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[en] The behavior of charged particles (electrons and positive and negative ions) in the D-region during the passage of weak shock and acoustic waves was studied. It is shown that under such conditions the photochemical equilibrium can be disrupted in the lower part of the D-region, which results in a condition under which the electron density does not follow the variations of neutral gas density

[en] The transport of charged particles in partially turbulent magnetic systems is investigated from first principles. A generalized compound transport model is proposed, providing an explicit relation between the mean-square deviation of the particle parallel and perpendicular to a magnetic mean field, and the mean-square deviation which characterizes the stochastic field-line topology. The model is applied in various cases of study, and the relation to previous models is discussed

[en] An expression for the energy loss cross section of a particle of mass m₁ and velocity v₁ colliding with particles of mass m₂ having a distribution of velocities v₂ is obtained. The energy loss cross section is proportional to the momentum transfer cross-section which depends upon the elastic scattering intensity in the target-projectile center-of-mass system. When applied to the scattering of electrons by incident atoms moving at velocities v₁ approximately v₂ the momentum transfer cross section shows strong oscillations with Z₁ in the same regions as those observed in the electronic stopping power. These oscillations are connected with the shell structure of the periodic table by an analysis of the phase shift induced in the electron wavefunctions of different angular momentum. By considering the Coulomb scattering from a bare incident particle, the connection with other theories of stopping, when v₁ much less than v₂ and v₁ much greater than v₂ respectively, is established. (U.S.)

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[en] In the Langevin description of Brownian motion, the action of the surrounding medium upon the Brownian particle is split up into a systematic friction force of Stokes type and a randomly fluctuating force, alternatively termed noise. That simple description accounts for several basic features of particle transport in a medium, making it attractive to teach at the undergraduate level, but its range of applicability is limited. The limitation is illustrated here by showing that the Langevin description fails to account realistically for the transport of a charged particle in a medium under crossed electric and magnetic fields and the ensuing Hall effect. That particular failure is rooted in the concept of the friction force rather than in the accompanying random force. It is then shown that the framework of kinetic theory offers a better account of the Hall effect. It is concluded that the Langevin description is nothing but an extension of Drude's transport model subsuming diffusion, and so it inherits basic limitations from that model. This paper thus describes the interrelationship of the Langevin approach, the Drude model and kinetic theory, in a specific transport problem of physical interest

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[en] The spatial topology of magnetic field lines can be chaotic for fields generated by simple current configurations. This is illustrated for a system consisting of a circular current loop and a straight current wire. An asymmetric configuration of the current system leads to three-dimensional spatially chaotic magnetic fields. The motion of charged particles in these fields is not necessarily chaotic and exhibits intriguing dynamical properties. Particles having initial velocities closely aligned with the direction of the local magnetic field are likely to follow chaotic orbits in phase space. Other particles follow coherent and periodic orbits; these orbits being the same as in the symmetric current configuration for which the field lines are not chaotic. An important feature of particles with chaotic motion is that they undergo spatial transport across magnetic field lines. The cross-field diffusion is of interest in a variety of magnetized plasmas including laboratory and astrophysical plasmas.

[en] The total energy loss dependence on both the thickness of detector and the Lorentz factor of the charged particle is discussed. Special attention is given to the conditions under which the Feymi density effect is absent. The obtained results are compared with experiments