Laser Cleaning of Mirror Surface for Optical Diagnostic Systems of the International Thermonuclear Experimental Reactor

The development of cleaning optics and deposition-mitigating techniques is a key factor in the construction and operation of optical diagnostics in ITER. The cleaning of optical surface by pulsed radiation from a fiber laser is an effective method that can recover optical properties of the mirror surface. The possibility of cleaning metallic mirrors from films with complex composition by pulsed radiation from a fiber laser has been experimentally researched. It has been shown that the high initial reflection characteristics of optical elements can be recovered by choosing regimes of radiation effect on the deposited surface. Efficient cleaning is ensured by radiation with the power density of less than 107 W/cm2. At this relatively low power density, pollutions are removed in a solid phase and the thermal effect on the mirror is insignificant. Preliminary experiments of the metal mirrors cleaning by fiber laser radiation have demonstrated the possibility of hardware implementation techniques.

Contribution of joint experiments on small tokamaks in the framework of IAEA coordinated research projects to mainstream fusion research

Joint experiments(JEs)on small tokamaks have been regularly performed between 2005 and 2015 under the framework of the International Atomic Energy Agency(IAEA)coordinated research projects(CRPs).This paper describes the background and the rationale for these experiments,how they were organized and executed,main areas of research covered during these experiments,main results,contributions to mainstream fusion research,and discusses lessons learned and outcomes from these activities.We underline several of the most important scientific outputs and also specific outputs in the education of young scientists and scientists from developing countries and their importance.

Mesenchymal stem cell-derived extracellular vesicles in skin wound healing: the risk of senescent drift induction in secretome-based therapeutics

Regulatory changes in senescent cells could potentially affect the composition of extracellular vehicles(EVs),specifically altering their size and cargo.As a result,the released senescent EVs contain an unpredictable cocktail of growth factors and cytokines.These biomolecules have dual effects,potentially guiding the induction of senescence in affected cells and promoting an inflammation-related“domino effect”within the cellular environment,ultimately leading to tissue inflammaging.

Nanomotion of bacteria to determine metabolic profile

In addition to their visible motion such as swimming(e.g.,with the help offlagella),bacteria can also exhibit nanomotion that is detectable only with highly sensitive instruments,and this study shows that it is possible to detect bacterial nanomotion using an AFM detection system.The results show that the nanomotion characteristics depend on the bacterial strain,and that nanomotion can be used to sense the metabolic activity of bacteria because the oscillations are sensitive to the food preferences of the bacteria and the type of surrounding medium.

Kinetics of dense plasma in the field of short laser pulses:A generalized approach

A generalized kinetic model of atomic level populations in an optically dense plasma excited by laser pulses of arbitrary duration is formulated and studied.This model is based on a nonstationary expression for the probability of excitation of an atomic transition and takes into account the effects of laser pulse penetration into an optically dense medium.A universal formula for the excitation probability as a function of time and propagation length is derived and applied to the case of a Lorentzian spectral profile of an atomic transition excited by a laser pulse with a Gaussian envelope.The features of nonstationary excitation probabilities are presented for different optical depths of the plasma,laser pulse durations,and carrier frequencies.The formulas derived here will be useful for the description of atomic populations excited by laser pulses under realistic conditions of dense plasmas.

Collective coherent emission of electrons in strong laser fields and perspective for hard x-ray lasers

Coherent motion of particles in a plasma can imprint itself on radiation.The recent advent of high-power lasers—allowing the nonlinear inverse Compton-scattering regime to be reached—has opened the possibility of looking at collective effects in laser–plasma interactions.Under certain conditions,the collective interaction of many electrons with a laser pulse can generate coherent radiation in the hard x-ray regime.This perspective paper explains the limitations under which such a regime might be attained.

Accounting for Quadratic and Cubic Invariants in Continuum Mechanics–An Overview

The differential equations of continuum mechanics are the basis of an uncountable variety of phenomena and technological processes in fluid-dynamics and related fields.These equations contain derivatives of the first order with respect to time.The derivation of the equations of continuum mechanics uses the limit transitions of the tendency of the volume increment and the time increment to zero.Derivatives are used to derive the wave equation.The differential wave equation is second order in time.Therefore,increments of volume and increments of time in continuum mechanics should be considered as small but finite quantities for problems of wave formation.This is important for calculating the generation of sound waves and water hammer waves.Therefore,the Euler continuity equation with finite time increments is of interest.The finiteness of the time increment makes it possible to take into account the quadratic and cubic invariants of the strain rate tensor.This is a new branch in hydrodynamics.Quadratic and cubic invariants will be used in differential wave equations of the second and third order in time.

Characterization of bright betatron radiation generated by direct laser acceleration of electrons in plasma of near critical density

Directed x-rays produced in the interaction of sub-picosecond laser pulses of moderate relativistic intensity with plasma of near-critical density are investigated. Synchrotron-like (betatron) radiation occurs in the process of direct laser acceleration (DLA) of electrons in a relativisticlaser channel when the electrons undergo transverse betatron oscillations in self-generated quasi-static electric and magnetic fields. In anexperiment at the PHELIX laser system, high-current directed beams of DLA electrons with a mean energy ten times higher than the ponderomotive potential and maximum energy up to 100 MeV were measured at 10^(19) W/cm^(2)laser intensity. The spectrum of directed x-raysin the range of 5–60 keV was evaluated using two sets of Ross filters placed at 0°and 10°to the laser pulse propagation axis. The differential x-ray absorption method allowed for absolute measurements of the angular-dependent photon fluence. We report 10^(13) photons/sr withenergies >5 keV measured at 0°to the laser axis and a brilliance of 10^(21) photons s^(−1) mm^(−2) mrad−2(0.1%BW)−1. The angular distributionof the emission has an FWHM of 14°–16°. Thanks to the ultra-high photon fluence, point-like radiation source, and ultra-short emissiontime, DLA-based keV backlighters are promising for various applications in high-energy-density research with kilojoule petawatt-class laserfacilities.

Ultrarelativistic Fe plasma with GJ/cm^(3) energy density created by femtosecond laser pulses

The generation of a plasma with an ultrahigh energy density of 1.2 GJ/cm^(3)(which corresponds to about 12 Gbar pressure) is investigated by irradiating thin stainless-steel foils with high-contrast femtosecond laser pulses with relativistic intensities of up to 10^(22) W/cm^(2).The plasma parameters are determined by X-ray spectroscopy.The results show that most of the laser energy is absorbed by the plasma at solid density,indicating that no pre-plasma is generated in the current experimental setup.

页岩微米孔隙结构重构的非光滑正则化及快速梯度优化算法

页岩微观结构认识是页岩气勘探开发的基础.传统的探测手段是基于表面的有损观测方法.本文应用上海光源同步辐射技术对页岩结构进行无损探测获取投影数据,该技术可以避免X射线硬化.我们利用X射线计算机断层成像技术进行图像恢复,提出了L1模+TV(全变差)非光滑正则化方法抑制噪声影响,提高图像对比度.实验证明,该方法是准确重建页岩微观结构的有效方法.

基于Q级联理论估算同位素生产的成本

在决定某种同位素的生产之前,有必要进行生产的经济性分析,以了解和确保生产的经济可行性。本文给出一种用离心法生产非铀同位素的成本分析方法。利用Q模型级联(简称Q级联)理论得到同位素分离的原料利用率与级联相对总流量的关系。通过利用公开的离心法铀同位素分离的单位分离功价格数据,避免生产成本分析中涉及分离单元成本和人员成本等多个复杂因素,在假定分离部分成本正比于分离工厂规模情况下,导出了成本分析的简单公式,可根据原料成本、铀单位分离功价格、原料利用率等对产品成本进行评估和优化。并以铅同位素208Pb的生产为例,对成本分析的过程进行了阐述。结果表明:利用本文的方法,成本分析简单易行。

High energy density physics with intense ion beams

We review the development of High Energy Density Physics(HEDP)with intense heavy ion beams as a tool to induce extreme states of matter.The development of this field connects intimately to the advances in accelerator physics and technology.We will cover the generation of intense heavy ion beams starting from the ion source and follow the acceleration process and transport to the target.Intensity limitations and potential solutions to overcome these limitations are discussed.This is exemplified by citing examples from existing machines at the Gesellschaft fur Schwerionenforschung(GSI-Darmstadt),the Institute of Theoretical and Experimental Physics in Moscow(ITEP-Moscow),and the Institute of Modern Physics(IMP-Lanzhou).Facilities under construction like the FAIR facility in Darmstadt and the High Intensity Accelerator Facility(HIAF),proposed for China will be included.Developments elsewhere are covered where it seems appropriate along with a report of recent results and achievements.

Influence of Particle Size Distribution on the Optical Properties of Fine-Dispersed Suspensions

Nanofluids have great potential for solar energy harvesting due to their suitable optical and thermophysical properties.One of the promising applications of nanofluids is utilization in solar collectors with the direct absorption of light(DASC).The design of a DASC requires detailed knowledge of the optical properties of nanofluids,which can be significantly affected by the particle size distribution.The paper presents the method to take into account the particle size distribution when calculating nanofluid extinction spectra.To validate the proposed model,the particle size distribution and spectral absorbance were measured for aqueous suspension with multi-walled graphite nanotubes;the minimum size of primary nanoparticles was 49 nm.The proposed model is compared with experiments demonstrating the concentration averaged and maximum discrepancies of 6.6%and 32.2%against 12.6%and 77.7%for a model assuming a monosized suspension.

Ignition of nanothermites by a laser diode pulse

Experimental investigation has been carried out for laser ignition and combustion of nanothermites based on aluminum and oxides of copper,bismuth and molybdenum.Ultrasonic mixing of nanosized powders was used to produce compositions.For thermite ignition,initiating laser pulse with a maximum intensity of 770 W/cm2 was generated by a laser diode with a wavelength of 808 nm.The ignition delay times,the minimum initiation energy density,and the average burning rate at various thermite densities and mass fractions of components were determined by recording the emission of radiation of the reaction products using a multichannel pyrometer jointly with a high-speed video camera.The effect of adding carbon black on the threshold parameters of a laser pulse was also studied.Based on the obtained results,certain assumptions were put forward with regard to the mechanism of nanothermites’ignition by laser radiation and their burning.In particular,the assumptions were made on the two-stage process of the reaction initiation and jet burning mechanism of porous nanothermites.

Growth of 4＂ diameter polycrystailine diamond wafers with high thermal conductivity by 915 MHz microwave plasma chemical vapor deposition

Polycrystalline diamond（PCD） films 100 mm in diameter are grown by 915 MHz microwave plasma chemical vapor deposition（MPCVD） at different process parameters,and their thermal conductivity（TC） is evaluated by a laser flash technique（LFT） in the temperature range of230-380 K.The phase purity and quality of the films are assessed by micro-Raman spectroscopy based on the diamond Raman peak width and the amorphous carbon（a-C） presence in the spectra.Decreasing and increasing dependencies for TC with temperature are found for high and low quality samples,respectively.TC,as high as 1950 ± 230 W m-1 K-1 at room temperature,is measured for the most perfect material.A linear correlation between the TC at room temperature and the fraction of the diamond component in the Raman spectrum for the films is established.

Structural and electrical properties of carbon-ion-implanted ultrananocrystalline diamond films

We investigate the structural and electrical properties of carbon-ion-implanted ultrananocrystalline diamond（UNCD）films. Impedance spectroscopy measurements show that the impedance of diamond grains is relatively stable, while that of grain boundaries（GBs）（Rb） significantly increases after the C~＋ implantation, and decreases with the increase in the annealing temperature（Ta） from 650℃ to 1000℃. This implies that the C~＋ implantation has a more significant impact on the conductivity of GBs. Conductive atomic force microscopy demonstrates that the number of conductive sites increases in GB regions at Ta above 900℃, owing to the formation of a nanographitic phase confirmed by high-resolution transmission electronic microscopy. Visible-light Raman spectra show that resistive trans-polyacetylene oligomers desorb from GBs at Ta above 900℃, which leads to lower Rb of samples annealed at 900 and 1000℃. With the increase in Ta to 1000℃, diamond grains become smaller with longer GBs modified by a more ordered nanographitic phase, supplying more conductive sites and leading to a lower Rb.

Recent progress in matter in extreme states created by laser

I.INTRODUCTION Strong interest in the modeling of planetary interiors,dwarf stars,and the physical conditions necessary to achieve inertial confinement fusion(ICF)have driven attention to the properties of matter at high density,temperature,and pressure(beyond the megabar limit).Extreme states of matter have been studied using gas guns,explosives,and Z-pinches,among other methods(see,e.g.,Refs.1–4).However in recent years,lasers have become the most reliable standard tool for creating extreme states of matter.

Focal-shape effects on the efficiency of the tunnelionization probe for extreme laser intensities

We examine the effect of laser focusing on the effectiveness of a recently discussed scheme[M.F.Ciappina et al.,Phys.Rev.A 99,043405(2019)and M.F.Ciappina and S.V.Popruzhenko,Laser Phys.Lett.17,025301(2020)]for in situ determination of ultrahigh intensities of electromagnetic radiation delivered by multi-petawatt laser facilities.Using two model intensity distributions in the focus of a laser beam,we show how the resulting yields of highly charged ions generated in the process of multiple sequential tunneling of electrons from atoms depend on the shapes of these distributions.Our findings lead to the conclusion that an accurate extraction of the peak laser intensity can be made either in the near-threshold regime,when the production of the highest charge state happens only in a small part of the laser focus close to the point where the intensity is maximal or through the determination of the points where the ion yields of close charges become equal.We show that for realistic parameters of the gas target,the number of ions generated in the central part of the focus in the threshold regime should be sufficient for a reliable measurement with highly sensitive time-of-flight detectors.Although the positions of the intersection points generally depend on the focal shape,they can be used to localize the peak intensity value in certain intervals.Finally,the slope of the intensity-dependent ion yields is shown to be robust with respect to both the focal spot size and the spatial distribution of the laser intensity in the focus.When these slopes can be measured,they will provide the most accurate determination of the peak intensity value within the considered tunnel ionization scheme.In addition to this analysis,we discuss the method in comparison with other recently proposed approaches for direct measurement of extreme laser intensities.

XFEL and HHG interaction with matter:Effects of ultrashort pulses and random spikes

The theory of photoionization describing the interaction of x-ray free-electron laser(XFEL)pulses and high-harmonic-generated(HHG)radiation is generalized to ultrashort laser pulses,where the concept of the standard ionization probability per unit time in Fermi’s golden rule and in Einstein’s theory breaks down.Numerical calculations carried out in terms of a generalized photoionization probability for the total duration of pulses in the near-threshold regime demonstrate essentially nonlinear behavior,while absolute values may change by orders of magnitude for typical XFEL and HHG pulses.XFEL self-amplified spontaneous emission pulses are analyzed to reveal general features of photoionization for random and regular spikes:the dependences of the nonlinear photoionization probability on carrier frequency and spike duration are very similar,allowing an analytical expectation value approach that is valid even when there is only limited knowledge of random and regular parameters.Numerical simulations carried out for typical parameters demonstrate excellent agreement.

Scattering of ultrashort laser pulses on plasmons in a Maxwellian plasma

On the basis of equations obtained in the framework of second-order quantum-mechanical perturbation theory,the standard approach to the calculation of scattering radiation probability is extended to the case of ultrashort laser pulses.Weinvestigate the mechanism of the appearance of plasmon peaks in the spectrum of the plasma form factor for different parameters of the problem.For the case in which scattering on plasmons dominates over scattering on electron density fluctuations caused by chaotic thermal motion,we derive analytical expressions describing the scattering probability of ultrashort laser pulses on plasmons.Together with this,we obtain a simple expression connecting the frequency of scattered radiation and the energy transmitted from the incident pulse to plasmon,and vice versa.In considering the scattering probability,our emphasis is on the dependence on the pulse duration.Weassess in detail the trends of this dependence for various relations between pulse carrier frequency and plasmon energy.