Plasma Oscillations and Their Influence on Certain Properties of Nonideal Plasma

The hypothesis is proposed that Langmuir plasma oscillations can exist in nonideal plasma inspite of great collisional frequency. This possibility is confirmed by numerical estimations and the results of several experiments. The influence of plasma oscillations on electron states density and conductivity of nonideal plasma is considered. The simple formula obtained for conductivity agrees well with available experimental data.     

Analysis of the presence of small admixtures of heavy elements in the solar plasma by using the SAHA-S equation of state

The thermodynamic functions of a weakly nonideal plasma are extensively calculated for conditions typical of the depths of stars by using the SAHA-S equation of state. These calculations ensure precise analysis of the effect of the heavy-element content on adiabatic compressibility in the depths of the Sun. Comparison of model calculations with recent helioseismic data ensures more precise determination of solar-plasma composition. This comparison shows that the inclusion of additional components to the composition of heavy-element admixtures is a necessary condition for the theoretical equation of state and the results of analysis of solar oscillations to be consistent.     

Some properties of an ultimately nonideal metastable supercooled plasma

The formation of a metastable plasma state from an initial strongly nonideal state and certain properties of this metastable supercooled state are considered by directly modeling the dynamics of a system of many Coulomb particles. It is shown that the relaxation of the average kinetic energy of the particles can be characterized by a universal dimensionless function and, in particular, that an ultimate value degree of plasma nonidealness occurs which can be reached in the metastable state when no external action is present. The calculated binary correlation functions are in good agreement with the results of the Debye model, even outside its range of applicability. The time dependence of the total dipole moment of the system of particles is investigated. It is shown that there are oscillations of the total dipole moment. These collective oscillations take place at a frequency which is somewhat below the Langmuir frequency, the oscillations of the free and bound electrons occurring in antiphase. A hypothesis is advanced to the effect that recombination relaxation is frozen on account of the interaction of quasibound electrons with the Langmuir oscillations of the free electrons. Institute of General Physics, Academy of Sciences of the Russian Federation. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 3–16, October, 1996.     

Limiting nonideal metastable supercooled plasma

Direct modeling of the dynamics of a system of many Coulomb particles is applied to analyze the formation stage of a metastable plasma state from an initial, highly nonideal state, and also to consider some properties of this metastable supercooled state. It is shown that relaxation of the average particle kinetic energy may be characterized by a universal dimensionless function and in particular, there is a limiting degree of plasma nonideality which may be achieved in the metastable state, in the absence of any external influence. The calculated pair correlation functions agree with the results of the Debye model, even outside its limits of validity. The time dependence of the total dipole moment of the particle system is investigated. It is shown that oscillations of the total dipole moment are observed. These collective oscillations take place at a frequency slightly below the Langmuir frequency and the oscillations of free and bound electrons are in antiphase. The hypothesis is put forward that recombination relaxation is frozen as a result of interaction between quasibound electrons and Langmuir oscillations of free electrons. Zh. Tekh. Fiz. 67, 42–52 (August 1997)     

Analysis of mass transfer in dissipative nonideal systems: Numerical simulation

The results of a numerical analysis of mass transfer in extended quasi-two-dimensional and three-dimensional dissipative nonideal systems are presented. Pair interaction between particles is modeled by isotropic repulsive potentials represented by combinations of power laws and exponentials. Simulations are performed for parameter values characteristic of laboratory dusty plasmas. It is shown that short-time particle dynamics in nonideal liquid systems is similar to evolution of thermal oscillations at crystal lattice sites.     

Simulations of mass-transport processes on short observation time scales in nonideal dissipative systems

We present the results of our numerical simulations of mass-transport processes on short observation time scales for extended quasi-two-dimensional and three-dimensional nonideal dissipative systems of macroparticles interacting through a screened Coulomb potential. The simulations were performed for the parameters corresponding to the experimental conditions in laboratory dusty plasmas. The evolution of the rms macroparticle displacement on short observation time scales in nonideal liquid systems is shown to be similar to the evolution of the thermal particle oscillations at lattice sites.     

Kinetic theory of a nonideal plasma: Dispersion relations

The kinetic theory of plasma based on the construction of propagators for the plasma particle distribution function is generalized to the case of a nonideal plasma. This theory is used for calculating the permittivity of a homogeneous nonideal plasma consisting of one species of ions neutralized by the polarized electron background. The dispersion relations are derived for ion-acoustic and low-frequency transverse waves in the plasma.     

Laser cooling of recombining electron-ion plasma

A method of producing and confining ultracold electron-ion plasma with a strongly nonideal ion subsystem is considered. The method is based on the laser cooling of plasma ions by the radiation resonant with the ion quantum transition. A model is developed for the laser cooling of recombining plasma. Computer simulation based on this model showed that the ion nonideality parameter can be as large as ～100. The data obtained demonstrate that the production of ultracold nonideal plasma is quite possible.     

Thermodynamics and correlation functions of an ultracold nonideal Rydberg plasma

A pseudopotential model is suggested to describe the thermodynamics and correlation functions of an ultracold, strongly nonideal Rydberg plasma. The Monte Carlo method is used to determine the energy, pressure, and correlation functions in the ranges of temperatures T=0.1–10 K and densities n=10^?2–10¹⁶ cm^?3. For a weakly nonideal plasma, the results closely agree with the Debye asymptotic behavior. For a strongly nonideal plasma, many-particle clusters and a spatial order in the arrangement of plasma electrons and ions have been found to be formed.     

Electron-ion Coulomb Bremsstrahlung in nonideal plasmas

The classical electron-ion Coulomb Bremsstrahlung process is investigated in nonideal plasmas. An effective pseudopotential model taking into account the plasma screening and collective effects is applied to describe the electron-ion interaction potential in a classical nonideal plasma. The classical straight-line trajectory method is applied to the motion of the projectile electron in order to visualize the variation of the differential Bremsstrahlung radiation cross-section (DBRCS) as a function of the scaled impact parameter, nonideal plasma parameter, projectile energy, photon energy, and Debye length. The results show that the DBRCS in ideal plasmas described by the Debye-Hückel potential is always greater than that in nonideal plasmas, i.e., the collective effects reduce the DBRCS for both the soft and hard photon cases. For large impact parameters, the DBRCS for the soft photon case is found to be always greater than that for the hard photon case. Received 1st December 1999     

On the theory of nonlinear response in a nonideal plasma

A theory of nonlinear response is developed for studying nonlinear phenomena and nonlinear transport processes in nonideal Coulomb systems. Temporal plasma echo and transformation of waves in a nonideal Coulomb system are studied on the basis of the theory of nonlinear response to mechanical perturbations. General constraints imposed on nonlinear response functions are considered, and the model for determining quadratic response functions is formulated. The conditions for the emergence of temporal plasma echo and wave transformation are determined. It is shown that these nonlinear effects in a nonideal plasma can be initiated by ultrashort field pulses. A theory of transport is developed for determining the Burnett transport properties of a nonideal multielement plasma. A procedure is proposed for comparing the phenomenological conservation equations for a charged continuous medium and equations of motion for the operators of corresponding dynamic variables. The Mori algorithm is used for deriving the equations of motion for operators of dynamic variables in the form of generalized Langevin equations. The linearized Burnett approximation is considered in detail. The properties of the matrices of coefficients of higher-order derivatives in the system of conservation equations in the linearized Burnett approximation, which are important for hydrodynamic applications, are discussed. Various versions of the theory of nonlinear response are compared.     

Electron captures by positrons from hydrogenic ions in nonideal classical plasmas

In nonideal classical plasmas, the electron captures by positrons from hydrogenic ions are investigated. An effective pseudopotential model taking into account the plasma screening effects and collective effects is applied to describe the interaction potential in nonideal plasmas. The classical Bohr-Lindhard model has been applied to obtain the electron capture radius and electron capture probability. The modified hyperbolic trajectory method is applied to the motion of the projectile positron in order to visualize the electron capture probability as a function of the impact parameter, nonideal plasma parameter, projectile velocity, and plasma parameters. The results show that the electron capture probability in nonideal plasmas is always greater than that in ideal plasmas descried by the Debye-Hückel potential, i.e., the collective effect increases the electron capture probability. It is also found that the collective effect is decreased with increasing the projectile velocity. Received 21 January 2000 and Received in final form 27 April 2000     

Thermoelectric properties of a plasma at megabar pressures

A nonideal hydrogen plasma is theoretically studied for the first time as the working medium of a thermoelectric generator. A method is proposed for the calculation of the electrical conductivity, Seebeck coefficient, and thermal conductivity of the nonideal plasma in a wide range of densities and temperatures, including the region of strong degeneracy of electrons, which is achieved in experiments on the quasi-isentropic compression of deuterium and where a “plasma phase transition” (transition with a sharp change in the component composition) is possibly implemented. In this method, the kinetic coefficients are calculated together with the equation of states of the nonideal plasma. It is shown for the first time that the Seebeck coefficient in such a medium reaches 5500 μV/(K cm), which is an order of magnitude larger than that in currently available semiconductor materials used in thermoelectric generators. It is found that the figure of merit in hydrogen, which has a high thermal conductivity, at megabar pressures reaches 0.4, which is only slightly below that in currently available semiconductor materials.     

Plasma waves in a nonideal plasma

This paper shows how the concepts commonly used for a Debye plasma—Landau damping, collisional damping, short-range and long-range collisions, and plasma waves—must be revised to describe a nonideal electron-ion plasma. The degrees of freedom of a nonideal plasma are divided into collective and individual. The increase and saturation of the fraction of collective degrees of freedom as the coupling constant increases is discussed. The Tatarskii approach for a system of coupled oscillators makes it possible to model the collective degrees of freedom of a nonideal plasma by a set of Langevin oscillators in a thermostat. The correlation energy and the energy of the plasma waves are found. The concepts developed here made it possible to determine the dispersion of the plasma waves and their damping. The effect of damping on the discrepancy between the position of the maximum of the dynamic structure factor and the real part of the solution of the dispersion equation is considered. The effective collision frequency of the individual degrees of freedom (the electrons) is estimated, taking into account both short-range pairwise scattering and scattering at plasma waves. Zh. éksp. Teor. Fiz. 113, 880–896 (March 1998)     

Collisional recombination in nonideal plasmas

We suggest a model that allows one to consider the kinetics of collisional recombination in a nonideal plasma and to calculate its rate by the molecular dynamics method. We have found that the dependence of the collisional recombination rate on the plasma coupling parameter differs significantly from the extrapolation of the three-body recombination rate to the nonideal region. The recombination rate in a strongly coupled plasma has been found to decrease with increasing coupling parameter. We have established that the effect of plasma nonideality increases with ion charge. The recombination kinetics is shown to depend significantly on how the ions are arranged in the medium. Collisional recombination transforms into three-body one as the coupling parameter of the medium decreases.     

Coulomb ensemble of charged diamagnetic macroparticles in an inhomogeneous magnetic field under microgravity conditions

The formation of strongly nonideal Coulomb systems of a large number (∼104) of charged diamagnetic macroparticles in a cusp magnetic trap under microgravity conditions has been experimentally studied. The experiments have performed in the Russian segment of the International Space Station in the framework of the Coulomb Crystal experiment. Using the data of the videorecording of the positions of the particles in the magnetic trap, the magnetic susceptibility and charge of the particles have been estimated and the period of the oscillations of the cloud of the particles, as well as the damping rate of oscillations, has been determined.     

Rydberg matter as a metastable state of strongly nonideal plasma

The phase diagram of cesium is complemented by an isolated region of metastable states of a strongly nonideal plasma.     

Optical spectra of hydrogen plasma at electron concentrations above 1019 cm−3

The optical spectra of a dense (nonideal) plasma formed in a pulsed discharge in a closed quartz capillary were studied. The emission spectra of pure hydrogen plasma at a temperature of 23000 K and an electron concentration of ～1.5×10¹⁹ cm^?3, twice the value achieved earlier, were obtained. The plasma diagnostics was carried out by spectroscopic methods taking into account the radial inhomogeneity of the plasma column. The spectral intensity measured in the Balmer region (300–800 nm) was found to be lower than that calculated by the model of weakly nonideal plasma, an effect not observed at lower densities. Possible reasons for the discrepancy between the experiment and the calculation were considered. One of them being the specific density effect of a relative rise in plasma transmission with increasing density.     

Electrical Conductivity of Nonideal Quasi-Metallic Plasmas

Electrical conductivity formulas are derived from first principles for fully ionized nonideal plasmas. The theory is applicable to an electron-ion system with a 1) Maxwell electron distribution with an arbitrary interaction parameter ? = Ze2n1/3/KT (ratio of the mean coulomb interaction and thermal energies) and 2) Fermi electron distribution with an interaction parameter ? = Ze2n1/3h?2m-1 n2/3 (ratio of the coulomb interaction and Fermi energies). The momentum relaxation time of the electrons in the plasma is calculated based on plane electron wave functions interacting with the continuum oscillations (plasma waves) through a shielded coulomb potential Us(r) = esee exp (-r/?s)/r, which takes into account both electron-ion interactions (s = i) and electron-electron interactions (s = e). It is shown that the resulting conductivity formulas are applicable to higher densities, for which the ideal plasma conductivity theory breaks down because the Debye radius loses its physical meaning as a shielding length and upper impact parameter. The conductivity obtained for classical plasma is of the form ?c = ?c*(KT)3/2/m1/2e2 and agrees with the ideal plasma conductivity formula with respect to the temperature and density dependence for ?/Z ? 0, but its magnitude is significantly reduced as ?/Z increases. For quantum plasmas, the conductivity obtained is of the form ?Q = ?Q*h3n/m2Ze2, which shows that the degenerate plasma behaves like a low-temperature metal.     

Degeneration of electrons in nonideal plasma

The Monte-Carlo method was used for studying the influence of the plasma nonideality on the degeneration of the electrons. Comparison with analytical results was made for a weakly nonideal plasma.