The article contains an error regarding the electron spectra displayed in Figs.4 and 5 and the data extracted from these spectra.The measurements were made with the SESAME magnetic spectrometer,the working principle o...The article contains an error regarding the electron spectra displayed in Figs.4 and 5 and the data extracted from these spectra.The measurements were made with the SESAME magnetic spectrometer,the working principle of which is recalled in Fig.1.Specifically,a magnetic dipole is used to separate charged particles(electrons in the case of this experiment)depending on their energy,charge and mass.The deflected particles then hit an imaging plate(IP)and deposit energy in its sensitive layer.The kinetic energy of the particles can be evaluated from their impact position on the IP and their number can be inferred from the local energy deposition.展开更多
Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of supr...Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.展开更多
This article reports the first measurements of high-energy photons produced with the high-intensity PETawatt Aquitaine Laser(PETAL)laser.The experiments were performed during the commissioning of the laser.The laser h...This article reports the first measurements of high-energy photons produced with the high-intensity PETawatt Aquitaine Laser(PETAL)laser.The experiments were performed during the commissioning of the laser.The laser had an energy of about 400 J,an intensity of 8×10^(18)W cm^(−2),and a pulse duration of 660 fs(FWHM).It was shot at a 2 mm-thick solid tungsten target.The high-energy photons were produced mainly from the bremsstrahlung process for relativistic electrons accelerated inside a plasma generated on the front side of the target.This paper reports measurements of electrons,protons and photons.Hot electrons up to35 MeV with a few-MeV temperature were recorded by a spectrometer,called SESAME(SpectreÉlectronS Angulaire MoyenneÉnergie).K-and L-shells were clearly detected by a photon spectrometer called SPECTIX(Spectromètre PetalàCristal en TransmIssion pour le rayonnnement X).High-energy photons were diagnosed by CRACC-X(Cassette de RAdiographie Centre Chambre-rayonnement X),a bremsstrahlung cannon.Bremsstrahlung cannon analysis is strongly dependent on the hypothesis adopted for the spectral shape.Different shapes can exhibit similar reproductions of the experimental data.To eliminate dependence on the shape hypothesis and to facilitate analysis of the data,simulations of the interaction were performed.To model the mechanisms involved,a simulation chain including hydrodynamic,particle-in-cell,and Monte Carlo simulations was used.The simulations model the preplasma generated at the front of the target by the PETAL laser prepulse,the acceleration of electrons inside the plasma,the generation of MeV-range photons from these electrons,and the response of the detector impacted by the energetic photon beam.All this work enabled reproduction of the experimental data.The high-energy photons produced have a large emission angle and an exponential distribution shape.In addition to the analysis of the photon spectra,positron production was also investigated.Indeed,if high-energy photons are generated inside the solid target,some positron/electron pairs may be produced by the Bethe–Heitler process.Therefore,the positron production achievable within the PETAL laser facility was quantified.To conclude the study,the possibility of creating electron/positron pairs through the linear Breit–Wheeler process with PETAL was investigated.展开更多
The high-energy petawatt PETAL laser system was commissioned at CEA’s Laser M´egajoule facility during the 2017–2018 period.This paper reports in detail on the first experimental results obtained at PETAL on en...The high-energy petawatt PETAL laser system was commissioned at CEA’s Laser M´egajoule facility during the 2017–2018 period.This paper reports in detail on the first experimental results obtained at PETAL on energetic particle and photon generation from solid foil targets,with special emphasis on proton acceleration.Despite a moderately relativistic(<1019 W/cm^(2))laser intensity,proton energies as high as 51 MeV have been measured significantly above those expected from preliminary numerical simulations using idealized interaction conditions.Multidimensional hydrodynamic and kinetic simulations,taking into account the actual laser parameters,show the importance of the energetic electron production in the extended low-density preplasma created by the laser pedestal.This hot-electron generation occurs through two main pathways:(i)stimulated backscattering of the incoming laser light,triggering stochastic electron heating in the resulting counterpropagating laser beams;(ii)laser filamentation,leading to local intensifications of the laser field and plasma channeling,both of which tend to boost the electron acceleration.Moreover,owing to the large(∼100μm)waist and picosecond duration of the PETAL beam,the hot electrons can sustain a high electrostatic field at the target rear side for an extended period,thus enabling efficient target normal sheath acceleration of the rear-side protons.The particle distributions predicted by our numerical simulations are consistent with the measurements.展开更多
Laser-driven neutron sources could offer a promising alternative to those based on conventional accelerator technologies in delivering compact beams of high brightness and short duration.We examine this through partic...Laser-driven neutron sources could offer a promising alternative to those based on conventional accelerator technologies in delivering compact beams of high brightness and short duration.We examine this through particle-in-cell and Monte Carlo simulations that model,respectively,the laser acceleration of protons from thin-foil targets and their subsequent conversion into neutrons in secondary lead targets.Laser parameters relevant to the 0.5 PW LMJ-PETAL and 0.6–6 PW Apollon systems are considered.Owing to its high intensity,the 20-fs-duration 0.6 PW Apollon laser is expected to accelerate protons up to above 100MeV,thereby unlocking efficient neutron generation via spallation reactions.As a result,despite a 30-fold lower pulse energy than the LMJ-PETAL laser,the 0.6 PW Apollon laser should perform comparably well both in terms of neutron yield and flux.Notably,we predict that very compact neutron pulses,of∼10 ps duration and∼100μm spot size,can be released provided the lead convertor target is thin enough(∼100μm).These sources are characterized by extreme fluxes,of the order of 10^(23) n cm^(−2) s^(−1),and even ten times higher when using the 6 PW Apollon laser.Such values surpass those currently achievable at large-scale accelerator-based neutron sources(∼10^(16) n cm^(−2) s^(−1)),or reported from previous laser experiments using low-Z converters(∼10^(18) n cm^(−2) s^(−1)).By showing that such laser systems can produce neutron pulses significantly brighter than existing sources,our findings open a path toward attractive novel applications,such as flash neutron radiography and laboratory studies of heavy-ion nucleosynthesis.展开更多
We propose a semi-analytical modeling of smoothed laser beam deviation induced by plasma flows.Based on a Gaussian description of speckles,the model includes spatial,temporal,and polarization smoothing techniques,thro...We propose a semi-analytical modeling of smoothed laser beam deviation induced by plasma flows.Based on a Gaussian description of speckles,the model includes spatial,temporal,and polarization smoothing techniques,through fits coming from hydrodynamic simulations with a paraxial description of electromagnetic waves.This beam bending model is then incorporated into a ray tracing algorithm and carefully validated.When applied as a post-process to the propagation of the inner cone in a full-scale simulation of a National Ignition Facility(NIF)experiment,the beam bending along the path of the laser affects the refraction conditions inside the hohlraum and the energy deposition,and could explain some anomalous refraction measurements,namely,the so-called glint observed in some NIF experiments.展开更多
文摘The article contains an error regarding the electron spectra displayed in Figs.4 and 5 and the data extracted from these spectra.The measurements were made with the SESAME magnetic spectrometer,the working principle of which is recalled in Fig.1.Specifically,a magnetic dipole is used to separate charged particles(electrons in the case of this experiment)depending on their energy,charge and mass.The deflected particles then hit an imaging plate(IP)and deposit energy in its sensitive layer.The kinetic energy of the particles can be evaluated from their impact position on the IP and their number can be inferred from the local energy deposition.
基金financial support from the LASERLAB-EUROPE Access to Research Infrastructure Activity (Application No. 23068)carried out within the framework of EUROfusion Enabling Research Projects AWP21-ENR-01-CEA02 and AWP24-ENR-IFE-02-CEA-02+3 种基金received funding from Euratom Research and Training Programme 2021–2025 under Grant No. 633053supported by the Ministry of Youth and Sports of the Czech Republic [Project No. LM2023068 (PALS RI)]by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDA25030200 and XDA25010100)supported by COST (European Cooperation in Science and Technology) through Action CA21128 PROBONO (PROton BOron Nuclear Fusion: from energy production to medical applicatiOns)
文摘Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.
基金support by GENCI France through awarding us access to HPC resources at TGCC/CCRT(Grant Nos.A0110512943 and A0130512943)funded by the French Agence Nationale de la Recherche under Grant No.ANR-10-EQPX-42-01funded by the LabEx LAPHIA of the University of Bordeaux under Grant No.ANR-10-IDEX-03-02.
文摘This article reports the first measurements of high-energy photons produced with the high-intensity PETawatt Aquitaine Laser(PETAL)laser.The experiments were performed during the commissioning of the laser.The laser had an energy of about 400 J,an intensity of 8×10^(18)W cm^(−2),and a pulse duration of 660 fs(FWHM).It was shot at a 2 mm-thick solid tungsten target.The high-energy photons were produced mainly from the bremsstrahlung process for relativistic electrons accelerated inside a plasma generated on the front side of the target.This paper reports measurements of electrons,protons and photons.Hot electrons up to35 MeV with a few-MeV temperature were recorded by a spectrometer,called SESAME(SpectreÉlectronS Angulaire MoyenneÉnergie).K-and L-shells were clearly detected by a photon spectrometer called SPECTIX(Spectromètre PetalàCristal en TransmIssion pour le rayonnnement X).High-energy photons were diagnosed by CRACC-X(Cassette de RAdiographie Centre Chambre-rayonnement X),a bremsstrahlung cannon.Bremsstrahlung cannon analysis is strongly dependent on the hypothesis adopted for the spectral shape.Different shapes can exhibit similar reproductions of the experimental data.To eliminate dependence on the shape hypothesis and to facilitate analysis of the data,simulations of the interaction were performed.To model the mechanisms involved,a simulation chain including hydrodynamic,particle-in-cell,and Monte Carlo simulations was used.The simulations model the preplasma generated at the front of the target by the PETAL laser prepulse,the acceleration of electrons inside the plasma,the generation of MeV-range photons from these electrons,and the response of the detector impacted by the energetic photon beam.All this work enabled reproduction of the experimental data.The high-energy photons produced have a large emission angle and an exponential distribution shape.In addition to the analysis of the photon spectra,positron production was also investigated.Indeed,if high-energy photons are generated inside the solid target,some positron/electron pairs may be produced by the Bethe–Heitler process.Therefore,the positron production achievable within the PETAL laser facility was quantified.To conclude the study,the possibility of creating electron/positron pairs through the linear Breit–Wheeler process with PETAL was investigated.
基金funding from the Conseil Regional d’Aquitaine,the French Ministry of Research,and the European Unionfunded by the French Agence Nationale de la Recherche under Grant No.ANR-10-EQPX-42-01+1 种基金funded by the LabEx LAPHIA of the University of Bordeaux under Grant No.ANR-10-IDEX-03-02supported by Association Lasers et Plasmas and by the CEA。
文摘The high-energy petawatt PETAL laser system was commissioned at CEA’s Laser M´egajoule facility during the 2017–2018 period.This paper reports in detail on the first experimental results obtained at PETAL on energetic particle and photon generation from solid foil targets,with special emphasis on proton acceleration.Despite a moderately relativistic(<1019 W/cm^(2))laser intensity,proton energies as high as 51 MeV have been measured significantly above those expected from preliminary numerical simulations using idealized interaction conditions.Multidimensional hydrodynamic and kinetic simulations,taking into account the actual laser parameters,show the importance of the energetic electron production in the extended low-density preplasma created by the laser pedestal.This hot-electron generation occurs through two main pathways:(i)stimulated backscattering of the incoming laser light,triggering stochastic electron heating in the resulting counterpropagating laser beams;(ii)laser filamentation,leading to local intensifications of the laser field and plasma channeling,both of which tend to boost the electron acceleration.Moreover,owing to the large(∼100μm)waist and picosecond duration of the PETAL beam,the hot electrons can sustain a high electrostatic field at the target rear side for an extended period,thus enabling efficient target normal sheath acceleration of the rear-side protons.The particle distributions predicted by our numerical simulations are consistent with the measurements.
基金This work was supported by the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(Grant Agreement No.787539)It was also supported by Grant No.ANR-17-CE30-0026-Pinnacle from the Agence Nationale de la Recherche+6 种基金We acknowledge GENCI,France,for granting us access to HPC resources at TGCC/CCRT(Allocation No.A0010506129)S.N.C.acknowledges support from the Extreme Light Infrastructure Nuclear Physics(ELI-NP)Phase II,a project co-financed by the Romanian Government and the European Union through the European Regional Development Fund-the Competitiveness Operational Programme(1/07 July 2016,COP,ID 1334)by the project ELI-RO-2020-23 funded by IFA(Romania)The PETAL laser was designed and constructed by CEA under the financial auspices of the Conseil Régional d’Aquitaine,the French Ministry of Research,and the European UnionThe CRACC diagnostic was designed and commissioned on the LMJ-PETAL facility as a result of the PETAL+project coordinated by University of Bordeaux and funded by the French Agence Nationale de la Recherche under Grant No.ANR-10-EQPX-42-01The LMJ-PETAL experiment presented in this article was supported by the Association Lasers et Plasmas and by CEAThe diagnostics used in the experiment have been realized in the framework of the EquipEx PETAL+via Contract No.ANR-10-EQPX-0048.
文摘Laser-driven neutron sources could offer a promising alternative to those based on conventional accelerator technologies in delivering compact beams of high brightness and short duration.We examine this through particle-in-cell and Monte Carlo simulations that model,respectively,the laser acceleration of protons from thin-foil targets and their subsequent conversion into neutrons in secondary lead targets.Laser parameters relevant to the 0.5 PW LMJ-PETAL and 0.6–6 PW Apollon systems are considered.Owing to its high intensity,the 20-fs-duration 0.6 PW Apollon laser is expected to accelerate protons up to above 100MeV,thereby unlocking efficient neutron generation via spallation reactions.As a result,despite a 30-fold lower pulse energy than the LMJ-PETAL laser,the 0.6 PW Apollon laser should perform comparably well both in terms of neutron yield and flux.Notably,we predict that very compact neutron pulses,of∼10 ps duration and∼100μm spot size,can be released provided the lead convertor target is thin enough(∼100μm).These sources are characterized by extreme fluxes,of the order of 10^(23) n cm^(−2) s^(−1),and even ten times higher when using the 6 PW Apollon laser.Such values surpass those currently achievable at large-scale accelerator-based neutron sources(∼10^(16) n cm^(−2) s^(−1)),or reported from previous laser experiments using low-Z converters(∼10^(18) n cm^(−2) s^(−1)).By showing that such laser systems can produce neutron pulses significantly brighter than existing sources,our findings open a path toward attractive novel applications,such as flash neutron radiography and laboratory studies of heavy-ion nucleosynthesis.
文摘We propose a semi-analytical modeling of smoothed laser beam deviation induced by plasma flows.Based on a Gaussian description of speckles,the model includes spatial,temporal,and polarization smoothing techniques,through fits coming from hydrodynamic simulations with a paraxial description of electromagnetic waves.This beam bending model is then incorporated into a ray tracing algorithm and carefully validated.When applied as a post-process to the propagation of the inner cone in a full-scale simulation of a National Ignition Facility(NIF)experiment,the beam bending along the path of the laser affects the refraction conditions inside the hohlraum and the energy deposition,and could explain some anomalous refraction measurements,namely,the so-called glint observed in some NIF experiments.
