Physical Review Letters 12/2012; 109(24):244802. · 7.37 Impact Factor
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ABSTRACT: The effective increase of the critical density associated with the interaction of relativistically intense laser pulses with overcritical plasmas, known as self-induced transparency, is revisited for the case of circular polarization. A comparison of particle-in-cell simulations to the predictions of a relativistic cold-fluid model for the transparency threshold demonstrates that kinetic effects, such as electron heating, can lead to a substantial increase of the effective critical density compared to cold-fluid theory. These results are interpreted by a study of separatrices in the single-electron phase space corresponding to dynamics in the stationary fields predicted by the cold-fluid model. It is shown that perturbations due to electron heating exceeding a certain finite threshold can force electrons to escape into the vacuum, leading to laser pulse propagation. The modification of the transparency threshold is linked to the temporal pulse profile, through its effect on electron heating.
Physical Review E 11/2012; 86(5-2):056404. · 2.26 Impact Factor
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ABSTRACT: The effective increase of the critical density associated with the
interaction of relativistically intense laser pulses with overcritical plasmas,
known as self-induced transparency, is revisited for the case of circular
polarization. A comparison of particle-in-cell simulations to the predictions
of a relativistic cold-fluid model for the transparency threshold demonstrates
that kinetic effects, such as electron heating, can lead to a substantial
increase of the effective critical density compared to cold-fluid theory. These
results are interpreted by a study of separatrices in the single-electron phase
space corresponding to dynamics in the stationary fields predicted by the
cold-fluid model. It is shown that perturbations due to electron heating
exceeding a certain finite threshold can force electrons to escape into the
vacuum, leading to laser pulse propagation. The modification of the
transparency threshold is linked to the temporal pulse profile, through its
effect on electron heating.
09/2012;
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ABSTRACT: Radiation losses of electrons in ultraintense laser fields constitute a process that can be important for electron and ion acceleration and creation of secondary emissions. The importance of this effect for ion acceleration to high energies is studied as a function of the laser intensity and the target thickness and density. For instance, in the piston regime, radiation losses lead to a reduction of the piston velocity and to less-efficient ion acceleration. Radiation losses have been implemented in the relativistic particle-in-cell code by using a renormalized Lorentz-Abraham-Dirac model.
Physical Review E 09/2012; 86(3-2):036401. · 2.26 Impact Factor
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R H H Scott,
C Beaucourt,
H-P Schlenvoigt,
K Markey,
K L Lancaster,
C P Ridgers,
C M Brenner,
J Pasley,
R J Gray,
I O Musgrave, [......],
S D Baton,
J J Santos,
J-L Feugeas,
Ph Nicolaï,
G Malka, V T Tikhonchuk,
P McKenna,
D Neely,
S J Rose,
P A Norreys
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ABSTRACT: This Letter describes the first experimental demonstration of the guiding of a relativistic electron beam in a solid target using two colinear, relativistically intense, picosecond laser pulses. The first pulse creates a magnetic field that guides the higher-current, fast-electron beam generated by the second pulse. The effects of intensity ratio, delay, total energy, and intrinsic prepulse are examined. Thermal and Kα imaging show reduced emission size, increased peak emission, and increased total emission at delays of 4-6 ps, an intensity ratio of 10∶1 (second:first) and a total energy of 186 J. In comparison to a single, high-contrast shot, the inferred fast-electron divergence is reduced by 2.7 times, while the fast-electron current density is increased by a factor of 1.8. The enhancements are reproduced with modeling and are shown to be due to the self-generation of magnetic fields. Such a scheme could be of considerable benefit to fast-ignition inertial fusion.
Physical Review Letters 07/2012; 109(1):015001. · 7.37 Impact Factor
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ABSTRACT: The European High Power laser Energy Research (HiPER) project aims at demonstrating the feasibility of high gain inertial
confinement fusion (ICF) using the fast ignitor approach. A baseline target has been recently developed by Atzeni et al. [Phys.
Plasmas 14, 052702 (2007)]. The radiative transport have a minor effect on the peak areal density but decreased by 20% the
peak density. We have found that with 95 kJ of absorbed laser energy one can assemble the fuel with a peak density around
500 g/cm3 and a peak areal density of 1.2 g/cm2. This implies a total target gain of about 60.
The European Physical Journal Special Topics 05/2012; 175(1):83-88. · 1.56 Impact Factor
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ABSTRACT: Supersonic plasma jets are ubiquitous in astrophysics. Our study focus on the jets emanated from Herbig-Haro (HH) objects.
They have velocities of a few hundred km/s and are extending over the distances more than a parsec. Interaction of the jets
with surrounding matter produces two specific structures in the jet head: the bow shock and the Mach disk. The radiative cooling
of these shocks affects strongly the jet dynamics.
A tool to understand the physics of these jets is the laboratory experiment. A supersonic jet interaction with surrounding
plasma was studied on the PALS laser facility. Acollimated high-Z plasma jet with a velocity exceeding 400 km/s was generated
and propagated over a few millimeters length. Here we report on study the effect of radiative cooling on the head jet structure
with a 2D radiative hydrodynamic code. The simulation results demonstrated the scalability of the experimental observations
to the HH jets.
Astrophysics and Space Science 04/2012; 322(1):85-90. · 1.69 Impact Factor
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ABSTRACT: Interaction of high intensity laser pulses, (I > 1018W/cm2) with solid targets is an efficient way of production of high current relativistic electron beams (j
b
~ 10 kA/μm2). Such currents can be transported only under the condition of their charge and current neutralization by the target electrons.
This effect is highly dependent on the target conductivity. In a dielectric target, the free electrons are generated due to
the field and collisional ionization self-induced by the relativistic electrons. The ionization process is unstable and it
can lead to a beam filamentation. We demonstrate here that the electric field ionization is responsible for this instability,
and it develops on spatial scales significantly larger than the ionization front thickness.
The European Physical Journal Special Topics 04/2012; 175(1):127-132. · 1.56 Impact Factor
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ABSTRACT: Laser interactions with mass-limited targets (MLT) are studied via 2D3V relativistic electromagnetic PIC simulations. Analytical
estimates are derived to clarify the simulation results. MLT limit undesirable spread of absorbed laser energy out of the
interaction zone. MLT, such as droplets, are shown here to enhance the achievable fast ion energy significantly. For given
target dimensions, the existence is demonstrated of an optimum laser beam diameter when ion acceleration is efficient and
geometrical energy losses are still acceptable. Ion energy also depends on target geometrical form and shaped targets are
found to be preferable for high ion energy.
The European Physical Journal Special Topics 04/2012; 175(1):123-126. · 1.56 Impact Factor
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ABSTRACT: Short laser pulses at super-high intensities such as those proposed in the Extreme Light Infrastructure (ELI) project
open new prospects for efficient acceleration of ions in overdense plasmas. A simple analytical model and numerical simulations
demonstrate that pulses with intensities exceeding 1022W/cm2 may efficiently accelerate ions to high energies up to a few GeV.
Maximum ion energy and the energy spectrum of the accelerated ions can be tuned by an appropriate choice of laser pulse intensity
and duration at a given plasma density distribution.
The European Physical Journal D 04/2012; 55(2):393-398. · 1.48 Impact Factor
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ABSTRACT: Two-plasmon-decay (TPD) instability is investigated for conditions relevant for the shock-ignition (SI) scheme of inertial confinement fusion. Two-dimensional particle-in-cell simulations show that in a hot, large-scale plasma, TPD develops in concomitance with stimulated Raman scattering (SRS). It is active only during the first picosecond of interaction, and then it is rapidly saturated due to plasma cavitation. TPD-excited plasma waves extend to small wavelengths, above the standard Landau cutoff. The hot electron spectrum created by SRS and TPD is relatively soft, limited to energies below 100 keV, which should not be a danger for the fuel core preheat in the SI scenario.
Physical Review E 01/2012; 85(1 Pt 2):016403. · 2.26 Impact Factor
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S Depierreux,
C Goyon,
K Lewis,
H Bandulet,
D T Michel,
G Loisel,
V Yahia,
V Tassin,
C Stenz,
N G Borisenko, [......],
J Limpouch,
P E Masson Laborde,
P Loiseau,
M Casanova,
Ph Nicolaï,
S Hüller,
D Pesme,
C Riconda, V T Tikhonchuk,
C Labaune
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ABSTRACT: This paper presents an analysis of laser–plasma interaction risks of the shock ignition (SI) scheme and experimental results under conditions relevant to the corona of a compressed target. Experiments are performed on the LIL facility at the 10 kJ level, on the LULI 2000 facility with two beams at the kJ level and on the LULI 6-beam facility with 100 J in each beam. Different aspects of the interaction of the SI pulse are studied exploiting either the flexibility of the LULI 6-beam facility to produce a very high intensity pulse or the high energy of the LIL to produce long and hot plasmas. A continuity is found allowing us to draw some conclusions regarding the coupling quality and efficiency of the SI spike pulse. It is shown that the propagation of the SI beams in the underdense plasma present in the corona of inertial confinement fusion targets could strongly modify the initial spot size of the beam through filamentation. Detailed experimental studies of the growth and saturation of backscattering instabilities in these plasmas indicate that significant levels of stimulated scattering reflectivities (larger than 40%) may be reached at least for some time during the SI pulse.
Plasma Physics and Controlled Fusion 11/2011; 53(12):124034. · 2.42 Impact Factor
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ABSTRACT: Propagation of laser-supported ionization wave in homogeneous and porous materials with a mean density less than the critical plasma density is studied theoretically in the one-dimensional geometry. It is shown that the velocity of the ionization wave in a foam is significantly decreased in comparison with the similar wave in a homogeneous fully ionized plasma of the same density. That difference is attributed to the ionization and hydro-homogenization processes forming an under-critical density environment in the front of ionization wave. The rate of energy transfer from laser to plasma is found to be in a good agreement with available experimental data.
Physics of Plasmas 10/2011; 18(10):103114-103114-10. · 2.15 Impact Factor
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ABSTRACT: Shock ignition is an inertial confinement fusion scheme where the ignition conditions are achieved in two steps. First, the DT shell is compressed at a low implosion velocity creating a central core at a low temperature and a high density. Then, a strong spherical converging shock is launched before the fuel stagnation time. It increases the central pressure and ignites the core. It is shown in this paper that this latter phase can be described analytically by using a self-similar solution to the equations of ideal hydrodynamics. A high and uniformly distributed pressure in the hot spot can be created thus providing favorable conditions for ignition. Analytic ignition criteria are obtained that relate the areal density of the compressed core with the shock velocity. The conclusions of the analytical model are confirmed in full hydrodynamic simulations.
Physics of Plasmas 10/2011; 18(10):102702-102702-9. · 2.15 Impact Factor
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ABSTRACT: The shock ignition concept implies laser pulse intensities higher than 1015 W/cm2 (at the wavelength of 351 nm), which is the commonly accepted limit where the inverse bremsstruhlung absorption dominates. The transition from collisional to collisionless absorption in laser plasma interactions at higher intensities is studied in the present paper with the help of large scale one-dimensional particle-in-cell simulations. The initial parameters are defined by the hydrodynamic simulations corresponding to recent experiments. The simulations predict that a quasi-steady regime of laser plasma interaction is attained where the total laser energy absorption stays on the level of ∼65% in the laser intensity range 1015–1016 W/cm2. However, the relation between the collisional and collisionless processes changes significantly. This is manifested in the energy spectrum of electrons transporting the absorbed laser energy and in the spectrum of the reflected laser light.
Physics of Plasmas 08/2011; 18(8):082709-082709-12. · 2.15 Impact Factor
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ABSTRACT: We address the problem of energy dispersion of radiation pressure accelerated
(RPA) ion beams emerging from a thin (solid) target. Two different acceleration
schemes, namely phase-stable acceleration and multi-stage acceleration, are
considered by means of analytical modelling and one-dimensional
particle-in-cell simulations. Our investigations offer a deeper understanding
of RPA and allow us to derive some guidelines for generating monoenergetic ion
beams.
05/2011;
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ABSTRACT: Carbon ions are used to heat the precompressed deuterium–tritium (DT) fuel in a cone-guided fast ignitor scheme with an areal mass density of about 2.6 g cm−2. An ultra-intense laser pulse with a focal intensity of 1.45 × 1022 W cm−2 accelerates the carbon ions to an energy of 450 MeV from a homogeneous layer of 0.2 g/cm3 density, which fills the head of the gold cone. Pellet ignition was observed in hybrid numerical simulations for a laser energy of about 65 kJ in a rectangular pulse of 4 ps duration. This corresponds to estimated overall efficiencies of more than 24% for ion acceleration and 17% for core heating. Reducing the laser intensity to the value 5 × 1021 W cm−2, carbon ions with the energy of 175 MeV will be accelerated, and ignition occurred in hydrodynamic simulations for a laser energy of 115 kJ at a reduced heating efficiency of 6%. The comparison with ignition of a large-scale DT pellet, showing similar hydrodynamic characteristics and heated by in situ accelerated DT ions with 10 MeV mean energy, demonstrates the advantage of the carbon ion ignitor beam due to the more effective acceleration and expected higher directionality.
Plasma Physics and Controlled Fusion 03/2011; 53(4):045014. · 2.42 Impact Factor
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L Lancia,
M. Grech,
S Weber,
J R Marquès,
L Romagnani,
M Nakatsutsumi,
P Antici,
A. Bellue,
N. Bourgeois,
J-L Feugeas,
T Grismayer,
T. Lin,
Ph. Nicolaï,
B. Nkonga,
P Audebert,
R Kodama, V T Tikhonchuk,
J Fuchs
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ABSTRACT: Electrostatic (E) fields associated with the interaction of a
well-controlled, high-power, nanosecond laser pulse with an underdense plasma
are diagnosed by proton radiography. Using a current 3D wave propagation code
equipped with nonlinear and nonlocal hydrodynamics, we can model the measured
E-fields that are driven by the laser ponderomotive force in the region where
the laser undergoes filamentation. However, strong fields of up to 110 MV/m
measured in the first millimeter of propagation cannot be reproduced in the
simulations. This could point to the presence of unexpected strong thermal
electron pressure gradients possibly linked to ion acoustic turbulence, thus
emphasizing the need for the development of full kinetic collisional
simulations in order to properly model laser-plasma interaction in these
strongly nonlinear conditions.
01/2011;
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ABSTRACT: The dynamics of double ablation front (DAF) structures is studied for planar targets with moderate atomic number ablators. These structures are obtained in hydrodynamic simulations for various materials and laser intensities and are qualitatively characterized during the acceleration stage of the target. The importance of the radiative transport for the DAF dynamics is then demonstrated. Simulated hydrodynamic profiles are compared with a theoretical model, showing the consistency of the model and the relevant parameters for the dynamics description. The stability of DAF structures with respect to two-dimensional perturbations is studied using two different approaches: one considers the assumptions of the theoretical model and the other one a more complete physics. The numerical simulations performed with both approaches demonstrate good agreement of dispersion curves.
Physics of Plasmas 11/2010; 17(12):122701-122701-14. · 2.15 Impact Factor
