A time-dependent analytical solution is found for the velocity of a plane ionization wave generated under nanosecond laser pulse action on the surface of a flat layer of low-Z porous substance with density less than t...A time-dependent analytical solution is found for the velocity of a plane ionization wave generated under nanosecond laser pulse action on the surface of a flat layer of low-Z porous substance with density less than the critical density of the produced plasma.With corrections for the two-dimensional nature of the problem when a laser beam of finite radius interacts with a flat target,this solution is in quantitative agreement with measurements of ionization wave velocity in various experiments.The solution compared with experimental data covering wide ranges of performance conditions,namely,(3-8)×10^(14)W cm^(−2)for laser pulse intensity,0.3-3 ns for pulse duration,0.35-0.53μm for laser wavelength,100-1000μm for laser beam radius,380-950μm for layer thickness,4.5-12 mg cm^(−3)for average density of porous substance,and 1-25μm for average pore size.The parameters of the laser beam that ensure the generation of a plane ionization wave in a layer of subcritical porous matter are determined for the problem statements and are found to meet the requirements of practical applications.展开更多
Charge-changing processes of low-charged ions,used in hydrogen plasma probing by the heavy ion beam probe method,are considered.Along with the ionization of beam ions by plasma electrons and protons,the charge-exchang...Charge-changing processes of low-charged ions,used in hydrogen plasma probing by the heavy ion beam probe method,are considered.Along with the ionization of beam ions by plasma electrons and protons,the charge-exchange processes of ions on H atoms and protons are also studied.It is shown that charge exchange of beam ions on plasma protons and H atoms,which is rarely taken into account,plays an important role in beam–plasma interaction.New data on the cross sections and rates of ionization and charge-exchange processes are presented for Tl+and Tl2+ions,which are frequently used for plasma diagnostics.Calculations are performed for hydrogen plasma temperatures Te=1 eV–10 keV and densities Ne=1012–1014 cm−3 at relatively low and high ion-beam velocities vb=0.2 and 1.0 a.u.,respectively.Special attention is paid to the determination of the electron temperatures at which the charge-exchange processes on H atoms and protons are important.Multiple ionization of beam ions by plasma electrons and protons is briefly discussed.展开更多
The results of a study of the electrical explosion of aluminum foils with an artificial periodic surface structure created by laser engraving are presented.Experiments were carried out on pulsed high-current generator...The results of a study of the electrical explosion of aluminum foils with an artificial periodic surface structure created by laser engraving are presented.Experiments were carried out on pulsed high-current generators BIN(270 kA,300 kV,100 ns)and KING(200 kA,40 kV,200 ns)with Al foil of thicknesses 16 and 4μm,respectively.Images of the exploded foils were recorded by point projection radiography in the radiation from hybrid X-pinches.It is found that the application of an artificial periodic structure to the foil leads to a much more uniform and well-defined periodic structure of the exploded foil.Images recorded in the UV range using a microchannel-plate-intensified detector show that the radiation from a surface-modified foil is more uniform along the entire length and width of the foil than that from a foil without modification.展开更多
Collision of laser-driven subrelativistic high-density ion flows provides a way to create extremely compressed ion conglomerates and study their properties.This paper presents a theoretical study of the electrodynamic...Collision of laser-driven subrelativistic high-density ion flows provides a way to create extremely compressed ion conglomerates and study their properties.This paper presents a theoretical study of the electrodynamic implosion of ions inside a hollow spherical or cylindrical shell irradiated by femtosecond petawatt laser pulses.We propose to apply a very effective mechanism for ion acceleration in a self-consistent field with strong charge separation,based on the oscillation of laser-accelerated fast electrons in this field near the thin shell.Fast electrons are generated on the outer side of the shell under irradiation by the intense laser pulses.It is shown that ions,in particular protons,may be accelerated at the implosion stage to energies of tens and hundreds of MeV when a sub-micrometer shell is irradiated by femtosecond laser pulses with an intensity of 10^(21)–10^(23)W cm^(−2).展开更多
A neural network-based approach is proposed both for reconstructing the focal spot intensity profile and for estimating the peak intensity of a high-power tightly focused laser pulse using the angular energy distribut...A neural network-based approach is proposed both for reconstructing the focal spot intensity profile and for estimating the peak intensity of a high-power tightly focused laser pulse using the angular energy distributions of protons accelerated by the pulse from rarefied gases.For these purposes,we use a convolutional neural network architecture.Training and testing datasets are calculated using the test particle method,with the laser description in the form of Stratton-Chu integrals,which model laser pulses focused by an off-axis parabolic mirror down to the diffraction limit.To demonstrate the power and robustness of this method,we discuss the reconstruction of axially symmetric intensity profiles for laser pulses with intensities and focal diameters in the ranges of 10^(21)-10^(23) W cm^(−2) and ~(1-4)λ,respectively.This approach has prospects for implementation at higher intensities and with asymmetric laser beams,and it can provide a valuable diagnostic method for emerging extremely intense laser facilities.展开更多
Based on the idea of hypothetical 4-dimensial substance with an inverse population of energy levels, a model of accelerated expansion of the Universe has been developed, which describes Hubble diagrams with great accu...Based on the idea of hypothetical 4-dimensial substance with an inverse population of energy levels, a model of accelerated expansion of the Universe has been developed, which describes Hubble diagrams with great accuracy for type Ia supernovae, quasars and gamma-ray burst sources at the Hubble parameter value of 67.7 km/s/Mpc, coinciding with the value obtained from analysis of inhomogeneities of relic radiation. Calculations at the Hubble parameter value of 73.5 km/s/Mpc, obtained using the ΛCDM model based on the analysis of data on type Ia supernovae and cepheids, differ markedly from the observed data. An explanation of the two values of the Hubble constant is proposed. It is shown that in this model, the magnitude of 13.8 billion years characterizes not the age of the Universe, but the time of propagation of light from those galaxes whose acceleration of removal has a minimal value. Based on the recently discovered curvature of the Universe, estimates are given of the lower limits of its size and lifetime, which turned out to be at least 270 billon years. The probability of transition from the excited state to the underlying energy levels of a hypothetical 4-dimensial substance, as well as the low of increasing energy density as a result of transitions to the underlying levels of this substance, is determined.展开更多
A review of X-pinches of various configurations and of different materials as an X-ray source for various applications is presented. Theadvantages and disadvantages of different designs of X-pinches as a load for gene...A review of X-pinches of various configurations and of different materials as an X-ray source for various applications is presented. Theadvantages and disadvantages of different designs of X-pinches as a load for generators with a wide range of output parameters and as a sourceof X-ray radiation for X-ray point-projection imaging were analyzed.展开更多
Under certain conditions, ultrafast pulsed laser interaction with matter leads to the formation of self-organized conical as well as periodic surface structures (commonly reffered to as, laser induced periodic surfac...Under certain conditions, ultrafast pulsed laser interaction with matter leads to the formation of self-organized conical as well as periodic surface structures (commonly reffered to as, laser induced periodic surface structures, LIPSS). The purpose of the present investigations is to explore the effect of fsec laser fluence and ambient environments (Vacuum & 02) on the formation of LIPSS and conical structures on the Ti surface. The surface morphology was investigated by scanning electron microscope (SEM). The ablation threshold with single and multiple (N = 100) shots and the existence of an incubation effect was demonstrated by SEM investigations for both the vacuum and the 02 environment. The phase analysis and chemical composition of the exposed targets were performed by x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS), respectively. SEM investigations reveal the formation of LIPSS (nano & micro). FFT d-spacing calculations illustrate the dependence of periodicity on the fluence and ambient environment. The periodicity of nano-scale LIPSS is higher in the case of irradiation under vacuum conditions as compared to 02. Furthermore, the 02 environment reduces the ablation threshold. XRD data reveal that for the 02 environment, new phases (oxides of Ti) are formed. EDS analysis exhibits that after irradiation under vacuum conditions, the percentage of impurity element (A1) is reduced. The irradiation in the 02 environment results in 15% atomic diffusion of oxygen.展开更多
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...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.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
Dynamics and spectral transmission of Al plasma produced by extreme ultraviolet(EUV)irradiation of 0.75-mm thick Al foil is investigated.The EUV radiation with the peak power density in the range of 0.19-0.54 TW/cm 2 ...Dynamics and spectral transmission of Al plasma produced by extreme ultraviolet(EUV)irradiation of 0.75-mm thick Al foil is investigated.The EUV radiation with the peak power density in the range of 0.19-0.54 TW/cm 2 is provided by Z-pinch formed by W multiwire array implosion in the Angara-5-1 facility.Geometry of the experiment ensures that there are no plasma fluxes from the pinch toward the Al foil and plasma.The same EUV source is used as a back illuminator for obtaining the absorption spectrum of Al plasma in the wavelength range of 5e24 nm.It comprises absorption lines of ions Al^(4+),Al^(5+),Al^(6+),Al^(7+).Analysis of relative intensities of the lines shows that those ions are formed in dense Al plasma with a temperature of~20 eV.Dynamics of Al plasma has been investigated with transverse laser probing.We have also performed radiation-gas-dynamics simulations of plasma dynamics affected by external radiation,which includes self-consistent radiation transport in a plasma shell.The simulations show good agreement with an experimental absorption spectrum and with experimental data concerning plasma dynamics,as well as with the analysis of line absorption spectrum.This confirms the correctness of the physical model underlying these simulations.展开更多
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 demons...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.展开更多
Near-IR(wavelength≈1μm)laser ablation of bulk,chemically-inert gold in water was compared for different laser pulse width in broad the range of 300 fs–100 ns,comparing a number of key ablation characteristics:mass ...Near-IR(wavelength≈1μm)laser ablation of bulk,chemically-inert gold in water was compared for different laser pulse width in broad the range of 300 fs–100 ns,comparing a number of key ablation characteristics:mass loss,singleshot crater volume and extinction coefficient of the generated colloidal solutions taken in the spectral ranges of interband transitions and localized plasmon resonance.Comparing to related air-based ablation results,at the given fluences laser ablation in the liquid resulted in the maximum ablation yield per unit energy and maximum NP yield per pulse and per unit energy for the picosecond lasers,occurring at subcritical peak pulse powers for laser self-focusing.The self-focusing effect was demonstrated to yield in incomplete,effectively weaker focusing in the water filaments of ultrashort laser pulses with supercritical peak powers,comparing to linear(geometrical)focusing at sub-critical peak powers.At the other,nanosecondpulse extreme the high ablation yield per pulse,but low ablation yield per unit energy and low NP yield per pulse and per unit energy were related to strong ablation plasma screening,providing mass removal according to the well-established scaling relationships for plasma.Illustrative comparison of the ablation and nanoparticle generation efficiency versus the broad fs–ns laser pulse width range was enabled in terms of productivity,economicity,and ergonomicity,using the proposed universal quantitative criteria.展开更多
Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope...Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log Blc (G) are 3.60-3.95 and 1.75 correspondingly. Moreover, their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: logE(erg s-1) = 35.37-35.53 and 32.64. The correlation between gamma- ray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand, the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.展开更多
This paper presents characteristic features of the explosion of thin flat foils for currents and pulse risetimes ranging from 8 kA at 350 ns to1000 kA at ∼100 ns. Foils made of aluminum, copper, nickel, and titanium ...This paper presents characteristic features of the explosion of thin flat foils for currents and pulse risetimes ranging from 8 kA at 350 ns to1000 kA at ∼100 ns. Foils made of aluminum, copper, nickel, and titanium with thicknesses of 1–100 μm are tested. Various diagnostics inthe optical, UV, and x-ray spectral ranges are used to image the exploding foils from initial breakdown to complete destruction or pinching.It is shown that foil explosion is a complex process that depends on many factors, but features common to all foils are found that do notdepend on the parameters of the generators or, accordingly, on the energy deposited in the foil: for example, the breakdown of flat foils underdifferent conditions occurs at the edges of the foil. For the first time, the formation of a precursor over the central part of the foil is shown,which significantly changes the dynamics of the foil explosion.展开更多
Results of long time observations of the pulsar B0950+08 are given.These observations were carried out at the LPA radio telescope at the frequency of 111 MHz from January of 2016 to May of 2019(450 days).A strong vari...Results of long time observations of the pulsar B0950+08 are given.These observations were carried out at the LPA radio telescope at the frequency of 111 MHz from January of 2016 to May of 2019(450 days).A strong variability in emission of this pulsar has been detected with changes in signal to noise ratios hundreds of times.Part of the long-time flux density variability can be explained by refractive scintillations in the interstellar medium.The existence of radiation between the interpulse(IP)and main pulse(MP)was confirmed.It was more powerful than at high frequencies.We detected the unusual IP and precursor(Pr)radiation on 2017 August 1.On the basis of 65 strong IPs we found the correlations between energies of IP and Pr and between the phase of IP and the distance Pr–IP.It is shown that the observed peculiarities of this pulsar can be explained in the frame of the aligned rotator model.We estimated distances of radiation levels from the center of the neutron star.The calculated value of the initial period of 0.2 s means that not all pulsars are born with millisecond periods.The large age of the pulsar(6.8 million years)and the small angle between its magnetic moment and the rotation axis(less than 20°)confirm the suggestion related to pulsar evolution with respect to alignment.展开更多
The behavior of logarithmic moments of particle distributions in different rapidity windows is discussed for pp and PA collisions at high energies.The special role of those events,having no-particle in the rapidity wi...The behavior of logarithmic moments of particle distributions in different rapidity windows is discussed for pp and PA collisions at high energies.The special role of those events,having no-particle in the rapidity window,is stressed.展开更多
Heating a solid material with laser-accelerated fast electrons is a particularly useful method for generating a plane powerful shock wave with a pressure of several hundred or even thousands of Mbar in the laboratory....Heating a solid material with laser-accelerated fast electrons is a particularly useful method for generating a plane powerful shock wave with a pressure of several hundred or even thousands of Mbar in the laboratory.Behind the front of such a powerful shock wave,dense plasma is heated to a temperature of several keV.Then,a high rate of radiation energy loss occurs even in low-Z plasmas.In this paper,the strong compression of matter due to radiation cooling in a Gbar shock wave driven by fast electrons is studied using both computational and theoretical approaches.It is shown that the effect of radiation cooling leads to compression of matter in the peripheral region of the shock wave to a density several times greater than the density at its front.Heating a solid material by a petawatt flux of laser-accelerated fast electrons offers the opportunity to surpass the gigabar pressure level of plane shock waves generated by the impact of laser-accelerated pellets.Higher pressures of about 100 Gbar can be achieved under laboratory conditions only when a spherical target is imploded under the action of a terawatt laser pulse.展开更多
The results of experiments with rapidly exploding thin conductors inthe current-pause regime are presented.Copper wires 25mmin diameter and 12 mm in length serve as loads for a GVP pulsed generator based on a low-indu...The results of experiments with rapidly exploding thin conductors inthe current-pause regime are presented.Copper wires 25mmin diameter and 12 mm in length serve as loads for a GVP pulsed generator based on a low-inductance capacitor.The generator produces current pulses of up to 10 kA with dI/dt up to 50 A/ns.A 100–800-ns current-pause regime is obtained for charging voltages of 10–15 kV.The discharge channel structure is studied by shadow photography using 0.53-mm,10-ns second-harmonic pulses from aNd31:YAG laser.In the experiments,three types of secondary breakdown are observed,with different symmetry types,different current-pause durations,and different dependences on the energy deposited into the wire during its resistive heating.All of these breakdown types develop inside a tubular core that is produced in the current-pause stage and that remains almost undamaged by the breakdown.展开更多
Thermo-luminescence (TL) is a kind of luminescence decay measured with varying temperature. In the process of TL the decay parameter itself involves the temperature effect of traps. Thus the trap depth is inseparabl...Thermo-luminescence (TL) is a kind of luminescence decay measured with varying temperature. In the process of TL the decay parameter itself involves the temperature effect of traps. Thus the trap depth is inseparable from the decay parameter. There are two separate peaks in the TL curve of ZnS:Cu,Co if the measurement starts from liquid nitrogen temperature. In the experiment we started from zero Celsius temperature to isolate the deeper traps. We have proposed and realized three methods for simultaneous determination of trap depth and decay parameter based on the quasi-equilibrium model and experimental data. If we treat the case of kinetic order a = 1 as a = 2, the error might be as large as 100%.展开更多
文摘A time-dependent analytical solution is found for the velocity of a plane ionization wave generated under nanosecond laser pulse action on the surface of a flat layer of low-Z porous substance with density less than the critical density of the produced plasma.With corrections for the two-dimensional nature of the problem when a laser beam of finite radius interacts with a flat target,this solution is in quantitative agreement with measurements of ionization wave velocity in various experiments.The solution compared with experimental data covering wide ranges of performance conditions,namely,(3-8)×10^(14)W cm^(−2)for laser pulse intensity,0.3-3 ns for pulse duration,0.35-0.53μm for laser wavelength,100-1000μm for laser beam radius,380-950μm for layer thickness,4.5-12 mg cm^(−3)for average density of porous substance,and 1-25μm for average pore size.The parameters of the laser beam that ensure the generation of a plane ionization wave in a layer of subcritical porous matter are determined for the problem statements and are found to meet the requirements of practical applications.
文摘Charge-changing processes of low-charged ions,used in hydrogen plasma probing by the heavy ion beam probe method,are considered.Along with the ionization of beam ions by plasma electrons and protons,the charge-exchange processes of ions on H atoms and protons are also studied.It is shown that charge exchange of beam ions on plasma protons and H atoms,which is rarely taken into account,plays an important role in beam–plasma interaction.New data on the cross sections and rates of ionization and charge-exchange processes are presented for Tl+and Tl2+ions,which are frequently used for plasma diagnostics.Calculations are performed for hydrogen plasma temperatures Te=1 eV–10 keV and densities Ne=1012–1014 cm−3 at relatively low and high ion-beam velocities vb=0.2 and 1.0 a.u.,respectively.Special attention is paid to the determination of the electron temperatures at which the charge-exchange processes on H atoms and protons are important.Multiple ionization of beam ions by plasma electrons and protons is briefly discussed.
基金supported by the Russian Science Foundation,Project No.19-79-30086-P.
文摘The results of a study of the electrical explosion of aluminum foils with an artificial periodic surface structure created by laser engraving are presented.Experiments were carried out on pulsed high-current generators BIN(270 kA,300 kV,100 ns)and KING(200 kA,40 kV,200 ns)with Al foil of thicknesses 16 and 4μm,respectively.Images of the exploded foils were recorded by point projection radiography in the radiation from hybrid X-pinches.It is found that the application of an artificial periodic structure to the foil leads to a much more uniform and well-defined periodic structure of the exploded foil.Images recorded in the UV range using a microchannel-plate-intensified detector show that the radiation from a surface-modified foil is more uniform along the entire length and width of the foil than that from a foil without modification.
基金supported by the Russian Science Foundation under Project No.21-11-00102。
文摘Collision of laser-driven subrelativistic high-density ion flows provides a way to create extremely compressed ion conglomerates and study their properties.This paper presents a theoretical study of the electrodynamic implosion of ions inside a hollow spherical or cylindrical shell irradiated by femtosecond petawatt laser pulses.We propose to apply a very effective mechanism for ion acceleration in a self-consistent field with strong charge separation,based on the oscillation of laser-accelerated fast electrons in this field near the thin shell.Fast electrons are generated on the outer side of the shell under irradiation by the intense laser pulses.It is shown that ions,in particular protons,may be accelerated at the implosion stage to energies of tens and hundreds of MeV when a sub-micrometer shell is irradiated by femtosecond laser pulses with an intensity of 10^(21)–10^(23)W cm^(−2).
基金supported by RFBR,ROSATOM(Grant No.20-21-00023)the Ministry of Science and Higher Education of the Russian Federation(Agreement No.075-15-2021-1361)+1 种基金the Foundation for the Advancement of Theoretical Physics and Mathematics(“BASIS”)for financial support(Grant No.22-1-3-28-1)partially supported by resources of the NRNU MEPhI High-Performance Computing Center.
文摘A neural network-based approach is proposed both for reconstructing the focal spot intensity profile and for estimating the peak intensity of a high-power tightly focused laser pulse using the angular energy distributions of protons accelerated by the pulse from rarefied gases.For these purposes,we use a convolutional neural network architecture.Training and testing datasets are calculated using the test particle method,with the laser description in the form of Stratton-Chu integrals,which model laser pulses focused by an off-axis parabolic mirror down to the diffraction limit.To demonstrate the power and robustness of this method,we discuss the reconstruction of axially symmetric intensity profiles for laser pulses with intensities and focal diameters in the ranges of 10^(21)-10^(23) W cm^(−2) and ~(1-4)λ,respectively.This approach has prospects for implementation at higher intensities and with asymmetric laser beams,and it can provide a valuable diagnostic method for emerging extremely intense laser facilities.
文摘Based on the idea of hypothetical 4-dimensial substance with an inverse population of energy levels, a model of accelerated expansion of the Universe has been developed, which describes Hubble diagrams with great accuracy for type Ia supernovae, quasars and gamma-ray burst sources at the Hubble parameter value of 67.7 km/s/Mpc, coinciding with the value obtained from analysis of inhomogeneities of relic radiation. Calculations at the Hubble parameter value of 73.5 km/s/Mpc, obtained using the ΛCDM model based on the analysis of data on type Ia supernovae and cepheids, differ markedly from the observed data. An explanation of the two values of the Hubble constant is proposed. It is shown that in this model, the magnitude of 13.8 billion years characterizes not the age of the Universe, but the time of propagation of light from those galaxes whose acceleration of removal has a minimal value. Based on the recently discovered curvature of the Universe, estimates are given of the lower limits of its size and lifetime, which turned out to be at least 270 billon years. The probability of transition from the excited state to the underlying energy levels of a hypothetical 4-dimensial substance, as well as the low of increasing energy density as a result of transitions to the underlying levels of this substance, is determined.
基金The experiments carried out on the Nene,XP and COBRA generators were partly supported by the Stewardship Sciences Academic Alliances Program of the NNSA under DOE Cooperative Agreement No.DE-NA-0001836The experiments carried out on the BIN,MINI and KING generators were partly supported by the Russian Foundation for Basic Research,projects Nos.17-02-0039,18-08-00631an agreement with Cornell University,under Prime Agreement DE-NA0003764 from DOE.
文摘A review of X-pinches of various configurations and of different materials as an X-ray source for various applications is presented. Theadvantages and disadvantages of different designs of X-pinches as a load for generators with a wide range of output parameters and as a sourceof X-ray radiation for X-ray point-projection imaging were analyzed.
文摘Under certain conditions, ultrafast pulsed laser interaction with matter leads to the formation of self-organized conical as well as periodic surface structures (commonly reffered to as, laser induced periodic surface structures, LIPSS). The purpose of the present investigations is to explore the effect of fsec laser fluence and ambient environments (Vacuum & 02) on the formation of LIPSS and conical structures on the Ti surface. The surface morphology was investigated by scanning electron microscope (SEM). The ablation threshold with single and multiple (N = 100) shots and the existence of an incubation effect was demonstrated by SEM investigations for both the vacuum and the 02 environment. The phase analysis and chemical composition of the exposed targets were performed by x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS), respectively. SEM investigations reveal the formation of LIPSS (nano & micro). FFT d-spacing calculations illustrate the dependence of periodicity on the fluence and ambient environment. The periodicity of nano-scale LIPSS is higher in the case of irradiation under vacuum conditions as compared to 02. Furthermore, the 02 environment reduces the ablation threshold. XRD data reveal that for the 02 environment, new phases (oxides of Ti) are formed. EDS analysis exhibits that after irradiation under vacuum conditions, the percentage of impurity element (A1) is reduced. The irradiation in the 02 environment results in 15% atomic diffusion of oxygen.
基金The work described here was supported by the Cooperation Agreement between the Sorbonne University,Faculty of Sciences(Pierre and Marie Curie)and the Moscow Institute of Physics and Technology MIPTFinancial support from MIPT in the framework of Grant No.075-02-2019-967 and the 5-top-100 program is greatly acknowledgedThis work has also been supported by the Competitiveness Program of NRNU MEPhI in the framework of the Russian Academic Excellence Project.
文摘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.
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 work was partially supported by RSF under Grant No.16-12-10487by the RFBR project 15-02-04411 and 15-01-06195.
文摘Dynamics and spectral transmission of Al plasma produced by extreme ultraviolet(EUV)irradiation of 0.75-mm thick Al foil is investigated.The EUV radiation with the peak power density in the range of 0.19-0.54 TW/cm 2 is provided by Z-pinch formed by W multiwire array implosion in the Angara-5-1 facility.Geometry of the experiment ensures that there are no plasma fluxes from the pinch toward the Al foil and plasma.The same EUV source is used as a back illuminator for obtaining the absorption spectrum of Al plasma in the wavelength range of 5e24 nm.It comprises absorption lines of ions Al^(4+),Al^(5+),Al^(6+),Al^(7+).Analysis of relative intensities of the lines shows that those ions are formed in dense Al plasma with a temperature of~20 eV.Dynamics of Al plasma has been investigated with transverse laser probing.We have also performed radiation-gas-dynamics simulations of plasma dynamics affected by external radiation,which includes self-consistent radiation transport in a plasma shell.The simulations show good agreement with an experimental absorption spectrum and with experimental data concerning plasma dynamics,as well as with the analysis of line absorption spectrum.This confirms the correctness of the physical model underlying these simulations.
基金This work was supported by the Cooperation Agreement between the Sorbonne University(Faculty of Sciences)the Moscow Institute of Physics and Technology-MIPT.Financial support from MIPT under Grant No.075-02-2019-967 in the framework of the 5-top-100 program is greatly acknowledged.
文摘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.
基金the Ministry of Science and Higher Education of the Russian Federation(Project No.075-152020-775)。
文摘Near-IR(wavelength≈1μm)laser ablation of bulk,chemically-inert gold in water was compared for different laser pulse width in broad the range of 300 fs–100 ns,comparing a number of key ablation characteristics:mass loss,singleshot crater volume and extinction coefficient of the generated colloidal solutions taken in the spectral ranges of interband transitions and localized plasmon resonance.Comparing to related air-based ablation results,at the given fluences laser ablation in the liquid resulted in the maximum ablation yield per unit energy and maximum NP yield per pulse and per unit energy for the picosecond lasers,occurring at subcritical peak pulse powers for laser self-focusing.The self-focusing effect was demonstrated to yield in incomplete,effectively weaker focusing in the water filaments of ultrashort laser pulses with supercritical peak powers,comparing to linear(geometrical)focusing at sub-critical peak powers.At the other,nanosecondpulse extreme the high ablation yield per pulse,but low ablation yield per unit energy and low NP yield per pulse and per unit energy were related to strong ablation plasma screening,providing mass removal according to the well-established scaling relationships for plasma.Illustrative comparison of the ablation and nanoparticle generation efficiency versus the broad fs–ns laser pulse width range was enabled in terms of productivity,economicity,and ergonomicity,using the proposed universal quantitative criteria.
基金financial support of Basic Research Program of the Presidium of the Russian Academy of Sciences"Transitional and Explosive Processes in Astrophysics(P-41)"Russian Foundation for Basic Research(grant 16–02–00954)
文摘Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log Blc (G) are 3.60-3.95 and 1.75 correspondingly. Moreover, their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: logE(erg s-1) = 35.37-35.53 and 32.64. The correlation between gamma- ray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand, the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.
基金The research on the COBRA and XP generators is supported by Grant No.DE-NA0003764that on the BIN,KING,and GVP generators by the Russian Science Foundation,Project No.19-79-30086.
文摘This paper presents characteristic features of the explosion of thin flat foils for currents and pulse risetimes ranging from 8 kA at 350 ns to1000 kA at ∼100 ns. Foils made of aluminum, copper, nickel, and titanium with thicknesses of 1–100 μm are tested. Various diagnostics inthe optical, UV, and x-ray spectral ranges are used to image the exploding foils from initial breakdown to complete destruction or pinching.It is shown that foil explosion is a complex process that depends on many factors, but features common to all foils are found that do notdepend on the parameters of the generators or, accordingly, on the energy deposited in the foil: for example, the breakdown of flat foils underdifferent conditions occurs at the edges of the foil. For the first time, the formation of a precursor over the central part of the foil is shown,which significantly changes the dynamics of the foil explosion.
文摘Results of long time observations of the pulsar B0950+08 are given.These observations were carried out at the LPA radio telescope at the frequency of 111 MHz from January of 2016 to May of 2019(450 days).A strong variability in emission of this pulsar has been detected with changes in signal to noise ratios hundreds of times.Part of the long-time flux density variability can be explained by refractive scintillations in the interstellar medium.The existence of radiation between the interpulse(IP)and main pulse(MP)was confirmed.It was more powerful than at high frequencies.We detected the unusual IP and precursor(Pr)radiation on 2017 August 1.On the basis of 65 strong IPs we found the correlations between energies of IP and Pr and between the phase of IP and the distance Pr–IP.It is shown that the observed peculiarities of this pulsar can be explained in the frame of the aligned rotator model.We estimated distances of radiation levels from the center of the neutron star.The calculated value of the initial period of 0.2 s means that not all pulsars are born with millisecond periods.The large age of the pulsar(6.8 million years)and the small angle between its magnetic moment and the rotation axis(less than 20°)confirm the suggestion related to pulsar evolution with respect to alignment.
基金supported in part by the National Natural Science Foundation of China.
文摘The behavior of logarithmic moments of particle distributions in different rapidity windows is discussed for pp and PA collisions at high energies.The special role of those events,having no-particle in the rapidity window,is stressed.
文摘Heating a solid material with laser-accelerated fast electrons is a particularly useful method for generating a plane powerful shock wave with a pressure of several hundred or even thousands of Mbar in the laboratory.Behind the front of such a powerful shock wave,dense plasma is heated to a temperature of several keV.Then,a high rate of radiation energy loss occurs even in low-Z plasmas.In this paper,the strong compression of matter due to radiation cooling in a Gbar shock wave driven by fast electrons is studied using both computational and theoretical approaches.It is shown that the effect of radiation cooling leads to compression of matter in the peripheral region of the shock wave to a density several times greater than the density at its front.Heating a solid material by a petawatt flux of laser-accelerated fast electrons offers the opportunity to surpass the gigabar pressure level of plane shock waves generated by the impact of laser-accelerated pellets.Higher pressures of about 100 Gbar can be achieved under laboratory conditions only when a spherical target is imploded under the action of a terawatt laser pulse.
基金This work was supported in part by the NNSA Stewardship Sciences Academic Programs through DOE Cooperative Agreement DE-NA0001836.
文摘The results of experiments with rapidly exploding thin conductors inthe current-pause regime are presented.Copper wires 25mmin diameter and 12 mm in length serve as loads for a GVP pulsed generator based on a low-inductance capacitor.The generator produces current pulses of up to 10 kA with dI/dt up to 50 A/ns.A 100–800-ns current-pause regime is obtained for charging voltages of 10–15 kV.The discharge channel structure is studied by shadow photography using 0.53-mm,10-ns second-harmonic pulses from aNd31:YAG laser.In the experiments,three types of secondary breakdown are observed,with different symmetry types,different current-pause durations,and different dependences on the energy deposited into the wire during its resistive heating.All of these breakdown types develop inside a tubular core that is produced in the current-pause stage and that remains almost undamaged by the breakdown.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10374001, 10434030 and 60576016), the State Key Development Program for Basic Research of China (Grant No 2003CB314707), the Excellent Doctor's Science and Technology Innovation Foundation of Beijing Jiaotong University (Grant No 48011), Russian Foundation of Basic Research (Grant Nos 04-02- 16942 and 02-02-39007).
文摘Thermo-luminescence (TL) is a kind of luminescence decay measured with varying temperature. In the process of TL the decay parameter itself involves the temperature effect of traps. Thus the trap depth is inseparable from the decay parameter. There are two separate peaks in the TL curve of ZnS:Cu,Co if the measurement starts from liquid nitrogen temperature. In the experiment we started from zero Celsius temperature to isolate the deeper traps. We have proposed and realized three methods for simultaneous determination of trap depth and decay parameter based on the quasi-equilibrium model and experimental data. If we treat the case of kinetic order a = 1 as a = 2, the error might be as large as 100%.