The over-reflection of magnetoacoustic ion-cyclotron waves in a warm Hall plasma is investigated. It is shown that the effect of the Hall term is to strongly support over-reflection, thereby destabilizing the flow. Its relevance to the current-vortex sheet of the magnetosheath resulting from the interaction of the solar wind and the Earth's magnetopause is pointed out.

The structure of a microwave gas discharge produced and sustained by a surface wave (SW) propagating along a cylindrical metal antenna with a dielectric coating is studied. The SW that produces and sustains the microwave gas discharge propagates along an external magnetic field and has an eigenfrequency in the range between the electron cyclotron and electron plasma frequencies. The presence of a dielectric (vacuum) sheath region separating the antenna from the plasma is assumed. The spatial distributions of the produced plasma density, electromagnetic fields, energy flow density, phase velocity and reverse skin depth of the SW are obtained analytically and numerically.

The nonlinear evolution of Kelvin–Helmholtz instability is examined in 2+1 dimensions in the context of magnetohydrodynamics. When the velocity difference U is less than the critical velocity Uc, the equation governing the amplitude evolves into a self-focusing singularity. The self-focusing of waves predominates at short wavelengths, is directionally dependent, and also depends sensitively on the strength of the applied magnetic field. The minimum velocity that allows the existence of self-focusing increases with increasing magnetic field strength. The explosive instability at the second-harmonic resonance is also investigated.

Ion collisions in plasmas cause damping of hydromagnetic modes, but also a strong Hall effect if the collision time is of the same order as the gyroperiod. This is known to be very marked in the E region of the Earth's ionosphere, but should also occur in other partially ionized space and laboratory plasmas. In this work dynamic effects of such Hall currents are investigated theoretically. The linear modes that are obtained are, for sufficiently large scales, distinctly different from ordinary damped Alfvén modes, and similar to whistler waves even when the dynamic time scale is much longer than the ion gyroperiod. The dynamics of the coupling between planetary ionospheres and magnetospheric plasmas may be viewed as a reflection of Alfvén waves at a sharp boundary. By applying the results of the linear mode analysis, it is shown that the usually employed reflection coefficient needs to be replaced by a reflection tensor for large-scale waves due to self-induction of ionospheric Hall currents. This is similar to the magneto-optical Kerr effect, which is well-known in solid state physics. In the Earth's ionosphere, variations from incident torsional modes over periods as long as several minutes, which have been observed to occur over scales of a few thousand kilometres, are predicted to cause the generation of substantial eddy electric fields and compressional flows. Consequences for the energy exchange between ionosphere and magnetosphere and possibilities to observe the effect are discussed.

The interaction of a powerful non-symmetric laser pulse with a plasma is studied. The non-symmetry is manifested in an abrupt cut-off of the rear edge of the laser pulse compared with its leading edge. At the same time, three qualitatively different regions are distinguished: the leading edge, the rear edge and the region behind the pulse, where it leaves a wake in the form of generated fields. An analytical solution has been found that defines the longitudinal accelerating field at the end of the rear edge. The results of numerical calculations confirm our physical point of view that the non-symmetry of the laser pulse increases the duration of the ion channel behind the front, thereby enhancing the focusing and effective acceleration of electron bunches.

A microwave coherent backscattering experiment has been carried out on Mirabelle, a weakly ionized plasma device, with the objective of measuring the electron-density fluctuation level. The experiment is a preliminary step in order to prepare the detection system for a microwave stimulated-backscattering experiment. The incident electromagnetic wave is focused in front of a plane grid, which excites ion acoustic or electron Bernstein waves and induces fluctuations in the plasma. The backscattering signal is collected by the launching circuit and detected by homodyne mixing. The typical ratio of the scattered power to the incident power is about 10−12 and the relative density fluctuations is of the order of δne/ne ≈10−3 against a background electron density ne=(1–5)×109 cm−3. The backscattering measurement is also compared with Langmuir-probe measurements, and gives good agreement with the relative density fluctuations. The spectral width of the backscattered signal has also been studied, by taking into account effects due to the incident-wave focusing and plasma-wave damping.

The process of expansion into a vacuum of a collisionless plasma bunch with relativistic electron temperature is investigated for the one-dimensional case. Self-similar solutions for the evolution of the electron distribution function and ion acceleration are obtained, taking account of cooling of the electron component of plasma for the cases of non-relativistic and ultrarelativistic electron energies.

On account of nonlinear refraction, arising through the relativistic mass effect, a short intense laser pulse tends to accumulate its energy around the intensity maximum, leading to pulse compression over a length Zc≈ τ0c2ω2/ ω2pv, where τ0 and ω are the pulse duration and frequency of the laser, v is the oscillatory electron velocity and ωp is the plasma frequency. When the transverse extent of the laser is finite, nonlinear self-focusing interferes strongly with this process. The self-focusing occurs in a periodic manner on a shorter scale length. However, over long lengths of pulse propagation, pulse compression could be significant.

An intense short laser pulse incident on a metallic target produces an overdense plasma and excites a plasma surface wave via stimulated Compton scattering. The pump and the surface wave exert a beat-frequency ponderomotive force on the electrons in the skin layer, driving a heavily damped quasimode. The density perturbations due to the quasimode couple with the oscillatory velocity due to the pump to drive the surface wave. The growth period for the process turns out to be about 0.5 ps at a Nd[ratio ]glass laser intensity of 1016W cm−2 and a plasma density of 1.5 times the critical value.

The nonlinear dynamics and structure of plasmas with tightly twisted magnetic field lines have been studied using a toroidal plasma device. Stepwise magnetohydrodynamic (MHD) relaxation occurs, resulting in a discontinuous change in the pitch of magnetic field lines. This discrete nature of the pitch stems from the instability of kink (torsional) modes. The MHD relaxation stabilizes kink modes by selecting (self-organizing) appropriate pitches. The self-organized state displays the characteristic of a ‘dissipative structure’ in that it is accompanied by enhanced energy dissipation; the global resistance of the plasma current is substantially enhanced. The magnetic energy, which is generated by the internal plasma current, first changes into fluctuation energy through the kink instability, and then it goes mainly to ion thermal energy through viscous dissipation of the fluctuating flow. The viscosity dissipates the fluctuation energy with conservation of helicity. The self-organization of the stabilized magnetic field is characterized by the preferential conservation of the helicity.

We investigate the existence of MHD leaky waves in compressible and layered plasmas. We consider perturbations of complex frequency in a slab model with three layers. We develop a general method that includes the ‘cubic modes’ as well as other kinds of leaky waves, and allows us to derive many results in closed form. There are several physical mechanisms that can produce leakage. We give two numerical examples to exhibit the different behaviours that can arise. Finally we comment on the connection of the present results with those obtained by other authors, and correct some errors.

The problem of direct excitation of the shear Alfvén wave by antennas in the boundary of a fusion plasma is considered. In the plasma scrape-off layer the physics of this wave is determined by finite electron inertia. Expressions for the wave electric and magnetic field are derived without any assumption on the smallness of the ratio of frequency to ion cyclotron frequency. It is shown that the shear Alfvén wave propagates as a guided beam along the steady magnetic field over a wide range of frequencies below the ion cyclotron frequency, and is predominantly excited by current elements parallel to the steady magnetic field. A simple transmission-line analogy suggests that guidance of the Alfvén wave is also expected in the presence of strong plasma inhomogeneity.

The symmetry group of the Vlasov–Fokker–Planck equation (VFPE) is constructed. The effects of the Poisson equation on this group is studied, and different types of similarity solutions of the whole system of equations (VFPE+Poisson equation) are obtained.

An explosive instability of the ion-temperature-gradient (ITG)-driven modes (ηi modes) near the boundary of marginal stability is considered as a driving mechanism for subcritical turbulence. It is shown that boundedness of the wave interaction region leads to saturation of the instability. The possibility of coherent soliton-like structure formation in both slab and toroidal geometries is demonstrated by numerical simulation. An analytical soliton solution is found in some special cases.