A. Forlani

Localized solutions for circularly polarized electromagnetic waves in electron-positron plasmas

Two possible localized solutions are found for large amplitude, circularly polarized, electromagnetic waves in electron-positron plasmas. Depending on the longitudinal motion of the charges, a soliton (field amplitude) can propagate in a constant density plasma or a spatially localized vacuum cavity is formed and particles can be accelerated to very high velocities.

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.

Grain charge in dusty plasmas

Measurements [Barkan et al., Phys. Rev. Lett. 73, 3093 (1994)] of the grain charge in dusty plasmas have shown that it can be significantly reduced with respect to the single grain charge. This can have important consequences on the still open problem of strong vs weak coupling in many experiments with dusty plasmas. A simple charging model, based on the linearized Vlasov equations for the plasma particles, gives results in good agreement with the measurements and can be used to determine the grain charge in many experimental situations.

The equation of radiative transfer in the solar interior

We re-examine the theory of collective scattering, bremsstrahlung and the transport of radiation in the solar interior, including the effects of transition-bremsstrahlung, stimulated scattering, relativistic corrections and frequency diffusion during radiative transport, which transforms the transport equation into a differential equation (in frequency) for the radiative flux. When this is taken into account the transport equation can no longer be converted into the equation of radiative transfer where the total flux of radiation integrated over all frequencies is related to the temperature gradient via the Rosseland mean opacity. The concept of radiative opacity can only be introduced if the frequency diffusion is ignored or treated as a perturbation. In this case the change in the radiative opacity due to these effects is discussed in view of its importance for the neutrino production rate in the solar interior and compared with previous calculations.

Collective plasma effects in scattering of radiation in astrophysical plasmas

The contribution to the radiative transport due to collective scattering in astrophysical plasmas and a generalization of the Kompaneets equation is obtained. Both the stimulated and spontaneous scattering and the contribution of scattering on electrons and ions are taken into account and shown to be important over a broad range of frequencies ωpe<ω<ωpec/vTe (ωpe is the plasma frequency, c is the light velocity and vTe is the electron thermal velocity). A new expression for the Eddington luminosity including collective effects is derived. In the transport cross section the scattering on ions starts to contribute for ω⩽3ωpec/vTe while in the generalized Kompaneets equation the scattering on ions dominate for ω⩽ωpe(c/vTe)(me/mi)1/4. It is shown that the contribution related to the change of frequency during the stimulated and spontaneous scattering modifies the structure of the transport equation. A new transport equation is derived which contains a derivative of the intensity with respect to the frequency and in general such an equation does not allow the use of the concept of opacity as normally defined.The contribution to the radiative transport due to collective scattering in astrophysical plasmas and a generalization of the Kompaneets equation is obtained. Both the stimulated and spontaneous scattering and the contribution of scattering on electrons and ions are taken into account and shown to be important over a broad range of frequencies ωpe<ω<ωpec/vTe (ωpe is the plasma frequency, c is the light velocity and vTe is the electron thermal velocity). A new expression for the Eddington luminosity including collective effects is derived. In the transport cross section the scattering on ions starts to contribute for ω⩽3ωpec/vTe while in the generalized Kompaneets equation the scattering on ions dominate for ω⩽ωpe(c/vTe)(me/mi)1/4. It is shown that the contribution related to the change of frequency during the stimulated and spontaneous scattering modifies the structure of the transport equation. A new transport equation is derived which contains a derivative of the intensity with respect to the frequency ...

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.

Collective quantum scattering effects in transport of radiation in astrophysical plasmas

We consider the corrections due to quantum collective effects to transport of radiation in plasmas. Both stimulated and spontaneous quantum corrections are shown to be of the same order of magnitude or larger than the relativistic corrections related to the “comptonization” processes. The correction to the solar opacity is calculated.

Frequency diffusion during radiative transport in the solar interior

It is well known that the rate of production of solar neutrinos is very sensitive to small variations in the radiative opacity of the solar interior. In this paper we show that the reduction in frequency resulting from scattering and density inhomogeneity influences the radiative transport of energy and thus the solar opacity.

Relativistic corrections to collective photon scattering in plasmas

Abstract Relativistic corrections to Thomson scattering of photons in plasmas are well known [D. H. Sampson, Ap. J. 129, 734 (1959); J. R. Buchler and W. R. Yueh, Ap. J. 210, 440 (1976) (Ref. 1)]. Here we consider the case when collective effects also have to be taken into account and find the relativistic corrections to collective scattering in plasmas. Collective effects are due to the shielding clouds and are important when the wavelength of the scattering radiation is of the same size or larger than the Debye wavelength. This is the case, for instance, in the solar interior where relativistic corrections to Thomson scattering of photons have recently been taken into account in the calculation of the solar opacity [S. Rose, J. Phys. B: Atom. Molec. Phys. 26, L29 (1993); Iglesias and Rogers, Ap. J. 371, 408 (1991) (Ref. 2)] with the result of a few percent decrease. As an application of our results we show that when the relativistic corrections to collective scattering are included, the decrease in the opacity is 0.2%.