Starting from a memory-function formalism coupled with the Green– Kubo formula and an approximate expression for the generalized Coulomb logarithm, the electric conductivity of a dense high-temperature hydrogen plasma is studied. A pseudopotential model, taking account of short-range quantum effects and long-range screening-field effects, is employed to include quantum mechanical and polarization effects. An analytical formula for the Coulomb logarithm is proposed when the thermal de Broglie wavelengths are rather smaller than the Debye radius. A minimum in the curve of electrical conductivity is found and some physical evidence for its appearance is produced.

We explore the level of saturation of instabilities in a two-species plasma using a combination of matched asymptotic expansion and numerical computation. The plasma is assumed to be spatially periodic, and the domain size is chosen to allow a single mode to become unstable when a bump is added to the tail of the distribution of the lighter species. We consider two versions of the problem, arising when the mass ratio of the two species is either very small, or of the order of unity. For small mass ratios, the initial saturation level of the mode amplitude, as measured by the electric field disturbance, follows the ‘trapping scaling’. For mass ratios of order unity, nonlinear effects become important at the level predicted by Crawford and Jayaraman, but the instability does not saturate there and continues to grow. In both cases, the initial onset of nonlinearity does not reflect the longer- time evolution of the system. In fact, the system passes through multiple stages of evolution in which the electric field amplitude is not simply predicted; none of the previously published scalings are adequate. Eventually, for both cases, the distribution of the lighter ions becomes significantly rearranged, and much (though not all) of the destabilizing bump is flattened. A better predictor of the strength of the instability is given by the extent of these rearrangements.

This paper discusses the excitation of Bernstein waves by pickup ions, which occur in the low corona, particularly the active regions. The present research is motivated by the study of solar plasma and radio-emission processes. However, emphasis is placed in this paper on the stability analysis rather than applications of the result. The analysis encompasses two limiting cases: one is when the pickup ions have small velocity dispersion; the other is when the ion velocity dispersion is significant.

A theoretical investigation of the interaction between a charged-particle beam and ordinarily polarized surface waves at the first two harmonics of ion and electron cyclotron frequencies propagating across an external steady magnetic field is carried out. The case of weak plasma spatial dispersion when the Larmor radii of plasma particles are much less than the penetration depth of these waves into the plasma is considered. The indicated waves are eigenmodes of the planar plasma–vacuum–metal waveguide structure, which is exposed to a steady magnetic field oriented parallel to the plasma surface. It is supposed that a cold charged- particle beam propagates over the plasma surface in the vacuum region. The beam density is less than the plasma density. Excitation of these O modes at the first and second harmonics of electron and ion cyclotron frequencies caused by the both resonant beam and dissipative instabilities is studied analytically. The dependence of their growth rates on parameters of the considered waveguide structures is also examined.

A specific type of plasma-wave instability in a hot magnetoactive collisional plasma due to a weak external electric field and weak spatial inhomogeneity is considered for the cases of kinetic Alfvén-like waves. These low-frequency waves with ω [Lt ] Ωi (where Ωi is the ion gyrofrequency) are solutions of the corresponding dispersion relation. The model integral of Bhatnagar, Gross, and Krook is used for the description of collisions. The quasistatic time variation of the electric field amplitude makes it possible to use the ‘direct initiation’ mechanism to describe instability development. An expression for the growth rate is obtained in the framework of linear theory. The instability in question occurs for a certain equation of state of the plasma. For this equation of state, a numerical analysis of the obtained instabilities is performed.

Reconnective annihilation of magnetic field leads to the formation of magnetic flux cells with small scales, followed by enhanced transverse plasmons occurring in a thin current sheet with a very small vertical extent. The analysis here focuses on the nonlinear interaction between the flux and plasmons. The transverse plasmon field is modulationally unstable in the Lyapunov sense. When the initial pumping wave amplitude attains the threshold of instability, this instability occurs with a high growth rate. Nonlinear development of modulational instability eventually results in self-similar collapse, due to nonlinear equilibrium, giving rise to a spatially intermittent, collapsing magnetic flux, very similar to a turbulent pattern. The Maxwell stress tensor from the turbulence flux determines the anomalous magnetic viscosity, i.e. the parameter α. It is shown that the instability is responsible for the alternation of outburst or quiescent states in astrophysical accretion disks. When the instability occurs, the parameter α is large. In the quiescent state, the instability is suppressed, leading to a smaller, collapse-quenching value of α.