The mechanism of gyroresonant scattering of charged particles by small-amplitude, broadband electromagnetic waves is examined. By means of quasi-linear theory, a simple expression for the resonant pitch-angle diffusion coefficient $D_{\alpha \alpha}$ is developed, which is valid for parallel-propagating, small-amplitude, (R-mode or L-mode) electromagnetic waves of general spectral density. We calculate the average diffusion coefficient with respect to the pitch-angle $\alpha$, namely $\langle D_{\alpha\alpha}\rangle$, which provides a practical estimate for particle scattering rates as a function of particle kinetic energy. The results for $\langle D_{\alpha\alpha}\rangle$, corresponding to a Gaussian wave frequency spectrum, are used to estimate scattering rates for several types of wave–particle interactions in the terrestrial and Jovian magnetospheres.

Using a new technique following the Bogoliubov Mitropolsky method, higher-order nonlinear and dispersive effects are obtained for a kinetic Alfvén wave and ion-acoustic wave with two temperature isothermal electrons, starting from a set of equations that lead to a linear dispersion relation coupling kinetic Alfvén wave ion-acoustic wave. Higher-order solitary wave profiles are obtained for both waves. Graphs are plotted showing the variation of both the Mach number and soliton width against the soliton amplitude for different angles of propagation with the applied magnetic field. Amplitude, width and velocity are found to be greater for larger angles of propagation for both waves. It is found that the higher-order ion-acoustic wave moves faster than the Korteweg–de Vries (KdV) wave, but the higher-order Alfvén wave is slower. The higher-order amplitude and width of both waves are found to be less than those of KdV waves. The potential structure and widths of the double layer for both waves are shown graphically. It is found that the amplitude of the double layer is independent of the angles of propagation, but the widths are greater for larger angles of propagation for both waves.

The dynamics of thermally-isolated Z-pinches carrying power law in time total currents (${\sim} t^S$) in magnetized resistive plasmas is studied. Time–space separable self-similar solutions with cylindrical symmetry are considered. The non-dimensional variables are chosen in a way that makes the problem consistent with the moderately resistive magnetohydrodynamic (MHD) model. For $S\,{=}\,{-}\frac15$ and Lundquist number $Lu\,{>}\, 1.5$ a non-equilibrium solution is obtained in addition to the conventional solutions for either exact, $S\,{=}\,{\pm}\frac13$, or asymptotic, $Lu\,{=}\,\infty$, equilibria (the latter is homogeneously valid for long times only if $S\,{>}\,{-}\frac15$). The problem is treated asymptotically for high dimensionless thermal-conductivity, which is proportional to the square root of the ion/electron mass ratio. To obtain a closure condition for the leading-order isothermal solution, the first-order terms in the energy equation are invoked. Radial profiles are found explicitly which depend on $S$ for equilibrium, and on $Lu$ for non-equilibrium solutions. The multiplicity of the self-similar solutions is investigated.

For a particle moving in a non-uniform static magnetic field under the action of a wave, ponderomotive effects result from radiofrequency-driven oscillations nonlinearly coupled with Larmor rotation. Using the Lagrangian and Hamiltonian formalisms, we show how, despite this coupling, two independent integrals of the particle motion are approximately conserved. These are the magnetic moment of free Larmor rotation and the quasi-energy of the guiding center motion parallel to the d.c. magnetic field. Under the assumption of non-resonant interaction of the particle with the radiofrequency field, these integrals represent adiabatic invariants of the particle motion.

The influence of the trapped electrons fraction on the growth-rate of the ion temperature gradient (ITG) modes is studied numerically for JET relevant conditions. As a possible mechanism for increasing the ITG mode growth rate with an increase in the fraction of trapped electrons, a shift in the real frequency is assumed that leads to less Landau damping. Another possible mechanism is the destabilizing contribution of dissipation effects.

We analytically and numerically discuss the plasma distribution and electron temperature enhancement in striations for a given heating source. It is shown that, in stationary conditions, the reduced plasma concentration and the temperature enhancement should be of the same order of magnitude. We deduce that the electron temperature inside striations cannot greatly exceed that in the heated volume. The elongation of striations is calculated for different transverse scales and heating powers. We show that medium sized irregularities are associated with striations and develop after the formation of striations. The peculiarities of the relaxation process for small-scale and medium sized artificial irregularities are investigated and it is found that the relaxation of small-scale irregularities exhibits two time scales, in qualitative agreement with experimental observations.

The radial profiles of current and flow permitted by the relaxed states of a two-fluid cylindrical plasma system using double Beltrami formulation are presented. The relaxed states are then compared with those of the internal conductor plasma configuration. The results show that for appropriate boundary conditions and scale parameters, field-aligned currents and flows could be minimized to a greater extent in an internal conductor plasma system as compared with a simple cylindrical plasma configuration. Consequently, high beta relaxed states with minimum values of parallel components of current and flow could be created using internal conductor plasma configurations.

The influence of non-thermal ions on linear dust-acoustic waves is studied in an unmagnetized plasma consisting of ions which have a non-thermal velocity distribution, Boltzmann-distributed electrons and streaming dust particles. A detailed examination is conducted of the dependence of the real frequency and growth rate of the excited instability on the dust drift speed, temperature, particle densities and the parameter $\alpha$ that determines the non-thermal nature of the energetic ions. Comparisons with approximate analytical solutions are also made.

An intense laser beam guided through a low-density plasma channel produces second harmonic emission that leaks out in the high-density outer region, propagating in a low-angle hollow cone with respect to channel axis. For a channel with interior density 0.25$n_{\rm cr}$, outer region density 0.64$n_{\rm cr}$ ($n_{\rm cr}$ being the critical density), laser wavelength 1 $\mu$ and channel radius ${\sim}5~\mu$m, the angle $\theta$ of the cone ${\sim}19^{\circ}$. The second harmonic power shows an oscillatory behavior with the density of the channel. It peaks at certain densities of the plasma channel. The heights of the peaks of second harmonic power are higher at greater densities.

A theory of self-fields in a free-electron laser with a helical wiggler and ion-channel guiding is presented. The effects of self-electric and magnetic fields on electron trajectories are investigated. It is shown that, under the Budker condition, there is one group of orbits (group I) for which the wiggler-induced self-magnetic field is negative and acts as a diamagnetic correction to the wiggler magnetic field. The function $\Phi $ that determines the rate of change of axial velocity with energy in the presence of the self-fields is derived and studied numerically.