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     

New longitudinal waves in electron-positron-ion quantum plasmas

A general quantum dispersion equation for electron-positron(hole)-ion quantum plasmas is derived and studied for some interesting cases. In an electron-positron-ion degenerate Fermi gas, with or without the Madelung term, a new type of zero sound waves are found. Whereas in an electron-hole-ion plasmas a new longitudinal quantum waves are revealed, which have no analogies in quantum electron-ion plasmas. The excitation of these quantum waves by a low-density monoenergetic straight electron beam is examined. Furthermore, the Korteweg-de Vries (KdV) equation for novel quantum waves is derived and the contribution of the Madelung term in the formation of the KdV solitons is discussed.     

Resistive Electrostatic Ion Cyclotron Instability in Plasmas

The stability of electrostatic ion cyclotron waves propagating obliquely with respect to the background magnetic field is studied for collisional, fully-ionized plasmas in which there is a relative field-aligned streaming between electrons and ions. It is found that electron-ion collisions, in conjunction with electron streaming, provides a mechanism for instability. The role of electron streaming is to supply a source of free energy and the role of electron-ion collisions is to restrict the field-aligned mobility of the electrons, thus preventing them from establishing a Boltzmann equilibrium. Ion-ion collisions and finite ion Larmor radius are found to exert a stabilizing influence. The instability is analyzed for both current-carrying plasmas and counterstreaming-beam-plasma systems.     

Ionization and Cohesion in Dense Plasmas

Approximate formulas are derived for the critical density and pressure at which the atoms of hydrogen-like plasmas become ionized due to overlapping of the wave functions. By this mechanism, not only the thermally excited but also the ground state atoms of alkali plasmas become ionized already at moderate pressures. Numerical examples are given for H, Li, Na, K, Rb, and Cs plasmas. It is shown that the (negative) electron-ion interaction energy balances the (positive) thermal energy for sufficiently high electron densities (e.g., n ~ 1020 cm-3 for T ~ 104 K) so that the plasma assumes a cohesive state similar to that of a (liquid) metal. From the quantum effects, the electron exchange energy contributes significantly to this "self-containment" of dense plasmas.     

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.     

Simulation and experiment on detached plasmas in the linear divertor simulator NAGDIS-II

We have performed two dimensional fluid B2 simulations on detached recombining plasmas to compare with experimental observations in a linear divertor plasma simulator. In detached helium plasmas associated with volumetric electron-ion recombination (collisional radiative recombination), an electron-ion energy exchange process followed by ion-neutral charge exchange is found to be a key to reduce the electron temperature along the magnetic field to be less than leV. The structural change of detached plasmas associated with molecular activated recombination has been also discussed in detail.     

Acceleration of Electron-Positron Plasmas to High Energies

It is suggested that electron-positron (e+ e-) plasma can be accelerated using the concept of cyclotron autoresonance between the particles and a linearly polarized laser radiation propagating along an axial magnetic field (Bz). This scheme can also be applied for other plasmas with oppositely charged particles of equal ?q?/m (e.g., positive and negative ions). An e+ e- plasma can be accelerated to about 2 GeV in the first meter along a 100-kG guide magnetic field by using an Nd: glass laser (?0 = 1 ?m) with intensity I0 = 1018 W/cm2. The acceleration scales asymptotically as (Bz, I0 ?0 Z2)1/3, where z is the axial distance.     

Nonthermal effects on the entanglement fidelity for elastic scatterings in Lorentzian plasmas

The nonthermal effects on the entanglement fidelity for the elastic electron-ion scattering are investigated in generalized Lorentzian plasmas. The dynamically screened effective potential and partial wave analysis are employed to obtain the entanglement fidelity in Lorentzian plasmas as a function of the spectral index, collision energy, and plasma parameters. It is shown that the entanglement fidelity increases with decreasing the collision energy, especially, for small Debye radii. It is also shown that the nonthermal effect enhances the entanglement fidelity in Lorentzian plasmas. In addition, it is found that the entanglement fidelity increases with an increase of the plasma temperature.     

Effects of magnetic field and temperature on the nonrelativistic bremsstrahlung process in magnetized anisotropic plasmas

The magnetic field and thermal effects on the nonrelativistic electron-ion bremsstrahlung process are investigated in magnetized anisotropic plasmas. The effective electron-ion interaction potential is obtained in the presence of an external magnetic field. Using the Born approximation for the initial and final states of the projectile electron, the bremsstrahlung radiation cross section and bremsstrahlung emission rate are obtained as functions of the electron energy, radiation photon energy, magnetic field strength, plasma temperature, and Debye length. It is shown that the effects of the magnetic field enhance the bremsstrahlung radiation cross section for low plasma temperatures and, however, suppress the bremsstrahlung cross section for high plasma temperatures. It is also shown that the magnetic field effects diminish the bremsstrahlung emission rate in magnetized high temperature plasmas.     

Simulation of Electron Temperature in Argon Clusters Subjected to Intense Laser Fields

Argon clusters subjected to intense femtosecond laser pulses are ionized by the optical fields and inelastic electron-ion collisions. The cluster plasmas absorb the laser energy through collisional inverse bremsstrahlung, leading the argon cluster plasmas to very hot states. The calculated electron temperature in the clusters indicates that the intense laser-cluster interactions are more energetic than interactions with molecules.     

Simulation of Electron Temperature in Argon Clusters Subjected to Intense Laser Fields

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Ultrarelativistic electron-positron plasma

Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.     

Electrostatic pair creation and recombination in quantum plasmas

The production of electron-positron pairs by electrostatic waves in quantum plasmas is investigated. In particular, a semiclassical governing set of equations for a self-consistent treatment of pair creation by the Schwinger mechanism in a quantum plasma is derived. This article was submitted by the authors in English.     

Electron-ion interaction in a weakly ionized gas

The effective electron-ion collision frequency has been measured in a weakly ionized gas. Results are in good agreement with classical theories for the electron-ion interaction in plasmas.     

Kinetic Nonlinear Buneman's Instability in Field-Free Isothermal Collisonal Plasma

A nonlinear dispersion relation is derived and solved for a 1-D electron-ion two-stream (Buneman) instability excited in an isothermal field-free plasma. The major nonlinear mechanism is the qualilinear modification of the background distribution function. We take into consideration the effect of Coulomb collisions which describes the broadening of the Cherenkov interaction of waves with particles. Nonlinear effects seem to lead, in field-free plasma, to the increase in the current velocity and consequently, to the growth of the instability and a rapid turbulent heating of plasma electrons. The methods used here to solve the Vlasov's kinetic equation may also be used to investigate other types of current micro-instabilities in plasmas.     

Dynamic non-Maxwellian screening effects on elastic collisions in Lorentzian plasmas

The dynamic plasma screening and non-Maxwellian effects on elastic electron-ion collisions are investigated in generalized Lorentzian distribution plasmas. The eikonal is employed to obtain the eikonal phase as a function of the spectral index, impact parameter, collision energy, thermal energy, and Debye length. The result shows that the non-Maxwellian effect suppresses the eikonal phase. It is found that the dynamic screening effect significantly enhances the elastic collision cross section for the low thermal energy case. In addition, the eikonal collision cross section is increased by the non-Maxwellian effect.     

Electrical Conductivity of Non-ideal Plasmas and the Ion Distribution Function

The theory of electrical conductivity of electron-ion-systems is developed for a density region which reaches from the region of non-ideal plasmas up to the region of liquid metals. The conductivity is expressed by quantum mechanical correlation functions. Different forms of the electron-ion pseudopotentials are considered. The ion distribution function is derived using the mean spherical approximation (MSA) theory or the nonlinear Debye-theory. Higher order scattering effects are treated by introducing scattering phase shifts for the statically screened electron-ion potential. The numerical results for the conductivity show a SPITZER-like behaviour in the low-density non-degenerate limit where higher order scattering is important, and a ZIMAN-like behaviour in the strongly degenerate high-density limit where the ion distribution functions and the form of the electron-ion pseudopotential become more important.     

Ionization equilibrium and radiative energy loss rates for C,N, and O ions in low-density plasmas

The results of calculations of the ionization equilibrium and radiative energy loss rates for C, N and O ions in low-density plasmas are presented for electron temperatures in the range 10⁴–10⁷ °K (～1–10³ eV). The ionization structure is determined using the steady-state corona model, in which electron impact ionization from the ground states is balanced by direct radiative and dielectronic recombination. Using an improved theory, detailed calculations are carried out for the dielectronic recombination rates in which account is taken of all radiative and autoionization processes involving a single-electron electricdipole transition of the recombining ion. The radiative energy loss processes considered are electron-impact excitation of resonance line emission, direct radiative recombination, dielectronic recombination, and electron-ion bremsstrahlung. For all three elements, resonance line emission resulting from 2s?2p transitions produces a broad maximum in the energy loss rate near 10⁵°K(～ 10 eV).     

Thee + e −→¯nn cross section predicted remarkably larger than thee + e −→¯pp one

It is shown that all global analyses of nucleon electromagnetic form factor data predict the electron-positron annihilation into neutron-antineutron cross section (for which there are no data till now) to be in a finite energy region substantially larger than the electron-positron annihilation into the proton-antiproton one.Dedicated to the memory of M. Gmitro.     

Fundamentals and applications of ion-ion plasmas

Ion-ion plasmas can form in the late afterglow of pulsed discharges or downstream of continuous wave discharges in electronegative gases. In ion-ion plasmas, negative ions replace electrons as the negative charge carriers. In the absence of electrons, ion-ion plasmas behave quite differently compared to conventional electron-ion plasmas. Application of a radio frequency bias to a substrate immersed in an ion-ion plasma can be used to extract alternately positive and negative ions, thereby minimizing charging on device features during micro-device fabrication. Ion-ion plasmas are also important in negative ion sources, dusty plasmas, and the D-layer of the earth's atmosphere.