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
X-ray absorption spectroscopy is a well-accepted diagnostic for experimental studies of warm dense matter.It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in the ...X-ray absorption spectroscopy is a well-accepted diagnostic for experimental studies of warm dense matter.It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in the spectral range of interest.In the present work,we discuss how to choose an optimum material and thickness to get a bright source in the wavelength range 2A–6A(∼2 keV to 6 keV)by considering relatively low-Z elements.We demonstrate that the highest emissivity of solid aluminum and silicon foil targets irradiated with a 1-ps high-contrast sub-kJ laser pulse is achieved when the target thickness is close to 10μm.An outer plastic layer can increase the emissivity even further.展开更多
Direct laser acceleration(DLA)of electrons in a plasma of near-critical electron density(NCD)and the associated synchrotron-like radiation are discussed for moderate relativistic laser intensity(normalized laser ampli...Direct laser acceleration(DLA)of electrons in a plasma of near-critical electron density(NCD)and the associated synchrotron-like radiation are discussed for moderate relativistic laser intensity(normalized laser amplitude a0≤4.3)and ps length pulse.This regime is typical of kJ PW-class laser facilities designed for high-energy-density(HED)research.In experiments at the PHELIX facility,it has been demonstrated that interaction of a 1019 W/cm2 sub-ps laser pulse with a sub-mm length NCD plasma results in the generation of high-current well-directed superponderomotive electrons with an effective temperature ten times higher than the ponderomotive potential[Rosmej et al.,Plasma Phys.Controlled Fusion 62,115024(2020)].Three-dimensional particle-in-cell simulations provide good agreement with the measured electron energy distribution and are used in the current work to study synchrotron radiation from the DLA-accelerated electrons.The resulting x-ray spectrum with a critical energy of 5 keV reveals an ultrahigh photon number of 731011 in the 1–30 keV photon energy range at the focused laser energy of 20 J.Numerical simulations of betatron x-ray phase contrast imaging based on the DLA process for the parameters of a PHELIX laser are presented.The results are of interest for applications in HED experiments,which require a ps x-ray pulse and a high photon flux.展开更多
Proton radiography has proved increasingly successful as a diagnostic for electric and magnetic fields in high-energy-density physics experiments.Most experiments use target-normal sheath acceleration sources with a w...Proton radiography has proved increasingly successful as a diagnostic for electric and magnetic fields in high-energy-density physics experiments.Most experiments use target-normal sheath acceleration sources with a wide energy range in the proton beam,since the velocity spread can help differentiate between electric and magnetic fields and provide time histories in a single shot.However,in magnetized plasma experiments with strong background fields,the broadband proton spectrum leads to velocity-spread-dependent displacement of the beam and significant blurring of the radiograph.We describe the origins of this blurring and show how it can be removed from experimental measurements,and we outline the conditions under which such deconvolutions are successful.As an example,we apply this method to a magnetized plasma experiment that used a background magnetic field of 3 T and in which the strong displacement and energy spread of the proton beam reduced the spatial resolution from tens of micrometers to a few millimeters.Application of the deconvolution procedure accurately recovers radiographs with resolutions better than 100μm,enabling the recovery of more accurate estimates of the path-integrated magnetic field.This work extends accurate proton radiography to a class of experiments with significant background magnetic fields,particularly those experiments with an applied external magnetic field.展开更多
Fourier transform infrared spectroscopy(FTIR)is one of the most widely used vibrational diagnostic techniques to investigate gas-phase reactive oxygen and nitrogen species(RONS).However,the technique carries intrinsic...Fourier transform infrared spectroscopy(FTIR)is one of the most widely used vibrational diagnostic techniques to investigate gas-phase reactive oxygen and nitrogen species(RONS).However,the technique carries intrinsic challenges,particularly in relation to interfering peaks in the spectral data.This study explores the interfacial processes that occur when reactive oxygen and nitrogen species generated by a non-equilibrium air plasma interact with the metal halide windows of an FTIR gas cell,leading to the appearance and evolution of spurious absorption peaks which complicate spectral interpretation.Raman spectroscopy,X-ray photoelectron spectroscopy,time of flight secondary ion mass spectrometry and attenuated total reflectance-FTIR spectroscopy were used to elucidate the origin of spurious absorption peaks spanning the 1400-1300 cm^(-1)spectral range as a result of KBr exposure to plasma generated species.It was found that plasma exposed KBr contained a lower atomic fraction of Br which was replaced by the NO3nitrate group,the main absorbance peak of which progressively evolved with plasma exposure and affected the window transparency over the corresponding FTIR region.A correlation was revealed between KNO_(3)formation,plasma power and exposure time to a growth and change in molecular vibrational energies corresponding to asymmetric NO3stretching vibrations in the KNO_(3)structure.展开更多
The spatial-intensity profile of light reflected during the interaction of an intense laser pulse with a microstructured target is investigated experimentally and the potential to apply this as a diagnostic of the int...The spatial-intensity profile of light reflected during the interaction of an intense laser pulse with a microstructured target is investigated experimentally and the potential to apply this as a diagnostic of the interaction physics is explored numerically. Diffraction and speckle patterns are measured in the specularly reflected light in the cases of targets with regular groove and needle-like structures, respectively, highlighting the potential to use this as a diagnostic of the evolving plasma surface. It is shown, via ray-tracing and numerical modelling, that for a laser focal spot diameter smaller than the periodicity of the target structure, the reflected light patterns can potentially be used to diagnose the degree of plasma expansion, and by extension the local plasma temperature, at the focus of the intense laser light. The reflected patterns could also be used to diagnose the size of the laser focal spot during a high-intensity interaction when using a regular structure with known spacing.展开更多
The Erasmus Plus programme’Innovative Education and Training in high power laser plasmas’,otherwise known as PowerLaPs,is described.The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre...The Erasmus Plus programme’Innovative Education and Training in high power laser plasmas’,otherwise known as PowerLaPs,is described.The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme where teaching takes place in five separate institutes with a range of different aims and styles of delivery.The ’in class’ time is limited to four weeks a year,and the programme spans two years.PowerLaPs aims to train students from across Europe in theoretical,applied and laboratory skills relevant to the pursuit of research in laserplasma interaction physics and inertial confinement fusion(ICF).Lectures are intermingled with laboratory sessions and continuous assessment activities.The programme,which is led by workers from the Technological Educational Institute(TEI)of Crete,and supported by co-workers from the Queen’s University Belfast,the University of Bordeaux,the Czech Technical-University in Prague,Ecole Polytechnique,the University of Ioannina,the University of Salamanca and the University of York,has just completed its first year.Thus far three Learning Teaching Training(LTT)activities have been held,at the Queen’s University Belfast,the University of Bordeaux and the Centre for Plasma Physics and Lasers(CPPL)of TEI Crete.The last of these was a two-week long Intensive Programme(IP),while the activities at the other two universities were each five days in length.Thus far work has concentrated upon training in both theoretical and experimental work in plasma physics,high power laser-matter interactions and high energy density physics.The nature of the programme will be described in detail and some metrics relating to the activities carried out to date will be presented.展开更多
The second and final year of the Erasmus Plus programme’Innovative Education and Training in high power laser plasmas’,otherwise known as PowerLaPs,is described.The PowerLaPs programme employs an innovative paradigm...The second and final year of the Erasmus Plus programme’Innovative Education and Training in high power laser plasmas’,otherwise known as PowerLaPs,is described.The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme,where teaching takes place in five separate institutes with a range of different aims and styles of delivery.The’in-class’time is limited to 4 weeks a year,and the programme spans 2 years.PowerLaPs aims to train students from across Europe in theoretical,applied and laboratory skills relevant to the pursuit of research in laser plasma interaction physics and inertial confinement fusion.Lectures are intermingled with laboratory sessions and continuous assessment activities.The programme,which is led by workers from the Hellenic Mediterranean University and supported by co-workers from the Queen’s University Belfast,the University of Bordeaux,the Czech Technical University in Prague,Ecole Polytechnique,the University of Ioannina,the University of Salamanca and the University of York,has just finished its second and final year.Six Learning Teaching Training activities have been held at the Queen’s University Belfast,the University of Bordeaux,the Czech Technical University,the University of Salamanca and the Institute of Plasma Physics and Lasers of the Hellenic Mediterranean University.The last of these institutes hosted two 2-week-long Intensive Programmes,while the activities at the other four universities were each 5 days in length.In addition,a’Multiplier Event’was held at the University of Ioannina,which will be briefly described.In this second year,the work has concentrated on training in both experimental diagnostics and simulation techniques appropriate to the study of plasma physics,high power laser matter interactions and high energy density physics.The nature of the programme will be described in detail,and some metrics relating to the activities carried out will be presented.In particular,this paper will focus on the overall assessment of the programme.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
A machine learning model was created to predict the electron spectrum generated by a GeV-class laser wakefield accelerator.The model was constructed from variational convolutional neural networks,which mapped the resu...A machine learning model was created to predict the electron spectrum generated by a GeV-class laser wakefield accelerator.The model was constructed from variational convolutional neural networks,which mapped the results of secondary laser and plasma diagnostics to the generated electron spectrum.An ensemble of trained networks was used to predict the electron spectrum and to provide an estimation of the uncertainty of that prediction.It is anticipated that this approach will be useful for inferring the electron spectrum prior to undergoing any process that can alter or destroy the beam.In addition,the model provides insight into the scaling of electron beam properties due to stochastic fluctuations in the laser energy and plasma electron density.展开更多
A multichannel calorimeter system is designed and constructed which is capable of delivering single-shot and broadband spectral measurement of terahertz(THz) radiation generated in intense laser–plasma interactions. ...A multichannel calorimeter system is designed and constructed which is capable of delivering single-shot and broadband spectral measurement of terahertz(THz) radiation generated in intense laser–plasma interactions. The generation mechanism of backward THz radiation(BTR) is studied by using the multichannel calorimeter system in an intense picosecond laser–solid interaction experiment. The dependence of the BTR energy and spectrum on laser energy, target thickness and pre-plasma scale length is obtained. These results indicate that coherent transition radiation is responsible for the low-frequency component(<1 THz) of BTR. It is also observed that a large-scale pre-plasma primarily enhances the high-frequency component(>3 THz) of BTR.展开更多
Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot...Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.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
This paper provides an up-to-date review of the problems related to the generation,detection and mitigation of strong electromagnetic pulses created in the interaction of high-power,high-energy laser pulses with diffe...This paper provides an up-to-date review of the problems related to the generation,detection and mitigation of strong electromagnetic pulses created in the interaction of high-power,high-energy laser pulses with different types of solid targets.It includes new experimental data obtained independently at several international laboratories.The mechanisms of electromagnetic field generation are analyzed and considered as a function of the intensity and the spectral range of emissions they produce.The major emphasis is put on the GHz frequency domain,which is the most damaging for electronics and may have important applications.The physics of electromagnetic emissions in other spectral domains,in particular THz and MHz,is also discussed.The theoretical models and numerical simulations are compared with the results of experimental measurements,with special attention to the methodology of measurements and complementary diagnostics.Understanding the underlying physical processes is the basis for developing techniques to mitigate the electromagnetic threat and to harness electromagnetic emissions,which may have promising applications.展开更多
A developing application of laser-driven currents is the generation of magnetic fields of picosecond-nanosecond duration with magnitudes exceeding B=10 T.Single-loop and helical coil targets can direct laser-driven di...A developing application of laser-driven currents is the generation of magnetic fields of picosecond-nanosecond duration with magnitudes exceeding B=10 T.Single-loop and helical coil targets can direct laser-driven discharge currents along wires to generate spatially uniform,quasi-static magnetic fields on the millimetre scale.Here,we present proton deflectometry across two axes of a single-loop coil ranging from 1 to 2 mm in diameter.Comparison with proton tracking simulations shows that measured magnetic fields are the result of kiloampere currents in the coil and electric charges distributed around the coil target.Using this dual-axis platform for proton deflectometry,robust measurements can be made of the evolution of magnetic fields in a capacitor coil target.展开更多
X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and appli...X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5 × 10^(20) and 2.5 × 10^(20) W∕cm^2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.展开更多
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.
基金The study was supported financially by the Russian Foundation for Basic Research(Grant No.20-02-00790)the Joint Institute for High Temperatures of the Russian Academy of Sciences(Topic Grant No.01201357846)The UK team received financial support from the Engineering and Physical Sciences Research Council(Grant Nos.EP/L01663X/1 and EP/H012605/1).
文摘X-ray absorption spectroscopy is a well-accepted diagnostic for experimental studies of warm dense matter.It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in the spectral range of interest.In the present work,we discuss how to choose an optimum material and thickness to get a bright source in the wavelength range 2A–6A(∼2 keV to 6 keV)by considering relatively low-Z elements.We demonstrate that the highest emissivity of solid aluminum and silicon foil targets irradiated with a 1-ps high-contrast sub-kJ laser pulse is achieved when the target thickness is close to 10μm.An outer plastic layer can increase the emissivity even further.
基金the DFG(Project No.PU 213/9),EPSRC Grant No.EP/P026796/1the Ministry of Science and Higher Education of the Russian Federation(Agreement with Joint Institute for High Temperatures RAS No 075-15-2020-785,dated September 23,2020).
文摘Direct laser acceleration(DLA)of electrons in a plasma of near-critical electron density(NCD)and the associated synchrotron-like radiation are discussed for moderate relativistic laser intensity(normalized laser amplitude a0≤4.3)and ps length pulse.This regime is typical of kJ PW-class laser facilities designed for high-energy-density(HED)research.In experiments at the PHELIX facility,it has been demonstrated that interaction of a 1019 W/cm2 sub-ps laser pulse with a sub-mm length NCD plasma results in the generation of high-current well-directed superponderomotive electrons with an effective temperature ten times higher than the ponderomotive potential[Rosmej et al.,Plasma Phys.Controlled Fusion 62,115024(2020)].Three-dimensional particle-in-cell simulations provide good agreement with the measured electron energy distribution and are used in the current work to study synchrotron radiation from the DLA-accelerated electrons.The resulting x-ray spectrum with a critical energy of 5 keV reveals an ultrahigh photon number of 731011 in the 1–30 keV photon energy range at the focused laser energy of 20 J.Numerical simulations of betatron x-ray phase contrast imaging based on the DLA process for the parameters of a PHELIX laser are presented.The results are of interest for applications in HED experiments,which require a ps x-ray pulse and a high photon flux.
基金the support of LLNL Academic Partnerships(Grant No.B618488)EUROfusion Enabling Research Grant Nos.AWP17-ENR-IFE-CCFE-01 and AWP17-ENR-IFECEA-02,and UK EPSRC Grant Nos.EP/P026796/1 and EP/R029148/1.
文摘Proton radiography has proved increasingly successful as a diagnostic for electric and magnetic fields in high-energy-density physics experiments.Most experiments use target-normal sheath acceleration sources with a wide energy range in the proton beam,since the velocity spread can help differentiate between electric and magnetic fields and provide time histories in a single shot.However,in magnetized plasma experiments with strong background fields,the broadband proton spectrum leads to velocity-spread-dependent displacement of the beam and significant blurring of the radiograph.We describe the origins of this blurring and show how it can be removed from experimental measurements,and we outline the conditions under which such deconvolutions are successful.As an example,we apply this method to a magnetized plasma experiment that used a background magnetic field of 3 T and in which the strong displacement and energy spread of the proton beam reduced the spatial resolution from tens of micrometers to a few millimeters.Application of the deconvolution procedure accurately recovers radiographs with resolutions better than 100μm,enabling the recovery of more accurate estimates of the path-integrated magnetic field.This work extends accurate proton radiography to a class of experiments with significant background magnetic fields,particularly those experiments with an applied external magnetic field.
基金financial support from the Public Agency for Research Activity of the Republic of Slovenia(awards J2-4490,J2-4451 and L2-4481)the UK Engineering and Physical Sciences Research Council(EPSRC)(awards EP/S025790/1 and EP/N021347/1)NATO(award G5814)
文摘Fourier transform infrared spectroscopy(FTIR)is one of the most widely used vibrational diagnostic techniques to investigate gas-phase reactive oxygen and nitrogen species(RONS).However,the technique carries intrinsic challenges,particularly in relation to interfering peaks in the spectral data.This study explores the interfacial processes that occur when reactive oxygen and nitrogen species generated by a non-equilibrium air plasma interact with the metal halide windows of an FTIR gas cell,leading to the appearance and evolution of spurious absorption peaks which complicate spectral interpretation.Raman spectroscopy,X-ray photoelectron spectroscopy,time of flight secondary ion mass spectrometry and attenuated total reflectance-FTIR spectroscopy were used to elucidate the origin of spurious absorption peaks spanning the 1400-1300 cm^(-1)spectral range as a result of KBr exposure to plasma generated species.It was found that plasma exposed KBr contained a lower atomic fraction of Br which was replaced by the NO3nitrate group,the main absorbance peak of which progressively evolved with plasma exposure and affected the window transparency over the corresponding FTIR region.A correlation was revealed between KNO_(3)formation,plasma power and exposure time to a growth and change in molecular vibrational energies corresponding to asymmetric NO3stretching vibrations in the KNO_(3)structure.
基金financially supported by EPSRC(grant numbers EP/R006202/1 and EP/K022415/1)the European Union Horizon 2020 research and innovation programme under grant agreement number 654148 Laserlab-Europe
文摘The spatial-intensity profile of light reflected during the interaction of an intense laser pulse with a microstructured target is investigated experimentally and the potential to apply this as a diagnostic of the interaction physics is explored numerically. Diffraction and speckle patterns are measured in the specularly reflected light in the cases of targets with regular groove and needle-like structures, respectively, highlighting the potential to use this as a diagnostic of the evolving plasma surface. It is shown, via ray-tracing and numerical modelling, that for a laser focal spot diameter smaller than the periodicity of the target structure, the reflected light patterns can potentially be used to diagnose the degree of plasma expansion, and by extension the local plasma temperature, at the focus of the intense laser light. The reflected patterns could also be used to diagnose the size of the laser focal spot during a high-intensity interaction when using a regular structure with known spacing.
基金financial support of the Erasmus Plus scheme and the IKY/Erasmus+Hellenic National Agency
文摘The Erasmus Plus programme’Innovative Education and Training in high power laser plasmas’,otherwise known as PowerLaPs,is described.The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme where teaching takes place in five separate institutes with a range of different aims and styles of delivery.The ’in class’ time is limited to four weeks a year,and the programme spans two years.PowerLaPs aims to train students from across Europe in theoretical,applied and laboratory skills relevant to the pursuit of research in laserplasma interaction physics and inertial confinement fusion(ICF).Lectures are intermingled with laboratory sessions and continuous assessment activities.The programme,which is led by workers from the Technological Educational Institute(TEI)of Crete,and supported by co-workers from the Queen’s University Belfast,the University of Bordeaux,the Czech Technical-University in Prague,Ecole Polytechnique,the University of Ioannina,the University of Salamanca and the University of York,has just completed its first year.Thus far three Learning Teaching Training(LTT)activities have been held,at the Queen’s University Belfast,the University of Bordeaux and the Centre for Plasma Physics and Lasers(CPPL)of TEI Crete.The last of these was a two-week long Intensive Programme(IP),while the activities at the other two universities were each five days in length.Thus far work has concentrated upon training in both theoretical and experimental work in plasma physics,high power laser-matter interactions and high energy density physics.The nature of the programme will be described in detail and some metrics relating to the activities carried out to date will be presented.
基金the financial support of the Erasmus Plus and the IKY/Erasmus+Hellenic National Agencythe support of the administrative teams of the universities involved in PowerLaPs+3 种基金support by computational time granted from the Greek Research and Technology Network(GRNET)in the National HPC facility ARIS under project ID pr007020 LaMIPlaS-IIsupport by‘ELILASERLAB Europe Synergy,HiPER and IPERION-CH.gr’(MIS 5002735),which is implemented under the Action‘Reinforcement of the Research and Innovation Infrastructure’funded by the Operational Programme‘Competitiveness,Entrepreneurship and Innovation’(NSRF 2014-2020)co-financed by Greece and the European Union(European Regional Development Fund)。
文摘The second and final year of the Erasmus Plus programme’Innovative Education and Training in high power laser plasmas’,otherwise known as PowerLaPs,is described.The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme,where teaching takes place in five separate institutes with a range of different aims and styles of delivery.The’in-class’time is limited to 4 weeks a year,and the programme spans 2 years.PowerLaPs aims to train students from across Europe in theoretical,applied and laboratory skills relevant to the pursuit of research in laser plasma interaction physics and inertial confinement fusion.Lectures are intermingled with laboratory sessions and continuous assessment activities.The programme,which is led by workers from the Hellenic Mediterranean University and supported by co-workers from the Queen’s University Belfast,the University of Bordeaux,the Czech Technical University in Prague,Ecole Polytechnique,the University of Ioannina,the University of Salamanca and the University of York,has just finished its second and final year.Six Learning Teaching Training activities have been held at the Queen’s University Belfast,the University of Bordeaux,the Czech Technical University,the University of Salamanca and the Institute of Plasma Physics and Lasers of the Hellenic Mediterranean University.The last of these institutes hosted two 2-week-long Intensive Programmes,while the activities at the other four universities were each 5 days in length.In addition,a’Multiplier Event’was held at the University of Ioannina,which will be briefly described.In this second year,the work has concentrated on training in both experimental diagnostics and simulation techniques appropriate to the study of plasma physics,high power laser matter interactions and high energy density physics.The nature of the programme will be described in detail,and some metrics relating to the activities carried out will be presented.In particular,this paper will focus on the overall assessment of the programme.
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supported by UK STFC ST/V001639/1,UK EPSRC EP/V049577/1 and EP/V044397/1Horizon 2020 funding under European Research Council(ERC)Grant Agreement No.682399+1 种基金support from the Royal Society URF-R1221874support from US DOE grant DESC0016804
文摘A machine learning model was created to predict the electron spectrum generated by a GeV-class laser wakefield accelerator.The model was constructed from variational convolutional neural networks,which mapped the results of secondary laser and plasma diagnostics to the generated electron spectrum.An ensemble of trained networks was used to predict the electron spectrum and to provide an estimation of the uncertainty of that prediction.It is anticipated that this approach will be useful for inferring the electron spectrum prior to undergoing any process that can alter or destroy the beam.In addition,the model provides insight into the scaling of electron beam properties due to stochastic fluctuations in the laser energy and plasma electron density.
基金supported by the Newton China–UK joint research grant on laser–ion acceleration and novel terahertz radiationEPSRC grant EP/K022415/1 on advanced laser–ion acceleration strategies toward next generation healthcare and EPSRC grant EP/R006202/1+2 种基金supported by the National NaturalScience Foundation of China(Nos.11520101003 and11861121001)the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDB16010200 and XDB07030300)support from the National Postdoctoral Program for Innovative Talents(No.BX201600106)
文摘A multichannel calorimeter system is designed and constructed which is capable of delivering single-shot and broadband spectral measurement of terahertz(THz) radiation generated in intense laser–plasma interactions. The generation mechanism of backward THz radiation(BTR) is studied by using the multichannel calorimeter system in an intense picosecond laser–solid interaction experiment. The dependence of the BTR energy and spectrum on laser energy, target thickness and pre-plasma scale length is obtained. These results indicate that coherent transition radiation is responsible for the low-frequency component(<1 THz) of BTR. It is also observed that a large-scale pre-plasma primarily enhances the high-frequency component(>3 THz) of BTR.
基金funding from EPSRC grants EP/L01663X/1 and EP/L000644/1the Newton UK grant+1 种基金the National Natural Science Foundation of China NSFC/11520101003the LLNL Academic Partnership in ICF
文摘Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.
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the framework of the EUROfusion Consortium and funded from the Euratom research and training programme 2014–2018 and 2019– 2020 under grant agreement No. 633053the ELI Beamlines Projects LQ1606 and 19-02545S with financial support from the Czech Science Foundation and the Ministry of Education, Youth and Sports of the Czech Republic+6 种基金support from the European Regional Development Fund, the project ELITAS CZ.02.1.01/0.0/0.0/16 013/0001793the National Programme of ‘Sustainability Ⅱ’ and ELI phase 2 CZ.02.1.01/0.0/0.0/15008/0000162The PETAL project was designed and built by the CEA under the financial auspices of the Region Nouvelle Aquitaine, the French Government and the European Unionsupported by EPSRC grants EP/K022415/1 and EP/R006202supported by the European Cluster of Advanced Laser Light Sources, EUCALL, which has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 654220funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 654148 Laserlab-Europethe use of the EPOCH PIC code (developed under EPSRC grant EP/G054940/1).
文摘This paper provides an up-to-date review of the problems related to the generation,detection and mitigation of strong electromagnetic pulses created in the interaction of high-power,high-energy laser pulses with different types of solid targets.It includes new experimental data obtained independently at several international laboratories.The mechanisms of electromagnetic field generation are analyzed and considered as a function of the intensity and the spectral range of emissions they produce.The major emphasis is put on the GHz frequency domain,which is the most damaging for electronics and may have important applications.The physics of electromagnetic emissions in other spectral domains,in particular THz and MHz,is also discussed.The theoretical models and numerical simulations are compared with the results of experimental measurements,with special attention to the methodology of measurements and complementary diagnostics.Understanding the underlying physical processes is the basis for developing techniques to mitigate the electromagnetic threat and to harness electromagnetic emissions,which may have promising applications.
基金This paper was supported by the LLNL Academic Partnership in ICF,EPSRC grants EP/L01663X/1 and EP/L000644/1the Czech Republic MSMT targeted support of Large Infrastructures+1 种基金ELI Beamlines Project LQ1606 of the National Programme of Sustainability IIThe contribution of the JIHT RAS team was completed within the framework of the Russian Ministry state assignment for Science and Higher Education(topic#01201357846).
文摘A developing application of laser-driven currents is the generation of magnetic fields of picosecond-nanosecond duration with magnitudes exceeding B=10 T.Single-loop and helical coil targets can direct laser-driven discharge currents along wires to generate spatially uniform,quasi-static magnetic fields on the millimetre scale.Here,we present proton deflectometry across two axes of a single-loop coil ranging from 1 to 2 mm in diameter.Comparison with proton tracking simulations shows that measured magnetic fields are the result of kiloampere currents in the coil and electric charges distributed around the coil target.Using this dual-axis platform for proton deflectometry,robust measurements can be made of the evolution of magnetic fields in a capacitor coil target.
基金Russian Science Foundation(RSF)(17-72-20272)Science and Technology Facilities Council(STFC)(EP/L000644/1)+3 种基金Engineering and Physical Sciences Research Council(EPSRC)(EP/L01663X/1)Los Alamos National Laboratory(LANL)National Nuclear Security Administration(NNSA)U.S.Department of Energy(DOE)(DE-AC5206NA25396)
文摘X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5 × 10^(20) and 2.5 × 10^(20) W∕cm^2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.