Self-similar electron distribution, inverse bremsstrahlung, and heat flux inhibition in high-Z nonuniform plasmas

Abstract

The self-similar distribution of electrons is found for a nonuniform underdense plasma that is heated by an intensive laser field. The distribution function is flat-topped for the low-energy electrons. And in the high-energy region, it has a well-pronounced high-energy tail. It is also found how the electron heat flux and the absorption coefficient depend upon both the ratios of electron mean-free path to the inhomogeneity scale of effective temperature and of the oscillation velocity to the thermal velocity. The actual shapes of electron energy distribution, the heat flux limitation, and the electromagnetic radiation absorption rate are given, both for a currentless plasma and for a plasma with a finite electric current.

Anomalous heat flux inhibition under high frequency radiation pulse absorption in electron–ion collisions

“…The addition δ f a defines electron current and heat flux along inhomogeneity direction. Like in [1] (see [7,8], also) discussing electron heat transport we assume, that electric field E 0 provides zero current density, that is we consider the heat flux in the absence of charge density redistribution. Taking into consideration Eq.…”

“…oscillation velocity in high frequency field to their thermal velocity v T have been fulfilled. It has been shown, that if time moment exceeds the momentum relaxation time, but less than the energy relaxation time of the electrons, which give the basic contribution to the heat flux density q, the considerable decrease of q value in comparison with the well-known results [4,[6][7][8] takes place. The greater Z the greater relative decrease in q.…”

“…In rarefied plasma, under high frequency field absorption owing to electron-ion collisions, the depleted by over thermal electrons flat-topped distribution is formed [2][3][4][5], that leads to the numerical decrease of heat flux value in comparison with q S-H (see, for example, [4,[6][7][8]). In particular, the formation of electron distribution of the form ∼ exp(−v 5 ) results in four times heat flux decrease.…”

Self-similar solution to the Fokker–Planck equation in inhomogeneous plasma

“…For the last 20 years, theoretical studies of the nonequilibrium electron distribution functions ͑EDF͒, which accompany nonlocal transport processes, have been the subject of numerous investigations. [1][2][3][4][5][6] Deviations of the EDF from Maxwellian have important effects on plasma wave damping, return current, nonequilibrium radiation, and density fluctuations. They could be identified experimentally in the spectra of Thomson scattered light, x-ray radiation and stimulated Raman scattering ͑SRS͒.…”

Emergence of kinetic behavior in streaming ultracold neutral plasmas

“…Because of the increasing mean free path with particle kinetic energy, the situation can already change for mean free path on the order of or longer than 1% of the length scale of plasma gradients [1]. This gives rise to kinetic effects such as streaming plasmas and non-local transport, which are intensely studied because of their importance in many plasma environments, such as high-density laser-produced plasmas [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and astrophysical plasmas like the solar wind [19], solar atmosphere [20,21], solar flares [22], and supernovae [23].…”