Methods of controlled formation of instabilities during the electrical explosion of thin foils

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.

A Model of Accelerated Expansion of the Universe Based on the Idea about a Hypothetical 4-Dimensial Substance with an Inverse Population of Energy Levels

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.

New Features of the Pulsar B0950+08 Radiation at the Frequency of 111 MHz

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.

Core structure and secondary breakdown of an exploding wire in the current-pause regime

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.

Quantitative evaluation of LAL productivity of colloidal nanomaterials:Which laser pulse width is more productive,ergonomic,and economic?

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.

Investigation of Al plasmas from thin foils irradiated by high-intensity extreme ultraviolet

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.

Highly efficient transient stimulated Raman scattering on secondary vibrational mode of BaWO_(4) crystal due to its constructive interference with self-phase modulation

An exceptionally high stimulated Raman scattering[SRS]conversion efficiency to the first Stokes component associated with the secondary[low-frequency and low intensity]vibrational mode v2[~330 cm^[-1]]was observed in a BaWO4 crystal in a highly transient regime of interaction.The effect takes place in the range of pump pulse energy from~0.1 to~0.5μJ with maximum energy conversion efficiency up to 35%at 0.2μJ.The nature of the observed effects is explained by interference of SRS and self-phase modulation,where the latter is related to a noninstantaneous orientational Kerr nonlinearity in the BaWO4 crystal.

Cross section of the Coulomb excitation of ^(229m)Th by low energy muons

The inelastic scattering cross section for muons,μ^(-),with energies E=9-100 eV from the ^(229)Th nuclei is calculated in the framework of the second order of the perturbation theory for quantum electrodynamics.The dominant contribution to the excitation of the low energy isomer ^(229m)Th(3/2^(+),8.19±0.12 eV)originates from the E2 multipole.The excitation cross section reaches the value of 10^(-21) cm^(2) in the range E≈10 eV.This value is four to five orders of magnitude larger than the electron excitation cross section and is sufficient for the efficient excitation of ^(229m)Th on the muon beam at the next generation of muon colliders.

Dielectronic recombination in non-LTE plasmas

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.

Extreme matter compression caused by radiation cooling effect in gigabar shock wave driven by laser-accelerated fast electrons

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.

Elastic Moduli in Cadmium Selenide Doped with Chromium

Temperature dependence of elastic moduli , , and the latter for the piezo-active and non-piezo-active versions, have been measured in the interval of 4 - 180 K at 28 - 262 MHz in a CdSe: Cr2+ crystal. Anomalies below 40 K have been found for all the moduli, except . The interpretation of the results has been carried out involving the Jahn-Teller effect and relaxation between the equivalent distortions of the tetrahedral CrSe4 centers.

NH_(3)laser THz emission under optical pumping by“long”(~100μs)CO_(2)laser pulses

Terahertz(THz)NH_(3) lasing with optical pumping by electron-beam-sustained discharge“long”(~100μs)CO_(2) laser pulses was obtained.The NH3laser emission pulses and the“long”pulses of the CO_(2) pump laser were simultaneously measured with nanosecond response time.The NH3 lasing duration and its delay with respect to the pump pulse were measured for various CO_(2) laser pulse energies.For the CO_(2) laser pump line 9R(30),three wavelengths of 67.2,83.8,and 88.9μm were recorded.For the CO_(2) laser pump line 9R(16),only a single NH3 laser line with a wavelength of 90.4μm was detected.

Proposal for a nuclear light source

This study considers a principal possibility of creating a nuclear light source of the vacuum ultra violet(VUV) range based on the ^(229)Th nucleus.This nuclear light source can help solve two main problems—excitation of the low-lying^(229m)Th isomer and precision measurement of the nuclear isomeric transition energy.The thorium nuclear light source is based on the nuclei implanted in a thin dielectric film with a large bandgap.While passing an electric current through the sample,the^(229)Th nuclei are excited to the low energy isomeric state 3/2^(+)(8.19±0.12eV) through the process of inelastic scattering of conduction electrons.The subsequent spontaneous decay of^(229m)Th is followed by the emission of γ quanta in the VUV range.The luminosity of the thorium nuclear light source is approximately 10^(5)photons/s per 1 A of current,per 1 ng of^(229)Th.The suggested scheme to obtain γ radiation from the^(229m)Th isomer can be considered as a type of nuclear analogue of the optical radiation from the usual metal-insulator-semiconductor(MIS) junction.

Powerful terahertz waves from long-wavelength infrared laser filaments

Strong terahertz(THz)electric and magnetic transients open up new horizons in science and applications.We review the most promising way of achieving sub-cycle THz pulses with extreme field strengths.During the nonlinear propagation of two-color mid-infrared and far-infrared ultrashort laser pulses,long,and thick plasma strings are produced,where strong photocurrents result in intense THz transients.The corresponding THz electric and magnetic field strengths can potentially reach the gigavolt per centimeter and kilotesla levels,respectively.The intensities of these THz fields enable extreme nonlinear optics and relativistic physics.We offer a comprehensive review,starting from the microscopic physical processes of light-matter interactions with mid-infrared and far-infrared ultrashort laser pulses,the theoretical and numerical advances in the nonlinear propagation of these laser fields,and the most important experimental demonstrations to date.

J/ψJ/ψ束缚态的存在合理吗?

得益于世界各大高能物理实验在强子谱研究中的进展,奇特强子态的研究是近20年来强子物理领域的热点.区别于传统夸克模型中三夸克构成的重子和正反夸克对构成的介子,奇特强子态包括由更多夸克构成的多夸克态、夸克胶子构成的混杂态、完全由胶子构成的胶球等.2020年,LHCb合作组公布了质子质子对撞中产生的J/ψJ/ψ不变质量分布,宣布测到了由4个粲夸克cccc构成的粒子X(6900).在随后的一项研究工作中,本文作者通过拟合实验数据发现了J/ψJ/ψ阈值附近存在一个分子态的迹象.这个态的存在最近也被另一课题组证实.那么这个J/ψJ/ψ分子态是由什么束缚在一起的呢?对低能强相互作用已有的认知能够解释它吗?本文作者研究了J/ψJ/ψ之间交换软胶子的相互作用,其长程部分可以由双π介子和双K介子交换来描述.他们发现,在合理的参数范围之间,这种介子交换的相互作用可以为J/ψJ/ψ形成束缚态提供很大一部分束缚力.这意味着J/ψJ/ψ之间的相互作用可能已经强到足以形成束缚态,而不像大家之前认为的那样小.这个J/ψJ/ψ分子态可以在今后的实验中进行寻找.如果得到证实,那么可以预期现实中会存在一系列类似的分子态,比如ηcηc以及对应的全底四夸克态.