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
In an experiment carried out at the Prague Asterix Laser System at laser intensities relevant to shock ignition conditions(I>10^(16) W/cm^(2)),the heating and transport of hot electrons were studied by using severa...In an experiment carried out at the Prague Asterix Laser System at laser intensities relevant to shock ignition conditions(I>10^(16) W/cm^(2)),the heating and transport of hot electrons were studied by using several complementary diagnostics,i.e.,K_(α)time-resolved imaging,hard x-ray filtering(a bremsstrahlung cannon),and electron spectroscopy.Ablators with differing composition from low Z(parylene N)to high Z(nickel)were used in multilayer planar targets to produce plasmas with different coronal temperature and collisionality and modify the conditions of hot-electron generation.The variety of available diagnostics allowed full characterization of the population of hot electrons,retrieving their conversion efficiency,time generation and duration,temperature,and angular divergence.The obtained results are shown to be consistent with those from detailed simulations and similar inertial confinement fusion experiments.Based on the measured data,the advantages,reliability,and complementarity of the experimental diagnostics are discussed.展开更多
The coupling of ultra-intense,ultra-short laser pulses with solid targets is heavily dependent on the properties of the vacuum–solid interface and is usually quite low.However,laser absorption can be enhanced via mic...The coupling of ultra-intense,ultra-short laser pulses with solid targets is heavily dependent on the properties of the vacuum–solid interface and is usually quite low.However,laser absorption can be enhanced via micro or nanopatterning of the target surface.Depending on the laser features and target geometry,conditions can be optimized for the generation of hot dense matter,which can be used to produce high-brightness radiation sources or even to accelerate particles to relativistic energies.In this context,ZnO nanowires were grown on metallic,thin-foil targets.The use of a thin-foil substrate was dictated by the need to achieve proton acceleration via target normal sheath acceleration at the rear side.The chemical process parameters were studied in-depth to provide control over the nanowire size,shape,and distribution.Moreover,the manufacturing process was optimized to provide accurate reproducibility of key parameters in the widest possible range and good homogeneity across the entire foil area.展开更多
Fast electron generation and transport in high-intensity laser–solid interactions induces X-ray emission and drives ion acceleration.Effective production of these sources hinges on an efficient laser absorption into ...Fast electron generation and transport in high-intensity laser–solid interactions induces X-ray emission and drives ion acceleration.Effective production of these sources hinges on an efficient laser absorption into the fast electron population and control of divergence as the beam propagates through the target.Nanowire targets can be employed to increase the laser absorption,but it is not yet clear how the fast electron beam properties are modified.Here we present novel measurements of the emittance of the exiting fast electron beam from irradiated solid planar and nanowire targets via a pepper-pot diagnostic.The measurements indicate a greater fast electron emittance is obtained from nanowire targets.Two-dimensional particle-in-cell simulations support this conclusion,revealing beam defocusing at the wire–substrate boundary,a higher fast electron temperature and transverse oscillatory motion around the wires.展开更多
Laser–plasma interaction(LPI)at intensities 1015–1016 W·cm^-2 is dominated by parametric instabilities which can be responsible for a significant amount of non-collisional absorption and generate large fluxes o...Laser–plasma interaction(LPI)at intensities 1015–1016 W·cm^-2 is dominated by parametric instabilities which can be responsible for a significant amount of non-collisional absorption and generate large fluxes of high-energy nonthermal electrons.Such a regime is of paramount importance for inertial confinement fusion(ICF)and in particular for the shock ignition scheme.In this paper we report on an experiment carried out at the Prague Asterix Laser System(PALS)facility to investigate the extent and time history of stimulated Raman scattering(SRS)and two-plasmon decay(TPD)instabilities,driven by the interaction of an infrared laser pulse at an intensity^1.2×1016 W·cm^-2 with a^100μm scalelength plasma produced from irradiation of a flat plastic target.The laser pulse duration(300 ps)and the high value of plasma temperature(~4 ke V)expected from hydrodynamic simulations make these results interesting for a deeper understanding of LPI in shock ignition conditions.Experimental results show that absolute TPD/SRS,driven at a quarter of the critical density,and convective SRS,driven at lower plasma densities,are well separated in time,with absolute instabilities driven at early times of interaction and convective backward SRS emerging at the laser peak and persisting all over the tail of the pulse.Side-scattering SRS,driven at low plasma densities,is also clearly observed.Experimental results are compared to fully kinetic large-scale,two-dimensional simulations.Particle-in-cell results,beyond reproducing the framework delineated by the experimental measurements,reveal the importance of filamentation instability in ruling the onset of SRS and stimulated Brillouin scattering instabilities and confirm the crucial role of collisionless absorption in the LPI energy balance.展开更多
We report results and modelling of an experiment performed at the Target Area West Vulcan laser facility,aimed at investigating laser±plasma interaction in conditions that are of interest for the shock ignition s...We report results and modelling of an experiment performed at the Target Area West Vulcan laser facility,aimed at investigating laser±plasma interaction in conditions that are of interest for the shock ignition scheme in inertial confinement fusion(ICF),that is,laser intensity higher than 10^(16) W/cm^(2) impinging on a hot(T>1 keV),inhomogeneous and long scalelength pre-formed plasma.Measurements show a significant stimulated Raman scattering(SRS)backscattering(;%-20%of laser energy)driven at low plasma densities and no signatures of two-plasmon decay(TPD)/SRS driven at the quarter critical density region.Results are satisfactorily reproduced by an analytical model accounting for the convective SRS growth in independent laser speckles,in conditions where the reflectivity is dominated by the contribution from the most intense speckles,where SRS becomes saturated.Analytical and kinetic simulations well reproduce the onset of SRS at low plasma densities in a regime strongly affected by non-linear Landau damping and by filamentation of the most intense laser speckles.The absence of TPD/SRS at higher densities is explained by pump depletion and plasma smoothing driven by filamentation.The prevalence of laser coupling in the low-density profile justifies the low temperature measured for hot electrons(7-12 keV),which is well reproduced by numerical simulations.展开更多
Laser–plasma interaction and hot electrons have been characterized in detail in laser irradiation conditions relevant for direct-drive inertial confinement fusion.The experiment was carried out at the Gekko XII laser...Laser–plasma interaction and hot electrons have been characterized in detail in laser irradiation conditions relevant for direct-drive inertial confinement fusion.The experiment was carried out at the Gekko XII laser facility in multibeam planar target geometry at an intensity of approximately 3×10^(15)W/cm^(2).Experimental data suggest that high-energy electrons,with temperatures of 20–50 keV and conversion efficiencies ofη<1%,were mainly produced by the damping of electron plasma waves driven by two-plasmon decay(TPD).Stimulated Raman scattering(SRS)is observed in a near-threshold growth regime,producing a reflectivity of approximately 0.01%,and is well described by an analytical model accounting for the convective growth in independent speckles.The experiment reveals that both TPD and SRS are collectively driven by multiple beams,resulting in a more vigorous growth than that driven by single-beam laser intensity.展开更多
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This work was carried out within the framework of the EUROfusion Consortium,funded by the European Union via the Euratom Research and Training Programme(Grant No.101052200-EUROfusion)Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or the European Commission.Neither the European Union nor the European Commission can be held responsible for them.The involved teams have operated within the framework of the Enabling Research Project:Grant No.ENR-IFE.01.CEA“Advancing shock ignition for direct-drive inertial fusion.”The work was also supported by the Natural Sciences and Engineering Research Council of Canada(Grant No.RGPIN-2019-05013)+5 种基金The authors acknowledge support of the PALS Infrastructure within the MŠMT(MEYS)project Grant No.LM2023068Staff members of the PALS Research Center appreciate financial support(Grant No.LM2023068)from the Czech Ministry of Education,Youth and Sports facilitating operation of the PALS facilityThe work of JIHT RAS team was supported by the Ministry of Science and Higher Education of the Russian Federation(State Assignment No.075-01129-23-00)The work at NRMU MEPhI was supported by the Ministry of Science and Higher Education of the Russian Federation(Agreement No.075-15-2021-1361)This project has received funding from the CNR funded Italian research Network ELI-Italy(D.M.No.63108.08.2016)This work was funded by United Kingdom EPSRC Grants No.EP/P026796/1 and No.EP/L01663X/1.The results presented in this paper are based on work carried out between September 2018 and December 2021.
文摘In an experiment carried out at the Prague Asterix Laser System at laser intensities relevant to shock ignition conditions(I>10^(16) W/cm^(2)),the heating and transport of hot electrons were studied by using several complementary diagnostics,i.e.,K_(α)time-resolved imaging,hard x-ray filtering(a bremsstrahlung cannon),and electron spectroscopy.Ablators with differing composition from low Z(parylene N)to high Z(nickel)were used in multilayer planar targets to produce plasmas with different coronal temperature and collisionality and modify the conditions of hot-electron generation.The variety of available diagnostics allowed full characterization of the population of hot electrons,retrieving their conversion efficiency,time generation and duration,temperature,and angular divergence.The obtained results are shown to be consistent with those from detailed simulations and similar inertial confinement fusion experiments.Based on the measured data,the advantages,reliability,and complementarity of the experimental diagnostics are discussed.
文摘The coupling of ultra-intense,ultra-short laser pulses with solid targets is heavily dependent on the properties of the vacuum–solid interface and is usually quite low.However,laser absorption can be enhanced via micro or nanopatterning of the target surface.Depending on the laser features and target geometry,conditions can be optimized for the generation of hot dense matter,which can be used to produce high-brightness radiation sources or even to accelerate particles to relativistic energies.In this context,ZnO nanowires were grown on metallic,thin-foil targets.The use of a thin-foil substrate was dictated by the need to achieve proton acceleration via target normal sheath acceleration at the rear side.The chemical process parameters were studied in-depth to provide control over the nanowire size,shape,and distribution.Moreover,the manufacturing process was optimized to provide accurate reproducibility of key parameters in the widest possible range and good homogeneity across the entire foil area.
基金the NextGenerationEU(PNRR)Integrated Infrastructure Initiative in Photonic and Quantum Sciences(IPHOQS)(CUP B53C22001750006,ID D2B8D520,IR0000016)EuPRAXIA Advanced Photon Sources(EuAPS)(CUP I93C21000160006,IR0000030)+3 种基金funding from the Engineering and Physical Sciences Research Council(EP/L01663X/1)the Royal Society International Exchange(IES/R3/170248)Computing resources were provided by STFC Scientific Computing Department’s SCARF clusterfunded by the UK EPSRC(grants EP/G054950/1,EP/G056803/1,EP/G055165/1 and EP/M022463/1).
文摘Fast electron generation and transport in high-intensity laser–solid interactions induces X-ray emission and drives ion acceleration.Effective production of these sources hinges on an efficient laser absorption into the fast electron population and control of divergence as the beam propagates through the target.Nanowire targets can be employed to increase the laser absorption,but it is not yet clear how the fast electron beam properties are modified.Here we present novel measurements of the emittance of the exiting fast electron beam from irradiated solid planar and nanowire targets via a pepper-pot diagnostic.The measurements indicate a greater fast electron emittance is obtained from nanowire targets.Two-dimensional particle-in-cell simulations support this conclusion,revealing beam defocusing at the wire–substrate boundary,a higher fast electron temperature and transverse oscillatory motion around the wires.
基金financial support from the LASERLAB-EUROPE Access to Research Infrastructure activity within the ECs seventh Framework Programfunding from the Euratom research and training programme 2014–2018 under grant agreement No. 633053+4 种基金partially supported by the project ELITAS (ELI Tools for Advanced Simulation) CZ.02.1.01/0.0/0.0/16 013/0001793HIFI (High Field Initiative, CZ.02.1.01/0.0/0.0/15 003/0000449)ADONIS (Advanced research using high-intensity laser produced photons and particles, CZ.02.1.01/0.0/0.0/16 019/0000789)ELITAS (ELI Tools for Advanced Simulations,CZ.02.1.01/0.0/0.0/16 013/0001793)financial support from the Czech Ministry of Education, Youth and Sports within grants LTT17015, LM2015083, and CZ.02.1.01/0.0/0.0/16 013/0001552 (EF16 013/0001552)
文摘Laser–plasma interaction(LPI)at intensities 1015–1016 W·cm^-2 is dominated by parametric instabilities which can be responsible for a significant amount of non-collisional absorption and generate large fluxes of high-energy nonthermal electrons.Such a regime is of paramount importance for inertial confinement fusion(ICF)and in particular for the shock ignition scheme.In this paper we report on an experiment carried out at the Prague Asterix Laser System(PALS)facility to investigate the extent and time history of stimulated Raman scattering(SRS)and two-plasmon decay(TPD)instabilities,driven by the interaction of an infrared laser pulse at an intensity^1.2×1016 W·cm^-2 with a^100μm scalelength plasma produced from irradiation of a flat plastic target.The laser pulse duration(300 ps)and the high value of plasma temperature(~4 ke V)expected from hydrodynamic simulations make these results interesting for a deeper understanding of LPI in shock ignition conditions.Experimental results show that absolute TPD/SRS,driven at a quarter of the critical density,and convective SRS,driven at lower plasma densities,are well separated in time,with absolute instabilities driven at early times of interaction and convective backward SRS emerging at the laser peak and persisting all over the tail of the pulse.Side-scattering SRS,driven at low plasma densities,is also clearly observed.Experimental results are compared to fully kinetic large-scale,two-dimensional simulations.Particle-in-cell results,beyond reproducing the framework delineated by the experimental measurements,reveal the importance of filamentation instability in ruling the onset of SRS and stimulated Brillouin scattering instabilities and confirm the crucial role of collisionless absorption in the LPI energy balance.
基金financial support from the LASERLAB-EUROPE Access to Research Infrastructure activity within the EC’s seventh Framework Program(Application No.18110033)carried out within the framework of the EUROfusion Enabling research projects AWP19-20-ENR-IFE19.CEA01 and AWP21-ENR-01-CEA-02+2 种基金funding from the Euratom research and training programme 20192020 and 2021-2025 under grant No.633053financial support from the CNR-funded Italian research Network ELI-Italy(D.M.No.63108.08.2016)the Czech Ministry of Education,Youth and Sports,project LTT17015。
文摘We report results and modelling of an experiment performed at the Target Area West Vulcan laser facility,aimed at investigating laser±plasma interaction in conditions that are of interest for the shock ignition scheme in inertial confinement fusion(ICF),that is,laser intensity higher than 10^(16) W/cm^(2) impinging on a hot(T>1 keV),inhomogeneous and long scalelength pre-formed plasma.Measurements show a significant stimulated Raman scattering(SRS)backscattering(;%-20%of laser energy)driven at low plasma densities and no signatures of two-plasmon decay(TPD)/SRS driven at the quarter critical density region.Results are satisfactorily reproduced by an analytical model accounting for the convective SRS growth in independent laser speckles,in conditions where the reflectivity is dominated by the contribution from the most intense speckles,where SRS becomes saturated.Analytical and kinetic simulations well reproduce the onset of SRS at low plasma densities in a regime strongly affected by non-linear Landau damping and by filamentation of the most intense laser speckles.The absence of TPD/SRS at higher densities is explained by pump depletion and plasma smoothing driven by filamentation.The prevalence of laser coupling in the low-density profile justifies the low temperature measured for hot electrons(7-12 keV),which is well reproduced by numerical simulations.
基金This work was carried out within the framework of the EUROfusion Consortium,funded by the European Union via the Euratom Research and Training Programme(Grant Agreement No.101052200–EUROfusion)The views and opinions expressed are however those of the author(s)only and do not necessarily reflect those of the European Union or the European Commission.Neither the European Union nor the European Commission can be held responsible for them.The involved teams have operated within the framework of the Enabling Research Project:ENR-IFE.01.CEA‘Advancing shock ignition for direct-drive inertial fusion’This work was also done with the support and under the auspices of the NIFS Collaboration Research program(2021NIFS18KUGK123).
文摘Laser–plasma interaction and hot electrons have been characterized in detail in laser irradiation conditions relevant for direct-drive inertial confinement fusion.The experiment was carried out at the Gekko XII laser facility in multibeam planar target geometry at an intensity of approximately 3×10^(15)W/cm^(2).Experimental data suggest that high-energy electrons,with temperatures of 20–50 keV and conversion efficiencies ofη<1%,were mainly produced by the damping of electron plasma waves driven by two-plasmon decay(TPD).Stimulated Raman scattering(SRS)is observed in a near-threshold growth regime,producing a reflectivity of approximately 0.01%,and is well described by an analytical model accounting for the convective growth in independent speckles.The experiment reveals that both TPD and SRS are collectively driven by multiple beams,resulting in a more vigorous growth than that driven by single-beam laser intensity.
