The hydrodynamic expansion of plasmas produced by laser beams focused on thin-foil targets is studied using a self-similar approach. The model is useful for studying long-scale-length plasmas, produced by uniform laser irradiation, which become fully underdense during the laser pulse. An essentially qualitative analysis of the hydrodynamics system in Cartesian geometry is given. In particular, a useful expression is obtained by integration of the thermal energy equation.

The dynamics of a free electron gas interacting with neutral and excited atoms whose populations are assumed fixed is considered in the case of a three-dimensional model. An analytical form of the time-dependent electron distribution function for arbitrary initial conditions is obtained when interactions are only inelastic and superelastic between two atomic levels. It is shown that this electron gas reaches a stationary state. We deduce an experimental method for the measurement of the population of excited atoms in a neutral gas by injecting a dilute electron beam into the gas.

The evolution of magnetic flux ropes in a sheared plasma flow is investigated. When the magnetic field outside the flux rope lies parallel to the axis of the flux rope, a flux rope of circular cross-section, whose centre is located at the midpoint of the shear layer, has its shape distorted, but remains in the shear layer. Small displacements of the flux-rope centre above or below the midpoint of the shear layer lead to the flux-rope being expelled from the shear layer. This motion arises because small asymmetries in the plasma pressure around the flux-rope boundary leads to a force that forces the flux rope into a region of uniform flow. When the magnetic field outside the flux rope lies in a plane perpendicular to the flux-rope axis, the flux rope and external magnetic field reconnect with each other, leading to the destruction of the flux rope.

The dielectric tensor for a multicomponent magnetized dusty plasma, including the effect of capture of plasma electrons and ions by the dust particles, is rewritten in order to provide expressions more suitable for applications. We use this tensor to study the spatial absorption of a magnetosonic wave, including effects up to second order in the Larmor radius. We analyse the absorption of the wave due to the presence of dust particles with variable charge and the modification of this absorption due to finite-Larmor-radius effects.

It is well known that ion-beam–plasma interactions can destabilize right- and left-hand polarized electromagnetic waves. Owing to the fact that these instabilities have mostly been studied numerically by solving the hot-plasma dispersion relation, their fluid nature has often gone unnoticed. Choosing the ion background to be the rest frame, it is shown that the right-hand polarized instabilities are the result of a merging of the magnetosonic/electron-cyclotron branch of the dispersion relation with the ion beam. For any given ion-beam density and sufficiently large beam velocity, there are always two right- and two left-hand polarized instabilities leading to forward-propagating electromagnetic waves. It is also shown that all right-hand polarized instabilities are resonant instabilities, satisfying ω−kU+Ωp ≈ 0 around their maximum growth rate (ω and k are the frequency and the wavenumber respectively, U is the beam velocity, and Ωp is the proton gyrofrequency). Likewise, when the two left-hand instabilities are simultaneously present, they are also resonant instabilities satisfying ω ≈ Ωp. The high-frequency right-hand resonant instability (ω [Gt ] Ωp) has a maximum growth rate that depends only on the ratio between the beam density and the total density. The range of the unstable spectrum decreases with increasing beam velocity, leading to highly monochromatic radiation.

Plasma screening effects on inelastic Compton scattering of photons by bound atomic electrons of hydrogenic target ions in weakly coupled plasmas are investigated. The particle interaction potential in weakly coupled plasmas is obtained using the Debye–Hückel model. The screened wave functions and energy eigenvalues for the ground and excited states of the target ion are obtained using the Ritz variational method. The expression for the lowest-order transition matrix element is obtained from a two-photon process associated with terms quadratic in the vector potential A. The inelastic Compton scattering cross-section from the 1s ground state to the 2p excited state is obtained as a function of the incident photon energy, including plasma screening effects. It is found that plasma screening effects significantly reduce the inelastic Compton scattering cross-section.