Table of contents

This special issue contains papers presented at the International Conference on Strongly Coupled Coulomb Systems (SCCS), held from 29 July–2 August 2008 at the University of Camerino. Camerino is an ancient hill-top town located in the Apennine mountains of Italy, 200 kilometres northeast of Rome, with a university dating back to 1336.

The Camerino conference was the 11th in a series which started in 1977:

• 1977: Orleans-la-Source, France, as a NATO Advanced Study Institute on Strongly Coupled Plasmas (hosted by Marc Feix and Gabor J Kalman)

• 1982: Les Houches, France (hosted by Marc Baus and Jean-Pierre Hansen)

• 1986: Santa Cruz, California, USA (hosted by Forrest J Rogers and Hugh E DeWitt)

• 1989: Tokyo, Japan (hosted by Setsuo Ichimaru)

• 1992: Rochester, New York, USA (hosted by Hugh M Van Horn and Setsuo Ichimaru)

• 1995: Binz, Germany (hosted by Wolf Dietrich Kraeft and Manfred Schlanges)

• 1997: Boston, Massachusetts, USA (hosted by Gabor J Kalman)

• 1999: St Malo, France (hosted by Claude Deutsch and Bernard Jancovici)

• 2002: Santa Fe, New Mexico, USA (hosted by John F Benage and Michael S Murillo)

• 2005: Moscow, Russia (hosted by Vladimir E Fortov and Vladimir Vorob'ev).

The name of the series was changed in 1996 from Strongly Coupled Plasmas to Strongly Coupled Coulomb Systems to reflect a wider range of topics. 'Strongly Coupled Coulomb Systems' encompasses diverse many-body systems and physical conditions.

The purpose of the conferences is to provide a regular international forum for the presentation and discussion of research achievements and ideas relating to a variety of plasma, liquid and condensed matter systems that are dominated by strong Coulomb interactions between their constituents. Each meeting has seen an evolution of topics and emphases that have followed new discoveries and new techniques. The field has continued to see new experimental tools and access to new strongly coupled conditions, most recently in the areas of warm matter, dusty plasmas, condensed matter and ultra-cold plasmas.

One hundred and thirty participants came from twenty countries and four continents to participate in the conference. Those giving presentations were asked to contribute to this special issue to make a representative record of an interesting conference.

We thank the International Advisory Board and the Programme Committee for their support and suggestions. We thank the Local Organizing Committee (Stefania De Palo, Vittorio Pellegrini, Andrea Perali and Pierbiagio Pieri) for all their efforts. We highlight for special mention the dedication displayed by Andrea Perali, by Rocco di Marco for computer support, and by our tireless conference secretary Fiorella Paino. The knowledgeable guided tour of the historic centre of Camerino given by Fiorella Paino was appreciated by many participants. It is no exaggeration to say that without the extraordinary efforts put in by these three, the conference could not have been the success that it was. For their sustained interest and support we thank Fulvio Esposito, Rector of the University of Camerino, Fabio Beltram, Director of NEST, Scuola Normale Superiore, Pisa, and Daniel Cox, Co-Director of ICAM, University of California at Davis. We thank the Institute of Complex and Adaptive Matter ICAM–I2CAM, USA for providing a video record of the conference on the web (found at http://sccs2008.df.unicam.it/). Finally we thank the conference sponsors for their very generous support: the University of Camerino, the Institute of Complex and Adaptive Matter ICAM–I2CAM, USA, the International Centre for Theoretical Physics ICTP Trieste, and CNR-INFM DEMOCRITOS Modeling Center for Research in Atomistic Simulation, Trieste.

Participants at the International Conference on Strongly Coupled Coulomb Systems (SCCS) (University of Camerino, Italy, 29 July–2 August 2008).

Hot dense helium is studied with first-principle computer simulations. By combining path integral Monte Carlo and density functional molecular dynamics, a large temperature and density interval ranging from 1000 to 1 000 000 K and 0.4 to 5.4 g cm⁻³ becomes accessible to first-principle simulations and the changes in the structure of dense hot fluids can be investigated. The focus of this paper is on pair correlation functions between nuclei, between electrons, and between electrons and nuclei. The density and temperature dependence of these correlation functions is analyzed in order to describe the structure of the dense fluid helium at extreme conditions.

We study thermodynamic properties and the electrical conductivity of dense hydrogen and deuterium using three methods: classical reactive Monte Carlo, direct path integral Monte Carlo (PIMC) and a quantum dynamics method in the Wigner representation of quantum mechanics. We report the calculation of the deuterium compression quasi-isentrope in good agreement with experiments. We also solve the Wigner–Liouville equation of dense degenerate hydrogen calculating the initial equilibrium state by the PIMC method. The obtained particle trajectories determine the momentum–momentum correlation functions and the electrical conductivity and are compared with available theories and simulations.

The relativistic heavy-ion collider (RHIC) was built to re-create and study in the laboratory the extremely hot and dense matter that filled our entire universe during its first few microseconds. Its operation since June 2000 has been extremely successful, and the four large RHIC experiments have produced an impressive body of data which indeed provide compelling evidence for the formation of thermally equilibrated matter at unprecedented temperatures and energy densities—a 'quark–gluon plasma (QGP)'. A surprise has been the discovery that this plasma behaves like an almost perfect fluid, with extremely low viscosity. Theorists had expected a weakly interacting gas of quarks and gluons, but instead we seem to have created a strongly coupled plasma liquid. The experimental evidence strongly relies on a feature called 'elliptic flow' in off-central collisions, with additional support from other observations. This paper explains how we probe the strongly coupled QGP, describes the ideas and measurements which led to the conclusion that the QGP is an almost perfect liquid, and shows how they tie relativistic heavy-ion physics into other burgeoning fields of modern physics, such as strongly coupled Coulomb plasmas, ultracold systems of trapped atoms and superstring theory.

Ultra-relativistic electromagnetic plasmas can be used for improving our understanding of the quark–gluon plasma. In the weakly coupled regime, both plasmas can be described by transport theoretical and quantum field theoretical methods leading to similar results for the plasma properties (dielectric tensor, dispersion relations, plasma frequency, Debye screening, transport coefficients, damping and particle production rates). In particular, future experiments with ultra-relativistic electron–positron plasmas in ultra-strong laser fields might open the possibility of testing these predictions, e.g. the existence of a new fermionic plasma wave (plasmino). In the strongly coupled regime, electromagnetic plasmas such as complex plasmas can be used as models or at least analogies for the quark–gluon plasma possibly produced in relativistic heavy-ion experiments. For example, pair correlation functions can be used to investigate the equation of state and cross section enhancement for parton scattering can be explained.

The method of moments is used to calculate the dynamic conductivity of strongly coupled fully ionized hydrogen plasmas. The electron density n_e and temperature T vary in the domains 10²¹ < n_e < 10²⁴ cm⁻³, 10⁴ K < T < 10⁶ K. The results are compared to some theoretical data.

The modulation of the equation of state by the chemical composition leads to a natural method to determine the helium and heavy-element abundance in the sun and stars. For solar helium this has indeed become the only reliable method. However, one has to keep in mind that the result is only as good as the quality of the equation of state. So far, there are only theoretical formalisms, but no experiments, for the relevant physical conditions. It is obvious that sharp theoretical tools in the form of smooth thermodynamic (and opacity) quantities are crucial for the interpretation of the astrophysical data, both for abundance determinations and improvements of the theory. An emulator of the OPAL equation of state was developed, by which the OPAL equation of state can be applied directly in stellar models, without recourse to pre-computed tables.

A model in the framework of a chemical picture for the equation of state of warm dense hydrogen (SAHA-D) is presented. An intense short-range repulsion of neutral particles is described in a simplified form (the soft sphere model). Coulomb corrections are used via a modified pseudopotential model. The results of calculations of principal Hugoniots, double shock and isoenrope are compared with experiment and first principle calculations.

Macroscopic plasma polarization, which is created by gravitation and other mass-acting (inertial) forces in massive astrophysical objects (MAOs), is under discussion. A non-ideality effect due to strong Coulomb interaction of charged particles is introduced into consideration as a new source of such polarization. A simplified situation of a totally equilibrium isothermal star without relativistic effects and influence of magnetic field is considered. The study is based on a density functional approach combined with a 'local density approximation'. It leads to conditions of constancy for generalized (electro) chemical potentials and/or conditions of equilibrium for the forces acting on each charged species. A new 'non-ideality force' appears in this consideration. Hypothetical sequences of gravitational, inertial and non-ideality polarization on thermo- and hydrodynamics of MAO are under discussion.

An equation of state for a weakly non-ideal hydrogen plasma was developed to account for the influence of degenerate electrons on the contribution of bound states. Asymptotic expressions for the contribution were derived and compared. In this work, the reduced model EOS includes the ideal gas contribution with degenerate electrons and relativistic corrections, bound states contribution and the Coulomb interaction in the Debye–Hückel approximation. The influence of the electron degeneracy on the adiabatic exponent and the total pressure is shown.

Strong electron–electron interactions in dilute two-dimensional electron systems in silicon lead to Pauli spin susceptibility growing critically at low electron densities. This effect originates from renormalization of the effective mass rather than the g-factor. The relative mass enhancement is system and disorder independent, which suggests that it is determined by electron–electron interactions only.

We discuss the metal–insulator transition phenomenon in two dimensions in terms of a quantum critical point that controls a range of the low temperature insulator region as well as the usual quantum critical sector. We show that this extended range of criticality permits a determination of both the dynamical critical exponent z and the correlation length critical exponent ν from published data from a single experiment in the insulator critical region. The resulting value of the product zν is consistent with the temperature dependence of the resistance in the quantum critical sector. This provides strong quantitative evidence for the presence of a quantum critical point.

We investigate transport in 2D mesoscopic electron systems with disorder assuming a percolation mechanism through a network of disconnected conducting metallic domains. The size of the domains is determined by the level of disorder and the strength of the electron correlations. The domains are linked for transport by two competing mechanisms. The first mechanism is familiar thermally activated hopping. The second is quantum tunnelling between adjacent conducting regions bounded by equipotential contours of the same value. This mechanism leads to temperature-independent transmission at low temperatures. We calculate the transmission across the potential barriers separating adjacent domains, and we obtain agreement with recent experimental measurements of temperature-dependent resistivities in mesoscopic 2D systems. We also obtain consistent values for the spatial separation of the domains and the average variation in the random disorder potential. Finally, we show that the effect of quantum coherence can result in a small downturn in the resistivity at low temperatures, again in good agreement with the recent experimental results.

Starting from the quantum Monte Carlo (QMC) prediction for the ground-state energy of a clean two-dimensional one-valley (2D1V) electron gas, we estimate the energy correction due to scattering sources present in actual devices such as AlAs quantum wells and GaAs heterostructures. We find that the effect of uncorrelated disorder, in the lowest (second) order in perturbation theory, is to enhance the spin susceptibility leading to its eventual divergence. In the density region where the Born approximation is able to reproduce the experimental mobility, the prediction for the spin susceptibility yielded by perturbation theory is in very good agreement with the available experimental evidence.

We investigate structures of 2D quantum electron–hole (e–h) plasmas by the direct path integral Monte Carlo method (PIMC) in a wide range of temperature, density and hole-to-electron mass ratio. Our simulation includes a region of appearance and decay of the bound states (excitons and biexcitons), the Mott transition from the neutral e–h plasma to metallic-like clusters, formation from clusters of the hexatic-like liquid and formation of the crystal-like lattice.

At low energies, electrons in doped graphene sheets are described by a massless Dirac fermion Hamiltonian. In this work, we present a semi-analytical expression for the dynamical density–density linear-response function of non-interacting massless Dirac fermions (the so-called 'Lindhard' function) at finite temperature. This result is crucial to describe finite-temperature screening of interacting massless Dirac fermions within the random phase approximation. In particular, we use it to make quantitative predictions for the specific heat and the compressibility of doped graphene sheets. We find that, at low temperatures, the specific heat has the usual normal-Fermi-liquid linear-in-temperature behavior, with a slope that is solely controlled by the renormalized quasiparticle velocity.

Using an adiabatic approximation, we derive an effective interaction potential for spatially indirect excitons in quantum well structures. Using this potential and path integral Monte Carlo simulations, we study exciton crystallization and the quantum melting phase transition in a macroscopic system of 2D excitons. Furthermore, the superfluid fraction is calculated as a function of density and is shown to vanish upon crystallization.

We address the question of collective excitations in two-dimensional (2D) dipolar systems. The main issue is that such systems have no Hartree and no random-phase-approximation (RPA) limits and calculations have to include particle correlations from the outset. We focus on the longitudinal collective mode representing the density oscillations of the dipoles and on the transverse collective mode representing shear waves. Our theoretical approach is based on the quasi-localized charge approximation (QLCA) adapted to point-dipole systems interacting through a 1/r³ potential. Our analytical calculation is accompanied by classical molecular dynamics (MD) simulation. At long wavelengths, the longitudinal and transverse collective excitations exhibit acoustic behaviors with phase velocities that vary linearly with the dipole strength and are wholly maintained by particle correlations. At finite wavenumbers, the mode dispersion resulting from our classical MD simulations shows a roton-like behavior. Comparison with the quantum Monte Carlo dispersion generated through the Feynman relation (Astrakharchik et al 2007 Phys. Rev. Lett.98 060405) shows a remarkably good quantitative agreement between the two.

In the collective mode spectrum of a relativistic, strongly coupled plasma, novel physical effects emerge, which are absent both in the weakly coupled relativistic and in the strongly coupled non-relativistic plasmas. Inspired by the pseudo-relativistic behavior of the electron gas in two-dimensional graphene layers, we address the problem of a classical two-dimensional, ultra-relativistic system of charged particles. We investigate the mode dispersion and damping both through molecular dynamics simulations and analytically via the quasi-localized charge approximation and develop modifications of the theory appropriate for this system. The new aspect introduced in the simulation is the decoupling of particle velocities from the particle momenta. As for new physical features, their origin is to be sought in the constancy of particle speeds and in the broad distribution of 'plasma frequencies', mimicking the similar distribution of momenta is causing the system to emulate the behavior of a collection of an infinite number of oscillators. Of particular interest is the strongly reduced damping at weak coupling, brought about by the disappearance of the Landau damping and the greatly enhanced damping at strong coupling, caused by the phase mixing of the coupled plasma oscillators. We suggest the possible experimental detection of these effects in graphene.

This paper presents a few case studies of finite electron systems for which strong correlations play a dominant role. In simple metal clusters, the valence electrons determine the stability and shape of the clusters. The ionic skeleton of alkali metals is soft, and cluster geometries are often solely determined by electron correlations. In quantum dots and rings, the electrons may be confined by an external electrostatic potential formed by a gated heterostructure. In the low-density limit, the electrons may form the so-called Wigner molecules, for which the many-body quantum spectra reveal the classical vibration modes. High rotational states increase the tendency for the electrons to localize. At low angular momenta, the electrons may form a quantum Hall liquid with vortices. In this case, the vortices act as quasi-particles with long-range effective interactions that localize in a vortex molecule, in much analogy with the electron localization at strong rotation.

A nonequilibrium Green's functions (NEGF) approach for spatially inhomogeneous, strongly correlated artificial atoms is presented and applied to compute the time-dependent properties starting from a (correlated) initial few-electron state at finite temperatures. In the regime of moderate-to-strong coupling, we consider the Kohn mode of a three-electron system in a parabolic confinement excited by a short-pulsed classical laser field treated in the dipole approximation. In particular, we numerically confirm that this mode is preserved within a conserving (e.g., Hartree–Fock or second Born) theory.

By carrying out extensive lattice regularized diffusion Monte Carlo calculations, we study the spin and density dependence of the ground-state energy for a quasi-one-dimensional electron gas, with harmonic transverse confinement and long-range 1/r interactions. We present a parametrization of the exchange–correlation energy suitable for spin density functional calculations, which fulfils exact low and high density limits.

We analyze thermodynamics of fine particle (dusty) plasmas, regarding them as systems composed of charged particles with hard cores interacting via the repulsive Yukawa potential and the ambient plasma (of ions and electrons), taking the contribution of the latter properly into account. When the Coulomb coupling between fine particles becomes sufficiently strong, the isothermal compressibility of the whole system diverges and we have a phase separation and an associated critical point. The enhancement of long-wavelength density fluctuations near the critical point is shown. Experimental conditions of fine particle plasmas, densities and temperatures of components and the fine particle size are obtained corresponding to characteristic parameters around the critical point and the dependence on ion species and other factors is discussed. These phenomena will be observed in the bulk three-dimensional system which may be realized on the ground by somehow canceling the effect of gravity on fine particles. Experiments under the microgravity environment are naturally expected to provide a chance of observation.

A combined theoretical and experimental analysis of the normal modes of three-dimensional spherically confined Yukawa clusters is presented. Particular attention is paid to the breathing mode and the existence of multiple monopole oscillations in Yukawa systems. Finally, the influence of dissipation on the mode spectrum is investigated.

The effective pair-wise interaction potential is reconstructed by the Shommers technique on the basis of the measured pair correlation functions in complex plasma. This potential appears to have an attraction branch. We show that the field of the trap cannot be the only reason for this attraction.

We perform non-equilibrium simulations to study heat conduction in two-dimensional strongly coupled dusty plasmas. Temperature gradients are established by heating one part of the otherwise equilibrium system to a higher temperature. Heat conductivity is measured directly from the stationary temperature profile and heat flux. Particular attention is paid to the influence of damping effect on the heat conduction. It is found that the heat conductivity increases with the decrease of the damping rate, while its magnitude agrees with previous experimental measurement.

In the present work, the behavior of dust particles near an attracting Langmuir cylindrical probe in glow discharge plasma was investigated experimentally. Trajectories of dust particles for different initial kinetic energies and impact parameters were analyzed numerically. The comparision between experimental and simulation results are made. The results obtained can be used for the development of new dusty plasma diagnostic techniques.

A new model for the formation of trapped ions around a negatively charged dust particle immersed in low-density non-equilibrium plasma of gas discharge is presented. It is shown that the ionic coat leads to a shielding of the proper charge of the dust particle. In experiments it is only possible to detect the effective charge of a dust particle that is equal to the difference between the proper charge of the particle and the charge of trapped ions.

The distributions of dust particle density in the various types of electromagnetic and gravitational traps are discussed to clarify the specific behaviour of these distributions for changing parameters of plasma. Correlations between the dust particles (Yukawa interaction potential) are taken into account by the use of the density functional formalism for finite temperatures in electro-gravitational and spherical traps. Because the volume and in many cases the number of particles (with change of the external conditions) in the traps are undetermined quantities, we suggest a possible determination for the average density in traps.

Computer simulation methods represent a complementary approach to experimental and theoretical studies, and they have become invaluable tools for the description of many-particle systems in numerous disciplines of science. One of the main and widely applied approaches is the molecular dynamics simulation, which makes it possible to trace the phase-space trajectories of particles thereby providing information about the time evolution of the systems investigated. From the phase-space coordinates of the particles, it is possible to derive static, thermodynamic as well as transport properties and to obtain information about the collective excitations.

Hot dense radiative (HDR) plasmas common to inertial confinement fusion (ICF) and stellar interiors have high temperature (a few hundred eV to tens of keV), high density (tens to hundreds of g/cc) and high pressure (hundreds of Megabars to thousands of Gigabars). Typically, such plasmas undergo collisional, radiative, atomic and possibly thermonuclear processes. In order to describe HDR plasmas, computational physicists in ICF and astrophysics use atomic-scale microphysical models implemented in various simulation codes. Experimental validations of the models used for describing HDR plasmas are difficult to perform. Direct numerical simulation (DNS) of the many-body interactions of plasmas is a promising approach to model validation, but previous work either relies on the collisionless approximation or ignores radiation. We present a first attempt at a new numerical simulation technique to address a currently unsolved problem: the extension of molecular dynamics to collisional plasmas including emission and absorption of radiation. The new technique passes a key test: it relaxes to a blackbody spectrum for a plasma in local thermodynamic equilibrium. This new tool also provides a method for assessing the accuracy of energy and momentum exchange models in hot dense plasmas. As an example, we simulate the evolution of non-equilibrium electron, ion and radiation temperatures for a hydrogen plasma using the new molecular dynamics simulation capability.

We consider the hydrogen quantum plasma in the Saha regime, where it almost reduces to a partially ionized atomic gas. We briefly review the construction of systematic expansions of thermodynamical functions beyond Saha theory, which describes an ideal mixture of ionized protons, ionized electrons and hydrogen atoms in their ground state. Thanks to the existence of rigorous results, we first identify the simultaneous low-temperature and low-density limit in which Saha theory becomes asymptotically exact. Then, we argue that the screened cluster representation is well suited for calculating corrections, since that formalism accounts for all screening and recombination phenomena at work in a more tractable way than other many-body methods. We sketch the corresponding diagrammatical analysis, which leads to an exact asymptotic expansion for the equation of state. That scaled low-temperature expansion improves the analytical knowledge of the phase diagram. It also provides reliable numerical values over a rather wide range of temperatures and densities, as confirmed by comparisons to quantum Monte Carlo data.

A self-consistent joint description of free and weakly bound electron states in strongly coupled plasmas is presented. The existence of two problems is emphasized. The first one is a well-known restriction of the number of atomic excited states. Another one is a description of the smooth crossover from bound pair electron–ion excited states to collective excitations of free electrons. The fluctuation approach is developed to study the spectrum domain intermediate between low-lying excited atoms and free electron continuous energy levels. The molecular dynamics method is applied to study the plasma model since the method is able to distinguish all kinds of fluctuations. The electron–ion interaction is described by the temperature-independent cut-off Coulomb potential. The diagnostics of pair electron–ion fluctuations is developed. The concept of pair fluctuations elucidates the smooth vanishing of atomic states near the ionization limit. The approach suggested removes the artificial break of the electron state density at the ionization limit: atomic state density divergent at the negative energy side and free electron state density starting from zero density at the positive energy side.

We investigate the effects of Pauli blocking on the properties of hydrogen at high pressures, where recent experiments have shown a transition from insulating behavior to metal-like conductivity. Since the Pauli principle prevents multiple occupation of electron states (Pauli blocking), atomic states disintegrate subsequently at high densities (Mott effect). We calculate the energy shifts due to Pauli blocking and discuss the Mott effect solving an effective Schrödinger equation for strongly correlated systems. The ionization equilibrium is treated on the basis of a chemical approach. Results for the ionization equilibrium and the pressure in the region 4000 K <T < 20 000 K are presented. We show that the transition to a highly conducting state is softer than found in earlier work. A first-order phase transition is observed at T < 6450 K, but a diffuse transition appears still up to 20 000 K.

In the present work an electron impact ionization cross section is considered. The electron impact ionization cross section is calculated with the help of a variable phase approach to potential scattering. The Calogero equation is numerically solved, based on a pseudopotential model of interaction between partially ionized plasma particles, which accounts for correlation effects. As a result, scattering phase shifts are obtained. On the basis of the scattering phase shifts, the ionization cross section is calculated.

It has recently been shown that the Bethe–Larkin formula for the energy losses of fast heavy-ion projectiles in dense hydrogen plasmas is corrected by the electron–ion correlations (Ballester and Tkachenko 2008 Phys. Rev. Lett.101 075002). We report numerical estimates of this correction based on the values of g_ei(0) obtained by numerical simulations (Militzer and Pollock 2000 Phys. Rev. E 61 3470). We also extend this result to the case of projectiles with dicluster charge distribution. We show that the experimental visibility of the electron–ion correlation correction is enhanced in the case of dicluster projectiles with randomly orientated charge centers. Although we consider here the hydrogen plasmas to make the effect physically more clear, the generalization to multispecies plasmas is straightforward.

We calculate the excitation spectrum of the electron liquid using the formalism of correlated basis functions including time-dependent pair correlations. Using the static structure factor of the ground state as sole input, our formalism is naturally suited for studying correlation effects on the energy loss function. The most prominent example is the double plasmon, for which our results are in good agreement with recent experiments on various alkali metals.

We apply a theory (Böhm et al 2006 AIP Conf. Proc.850 111, 2007 Int. J. Mod. Phys. B 21 2055) developed recently on dynamic two-pair fluctuations to layered systems, such as electrons in semiconductor hetero-structures or He on graphite. The theory fulfils the zeroth and first frequency moment sum rule. Results are presented for the static effective particle–hole interaction, the dynamic structure function and the dispersion of the plasmon.

We discuss a new simple field theory approach of Coulomb systems. Using a description in terms of fields, we introduce in a new way the statistical degrees of freedom in relation to the quantum mechanics. We show by a series of examples that these fundamental entropic effects can help account for physical phenomena in relation to Coulomb systems whether symmetric or asymmetric in valence. Overall, this gives a new understanding of these systems.

We re-investigate some classical approaches for collisional absorption of laser radiation in dense plasmas and compare them to quantum theories. The typical break-down of the classical approaches can be avoided by using the quantum dielectric function in the seminal Dawson and Oberman formula which is equivalent to recently published quantum theories of collisional absorption. Strong electron–ion scattering can however be included more easily in classical approaches.

We present evidence for higher harmonic generation observed as additional peaks in the dynamical structure function and current–current fluctuation spectra in several types of strongly coupled plasmas. Results are presented on the dependence of the strength of the second and higher harmonic oscillations on the coupling parameter and the wave number.

The generation of energetic ions and DD neutrons from microfusion at the interelectrode space of a low-energy nanosecond vacuum discharge has been demonstrated recently [1, 2]. However, the physics of fusion processes and some results regarding the neutron yield from the database accumulated were poorly understood. The present work presents a detailed particle-in-cell (PIC) simulation of the discharge experimental conditions using a fully electrodynamic code. The dynamics of all charge particles was reconstructed in time and anode–cathode (AC) space. The principal role of a virtual cathode (VC) and the corresponding single and double potential wells formed in the interelectrode space are recognized. The calculated depth of the quasistationary potential well (PW) of the VC is about 50–60 keV, and the D⁺ ions being trapped by this well accelerate up to energy values needed to provide collisional DD nuclear synthesis. The correlation between the calculated potential well structures (and dynamics) and the neutron yield observed is discussed. In particular, ions in the potential well undergo high-frequency (∼80 MHz) harmonic oscillations accompanied by a corresponding regime of oscillatory neutron yield. Both experiment and PIC simulations illustrate favorable scaling of the fusion power density for the chosen IECF scheme based on nanosecond vacuum discharge.

The molecular dynamics model of collisional recombination in strongly coupled plasmas is developed in the frames of the fluctuation approach. A non-monotonic nonideality dependence of the collisional recombination rate is discovered for all multiplicities of ionization studied. The rate is drastically suppressed with respect to the extrapolation of the ideal plasma three-body recombination conventional expression. The mechanisms of the suppression are discussed. The value of the suppression agrees with the value which was measured for the ultracold plasma. Collisional recombination reduces to the three-body recombination at the decrease of the nonideality.

We present component-resolved and total pair distribution functions for a 2DEG with two symmetric valleys. Our results are based on quantum Monte Carlo simulations performed at several densities and spin polarizations.

The problem of wave packet broadening in the method of wave packet molecular dynamics simulations of electron–ion nonideal plasmas is discussed. It is shown that when using a harmonic restrictive potential for the packet widths, simulation results depend strongly on the constraint parameter. Two new approaches to constraining the packet broadening in a less stringent way are analyzed: periodic boundary conditions for widths and a dynamic constraint, based on filtering close particle collisions. These different ways to localize electrons are compared by calculating the dynamical plasma collision rate and the particle pair distribution functions.

The electron–atom interaction is considered in dense partially ionized plasmas. The separable potential is constructed from scattering data using effective radius theory. Parameters of the interaction potential were obtained from phase shifts, scattering length and effective radius. The binding energy of the electron in the H⁻ ion is determined for the singlet channel on the basis of the reconstructed separable potential. In dense plasmas, the influence of the Pauli exclusion principle on the phase shifts and the binding energy is considered. Due to the Pauli blocking, the binding energy vanishes at the Mott density. At that density the behavior of the phase shifts is drastically changed. This leads to modifications of macroscopic properties such as composition and transport coefficients.

The theory of nonlinear transport is elaborated to determine the Burnett transport properties of non-ideal multi-element plasma and neutral systems. The procedure for the comparison of the phenomenological conservation equations of a continuous dense medium and the microscopic equations for dynamical variable operators is used for the definition of these properties. The Mori algorithm is developed to derive the equations of motion of dynamical value operators of a non-ideal system in the form of the generalized nonlinear Langevin equations. In consequence, the microscopic expressions of transport coefficients corresponding to second-order thermal disturbances (temperature, mass velocity, etc) have been found in the long wavelength and low frequency limits.

Coulomb excitations of open sd-shell nuclei are investigated. Microscopic theory is employed to calculate the C2 form factors for the first two 2⁺ states in ²²Ne, ²⁶Mg and ³⁰Si. These collective transitions are discussed taking into account core-polarization effects. Remarkable agreements are obtained between the measured and calculated form factors for the first 2⁺ states. No strong conclusion can be drawn for the second 2⁺ states.

Laser excited small metallic clusters are simulated using classical pseudo potential molecular dynamics simulations. Time-dependent distribution functions are obtained from the electron and ion trajectories in order to investigate plasma properties. The question of local thermodynamic equilibrium is addressed, and size effects are considered. Results for the electron distribution in phase space are given, which are interpreted within equilibrium statistical physics. Momentum autocorrelation functions were calculated for different cluster sizes and for different expansion states from the expanding system after the laser–cluster interaction. A resonance behaviour of the autocorrelation function in finite systems was observed. First, results concerning collision frequencies in small clusters are given.

The kinetic and thermodynamic properties of non-ideal Al and Cu plasmas were investigated on the basis of pseudopotential models, taking screening and quantum-mechanical effects into account. For investigation of ionization stages, the Saha equations with corrections to non-ideality (lowering of ionization potentials) were used.

The effect of runaway electrons in partially ionized hydrogen plasma is investigated on the basis of pseudopotential models. The conditions of runaway electrons were determined. Dependences of an electron free path on the plasma density and coupling parameter were obtained. It is shown that if the quantum-mechanical and screening effects in non-ideal partially ionized plasma are taken into consideration, the collision frequency curve for electrons has maxima and free path curves for electrons have minima.

In non-ideal plasmas, the dielectric function has to be treated beyond the random phase approximation. Correlations as well as collisions have to be included. These corrections are known as (dynamical) local field corrections. Based on the Zubarev approach to linear response theory, a relaxation time approximation is proposed leading to an interpolation scheme between static local field corrections and the Drude model in the long-wavelength limit. The approach generalizes the Mermin approximation for the dielectric function and allows for the inclusion of a dynamical collision frequency. A numerical illustration is given for a classical two-component plasma at intermediate coupling.

The dynamics of fluctuations is considered for electrons near a positive ion or for charges in a confining trap. The stationary nonuniform equilibrium densities are discussed and contrasted. The linear response function for small perturbations of this nonuniform state is calculated from a linear Markov kinetic theory whose generator for the dynamics is exact in the short time limit. The kinetic equation is solved in terms of an effective mean field single particle dynamics determined by the local density and dynamical screening by a dielectric function for the nonuniform system. The autocorrelation function for the total force on the charges is discussed.

We present results for the ionic structure in dense, moderately to strongly coupled plasmas using two models: the mean spherical approximation (MSA) and the hypernetted chain (HNC) approach. While the first method allows for an analytical solution, the latter has to be solved iteratively. Independent of the coupling strength, the results show only small differences when the ions are considered to form an unscreened one-component plasma (OCP) system. If the electrons are treated as a polarizable background, the different ways to incorporate the screening yield, however, large discrepancies between the models, particularly for more strongly coupled plasmas.

The nonequilibrium phase-space dynamics of neutral, ultracold plasmas are described. The dynamics are placed in the context of the ultrafast dynamics of related systems that can be thought of as photo-initiated ultrafast systems, which include, among others, surfaces that are melted nonthermally, some artificial molecular machines and laser-excited clusters. The picture of energy landscape hopping is described to unify the dynamics of these diverse systems. The specific features of the temperature evolution of an ultracold plasma are then discussed in detail as they compare with the short-time dynamics of the velocity autocorrelation function. Finally, the phase-space dynamics of a one-dimensional ultracold plasma model are visualized via molecular dynamics calculations of phase-space trajectories.

Dense hydrogen is studied in the framework of wave packet simulations. In this semi-quantal method the electrons are represented by wave packets which are suitably parameterized, e.g. Gaussians. The time evolution of the system and the equilibrium properties are obtained with the help of a variational principle and by Monte Carlo sampling, respectively. A transition from a molecular to a metallic state is observed. The wave packets become delocalized and the electrical conductivity increases sharply. The phase diagram is calculated in a wide range of the pressure–density–temperature space. In the transition from the molecular to the metallic state the density increases in agreement with recent reverberating shock wave experiments.

Modeling of x-ray spectra emitted from a solid-density strongly coupled plasma formed in short-duration, high-power laser–matter interactions represents a highly challenging task due to extreme conditions found in these experiments. In this paper we present recent progress in the modeling and analysis of Kα emission from solid-density laser-produced titanium plasmas. The self-consistent modeling is based on collisional-radiative calculations that comprise many different processes and effects, such as satellite formation and blending, plasma polarization, Stark broadening, solid-density quantum effects and self-absorption. A rather strong dependence of the Kα shape on the bulk electron temperature is observed. Preliminary analysis of recently obtained experimental data shows a great utility of the calculations, allowing for inferring a temperature distribution of the bulk electrons from a single-shot measurement.

The amplitude and phase of the complex reflection coefficient of a weak probe laser pulse from strongly coupled Al plasma created on the surface of a metallic target by pump femtosecond laser pulses with intensities I ≲ 10¹⁵ W cm⁻² were measured using femtosecond interference microscopy. A theoretical model developed for the interaction of intense ultrashort laser pulses with solid targets on the basis of a two-temperature equation of state for an irradiated substance was used for numerical simulations of the dynamics of the formation and expansion of the plasma. A comparison of the experimental data with the simulated results shows that the model is suitable up to I ∼ 10¹⁴ W cm⁻². At higher intensities of the heating laser pulse, lower values of the reflection coefficient amplitude of Al plasma are observed in the experiment.

The ballistic model of collisional absorption in the presence of an intense laser field is exposed and the resulting collision frequencies are shown to be in good agreement with those obtained from the dielectric model. Advantages in favor of the ballistic model and shortcomings of both are discussed. Misleading physical interpretations from the dielectric model are shown to have their origin in a partially inadequate mathematical treatment.

A new code called VAAQP (variational average atom in quantum plasmas) is briefly described and its first results in the case of aluminium at solid density and temperatures between 0.05 and 12 eV are reported. The code is based on a new fully variational approach to plasmas at local equilibrium with both bound and free electrons treated quantum mechanically. This model which is derived from two first terms of the cluster expansion appears to be the quantum extension of the well-known atom-in-cell model based on the Thomas–Fermi theory (Thomas–Fermi average atom) that has been proposed in 1949 by Feynman, Metropolis and Teller. Similar to the case of Feynman et al's model the VAAQP approach, due to its fully variational character, respects the virial theorem and uses a simple formula for the electronic pressure. Comparisons to results obtained using other approaches are also shown and discussed in the aluminium case. The results confirm the feasibility of the quantum variational model in the warm dense matter regime. Effects of the variational treatment can lead in this regime to significant differences with respect to existing non-variational models.

The interaction of nanometer-sized silver clusters with intense laser fields is investigated using a modified nanoplasma model. In particular, the ionization dynamics is considered. The yield of highly charged ionic species can be controlled by pulse shaping. Using a genetic algorithm, optimal pulse shapes for the maximum yield of specific ionic charge states are calculated.

The emitted K_α-spectra of moderately ionized titanium radiators in a medium are used to determine plasma temperature and composition in electron heated target regions. A theoretical treatment of spectral line profiles using self-consistent Hartree–Fock and ion sphere model calculations to determine the influence of plasma polarization is applied. We confirm the importance of excited emitter states for line shape modeling.

Full scale equations of state (EOS) covering solid, fluid and plasma as needed for applications in warm dense matter physics are difficult to establish. We demonstrate how such an EOS can be constructed from available data.

The results of first experiments on reflectivity of polarized light on an explosively driven dense xenon plasma are presented. The study of polarized reflectivity properties of the plasma was accomplished using a laser light of wavelength λ = 1064 nm and at incident angles θ = 0–30°. With density ρ = 2.7 g cm⁻³, pressure P = 10.5 GPa and temperatures up to T ∼ 3⋅10⁴ K of the investigated plasma, conditions with strong Coulomb interaction (the nonideality parameter up to Г ∼ 2.0) were present. Reflectivities, which were calculated via the Helmholtz equation incorporating a density profile for the plasma surface, are compared to the experimental results.