High-temperature Dense Plasmas Research Articles

Influence of different charge-state ion distribution on elastic X-ray scattering in warm dense matter

The study of warm dense matter is very important for the evolution of celestial bodies and inertial confinement fusion, which often contains a mixture of multiple elements and different charge-state ions. The ionic structure and distribution of different charge-states directly affect the diagnosis and physical properties of warm dense matter. At the same time, the influence of high-temperature dense plasma on the ionic structure should be considered when we study the physical properties from the first-principle calculation of electron structure. In the present work, the radial distribution functions of multiple charge-state ions (gold, carbon-hydrogen mixture, and aluminum) are developed in the hypernetted-chain approximation, and elastic x-ray scattering of different charge-state ions are calculated in the warm dense matter regime. Firstly, the electron structure of different charge-state ions is self-consistently computed in the ionic sphere, in which the ion-sphere radii are determined by the plasma density and their charges. And then the ionic fraction is obtained by solving the modified Saha equation, with the interactions among different charge-state ions taken into account, and ion-ion pair potentials are obtained by Yukawa model. Finally, the ion features of x-ray elastic scattering for Al are calculated on the basis of electronic distribution around the nuclei and ionic radial distribution function. By comparing the results of different charge-sate ions with the result of mean charge-sate ion, it is shown that different statistical methods can affect the physical properties which are dependent on the electronic and ionic structure.

Spatial resolution study of soft X-ray laser backlight shadow imaging technique

The soft X-ray laser shadow imaging technique is a good tool for diagnosing shadow profiles near the critical surface of high-temperature dense plasma. The short-pulse plasma X-ray laser, driven by high-power laser, is used as the backlight, which spreads freely approximately 500 mm far, passes through the plasma to be diagnosed, and changes its optical path by using a multi-layer spherical lens and multi-layer plane mirror, is attenuated by filters, and is recorded by a soft X-ray charge-coupled device (CCD). The plasma to be diagnosed can be driven by one or multiple laser beams, according to the needs of the physical research being conducted, and is imaged onto the CCD surface through a multilayer spherical lens. The shadow profile image of the plasma to be diagnosed at a particular time is obtained by using the instantaneous photographic mode of short-pulse soft X-ray laser backlight imaging. Compared with the traditional keV hard X-ray backlight technique, the soft X-ray laser shadow imaging technique has two distinct advantages. One is the appropriate wavelength of the probe light, which makes it possible to diagnose plasma near the critical surfac, and the other is a better spatial resolution because of the use of mature multilayer optical elements for near-normal incidence imaging. However, there has been no systematic study on the extent to which the spatial resolution of the imaging technology can be achieved. In this study, a careful analysis is carried out considering three aspects:the optical path geometry, the diffraction limit, and the imaging aberration. The results show that a spatial resolution of approximately 2 m can be achieved. An experiment is carried out to measure the Rayleigh-Taylor instability of plasma from the lateral direction, by using the soft X-ray laser shadow imaging technique. Some microfluids with a width of several microns can be clearly distinguished in the experimental shadow image, indicating that the diagnostic technique has a good spatial resolution. Further analysis reveals that the main factor that limits the spatial resolution is the optical path geometry. It is possible to achieve a spatial resolution of up to 1 m by increasing the magnification, selecting CCDs with smaller receiving units, etc.

Electron Impact Excitations and Linear Polarization for 1s2 1S0—1s2p 3,1P1 Lines of Fe24+ Ions under Screened Coulomb Interactions

Electron impact excitation cross sections from the ground state to the individual magnetic sublevels of 1s2p3,1P1 states in high-temperature dense plasmas are calculated for highly charged He-like Fe24+ ions by using a fully relativistic distorted-wave method. The Debye—Hückel screening model is used to screen the projectile electron from the nucleus and target electrons. The linear polarization degrees for these lines are obtained. It is found that the cross sections at all incident energies decrease with the increase of the screening for these excitations. The influence of screening on linear polarization degrees of the 1P1 line is very small. The linear polarization degrees of 3P1 line decrease sharply at low incident energy with the increase of the screening.

Wave packet spreading and localization in electron-nuclear scattering

The wave packet molecular dynamics (WPMD) method provides a variational approximation to the solution of the time-dependent Schrödinger equation. Its application in the field of high-temperature dense plasmas has yielded diverging electron width (spreading), which results in diminishing electron-nuclear interactions. Electron spreading has previously been ascribed to a shortcoming of the WPMD method and has been counteracted by various heuristic additions to the models used. We employ more accurate methods to determine if spreading continues to be predicted by them and how WPMD can be improved. A scattering process involving a single dynamic electron interacting with a periodic array of statically screened protons is used as a model problem for comparison. We compare the numerically exact split operator Fourier transform method, the Wigner trajectory method, and the time-dependent variational principle (TDVP). Within the framework of the TDVP, we use the standard variational form of WPMD, the single Gaussian wave packet (WP), as well as a sum of Gaussian WPs, as in the split WP method. Wave packet spreading is predicted by all methods, so it is not the source of the unphysical diminishing of electron-nuclear interactions in WPMD at high temperatures. Instead, the Gaussian WP's inability to correctly reproduce breakup of the electron's probability density into localized density near the protons is responsible for the deviation from more accurate predictions. Extensions of WPMD must include a mechanism for breakup to occur in order to yield dynamics that lead to accurate electron densities.

One method of producing a high-temperature dense plasma

This paper considers the interaction between an absolutely rigid wall or a steel plate and the rarefaction wave arising in solid deuterium when a 30–150 GPa shock wave arrives at the free surface. It is shown that, in the entropy trace near the wall or interface with the plate, a high-temperature plasma arises, in which a thermonuclear fusion is possible, at least, for shock-wave pressures above 70 GPa. The dimension of the plasma region and the time of its establishment are proportional to the distance between the free surface and the wall. Estimates of the proportionality coefficients are given. It is noted that, in this case, unlike in other methods of high-temperature plasma generation, the time of existence of the plasma may not depend on the sound velocity in it. It is shown that, by using a conical solid-state target wit an exit hole, the shock-wave pressure in solid deuterium can be increased from 10 to 100 GPa.

Application of high velocity streams of dense plasma for the creating of high adhesive compounds of chemically noninteracting metals

The work presents the experimental results of investigation of the possibility of the creating of high adhesive compound of chemically noninteracting metals by means of pulse streams of high temperature dense plasma. The 4 kJ plasma focus installation was used as a source of pulse streams of plasma. In the experiment assemblies of Cu–W and Pb–Fe samples were used. The deep penetration of atoms Cu and Pb accordingly in W and Fe was found. The mechanisms of the penetration of chemically neutral atoms into a material of the target can be connected with the following processes: the energy transfer from plasma pulse to implanting atoms, the origin and distribution of shock waves in the material of a target, and also the Rayleigh-Taylor instability of the border of two combining materials.

Electron-impact ionization of atoms in high-temperature dense plasmas

Electron-impact ionization cross sections for atoms in high-temperature dense plasmas are calculated in a configuration-average distorted-wave method. For those conditions in which the Coulomb coupling parameter is small, we use the Debye-H\"uckel potential to screen the projectile electron from the nucleus and target electrons. Ionization cross sections are calculated for both ${\text{Ne}}^{4+}$ and ${\text{Au}}^{47+}$ at high temperatures and various electron densities up to $1.0\ifmmode\times\else\texttimes\fi{}{10}^{25}\text{ }{\text{cm}}^{\ensuremath{-}3}$. In general we find that as the density increases, the ionization cross section decreases at all incident energies. We also find that as the charge on the atomic ion becomes larger, the relative density effect becomes smaller.

High-power lasers at the Russian Federal Nuclear Center (VNIIEF)

The development of laser plants with different purposes, which originally began in the mid-1960s, are being successfully carried out at the Laser Physics Research Institute (LPRI). Investigations of the physical fundamentals of the laser operation, nonlinear optics, and the properties of high-temperature dense plasma that is formed under the action of the intensive laser emission on matter are realized at these plants.

High-power lasers at the Russian Federal Nuclear Center (VNIIEF)

The development of laser plants with different purposes, which originally began in the mid-1960s, are being successfully carried out at the Laser Physics Research Institute (LPRI). Investigations of the physical fundamentals of the laser operation, nonlinear optics, and the properties of high-temperature dense plasma that is formed under the action of the intensive laser emission on matter are realized at these plants.

Changes of internal properties of vanadium and structure of its surface under the effect of pulsed high-temperature deuterium plasma

The work presents experimental research of the influence of a pulse of high-temperature dense plasma on materials, which as are supposed, will be used in future thermonuclear power stations. The experiments were made on 4 kJ Plasma Focus installation. Such type of installations is capable to form pulse of axial plasma flows moving with velocity approximately 108 cm/s and plasma density is about 1018 cm−3. Pure vanadium was chosen in our researches, because it can be used as a basic element at the creation of low-activated alloys. We found that due to a pulse irradiation of vanadium by deuterium plasma, shock waves arises, which result in super-deep penetration of deuterium into a volume of the studied sample. This process is accompanied with the change of vanadium structure, the occurrence of pores in it, and changes of its mechanical properties. The break-away of vanadium particles from the backside surface of the sample and forming of craters were also observed.

Advanced plasma diagnostics for investigation of physical processes in laser-irradiated foam targets (abstract)

Recently the low-density foam-like materials have been found to be very attractive for various applications in high energy-density physics. Irradiation of these materials by powerful laser pulses is a promising approach for plasma formation with parameters being of interest for inertial confinement fusion, x-ray lasers, modeling of astrophysical phenomena, etc. This article is devoted to development and application of diagnostic methods in experiments on irradiation of planar low-density (0.5–10 mg/cm3) porous targets with powerful laser pulses (1013–1014 W/cm2). To obtain reliable information on high-temperature dense plasma formation, plasma dynamics, and energy transfer in the target interior, we used a number of optical and x-ray diagnostics providing high spatial (∼10 μm) and temporal (∼10 ps) resolution. High-speed x-ray imaging, multiframe optical shadowgraphy, and interferometry, as well as scattered laser light spectroscopy at the fundamental frequency and its harmonics were used in each experiment. Only being used simultaneously these diagnostic methods provide the possibility of understanding the complicated physical processes inside laser irradiated foam-like materials. The possibilities of the diagnostic complex are illustrated by examples of obtained results and corresponding data analysis.

K,L, andMspectra of a laser plasma suitable for active x-ray diagnostics

The emission spectra of a laser plasma were determined at wavelengths of 6–7 and 7.5–8.5 A for flat targets with atomic numbers Z = 6–83 using laser radiation of densities (1–4) × 1013 W/cm2. The experimentally determined intensities of the K, L, and M spectra (~ 1015–1016 photons/4π) were compared with the results of calculations of conversion of laser radiation into x-ray emission of a laser plasma. The results obtained made it possible to optimize a laser-plasma source of soft x rays, which could be used in particular as an x-probe of a high-temperature dense plasma.

Problems in estimating average degree of ionization for high-temperature dense plasmas

The average degree of ionization Z* for a high-density plasma is examined in Thomas-Fermi and Debye-Huckel-Thomas-Fermi statistical models. To clarify ambiguities in defining Z*, predictions from several versions of these models are compared for the case of a pure hydrogen plasma for ion number density N/sub 1/=10/sup 23/ cm/sup -3/, at kT=1--1000 eV. The results offer some insight regarding the validity of the statistical models.

Enhanced microwave scattering at the upper hybrid frequency

The results of an experiment of wave scattering by coherent phase density fluctuations at the upper hybrid resonance are presented. Enhanced microwave scattering from small amplitude density fluctuations at 110 kHz in an argon plasma is observed. The results show that the scattered field is generated in a small region where the frequency of the incident microwave beam equals the local upper hybrid frequency. The measured angle of the direction of maximum scattered power is in agreement with the conservation of momentum in the direction of the confining magnetic field. An absolute calibration of the detection chain leads to a value of the scattered flux in good agreement with the theoretical calculation. Possible applications of the present results as a diagnostic tool for high temperature dense plasma are discussed.