I shall shortly be stepping down from the position of Editor of Journal of Plasnia Physics, although continuing for a while more as an Associate Editor.

The radial self-similar expansion of negatively charged impurity or dust particles in a cylindrical geometry is investigated using the multi-fluid theory. Three different types of self-similar solutions are considered. Various asymptotic limits of physical interest in the self-similar space are shown to occur.

Short-wavelength coherent structures of ion Bernstein modes are studied on the basis of a nonlinear equation taking into account the effect of high-frequencey diamagnetism. Analytical solutions in the form of nonlinear periodic waves and envelope solitons are found, and their properties are discussed. The appearance of such structures may explain some phenomena observed in laboratory and space plasmas.

We investigate the implosion of a dense τ-pinch plasma driven by an annular finite-thickness gas-puff Z-pinch. The imploding Z-pinch traps an axial magnetic field Bz, compressing it to large values in an extremely short time. The temporal variation of Bz then induces an azimuthal τ current on the surface of a fibre placed on the axis, with a rise time an order of magnitude shorter than the rise time of the Z-pinch current. Our numerical results demonstrate that, for a thick gas-puff layer, maximum compression occurs before the current peaks.We also find that at peak compression, fuel densities of the order of 1025 cm-3 and temperatures above 10 keV can be achieved on a time scale of the order of 0.1 ns. Thus a Lawson parameter nτ ≈ 1014 s cm-3 for a DT fibre becomes achievable. The snowplough effect in the Z-pinch exercises a stabilization effect on the growth of sausage and Rayleigh—Taylor instabilities. In the limit of a very thin gas-puff layer, previous results are fully recovered.

Using a low-frequency, low-β model of a magnetized plasma, several nonlinear waves are studied. All the waves share the property that they have a self- consistent time-averaged current in the steady state. The first wave is a one- dimensional solitary wave that propagates obliquely to a static magnetic field. The wave magnetic field has a kink structure, which results in the production of the time-averaged current. A two-dimensional wave that propagates parallel to the background magnetic field is also discussed. This is a forced wave, requiring an antenna structure to support it in the steady state. The characteristics of the two-dimensional wave are dependent upon the wave speed, which in turn is determined by the speed of the travelling wave on the external antenna.

Self-consistent nonlinear changes of plasma parameters and characteristics of electromagnetic guided waves are studied with regard to the effect of self- focusing and waveguided channel formation in a cylindrical plasma waveguide. Besides the nonlinearity due to the ponderomotive force action usually involved, ionization nonlinearity specified for different regimes of particle loss mechanisms is considered. An azimuthally symmetric electromagnetic surface wave is the guided mode that forms and sustains the wave channel.The nonlinear dispersion law and the nonlinear changes in the wave field distribution and power flow are obtained, describing the effect of the self-focusing of the waves under conditions of weak nonlinearity.

Oblique propagation of ion-acoustic solitons in a magnetized low-β plasma consisting of warm positive and negative ion species along with hot electrons is studied. Using the reductive perturbation method, a KdV equation is derived for the system, which admits an obliquely propagating soliton solution. It is found that if the ions have finite temperatures then there exist two types of modes, namely slow and fast ion-acoustic modes. The parameter determining the nature of soliton (i.e. whether the system will support compressive or rarefactive solitons) is different for slow and fast modes. For the slow mode the parameter is the relative temperature of the two ion species, whereas for the fast mode it is the relative concentraion of the two ion species. For the fast mode it is found that there is a critical value of the negative-ion concentration below which only compressive solitons exist and above which rarefactive solitons exist. To discuss the soliton solution at the critical concentration, a modified KdV equation is derived. It is found that at the critical concentration of negative ions compressive and rarefactive solitons co-exist. The effects of temperature of different ion species, angle of obliqueness and magnetization on the characteristics of the solitons are discussed in detail.

We define a new generalized symmetrical permittivity tensor of rank two, χαβ in order to characterize the inductions in Maxwell's formalism for an isotropic relativistic plasma. We then show that only the Lorentz gauge allows one to write the field potentials with a propagator inversely proportional to this tensor. In this sense, we may say that the Lorentz gauge is the only one suitable for Maxwell's formalism.

The reflection and transmission coefficients for an electromagnetic beam propagating in an inhomogeneous plasma are calculated analytically using the Magnus approximation in different physical configurations. The theoretical predictions for such coefficients are expressed in simple analytical form, and are compared with the exact results obtained by numerical solution of the wave propagation equations, using the Berreman 4 × 4 matrix method. It is shown that the theoretical approach is able to reproduce the correct results for reflection and transmission coefficients over a wide range of physical parameters. The accuracy of the theoretical analysis, at different orders of approximation, is also discussed.

An advanced two-chamber model for the main plasma scrape-off and the divertor chamber of a tokamak is constructed. It is studied in the framework of catastrophe theory. The model shows bifurcations in the topology of the equilibrium surfaces. The results are in qualitative agreement with some of the experimentally observed features of the H-mode transition.

Helicon waves have been used for efficiently coupling radio-frequency power to plasmas, and are studied for their potential application for low-frequency current drive in tokamks. In this paper the electromagnetic field components and the dispersion relation for azimuthally independent helicon-wave oscillations in a cylindrical plasma column are derived. The coupling of transverse electric TE and transverse magnetic TM modes associated with these oscillations is discussed. The effect of the collisional damping on determining the nature of the TM mode (either surface wave or body wave) is analysed.

We derive the dielectric tensor of a hot plasma by including the smallgyroradius corrections up to the first harmonic (ω ≈ 2ωcα). We show that these corrections introduce radial wavenumbers associated with transverse electromagnetic modes (TEM). The special case of a cylindrical plasma column is discussed for a hydrogen plasma at the ion-cyclotron frequency and for an electron plasma at the electron-cyclotron frequency and its first harmonic.