The calculation of the optical properties of hot dense plasmas with a model that has self-consistent plasma physics is a grand challenge for high energy density science. Here we exploit a recently developed electronic structure model that uses multiple scattering theory to solve the Kohn-Sham density functional theory equations for dense plasmas. We calculate opacities in this regime, validate the method, and apply it to recent experimental measurements of opacity for Cr, Ni, and Fe. Good agreement is found in the quasicontinuum region for Cr and Ni, while the self-consistent plasma physics of the approach cannot explain the observed difference between models and the experiment for Fe.
We present the opacities of iron, aluminum, and bromine plasmas calculated using the Starrett and Saumon average-atom model allowing for ion correlations. We show that the use of earlier average-atom ion-correlation model of Rozsnyai, as has recently been done in the solar opacity calculations, overestimates the effect of ion correlations on plasma opacities. The reason for this overestimation is discussed.
We present calculations of the free-free XUV opacity of warm, solid-density aluminum at photon energies between the plasma frequency at 15 eV and the L-edge at 73 eV, using both density functional theory combined with molecular dynamics and a semi-analytical model in the RPA framework with the inclusion of local field corrections. As the temperature is increased from room temperature to 10 eV, with the ion and electron temperatures equal, we calculate an increase in the opacity in the range over which the degree of ionization is constant. The effect is less pronounced if only the electron temp…
Calculations of the opacity of hot, dense matter require models for plasma line broadening. However, the most general theories are too complex to calculate directly and some approximation is inevitably required. The most widely-used approaches focus on the line centre, where a Lorentzian shape is obtained. Here, we demonstrate that in the opposite limit, far from the line centre, the opacity can be expressed in terms of second-order transitions, such as electron-photon and two-photon processes. We suggest that this insight could form the basis for a new approach to improve calculations of opac…
Standard measures of opacity, the imaginary part of the atomic scattering factor $f_2$ and the x-ray mass attenuation coefficient $μ/ρ$, are evaluated in shock-heated boron, boron carbide and boron nitride plasmas. The Hugoniot equation, relating the temperature $T$ behind a shock wave to the compression ratio $ρ/ρ_0$ across the shock front, is used in connection with the plasma equation of state to determine the pressure $p$, effective plasma charge $Z^\ast$ and the K-shell occupation in terms of $ρ/ρ_0$. Solutions of the Hugoniot equation (determined within the framework of the generalized T…
We focus on studying the opacity of iron, chromium, and nickel plasmas at conditions relevant to experiments carried out at Sandia National Laboratories [J. E. Bailey et al., Nature 517, 56 (2015)]. We calculate the photo-absorption cross-sections and subsequent opacity for plasmas using linear response time-dependent density functional theory (TD-DFT). Our results indicate that the physics of channel mixing accounted for in linear response TD-DFT leads to an increase in the opacity in the bound-free quasi-continuum, where the Sandia experiments indicate that models under-predict iron opacity.…
The synthetic emission spectra and opacity of high-density, high-temperature germanium (Z=32) plasma from super-transition-array (STA) calculations are presented. The viability of the STA model, which is based on a statistical superconfigurations accounting approach for calculating the atomic and radiative properties, is examined by comparing and contrasting its results against the available experimental data and other theoretical calculations. First, we focus on the emission data. To model the data, the Eulerian radiation-hydrodynamics code FastRad3D is used in conjunction with STA to obtain …
It is generally believed that relativistically underdense plasma is transparent for intense laser radiation. However, particle-in-cell simulations reveal abnormal laser field absorption above the intensity threshold about~$3 \times 10^{24}~\mathrm{W}\,\mathrm{cm}^{-2}$ for the wavelength of $1~μ\mathrm{m}$. Above the threshold, the further increase of the laser intensity doesn't lead to the increase of the propagation distance. The simulations take into account emission of hard photons and subsequent pair photoproduction in the laser field. These effects lead to onset of a self-sustained elect…
Plasma screening and configuration interaction effects induced large enhancement on L-shell photoionization cross sections and opacity
National Key Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics（计算物理国家重点实验室，应用物理与计算数学研究所）；School of Optoelectronics, University of Chinese Academy of Sciences（中国科学院大学光电学院）；School of Mathematics and Physics, Qinghai University（青海大学理学院）；Center for Applied Physics and Technology, HEDPS, Peking University（北京大学高能量密度物理科学与技术研究院应用物理与技术中心）
该研究提出结合等离子体屏蔽和组态相互作用效应改进处理的不透明度模型，解释了铁、铬和镍不透明度相关差异，为太阳内部温度下 L 壳层不透明度测量提供系统解释，推动高能量密度等离子体中相关精确模拟。
We investigate how next-generation laser pulses at 10 PW $-$ 200 PW interact with a solid target in the presence of a relativistically underdense preplasma produced by amplified spontaneous emission (ASE). Laser hole boring and relativistic transparency are strongly restrained due to the generation of electron-positron pairs and $γ$-ray photons via quantum electrodynamics (QED) processes. A pair plasma with a density above the initial preplasma density is formed, counteracting the electron-free channel produced by the hole boring. This pair-dominated plasma can block the laser transport and tr…
Laboratory (laser and Z-pinch) opacity measurements of well-characterized plasmas provide data to assist inertial confinement fusion, astrophysics and atomic-physics research. In order to test the atomic-physics codes devoted to the calculation of radiative properties of hot plasmas, such experiments must fulfill a number of requirements. In this work, we discuss some sources of uncertainty in absorption-spectroscopy experiments, concerning areal mass, background emission, intensity of the backlighter and self-emission of the plasma. We also study the impact of spatial non-uniformities of the …
Recent R-matrix calculations claim to produce a significant enhancement in the opacity of Fe XVII due to atomic core excitations [S. N. Nahar & A.K. Pradhan, Phys. Rev. Letters 116, 235003 (2016), arXiv:1606.02731] and assert that this enhancement is consistent with recent measurements of higher-than-predicted iron opacities [J. E. Bailey et al., Nature 517, 56 (2015)]. This comment shows that the standard opacity models which have already been directly compared with experimental data produce photon absorption cross-sections for Fe XVII that are effectively equivalent to (and in fact larger th…
Opacity determines radiation transport through material media. In a plasma source the primary contributors to atomic opacity are bound-bound line transitions and bound-free photoionization into the continuum. We review the theoretical methodology for state-of-the-art photoionization calculations based on the R-matrix method as employed in the Opacity Project, the Iron Project, and solution of the heretofore unsolved problem of plasma broadening of autoionizing resonances due to electron impact, Stark (electric microfields), Doppler (thermal), and core-excitations. R-matrix opacity calculations…
The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperature-dependent absorption coefficient directly from an oversampled pool of single-…
The free-free opacity in dense systems is a property that both tests our fundamental understanding of correlated many-body systems, and is needed to understand the radiative properties of high energy-density plasmas. Despite its importance, predictive calculations of the free-free opacity remain challenging even in the condensed matter phase for simple metals. Here we show how the free-free opacity can be modelled at finite-temperatures via time-dependent density functional theory, and illustrate the importance of including local field corrections, core polarization and self-energy corrections…
The possibility of formation of quasibound states and ordered structures in dense plasma is investigated. The effective potentials of dense plasma are used. On the basis of these models the condition of the ordered structures formation in the system is obtained. It is shown that in the dense classical plasma the quasibound states form whereas the ordered structures form in the dense semiclassical plasma.
We investigate the rates for multielectron recombination within a dense plasma environment in local thermodynamic equilibrium (LTE). We find that these multielectron recombination rates can be high within dense plasmas, and they should be treated in the simulations of the plasmas created by intense radiation, in particular for plasmas created by intense VUV radiation from free-electron-laser (FEL) or for modelling the inertial confinement fusion (ICF) plasmas.
A theory for the ion acoustic wave damping in dense plasmas and warm dense matter, accounting for the Umklapp process, is presented. A higher decay rate compared to the prediction from the Landau damping theory is predicted for high-Z dense plasmas where the electron density ranges from $10^{21}$ to $ 10^{24} \mathrm{cm^{-3}}$ and the electron temperature is moderately higher than the Fermi energy.
Fermi Dirac free electron model is applied to very dense plasmas with medium or low temperatures. While Boltzmann statistics can lead to very high densities of ionized electrons, only at very high temperatures, Fermi Dirac statistics can support the high densities of ionized electrons at medium or low temperatures due to the high degeneracies obtained in this model. Since very dense plasmas may be obtained at low temperatures the corresponding black body radiation with the plasma luminosity will be quite small. On the other hand gravitational effects might be quite large due to the high densit…
Here we discuss the possibility of employment of ultrarelativistic electron and proton bunches for generation of high plasma wakefields in dense plasmas due to the Cherenkov resonance plasma-bunch interaction. We estimate the maximum amplitude of such a wake and minimum system length at which the maximum amplitude can be generated at the given bunch parameters.
Experimental tests are in progress to evaluate the accuracy of the modeled iron opacity at solar interior conditions, in particular to better constrain the solar abundance problem [S. Basu and H.M. Antia, Physics Reports 457, 217 (2008)]. Here we describe measurements addressing three of the key requirements for reliable opacity experiments: control of sample conditions, independent sample condition diagnostics, and verification of sample condition uniformity. The opacity samples consist of iron/magnesium layers tamped by plastic. By changing the plastic thicknesses, we have controlled the iro…
A self-consistent determination of the spectral function and the self-energy of electrons in a hot and dense plasma is reported. The self-energy is determined within the approximation of the screened potential. It is shown, that the quasi-particle concept is not an adequate concept for hot and dense plasmas, since the width of the spectral function has to be considered. As an example, the solar core plasma is discussed. An effective quasi-particle picture is introduced and results for the solar core plasma as well as for ICF plasmas are presented.
We present a model for the rate of temperature relaxation between electrons and ions in plasmas. The model includes self-consistently the effects of particle screening, electron degeneracy and correlations between electrons and ions. We successfully validate the model over a wide range of plasma coupling against molecular-dynamics simulations of classical plasma of like-charged electrons and ions. We present calculations of the relaxation rates in dense hydrogen and show that, while electron-ion correlation effects are indispensable in classical, like-charged plasmas at any density and tempera…
We present a theoretical investigation of the excitation of multiple electrostatic wakefields by the ponderomotive force of a short electromagnetic pulse propagating through a dense plasma. It is found that the inclusion of the quantum statistical pressure and quantum electron tunneling effects can qualitatively change the classical behavior of the wakefield. In addition to the well known plasma oscillation wakefield, with a wavelength of the order of the electron skin depth, which in a dense plasma is of the order of several nanometers, wakefields in dense plasmas with a shorter wavelength ar…
Propagation of right-hand circularly polarized laser into highly magnetized over-dense collisional plasma is analytically studied from basic equations. Highly magnetized plasma with density of 10^23 cm^-3 is efficiently heated from 100 eV to 1 keV within depth of around 20 μ{m} in one nanosecond by Nd:YAG laser with moderate irradiance of around 10^14 Wcm^-2.
The Coulomb log (log Λ) approximation is widely used to approximate electron transport coefficients in dense plasmas. It is a classical approximation to the momentum transport cross section. The accuracy of this approximation for electrical conductivity in dense plasmas is assessed by comparing to fully quantum mechanical calculations for realistic scattering potentials. It is found that the classical approximation is accurate to +/-10% when log Λ > 3, irrespective of the plasma species. The thermodynamic regime (density and temperature) for which log Λ > 3 corresponds to does, however, strong…
In the present paper we propose the use of desnity matrix formalism for the calculation of the atomic spectroscopic properties of autoionizing states in dense plasmas, i.e. warm dense matter and strongly coupled plasmas. This is motivated by the importance of taking into account the effect of the electric microfield generated by the plasma charge constituents in the calculation of the atomic populations of autoionizing states. For autoionizing states, electron densities justifying the statistical approach exceed solid density bringing serious doubts to the statistical approach even in dense pl…
We present an investigation for the generation of intense magnetic fields in dense plasmas with an anisotropic electron Fermi-Dirac distribution. For this purpose, we use a new linear dispersion relation for transverse waves in the Wigner-Maxwell dense quantum plasma system. Numerical analysis of the dispersion relation reveals the scaling of the growth rate as a function of the Fermi energy and the temperature anisotropy. The nonlinear saturation level of the magnetic fields is found through fully kinetic simulations, which indicates that the final amplitudes of the magnetic fields are propor…
By combining the linear theory and numerical simulations, we study the response of a radially bounded axisymmetric plasma to relativistic charged particle beams in a wide range of plasma densities. We present analytical expressions for the magnetic field generated in the dense plasma, prove vanishing of the wakefield potential beyond the trajectory of the outermost plasma electron, and follow the wakefield potential change as the plasma density decreases. At high plasma densities, wavefronts of electron density and radial electric field are distorted because of beam charge and current neutrali…
In the present paper we propose to update the standard calculation of Stark line profiles for autoionizing atomic states in dense plasmas, i.e. warm dense matter and strongly coupled plasmas. This is motivated by the importance of taking into account the effect of the electric microfield generated by the plasma charge constituents in the calculation of the atomic populations of autoionizing states which leads to the modification of the calculation of Stark line profiles in the frame of the standard theory. This is due to the properties of the autoionizing atomic states that are far from Boltzm…
Controlled fusion with advanced fuels requires average electron and ion energies above 100 keV (equivalent to 1.1 billion K) in a dense plasma. We have met this requirement and demonstrated electron and ion energies over 100 keV in a compact and inexpensive dense plasma focus device. We have achieved this in plasma "hot spots" or plasmoids that, in our best results, had a density-confinement-time-energy product of 5.0 x1015 keVsec/cm3, a record for any fusion experiment. We measured the electron energies with an X-ray detector instrument that demonstrated conclusively that the hard X-rays were…
This work is to continue the development of the general model, Multi-Average Ion Collisional-Radiative Model (MAICRM), to calculate the plasma spectral properties of hot dense plasmas. In this model, an average ion is used to characterize the average orbital occupations and the total populations of the configurations within a single charge state. The orbital occupations and population of the average ion are obtained by solving two sets of rate equations sequentially and iteratively. The calculated spectra of Xe and Au plasmas under different plasma conditions are in good agreement with the DCA…
We present a new theoretical approach for collisional absorption of laser energy in dense plasmas which accommodates arbitrary frequencies and high intensities of the laser field. We establish a connection between laser absorption by inverse Bremstrahlung and the stopping power. This relation is then applied to include strong correlations beyond the mean field approach. The results show an excellent agreement with molecular dynamics simulations up to very high coupling strength.
A precise calculation that translates shifts of X-ray K-absorption edges to variations of thermodynamic properties allows quantitative characterization of interior thermodynamic properties of warm dense plasmas by X-ray absorption techniques, which provides essential information for inertial confinement fusion and other astrophysical applications. We show that this interpretation can be achieved through an improved first-principles method. Our calculation shows that the shift of K-edges exhibits selective sensitivity to thermal parameters and thus would be a suitable temperature index to warm …
The dependence of the real and imaginary parts of the refractive index on the dielectric capacity was obtained for different values of the nonideality parameter, by the help of an ion-ion psevdopotential of fully ionized dense high-temperature plasma, taking into account local fields, quantum and collective effects.
The quantum diffraction and symmetry effects on the entanglement fidelity (EF) of different elastic electron-electron, ion-ion and electron-ion interactions are investigated in non-ideal dense plasma. The partial wave analysis and an effective screened interaction potential including quantum mechanical diffraction and symmetry effects are employed to obtain the EF in a non-ideal dense plasma. We show that collision energy and temperatures of electron and ion have a destroying role in the entanglement. In fact, by decreasing the temperature of any kind of particles, the quantum effects become d…
The screening of a test charge by partially degenerate non-ideal free electrons at conditions related to warm dense matter and dense plasmas is investigated using linear response theory and the local field correction based on ab inito Quantum Monte-Carlo simulations data. The analysis of the obtained results is performed by comparing to the random phase approximation and the Singwi-Tosi-Land-Sjölander approximation. The applicability of the long-wavelength approximation for the description of screening is investigated. The impact of electronic exchange-correlations effects on structural proper…
Orbital-free molecular dynamics simulations are used to benchmark two popular models for hot dense plasmas: the one component plasma (OCP) and the Yukawa model. A unified concept emerges where an effective OCP (eOCP) is constructed from the short-range structure of the plasma. An unambiguous ionization and the screening length can be defined and used for a Yukawa system, which reproduces the long range structure with finite compressibility. Similarly, the dispersion relation of longitudinal waves is consistent with the screened model at vanishing wavenumber but merges with the OCP at high wave…
The dense plasma focus is a plasma discharge powered by a capacitor bank. Standard diagnostics include measurement of the time derivative of the current through and the voltage across its connections with the capacitor bank. Interpretation of this diagnostic data often involves some assumptions regarding the representation of the dense plasma focus as a time varying inductance. One of the characteristic features of the current derivative waveform is a relatively sharp dip and an associated sharp voltage spike. This has often been interpreted as a result of a rapid rise in the time varying indu…
An extended first-principles molecular dynamics (FPMD) method based on Kohn-Sham scheme is proposed to elevate the temperature limit of the FPMD method in the calculation of dense plasmas. The extended method treats the wave functions of high energy electrons as plane waves analytically, and thus expands the application of the FPMD method to the region of hot dense plasmas without suffering from the formidable computational costs. In addition, the extended method inherits the high accuracy of the Kohn-Sham scheme and keeps the information of elec- tronic structures. This gives an edge to the e…
Results of experimental investigation of the ECR discharge in a single coil magnetic field as an alternative to RF and helicon discharges for wide-aperture dense plasma fluxes production are presented. A possibility of obtaining wide-aperture high density hydrogen plasma fluxes with homogenous transverse distribution was demonstrated in such a system. The prospects of using this system for obtaining high current ion beams are discussed.
In simulations of a 12.5PW laser (focused intensity I = 4x10^23W/cm^2) striking a solid aluminium target 10% of the laser energy is converted to gamma-rays. A dense electron-positron plasma is generated with a maximum density of 10^26/m^3; seven orders of magnitude denser than pure e-e+ plasmas generated with 1PW lasers. When the laser power is increased to 320PW (I = 10^25W/cm^2) 40% of the laser energy is converted to gamma-ray photons and 10% to electron-positron pairs. In both cases there is strong feedback between the QED emission processes and the plasma physics; the defining feature of …
The properties of a bound electron system immersed in a plasma environment are strongly modified by the surrounding plasma. The modification of a basic quantity, the ionization energy, is described by the electronic self-energy and by dynamical screening within the framework of the quantum statistical theory. Introducing the ionic dynamical structure factor as the indicator for the ionic micro-field, we demonstrate that ionic correlations and fluctuations play a critical role in determining the ionization potential depression. This is in particular true for mixtures of different ions with larg…
The charge states of ions in dense plasmas fluctuate due to collisional ionization and recombination. Here we show how, by modifying the ion interaction potential, these fluctuations can mediate energy exchange between the plasma electrons and ions. Moreover, we develop a theory for this novel electron-ion energy transfer mechanism. Calculations using a random walk approach for the fluctuations suggest that the energy exchange rate from charge state fluctuations could be comparable to direct electron-ion collisions. This mechanism is, however, predicted to exhibit a complex dependence on the t…
A new model for the electrical conductivity of dense plasmas with a mixture of ion species, containing no adjustable parameters, is presented. The model takes the temperature, mass density and relative abundances of the species as input. It takes into account partial ionization, ionic structure, and core-valence orthogonality, and uses quantum mechanical calculations of cross sections. Comparison to an existing high fidelity but computationally expensive method reveals good agreement. The new model is computationally efficient and can reach high temperatures. A new mixing rule is also presente…
We validate the application of our recent orbital-free density functional theory (DFT) approach, [Phys. Rev. Lett. 113, 155006 (2014)], for the calculation of ionic and electronic transport properties of dense plasmas. To this end, we calculate the self-diffusion coefficient, the viscosity coefficient, the electrical and thermal conductivities, and the reflectivity coefficient of hydrogen and aluminum plasmas. Very good agreement is found with orbital-based Kohn-Sham DFT calculations at lower temperatures. Because the method does not scale with temperature, we can produce results at much highe…
The interaction of two lasers with a difference frequency near that of the ambient plasma frequency produces beat waves that can resonantly accelerate thermal electrons. These beat waves can be used to drive electron current and thereby embed magnetic fields into the plasma [D. R. Welch et al., Phys. Rev. Lett. 109, 225002 (2012)]. In this paper, we present two-dimensional particle-in-cell simulations of the beat-wave current-drive process over a wide range of angles between the injected lasers, laser intensities, and plasma densities. We discuss the application of this technique to the magnet…
Compressed Ultrafast Photography of Plasmas Formed from Laser Breakdown of Dense Gases Reveals that Internal Processes Dominate Evolution at Early Times
Theoretical modelling of ionization potential depression and the related ionization equilibrium in dense plasmas, in particular in warm/hot dense matter, represents a significant challenge due to ionic coupling and electronic degeneracy effects. We present a quantum statistical model based on dynamical structure factors for the ionization potential depression, where quantum exchange and dynamical correlation effects in plasma environments are consistently and systematically taken into account in terms of the concept of self-energy. Under the condition of local thermodynamic equilibrium, the ch…
This paper, Part I of a series, describes a kinematic framework for the theory of a Dense Plasma Focus which is very similar to the GV model in spirit but which differs in its scope in four respects. First, the GV model derives most of its results from the mathematical properties of the solution of a certain partial differential equation derived from assumptions that apparently represent conservation of momentum but are not a rigorous application of the relevant physics. The present model is based on the scaling properties of the standard equations of motion, which lead to mathematical results…
