The dependences of the propagation characteristics of an intense microwave pulse on the intensity, frequency, width and shape of the pulse in an air- breakdown environment are examined. Numerical simulations lead to a useful empirical relation P3W = α = const, where P and W are the incident power and width of the pulse and α depends on the percentage of the pulse energy transferred from the source point to a given position. The results also show that, using a single unfocused microwave pulse transmitted upwards from the ground, the maximum electron density produced at, for example, 50 km altitude is limited by the tail erosion effect to below 106 cm-3. Repetitive-pulse and focused-beam approaches are then examined. Both approaches can increase the maximum electron density by no more than an order of magnitude. Hence a scheme using two obliquely propagating pulses intersecting at the desired height (e.g. 50 km) is considered. It is shown that the generated electron density at the lowest intersecting position can be enhanced by more than two orders of magnitude.

A quasi-one-dimensional model for the steady-state flow of a plasma in an ablative discharge capillary is presented for capillaries with non-constant cross- section. It is demonstrated that small modifications of the capillary geometry can lead to significant changes in the plasma exit parameters. In this respect, the possibility of obtaining an extended range of plasma parameters makes this type of ablative capillary a useful source of plasma for a variety of applications. Numerical solution of the equations of the model for the critical-flow case allows evaluation of the main fluid-dynamic and thermodynamic parameters of the plasma inside the capillary and at its exit.

Non-resonant ponderomotive force theory is applied to fluctuating electromagnetic fields in a plasma. Bootstrap-type relations between the radial transport velocity and the toroidal current driven by fluctuations are also discussed in the case of non-zero ponderomotive forces proportional to d/dr. A special case of fluctuating fields as measured in the SHEILA heliac is discussed.

Laser radiation propagating through a non-uniform plasma along the direction of the density gradient suffers total reflection at the critical layer. However, when a wiggler magnetic field exists near the critical layer, the laser drives a Langmuir wave. For suitable values of Bw and kw, the power transfer from the laser to the Langmuir wave could be as high as 60%. The Langmuir wave deposits its energy on the electrons via Landau damping. This may be an efficient mechanism of laser absorption when large self-generated magnetic fields exist in the plasma.

Electromagnetic and electrostatic instabilities driven by loss-cone particle distributions have been invoked to explain a variety of plasma phenomena observed in space and in the laboratory. In this paper we analyse how the loss- cone feature (as determined by the loss-cone index or indices) influences the growth of such instabilities in a fully ionized, homogeneous, hot plasma in a uniform magnetic field. Specifically, we consider three loss-cone distributions: a generalized Lorentzian (kappa) loss-cone distribution, the Dory—Guest—Harris distribution and the Ashour-Abdalla-Kennel distribution (involving a subtracted Maxwellian). Our findings are common to all three distributions. We find that, for parallel propagation, electromagnetic instabilities are only affected by the loss-cone indices in terms of their occurrence in the temperature anisotropy. However, for oblique propagation, even including propagation at small angles to the ambient magnetic field, the loss-cone indices do independently affect the growth of instabilities for electromagnetic waves, in contrast to certain claims in the literature. For electrostatic waves such that 1, where kx is the component of the wave vector perpendicular to the ambient magnetic field and pLa is the Larmor radius for particle species <r, we find that the loss-cone indices only enter the dispersion equation via the temperature anisotropy, and so in this case the loss-cone feature and perpendicular effective thermal speed do not independently affect wave growth.

The existence of various types of (fast) magnetoacoustic modes in different frequency regimes in a magnetized dusty plasma consisting of electrons, ions and dust particles is investigated. The analysis is carried out using an effective two-fluid MHD-like model which allows for the non-frozen motion of the component fluids. For frequencies much smaller than the dust particle gyro- frequency, we obtain a magnetoacoustic mode that is a generalization of the usual compressional fast hydromagnetic wave in an electron—ion plasma. In the higher-frequency regimes, we show the existence of two new types of modes called ‘Dust-magnetoacoustic waves’. Both modes are accompanied by compressional magnetic field and plasma number density perturbations, and are the electromagnetic generalizations of the dust-acoustic waves in an unmagnetized dusty plasma with thermal electrons and ions. For a two- component plasma, all three modes degenerate into the same fast magneto- acoustic wave found in the usual electron—ion plasmas. We also obtain another novel type of magneto-acoustic mode called a ‘dust—ion-magneto- acoustic wave’, which is an electromagnetic generalization of the dust—ion- acoustic wave. The dispersion relations as well as the frequency regimes for the existence of the various modes are explicitly obtained. An alternative derivation of the relevant governing equations using an approach similar to that employed in so-called ‘electron magnetohydrodynamics’ (EMHD) is also presented.

We reconsider the transport equation in the solar interior and calculate the effects on the opacity of photon scattering near the Raman resonance. Both spontaneous and stimulated scattering on thermal photons and thermal plasmons are taken into account, and changes in opacity (with respect to previous calculations) are calculated numerically and found to be negligible with respect to relativistic corrections to photon scattering.

A peculiarity of the quasi-optical propagation of a Gaussian beam of electromagnetic waves is that it requires a treatment taking account, step by step, of all of its rays together. The dispersion relation from which such a ray- tracing may be deduced is in fact characterized not only by the medium where the beam is launched but also by the intrinsic beam structure. The behaviour of three-dimensional Gaussian beams in the electron-cyclotron frequency range is considered, with particular attention paid to their propagation in toroidal plasmas of fusion interest (with ITER-like parameters and various magnetic equilibrium configurations), to the generality of their launching conditions and to their power deposition profiles around resonant layers.

An application of the self-consistent multiple-scattering theory of electromagnetic waves to drift turbulent vortices is presented. Using the known single-vortex solution, the integral equation describing the scattering from a finite density of drift turbulent vortices is obtained. Rather than solving this equation and then averaging, the averaging operation is taken first to obtain statistical moment equations, from which the coherent and incoherent scattering follow. These results are expressed in a Fourier basis, and the cross-section is evaluated. Limiting forms of the theory and straightforward generalizations are discussed.

We study an ideal MHD plasma with the non-vanishing invariants energy, crosshelicity and magnetic helicity, confined in a cylinder with infinitely conducting walls and an externally applied magnetic field B0. The magnetic and velocity fields are expanded in base vector fields, satisfying Δ × Bλ = Bλ. Boundary conditions are imposed to make the curl a self-adjoint operator. The three invariants depend on the time-dependent coefficients of the base vector fields, and are used to construct the partition function to gather statistical information about the equlibrium thermodynamic state to which the plasma relaxes after a turbulent transition. For zero external magnetic field but large magnetic helicity, the energy resides preferentially in magnetic field fluctuations. A sizeable fraction of the kinetic energy initially present is transformed into magnetic energy. The energy condenses via an inverse cascade predominantly to the lowest energy eigenstate, in agreement with results obtained by Taylor. However, since we consider the whole spectrum of eigenstates, the energy does not exclusively occupy the lowest eigenstate. If the eigenvalues are densely spaced (as in a thin torus), the higher eigenmodes also contain appreciable amounts of energy, resulting in a finite pressure of the plasma. For constant and finite external magnetic field, the average induced magnetic field exactly cancels the external field. This indicates that, on a statistical average, the plasma is diamagnetic or superconducting. Superimposed on the average statistical state are fluctuations that may become large if the magnetic helicity is large.