The scattering of free drift waves by drift vortices is investigated analytically in the Born and eikonal approximations. Scattering amplitudes and scattering cross-section are found for a wide range of parameters of the vortex and wave. It is shown that under certain conditions the wave–vortex interaction becomes very strong; that is, the scattering cross-section is much more than the vortex radius.

Measurements have been made of the striation formation time of an α-type RF discharge in nitrogen as a function of pressure, RF frequency, electrode separation and input power. A theoretical model is proposed that yields electron energy and density and striation formation time, given the measured discharge parameters of interelectrode voltage and separation, gas pressure and RF frequency. It is found that increasing the pressure and the electrode separation increase the striation formation time, while increasing the power and the RF frequency decrease the striation formation time. The model predicts that striations in the RF discharge are formed when the plasma charge density reaches some critical value at which the space charge distorts the interelectrode field.

A wave-front distortion of strong shock waves in gases for particular Mach numbers M has been repeatedly noted. We propose two approaches according to which there is a threshold Mach number above which the instability occurs; this Mach number is related to the unperturbed gas pressure P1. The first approach is macroscopic, and takes account of radiation; the second is microscopic, and takes account of radiation, electron diffusion to the walls of the shock tube and the non-equilibrium relaxation processes. A mechanism of four reactions is proposed. A nonlinear differential equation system is established. The latter becomes unstable for critical values of the Mach number.

The quantum Boltzmann collision operator is expanded to yield a degenerate form of the Fokker–Planck collision operator. This is analysed using Rosenbluth potentials to give a degenerate analogue of the Shkarofsky operator. The distribution function is then expanded about an equilibrium Fermi–Dirac distribution function using a tensor perturbation formulation to give a zeroth-order and a first-order collision operator. These equations are shown to satisfy the relevant conservation equations. It is shown that the distribution function relaxes to a Fermi–Dirac form through electron–electron collisions.

Heavy ions frequently appear as minor components in space plasmas, for example in the solar wind and in the vicinity of comets. Both the different components of ions and the associated plasma waves are observed by extraterrestrial in situ measurements. The influence of these ion components on the properties of plasma waves is investigated by means of the multi-fluid equations. The linear mode analysis is performed numerically for a three-component plasma with an ambient magnetic field. Both the dispersion relations and the polarizations of the freely propagating wave modes are given and subsequently discussed.

We investigate finite-amplitude magnetoconvection in a rotating fluid in the presence of a vertical magnetic field when the axis of rotation is parallel to a vertical magnetic field. We derive a nonlinear, time-dependent, one-dimensional Landau–Ginzburg equation near the onset of stationary convection at supercritical pitchfork bifurcation when

formula here

and a nonlinear time-dependent second-order ordinary differential equation when Ta=T*a (from below). Ta=T*a corresponds to codimension-two bifurcation (or secondary bifurcation), where the threshold for stationary convection at the pitchfork bifurcation coincides with the threshold for oscillatory convection at the Hopf bifurcation. We obtain steady-state solutions of the one-dimensional Landau–Ginzburg equation, and discuss the solution of the nonlinear time-dependent second-order ordinary differential equation.

It is found on the KT-5C tokamak that an edge fluctuation can be excited using a pair of floating Langmuir-probe pins. This fluctuation propagates along the magnetic field, with its amplitude decreasing drastically when it is off the magnetic field line, which is similar to the results obtained from experiments on the TEXT tokamak. Moreover, our experimental observations indicate that the excited fluctuation propagates with the electron directional motion, and is mainly manifested in an electron density fluctuation. Physically, this excited fluctuation could be considered as modulation of the external electric field by electrons, and is carried by the electron directional motion wherever it goes. These results are in good agreement with the proposed ballistic model that can be derived by solving the linearized Vlasov equation.

The possibility for a drift dipole vortex to trap free drift waves is demonstrated. Drift perturbations can be trapped near the centre of the vortex or at its sides. The localization domain and eigenfrequencies of trapped modes are obtained.

The nonlinear development of the double-tearing instability and the mode coupling of different helicities are investigated numerically in cylindrical geometry. The results show that double-tearing instability arises with a central-hollow current-density profile, and the coupling of different low-poloidal mode numbers m leads to rapid destabilization of modes with higher poloidal mode numbers. This instability ultimately leads to the resistive reconnection of parts of the fluxes and reduces the current gradient in the unstable region. It seems likely that this process would accelerate current penetration in the tokamak start-up phase, and it also possibly plays an important role in the triggering of solar flares.

Electromagnetic and kinematic boundary conditions for surface waves propagating on the plane interface between a vacuum and a drifting plasma or a stationary plasma are investigated using a specular reflection procedure. The boundary values of specular-reflection solutions are shown to agree with the kinematic relations involving surface charge and surface current. The specular-reflection solutions explicitly show the well-known fact that a cold fluid forms a surface charge on the interface while a warm fluid does not. If the plasma is drifting (beam), the cold fluid forms a surface current in addition, whereas a warm fluid forms neither a surface charge nor a surface current. Consequently, in a drifting cold plasma, the tangential magnetic field, as well as the normal component of the induction vector D is not continuous. We show that the specular-reflection procedure and the conventional matching method yield the same dispersion relations, as they should, and we correct the wrong notion found in literature that the two methods somehow yield different results.

An intense short laser pulse or a millimetre wave propagating through a plasma channel may act as a wiggler for the generation of shorter wavelengths. When a relativistic electron beam is launched into the channel from the opposite direction, the laser radiation is Compton/Raman backscattered to produce coherent radiation at shorter wavelengths. The scheme, however, requires a superior beam quality with energy spread less than 1% in the Raman regime.

The toroidal spread of laser blow-off injected lithium is studied. The temporal variation of the toroidal and radial distributions of the first two ionization stages of cross-field-injected lithium is measured around the injection location by a gated, image-intensified CCD camera. Broad atomic distribution and deep radial penetration of the injected beam is observed. The toroidal delay of the arrival of the Li+ ions is investigated by detecting the intensity of their line radiation at different toroidal positions away from the injection port. Possible explanations for the observations and the possible mechanism for the toroidal spread are discussed in detail. A comparison of the detected distribution of Li ions with a 1D simulation is presented.

In an experiment carried out in a linear, unmagnetized plasma, evolution and propagation of nonlinear, rarefactive ion–acoustic pulses have been investigated. The nonlinear rarefactive pulse is observed to undergo fissioning as it propagates. Measurements of the ion velocity distribution function within the pulse indicate strong modifications of the distribution functions at velocities in the neighbourhood of the ion acoustic speed. Wave–particle interaction is thus shown to play an important role in the observed behaviour. Large-amplitude rarefactive pulses, while showing multiple fissioning, also exhibit a large-amplitude, low-frequency (≈30 kHz) oscillatory tail, downstream of the main pulse. The oscillatory tail is unlike the expected Airy function that normally accompanies a weakly nonlinear rarefactive pulse. The observations suggest the existence of ion-hole-like structures on the downstream side. The mechanism of the excitation seems to be through modification of the ion phase space due to trapping of ions in the negative potential well of the rarefactive pulse.

The effects of dispersion of slow electromagnetic surface waves propagating across an external magnetic field in planar metallic waveguides with dielectric coating and non-uniform plasma filling on the harmonics of the electron cyclotron frequency are studied. The theoretical investigation of the surface modes is carried out using a kinetic description for the plasma particles and a mirror-reflection model for the interaction between particles and plasma boundary. The effect of the transverse plasma density inhomogeneity on the electron surface cyclotron-wave spectrum is investigated.

The effect of finite plasma rotation on the equilibrium of an axisymmetric toroidal magnetic trap is investigated. The nonlinear vector equations describing the equilibrium of a highly conducting, current-carrying plasma are reduced to a set of scalar partial differential equations. Based on Shafranov's well-known tokamak model, this set of equations is employed for the description of a kinetic (stationary) plasma equilibrium. Analytical expressions for the Shafranov shift Δ are found for the case of finite plasma rotation, where two regions of possible plasma equilibria are found corresponding to sub- and super-Alfvénic poloidal rotation. The shift Δ itself, however, turns out to depend essentially on the toroidal rotation only. It is shown that in the case of a stationary plasma flow, the solution of the Grad–Shafranov equation is at the same time also the solution of the stationary Strauss equation.

Maxwell's curl equations and the linearized balance equations for momentum and pressure tensor for a plasma in an external magnetic field are combined in a system of first-order partial differential equations for the field quantities. With the corresponding adjoint system, the Lagrange identity is established, leading to a symmetry relation between the Green functions for the original and the adjoint fields. With temporal mapping the adjoint field can be transformed into a ‘Lorentz-adjoint’ (physical) field, leading to a reciprocity relation between the Green functions for the original and for the Lorentz-adjoint fields.

A theory is proposed that describes in a self-consistent manner damping and particle acceleration within cavitons. The framework of the approach makes it possible to formulate a set of self-consistent equations taking into account the change in the particle distribution function due to the interaction with cavitons and the damping of the waves within the cavitons due to the interaction with resonant particles. The spatial inhomogeneity of the distribution function of resonant particles in the vicinity of a caviton produces a new type of damping. The new damping mechanism is present for any inhomogeneity produced both by the other cavitons (or empty cavitons) in a strongly turbulent plasma or by any other source. This new type of damping is important for arresting wave collapse.

The wavelengths and attenuation coefficients of dipolar left and right-hand circularly polarized waves in a radially inhomogeneous axially magnetized plasma column are computed by means of step approximation of the radial plasma density profile. A comparison with theoretical results assuming radial plasma homogeneity shows that the radial plasma inhomogeneity is significant for wave propagation. In particular, it facilitates the occurrence of backward waves and increases by up to one order of magnitude the wave attenuation coefficient compared with a homogeneous plasma column having the same average plasma density.

The electromagnetic–acoustic field in a waveguide filled with a magnetoplasma (or in a stratified magnetoplasma), as well as the corresponding formally adjoint field, are decomposed into eigenmodes. The amplitudes of incoming and outgoing modes for both fields are related by scattering matrices. It is shown that the transposed scattering matrix of one field is the inverse scattering matrix of the other. The fictitious formally adjoint field is temporally mapped into a physical Lorentz-adjoint field, whose scattering matrix is shown to be the transpose of the scattering matrix of the original field.

On the basis of a two-fluid, cold-plasma, linear stability calculation with linear friction between electrons and ions, the growth rate of Alfvén waves is derived from the dispersion relation for a uniformly magnetized plasma, in which the plasma resistivity and a uniform electric current carried by an electron beam are both considered. The growth rate is directly proportional to the plasma resistivity, the electric current density and the value of the parameter ωxpe/Ωe (where ωxpe and Ωe are the electron plasma and cyclotron frequency respectively). Moreover, the growth of Alfvén waves is mainly excited in a direction nearly parallel to the ambient magnetic field. The critical value of the velocity of the electron fluid is just equal to the Alfvén velocity. The results of this paper are compared with those for the linear tearing mode.