We present a method of solution of the quasi-linear diffusion equation for the averaged distribution function. The criterion for its validity is discussed. Using the solution obtained, we study the dynamics of the relaxation of a weak kinetic electron-beam instability and show that it saturates asymptotically at zero energy level. In a self-consistent manner, the distribution function for the beam particles will be shown to deform to a flat shape.

Oscillating two-stream instability (OTSI) of lower-hybrid pump waves has been studied in both large- and small-size devices. For large-size devices, the instability has been investigated by considering fast-ion-mode side-bands and employing local theory. The convective threshold due to the finite extent of the pump has been calculated. For small-size devices, the instability has been investigated by ignoring thermal effects on the side-bands but employing nonlocal theory. We have found that there is no important change in growth rates in both cases.

Surface-wave propagation along a double step is investigated within ideal compressible MHD. The occurrence of surface-wave leakage is emphasized and the relevant conditions are discussed. A numerical example is presented to illustrate the process.

An investigation is made of wave generation and radiation of third harmonics by s-polarized electromagnetic waves incident on a narrow inhomogeneous layer of a magnetoactive plasma. The amplitudes of the radiated third-harmonic waves are calculated. In contrast with second harmonics, third harmonics are radiated for the case of normally incident waves on an unmagnetized plasma.

An expression for the nonlinear wavenumber shift of an obiquely propagating ion-cyclotron whistler in the presence of negative ions are derived. The effects of the intensity of the wave, the ion-cyclotron frequency, the negative-ion concentration and the propagation angle on the wavenumber shift of whistlers is discussed. Numerical estimations are also made of the wavenumber shift.

From the Vlasov-fluid model, a set of approximate stability equations describing the stability of a cylindrically symmetric z–pinch is derived. The equations are derived in the limit of small gyroradius and include kinetic effects such as finite Larmor radius, particle drifts and resonant particles. In the limit of zero Larmor radius and short wavelengths, we apply the equations to the internal m = 0 and m = 1 modes. If the drift term mωD + kVD is neglected in the resonant denominators, we find stability criteria that are more optimistic than the corresponding stability criteria for perpendicular MHD. The neglect of the drift term is, however, not justified for the m = 1 mode, where mωD needs to be retained in order to preserve the property that this approximate model should have the same point of marginal stability as the exact Vlasov-fluid model. Retaining the drift terms, growth rates have been calculated for the m = 1 mode, for a constant-current-density equilibrium and for the Bennett equilibrium. For the Bennett profile, we obtain, when compared with perpendicular MHD, a substantial reduction in growth rate γ/γMHD ≈ 0·2.

An equilibrium model for a spherical field reversed configuration in the presence of a transverse rotating magnetic field is presented. It is shown that this quasi-static equilibrium is an exact solution of the time-dependent ideal magneto-hydrodynamic equations.

The renormalization-group method is applied to the problem of forced turbulence in the simplified Alfvén model of Chen and Mahajan. The effects of small unresolvable subgrid modes on the large-scale turbulence leads to a renormalized response function ε. In certain limits, the resulting recursion relation for the response function can be converted into a differential equation that can be solved analytically. For Gaussian forcing terms satisfying a power-law wavenumber correlation k–y but white-noise frequency spectrum, it is found that the response function exhibits second-harmonic generation of waves at frequency ω = 2ΛvA for all exponents y ≥ 0, where Λ is the wavenumber separating the subgrid and supergrid modes.

We consider here the nonlinear development of ion-acoustic waves in a magnetized plasma, and give a further discussion of the analytical properties of the Zakharov-Kuznestov equation that governs the latter problem. First we discuss the solitary-wave solutions and show that they give a good description of recent experimental results about the manner in which the magnetic field influences the solitary waves. We then exhibit recurrence and Lagrange stability of solutions of the Zakharov-Kuznestov equation.

The stability of the MHD equations describing the mutual interaction of cosmic rays, thermal plasma, magnetic field and Alfvén waves used in cosmic-ray-shock acceleration theory (e.g. McKenzie & Völk 1982) is analysed for linear compressive instabilities. It is found that the inclusion of wave effects implies that the forward propagating sub-Alfvénic mode is unstable on wavelength scales greater than 1 parsec. The role of the instability in astrophysical models is considered.

The active and reactive power resonantly absorbed by a linear passive system is calculated in terms of its continuum eigenfunctions and the spatial–temporal spectral density of the external force. An application to the resonance absorption of electromagnetic radiation by a cold inhomogeneous plasma is given.

The dispersion relation obtained from a linear analysis of the hydrodynamic system of equations of Duhau is used to study the behaviour of the fast and slow magnetosonic and entropy modes in an electron-heat-flux-conducting plasma. The evolution of the hydrodynamic modes different from the Alfvén mode are studied as the electron heat flux is increased from zero as well as around the borders of overstable regions, for any anisotropy condition of the ions. The development of the domains of mirror and electron-heat-flux overstabilities are established and the regions of absolute stability are shown

The generation of lower-hybrid waves in an inhomogeneous electron beam is examined. Wave amplitudes are invariably limited by the convective nature of the instability. The self-consistent shear of the magnetic-field geometry due to the beam current is limited to the role of dividing the general problem into separate cases according to the relative orientation of the wave vector and direction of inhomogeneity. Moreover, the limiting case of small shear is smoothly connected to the case where shear is altogether negligible. Estimates of the amplification of lower-hybrid waves propagating across the electron beam are made for the various cases.

A study is made of ion-acoustic solitons in a low-β magnetized plasma consisting of any number of adiabatic positive and negative ion species in addition to the presence of isothermal electrons. A KdV equation in three dimensions or KdV-ZK equation is derived. This equation admits comprehensive or rarefactive solitons propagating in any oblique direction with respect to the direction of the external magnetic field, depending on the density of the negative ion species. When the nonlinear coefficient of this equation vanishes, the nonlinear ion-acoustic wave is described by a modified KdV equation in three dimensions. This equation is also derived and its solitary-wave solutions are discussed. Both compressive and rarefactive solitons are possible. Finally, the three-dimensional stability of these solitons is investigated by the small-k perturbation expansion method of Rowlands and Infeld. Stability criteria and growth rates of instabilities are derived.

The equilibrium properties of a two-dimensional plasma are examined theoretically, using a model where the finite-Larmor-radius corrections to the simple guiding-centre description are included. The analysis is carried out in a truncated Fourier representation of the resulting equations. This system has three ‘rugged’ quadratic invariants. A canonical-ensemble probability distribution characterized by three temperatures is derived. The resulting partition function is obtained and the equilibrium spectral energy density is calculated. The possibility of negative-temperature states leading to an inverse energy cascade is pointed out.

The three-dimensional stability of solitary shear kinetic Alfvén waves in a low-β plasma is investigated by the method of Zakharov & Rubenchik (1974). It is found that there is no instability if the direction of perturbation falls within a certain region of space. The growth rate of the instability for the unstable region is determined. This growth rate is found to decrease with increasing angle between the direction of propagation of the solitary wave and the direction of the external uniform magnetic field. A particular case of the present analysis gives results on the stability of ion-acoustic solitons in a magnetized plasma.

The problem of propagation of an ion-acoustic soliton and its reflection in a weakly inhomogeneous plasma is considered, taking into account the effect of finite ion temperature. A reductive perturbation analysis is carried out to obtain expressions for the local speed, amplitude and width of the soliton. The peak value of the soliton amplitude increases and the soliton width decreases with increasing ion temperature. An equation describing the dependence of the reflected-wave amplitude on ion temperature is obtained. The amplitude of the reflected wave is observed to decrease with increasing ion temperature on account of Landau damping.

In order to find the equations for the nonlinear energy exchange between low-frequency waves in magnetized plasmas in the presence of pressure anisotropy, we start from the Chew–Goldberger–Low equations, the isothermal MHD equations, as well as a new hybrid system of equations. The coupling coefficients describing the interaction between two Alfvén waves and one magnetosonic wave as well as the interaction between two magnetosonic waves and one Alfvén wave are deduced.