V. N. Tsytovich

Dispersion properties of dusty plasmas

The presence of charged dust particles in a plasma can change its dispersion properties. From the linear response of an equilibrium dusty plasma to the propagation of small perturbations, we find an average dielectric function є(ω, k) for the system in the case when the grain space distribution is random, and ensemble averages are taken over the random variables. For the case of high-frequency plasma waves, when e ≈ 1-ω2p/ω2 for the unperturbed case (cold plasma), we find that є becomes complex in the presence of the dust, leading to possible damping in a domain where Landau damping is usually negligible (ω » kVT).

Transition scattering of waves on charged dust particles in a plasma

We consider the transition scattering of waves on charged dust particles in a plasma. The scattered power is first derived from perturbation theory, for the case of weakly charged grains, where linear screening by the plasma particles can be assumed. In the case of a highly charged grain we first determine the nonlinear screening by the plasma particles, in a model where the grain can be treated as a small spherical probe at floating potential, and then solve the nonlinear transition scattering due to the electron shielding cloud. One of the results of our calculation is that the radiation pressure on the grains can be greatly enhanced with respect to the case of usual Thomson scattering on free particles, and some possible astrophysical consequences are discussed.

Damping and absorption of high-frequency waves in dusty plasmas

By employing standard statistical techniques of linear fluctuation theory, it is shown how the ensemble averages over statistical distributions of charged massive grains in a dusty plasma can result in ‘‘average’’ dispersion relations for high‐frequency electromagnetic and electrostatic waves. The dispersion relations admit solutions for complex frequencies and wave numbers, suggesting that the waves can be damped (Imu2009ω≠0) or absorbed (Imu2009k≠0) in a dusty plasma.

Relativistic corrections to inverse bremsstrahlung in the solar interior

The cross-section of free-free transitions (inverse bremsstrahlung) in the solar interior is calculated including corrections due to relativistic dynamics and the distribution function of the electrons. The reduction of the radiative opacity due to these effects is discussed in view of its importance for the neutrino production rate in the solar interior.

Raman scattering of photons in the solar interior

We reconsider the transport equation in the solar interior and calculate the effects on the opacity of photon scattering near the Raman resonance. Both spontaneous and stimulated scattering on thermal photons and thermal plasmons are taken into account, and changes in opacity (with respect to previous calculations) are calculated numerically and found to be negligible with respect to relativistic corrections to photon scattering.

Plasma effects in the solar core and the solar neutrino problem

In this paper we review recent corrections to the theory of photon transport in a dense hot plasma (similar to conditions in the solar interior) and show that previous calculations overestimate the solar opacity. We also identify new effects which have never been taken into account. It is shown that these can significantly reduce the opacity and can therefore change the prediction of the solar neutrino flux from Standard Solar Models.

Collective effects in bremsstrahlung in plasmas

The results of recent developments in the theory of fluctuations in plasmas show that the previously used theory of bremsstrahlung is incomplete and the exact expressions for bremsstrahlung should include transition bremsstrahlung. The collective effects in bremsstrahlung known previously as Debye screening are changed to a qualitatively different structure, which removes the effect of ion polarization in bremsstrahlung and introduces a new effective polarization which depends on an effective ion charge and electron velocity. The results may be relevant for applications in plasmas when the wavelength is greater than the Debye length. It is shown that for the problem of photon transport in the solar interior the correct collective corrections to the bremsstrahlung change the opacity by only about −0·35%, which is less than was calculated previously when collective effects in bremsstrahlung where estimated without taking recent results of plasma fluctuation theory into account.

Theory of collisionless damping of cavitons and resonant particle acceleration

A theory is proposed that describes in a self-consistent manner damping and particle acceleration within cavitons. The framework of the approach makes it possible to formulate a set of self-consistent equations taking into account the change in the particle distribution function due to the interaction with cavitons and the damping of the waves within the cavitons due to the interaction with resonant particles. The spatial inhomogeneity of the distribution function of resonant particles in the vicinity of a caviton produces a new type of damping. The new damping mechanism is present for any inhomogeneity produced both by the other cavitons (or empty cavitons) in a strongly turbulent plasma or by any other source. This new type of damping is important for arresting wave collapse.

Broadening of the Raman resonance in photon scattering in plasmas

The broadening of the Raman resonance, due to the Doppler effect and particle collisions, is considered for the scattering of radiation in plasmas. The result is used to calculate the transport cross-section for the plasma in the solar interior and it is shown that the broadening effect can reduce the solar opacity. This result should therefore be taken into account in the Standard Solar Model, since a reduced opacity can change the predicted core temperature and hence the predicted flux of solar neutrinos.

Stimulated scattering and frequency diffusion of photons in plasmas

Abstract Stimulated scattering on electrons and frequency diffusion in the transport equation for photons in plasmas are considered including the collective plasma effects. The results are applied to the solar interior (where collective plasma effects are not negligible for a wide range of frequencies) to find the effect on the solar opacity.