摘要：Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensedmatter.However,the onlyway to determine crystal structures of materials above 100 GPa,namely,X-ray diffraction(XRD),especially for lowZ materials,remains nontrivial in the ultrahigh-pressure region,even with the availability of brilliant synchrotron X-ray sources.In thiswork,we performa systematic study,choosing hydrogen(the lowest X-ray scatterer)as the subject,to understand how to better perform XRD measurements of low Z materials at multimegabar pressures.The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254GPa at room temperature[C.Ji et al.,Nature 573,558–562(2019)].Wepresent our discoveries and experienceswith regard to several aspects of thiswork,namely,diamond anvil selection,sample configuration for ultrahigh-pressure XRDstudies,XRDdiagnostics for low Z materials,and related issues in data interpretation and pressure calibration.Webelieve that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures,eventually testing structural models of metallic hydrogen.
摘要：Investigations were carried out at the multistage hybrid Ti:sapphire–KrF laser facility GARPUN-MTW on the direct amplification of TW-power picosecondUVlaser pulses in e-beam-pumped KrF amplifiers and propagation along a 100mlaboratory air pass.The experiments identified the main nonlinear effects and their impact on the amplification efficiency,amplifier optics degradation,beam quality and focusability,and the evolution of radiation spectra.The research was performed towards an implementation of the shock-ignition concept of inertial-confinement fusion using krypton fluoride laser drivers.
摘要：We present here experimental results on the optimization of the mega-electronvolt ion source from the target front surface by using relativistic(10^(18)W/cm^(2))interactions with ultra-short laser pulses(50 fs).The source perturbation in the accelerated proton/ion beam was primarily controlled by the addition of a pre-pulse to main pulse contrast ratio.The 2D particle-in-cell simulations agreed well with the observed experimental results for the ion source perturbation and mitigation.This work provides insights into ion source perturbations(temporal and spatial)and the need to control them in intense laser–plasma interactions.Our results may assist in the efficient guiding of proton/ion beams to the core of fusion fuel or of ions in cancer therapy.
摘要：Specimens of materials for prospective use in chambers of nuclear fusion reactors with inertial plasma confinement,namely,W,ODS steels,Eurofer 97 steel,a number of ceramics,etc.,have been irradiated by dense plasma focus devices and a laser in the Q-switchedmode of operation with a wide range of parameters,including some that noticeably exceeded those expected in reactors.By means of 1-ns laser interferometry and neutron measurements,the characteristics of plasma streams and fast ion beams,as well as the dynamics of their interaction with solid-state targets,have been investigated.3D profilometry,optical and scanning electron microscopy,atomic emission spectroscopy,X-ray elemental and structural analyses,and precise weighing of specimens before and after irradiation have provided data on the roughening threshold and the susceptibility to damage of the materials under investigation.Analysis of the results,together with numerical modeling,has revealed the important role of shock waves in the damage processes.It has been shown that a so-called integral damage factor may be used only within restricted ranges of the irradiation parameters.It has also been found that in the irradiation regime with well-developed gasdynamic motion of secondary plasma,the overall amount of radiation energy is spent preferentially either on removing large masses of cool matter from the material surface or on heating a small amount of plasma to high temperature(and,consequently,imparting to it a high velocity),depending on the power flux density and characteristics of the pulsed irradiation.
摘要：The paper discusses a possible energy transformation that leads to the acceleration of fast ions and electrons.In plasma-focus discharges that occur during deuteriumfilling,which have amaximumcurrent of about 1MA,the accelerated deuterons produce fast fusion neutrons and fast electrons hard X-ray emissions.Their total energy,which is of the order of several kilojoules,can be delivered by the discharge through a magnetic dynamo and selforganization to the ordered plasma structures that are formed in a pinch during the several hundreds of nanoseconds of the pinch implosion,stagnation,and evolution of instabilities.This energy is finally released during the decay of the ordered plasma structures in the volume between the anode face and the umbrella front of the plasma and current sheath in the form of induced electric fields that accelerate fast electrons and ions.
摘要：Underwater shock waves generated by pulsed electrical discharges are an effective,economical,and environmentally friendly means of stimulating reservoirs,and this technology has received much attention and intensive research in the past few years.This paper reviews the main results of recent work on underwater electrical wire explosion(UEWE)for reservoir stimulation.Aplatform is developed for microsecond singlewire explosions in water,and diagnostics based on a voltage probe,current coil,pressure probe,photodiode,and spectrometer are used to characterize the UEWE process and accompanying shock waves.First,the UEWE characteristics under different discharge types are studied and general principles are clarified.Second,the shock-wave generation mechanism is investigated experimentally by interrupting the electrical energy injection into the wire at different stages of the wire-explosion process.It is found that the vaporization process is vital for the formation of shock waves,whereas the energy deposited after voltage collapse has only a limited effect.Furthermore,the relationships between the electrical-circuit and shock-wave parameters are investigated,and an empirical approach is developed for estimating the shock-wave parameters.Third,how the wire material and water state affect the wire-explosion process is studied.To adjust the shock-wave parameters,a promising method concerning energetic material load is proposed and tested.Finally,the fracturing effect of the pulsed-discharge shock waves is discussed,as briefly are some of the difficulties associated with UEWE-based reservoir stimulation.
摘要：Revised simulations of ALT-like devices are presented.The results from these simulations closely match those from experiments and demonstrate the capabilities of the devices as applied to ramp compression of metals to pressures of 20 Mbar by imploding liners driven by∼10 MG azimuthal magnetic fields(with currents up to 55 MA).These results can be applied to the design of experiments on isentropic compression of materials.
摘要：Non-resonant inelastic X-ray scattering(NRIXS)is a new technique for atomic and molecular physics that allows one to measure the electronic structures and dynamic parameters of the ground and excited states of atoms and molecules in momentum space.There is a clearly understood physical picture of NRIXS,which reveals its remarkable advantages of satisfying the first Born approximation and being able to excite dipoleforbidden transitions.Various physical properties of atoms and molecules,such as their elastic and inelastic squared form factors,optical oscillator strengths,and Compton profiles,can be explored using NRIXS under different experimental conditions.In this paper,we review newly developed experimental methods for NRIXS,together with its characteristics and various applications,with emphasis on the new insights into excitation mechanism and other new information revealed by this technique.The intrinsic connections and differences between NRIXS and fast electron impact spectroscopy are elucidated.Future applications of this method to atomic and molecular physics are also described.
摘要：Advances in X-ray laser sources have paved the way to relativistic attosecond X-ray laser pulses and opened up the possibility of exploring highenergy-density physics with this technology.With particle-in-cell simulations,we investigate the interaction of realistic metal crystals with relativistic X-ray laser pulses of parameters that will be available in the near future.A wakefield of the order of TV/cm is excited in the crystal and accelerates trapped electrons stably even though the wakefield is locally modulated by the crystal lattice.Electron injection either occurs at the sharp crystal-vacuum boundary or is controlled by coating the crystal with a high-density film.High-repetition-rate attosecond(20 as)monoenergetic electron beams of energy 125 MeV,charge 100 fC,and emittance 1.6310−9mrad can be produced by shining MHz X-ray laser pulses of energy 2.1 mJ onto coated crystals several micrometers thick.Such a miniature crystal accelerator,which has high reproducibility and allows sufficient control of the parameters of the electron beams,greatly expands the applications of X-ray free electron lasers.For example,it could serve as an ideal electron source for ultrafast electron diffraction and ultrafast electron microscopy to achieve attosecond resolution.
摘要：The generation of highly polarized high-energy brilliantγ-rays via laser–plasma interaction is investigated in the quantum radiation-reaction regime.We employ a quantum electrodynamics particle-in-cell code to describe spin-resolved electron dynamics semiclassically and photon emission and polarization quantum mechanically in the local constant field approximation.As an ultrastrong linearly polarized(LP)laser pulse irradiates a near-critical-density(NCD)plasma followed by an ultrathin planar aluminum target,the electrons in the NCD plasma are first accelerated by the driving laser to ultrarelativistic energies and then collide head-on with the laser pulse reflected by the aluminum target,emitting brilliant LPγ-rays via nonlinear Compton scattering with an average polarization of about 70%and energy up to hundreds of MeV.Suchγ-rays can be produced with currently achievable laser facilities and will find various applications in high-energy physics and laboratory astrophysics.
摘要：Interfacial magnetic field structures induced by transverse electron-scale shear instability(mushroom instability)are found to be strongly associated with electron and ion dynamics,which in turn will influence the development of the instability itself.We find that high-frequency electron oscillations are excited normal to the shear interface.Also,on a larger time scale,the bulk of the ions are gradually separated under the influence of local magnetic fields,eventually reaching an equilibrium related to the initial shear conditions.Wepresent a theoretical model of this behavior.Such separation on the scale of the electron skin depth will prevent different ions from mixing and will thereafter restrain the growth of higher-order instabilities.We also analyze the role of electron thermal motion in the generation of the magnetic field,and we find an increase in the instability growth rate with increasing plasma temperature.These results have potential for providing a more realistic description of relativistic plasma flows.
摘要：Accurate knowledge of the equation of state(EOS)of deuterium–tritium(DT)mixtures is critically important for inertial confinement fusion(ICF).Although the study of EOS is an old topic,there is a longstanding lack of global accurate EOS data for DT within a unified theoretical framework.DT fuel goes through very wide ranges of density and temperature from a cold condensed state to a hot dense plasma where ions are in a moderately or even strongly coupled state and electrons are in a partially or strongly degenerate state.The biggest challenge faced when using first-principles methods for obtaining accurate EOS data for DT fuel is the treatment of electron–ion interactions and the extremely high computational cost at high temperatures.In the present work,we perform extensive state-of-the-art ab initio quantum Langevin molecular dynamics simulations to obtain EOS data for DT mixtures at densities from 0.1 g/cm3 to 2000 g/cm3 and temperatures from 500 K to 2000 eV,which are relevant to ICF processes.Comparisons with average-atom molecular dynamics and orbital-free molecular dynamics simulations show that the ionic strong-coupling effect is important for determining the whole-range EOS.This work can supply accurate EOS data forDTmixtures within a unified ab initio framework,as well as providing a benchmark for various semiclassical methods.
摘要：Three tungsten powder samples—one coarse grained(c-W;grain size:1μm–3μm)and two nanocrystalline(n-W;average grain sizes:10nm and 50 nm)—are investigated under nonhydrostatic compression in a diamond anvil cell in separate experiments,and their in situ X-ray diffraction patterns are recorded.The maximum microscopic deviatoric stress in each tungsten sample,a measure of the yield strength,is determined by analyzing the diffraction line width.Over the entire pressure range,the strength of tungsten increases noticeably as the grain size is decreased from 1μm–3μmto 10 nm.The results show that the yield strength of tungsten with an average crystal size of 10nmis around 3.5 times that of the sample with a grain size of 1μm–3μm.
摘要：Novel phenomena andmethods related to dielectronic capture and dielectronic recombination are studied for non-local thermodynamic equilibrium(LTE)plasmas and for applications to non-LTE ionization balance.It is demonstrated thatmultichannel autoionization and radiative decay strongly suppress higher-order contributions to the total dielectronic recombination rates,which are overestimated by standard approaches by orders of magnitude.Excited-state coupling of dielectronic capture is shown to be much more important than ground-state contributions,and electron collisional excitation is also identified as a mechanism driving effective dielectronic recombination.A theoretical description of the effect of angularmomentum-changing collisions on dielectronic recombination is developed from an atomic kinetic point of view and is visualized with a simple analytical model.The perturbation of the autoionizing states due to electric fields is discussed with respect to ionization potential depression and perturbation of symmetry properties of autoionizationmatrix elements.The first steps in the development of statistical methods are presented and are realized in the framework of a local plasma frequency approach.Finally,the impact of collisional–radiative processes and atomic population kinetics on dielectronic recombination is critically discussed,and simple analytical formulas are presented.
摘要：Statistical models combined with the local plasma frequency approach applied to the atomic electron density are employed to study the photoionization cross-section for complex atoms.It is demonstrated that the Thomas–Fermi atom provides surprisingly good overall agreement even for complex outer-shell configurations,where quantum mechanical approaches that include electron correlations are exceedingly difficult.Quantum mechanical photoionization calculations are studied with respect to energy and nl quantum number for hydrogen-like and non-hydrogen-like atoms and ions.Ageneralized scaled photoionizationmodel(GSPM)based on the simultaneous introduction of effective charges for non-H-like energies and scaling charges for the reduced energy scale allows the development of analytical formulas for all states nl.Explicit expressions for nl1s,2s,2p,3s,3p,3d,4s,4p,4d,4f,and 5s are obtained.Application to H-like and non-H-like atoms and ions and to neutral atoms demonstrates the universality of the scaled analytical approach including inner-shell photoionization.Likewise,GSPMdescribes the near-threshold behavior and high-energy asymptotes well.Finally,we discuss the various models and the correspondence principle along with experimental data and with respect to a good compromise between generality and precision.The results are also relevant to large-scale integrated light–matter interaction simulations,e.g.,X-ray free-electron laser interactions with matter or photoionization driven by a broadband radiation field such as Planckian radiation.
摘要：Micro-focus computed tomography(CT),which allows the hyperfine structure within objects to be reconstructed,is a powerful nondestructive testing tool in many fields.However,current x-ray sources for micro-focus CT are typically limited by their relatively low photon energy and low flux.An all-optical inverse Compton scattering source(AOCS)based on laser wakefield acceleration can generate intense quasi-monoenergetic x/gamma-ray pulses in the kilo-to megaelectronvolt range with micrometer-level source size,and its potential application for micro-focus CT has become very attractive in recent years because of the rapid progress made in laser wakefield acceleration.Reported here is a successful experimental demonstration of high-fidelity micro-focus CT using an AOCS(∼70 keV)by imaging and reconstructing a test object with complex inner structures.A region-of-interest CT method is adopted to utilize the relatively small field of view of the AOCS to ensure high spatial resolution.This demonstration of AOCS-based region-of-interest micro-focus CT is a key step toward its application in the field of hyperfine nondestructive testing.
摘要：We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic,respectively.Distinct effects of the target materials are found on the total charge,cutoff energy,and beam spot of protons in the experiments,and these are described well by two-dimensional particle-in-cell simulations incorporating intrinsic material properties.It is found that with a laser intensity of 8×10^(19) W/cm^(2),target normal sheath acceleration is the dominant mechanism for both types of target.For a plastic target,the higher charge and cutoff energy of the protons are due to the greater energy coupling efficiencies from the intense laser beams,and the larger divergence angle of the protons is due to the deflection of hot electrons during transport in the targets.We also find that the energy loss of hot electrons in targets of different thickness has a significant effect on the proton cutoff energy.The consistent results obtained here further narrow the gap between simulations and experiments.
摘要：We consider a steady-state(but transient)situation in which a warm dense aggregate is a two-temperature system with equilibrium electrons at temperature T_(e),ions at T_(i),and T_(e)≠T_(i).Such states are achievable by pump–probe experiments.For warm dense hydrogen in such a twotemperature situation,we investigate nuclear quantum effects(NQEs)on structure and thermodynamic properties,thereby delineating the limitations of ordinary ab initio molecular dynamics.We use path integral moleculardynamics(PIMD)simulations driven by orbital-free density functional theory(OFDFT)calculations with state-of-the-art noninteracting free-energy and exchange-correlation functionals for the explicit temperature dependence.We calibrate the OFDFT calculations against conventional(explicit orbitals)Kohn–Sham DFT.We find that when the ratio of the ionic thermal de Broglie wavelength to the mean interionic distance is larger than about 0.30,the ionic radial distribution function is meaningfully affected by the inclusion of NQEs.Moreover,NQEs induce a substantial increase in both the ionic and electronic pressures.This confirms the importance of NQEs for highly accurate equation-of-state data on highly driven hydrogen.For Te>20 kK,increasing Te in the warm dense hydrogen has slight effects on the ionic radial distribution function and equation of state in the range of densities considered.In addition,we confirm that compared with thermostatted ring-polymer molecular dynamics,the primitive PIMD algorithm overestimates electronic pressures,a consequence of the overly localized ionic description from the primitive scheme.
摘要：The use of low-coherence light is expected to be one of the effective ways to suppress or even eliminate the laser–plasma instabilities that arise in attempts to achieve inertial confinement fusion.In this paper,a review of low-coherence high-power laser drivers and related key techniques is first presented.Work at typical low-coherence laser facilities,including Gekko XII,PHEBUS,Pharos III,and Kanal-2 is described.The many key techniques that are used in the research and development of low-coherence laser drivers are described and analyzed,including low-coherence source generation,amplification,harmonic conversion,and beam smoothing of low-coherence light.Then,recent progress achieved by our group in research on a broadband low-coherence laser driver is presented.During the development of our low-coherence high-power laser facility,we have proposed and implemented many key techniques for working with low-coherence light,including source generation,efficient amplification and propagation,harmonic conversion,beam smoothing,and precise beam control.Based on a series of technological breakthroughs,a kilojoule low-coherence laser driver named Kunwu with a coherence time of only 300 fs has been built,and the first round of physical experiments has been completed.This high-power laser facility provides not only a demonstration and verification platform for key techniques and system integration of a low-coherence laser driver,but also a new type of experimental platform for research into,for example,high-energy-density physics and,in particular,laser–plasma interactions.
摘要：A dream long held by physicists has been to raise the critical temperature(Tc)—the temperature below which the material exhibits no electrical resistance—of a superconductor to room temperature.The most recent excitement in that regard has centered on rare-earth superhydrides,of which LaH10 at 190 GPa has a remarkably high Tc of 260 K.
摘要：Diamonds may not be forever,but research interest in diamond has never ebbed.Owing to its highly symmetric crystal structure and strong covalentC–Cbonds,diamond possesses an exceptional combination of physical properties.Its hardness and thermal conductivity are the highest among covalent materials.It also has a large bandgap and electric breakdown field,as well as optical transparency over a wide range of wavelengths.All of these are essential for a wide range of applications in both industrial and scientific areas.Despite these outstanding advantages,however,diamond is extremely brittle,with inferior toughness and poor deformability.These shortcomings have caused undesired tool breakage and have imposed severe constraints on technological innovations.To surmount these intrinsic deficiencies,tremendous research effort has been dedicated to developing advanced diamond products,with great progress being achieved in the past few years.
摘要：For around three decades,high-pressure techniques have been used to study nanomaterials.In most studies,especially the early ones,x-ray diffraction and Raman and infrared spectroscopy were used to investigate the structural transition and equation of state.In recent years,the exploration has been extended to the plastic deformation of nanomaterials by using radial diamond-anvil-cell x-ray diffraction and transmission electron microscopy.Compared with the traditional techniques,high-pressure techniques are more advantageous in applying mechanical loads to nanosized samples and characterizing the structural and mechanical properties either in situ or ex situ,which could help to unveil the mysteries of mechanics at the nanoscale.With such knowledge,more-advanced materials could be fabricated for wider and specialized applications.This paper provides a brief review of recent progress.
摘要：This erratum1 is issued by the authors to note that part(b)of Fig.1 was erroneously excluded in the published version of the manuscript.A correct version of Fig.1 is provided here.The figure caption of Fig.1 is repeated here,however the captions and text of the document remain unchanged.
摘要：Metal halide perovskites(HPVs)have been greatly developed over the last decade,with various compositions,dimensionalities,and morphologies,leading to an emergence of high-performance photovoltaic and optoelectronic applications.Despite the tremendous progress made,challenges remain,which calls for a better understanding of the fundamental mechanisms.Pressure,a thermodynamic variable,provides a powerful tool to tune materials’structures and properties.In combination with in situ characterization methods,high-pressure research could provide a better fundamental understanding.In this review,we summarize the recent studies of the dramatic,pressure-induced changes that occur in HPVs,particularly the enhanced and emergent properties induced under high pressure and their structure-property relationships.We first introduce the characteristics of HPVs and the basic knowledge of high-pressure techniques,as well as in situ characterization methods.We then discuss the effects of pressure on HPVs with different compositions,dimensionalities,and morphologies,and underline their common features and anomalous behaviors.In the last section,we highlight the main challenges and provide suggestions for possible future research on high-pressure HPVs.
摘要：Recent advances in high-pressure technologies and large-scale experimental and computational facilities have enabled scientists,at an unprecedented rate,to discover and predict novel states and materials under the extreme pressure-temperature conditions found in deep,giant-planet interiors.Based on a well-documented body of work in this field of high-pressure research,we elucidate the fundamental principles that govern the chemistry of dense solids under extreme conditions.These include:(i)the pressure-induced evolution of chemical bonding and structure of molecular solids to extended covalent solids,ionic solids and,ultimately,metallic solids,as pressure increases to the terapascal regime;(ii)novel properties and complex transition mechanisms,arising from the subtle balance between electron hybridization(bonding)and electrostatic interaction(packing)in densely packed solids;and(iii)new dense framework solids with high energy densities,and with tunable properties and stabilities under ambient conditions.Examples are taken primarily fromlow-Z molecular systems that have scientific implications for giant-planet models,condensed materials physics,and solid-state core-electron chemistry.
摘要：The high-power laser energy research(HiPER)project was a European project for demonstrating the feasibility of inertial fusion energy based on using direct-drive targets in a shock ignition scheme using a drywall evacuated chamber.HiPER was intended to drive the transition from a scientific proof of principle to a demonstration power plant in Europe.The project was divided into three realistic scenarios(Experimental,Prototype,and Demo)to help identify open problems and select appropriate technologies to solve them.One of the problems identified was the lack of appropriate plasma-facing materials(PFMs)for the reaction chamber.Therefore,a major challenge was to develop radiation-resistant materials able to withstand the large thermal loads and radiation in these reactors.In this paper,we describe the main threats that coarse-grained Wwould face in the diverse HiPER scenarios.Based on purely thermomechanical considerations,theWlifetimes for the HiPER Prototype and Demo scenarios are limited by fatigue to 14000 h and 28 h,respectively.The combined effects of thermal load and atomistic damage significantly reduce these lifetimes to just∼1000 shots for the Experimental scenario and a few minutes and seconds for the Prototype and Demo scenarios,respectively.Thus,coarse-grainedWis not an appropriatePFMfor the Prototype or Demo scenarios.Therefore,alternatives to this material need to be identified.Here,we review some of the different approaches that are being investigated,highlight the work done to characterize these new materials,and suggest further experiments.
