A dispersion equation is derived for a cylindrical waveguide of circular cross-section partially filled with chiroplasma. The propagation characteristics of electromagnetic waves in the family of waveguide modes are studied. The dispersion curves are given. It is found that the propagation constant changes almost linearly with the chirality admittance for the parameters that we choose, and increases with increasing filled area.

The concept of magnetic entropy, the entropy pertaining to a magnetic configuration, is introduced and illustrated through its application to the description of the magnetic states assumed preferentially by a tokamak and of the transition between them. The magnetic equilibria associated with stationary magnetic entropy admit a bifurcation, and a new state can arise that can be attained spontaneously with an increase in the magnetic entropy. The thermodynamic relations between entropy production, heat transport and plasma energy allow one to express quantitatively the modifications of these quantities generated by the magnetic transition to the new state and to identify it with the L–H transition. The power and temperature thresholds of the transition are expressed in terms of the confinement time of the L state, and definite scalings are derived that compare favourably with observations. The theory implies the hysteresis and the upper density limit of the H state.

The time evolution of an incompressible non-ideal magnetohydrodynamic (MHD), current-carrying plasma with mass flow is investigated. An approach for the reduction of the nonlinear vector MHD equations to a set of scalar partial differential equations is supposed. Analytical time-dependent solutions of this system are presented. They describe kinetic plasma equilibria both with well-defined nested-in magnetic and velocity surfaces and in the form of vortices. The obtained solutions may be called ‘diffusion-like’, since their temporal structure is very similar to the solutions of the diffusion problem. It is shown that the magnetic field and the velocity have different dumping rates. In the asymptotic limit t→∞, the plasma slowly relaxes towards the hydrostatic equilibrium of gravitating systems.

We derive a system of nonlinear equations that govern the dynamics of low-frequency short-wavelength electromagnetic waves in the presence of equilibrium density, temperature, magnetic field and velocity gradients. In the linear limit, a local dispersion relation is obtained and analyzed. New ηe-driven electromagnetic drift modes and instabilities are shown to exist. In the nonlinear case, the temporal behaviour of a nonlinear dissipative system can be written in the form of Lorenz- and Stenflo-type equations that admit chaotic trajectories. On the other hand, the stationary solutions of the nonlinear system can be represented in the form of dipolar and vortex-chain solutions.

Wave modes in a strongly magnetized pair plasma slab (beam) embedded in a pair plasma of different number density are considered for highly relativistic beam flow relative to the bounding plasma. Approximate analytical results are obtained and compared with numerical calculations and with the thin-beam approximation derived in Part 1 [J. Plasma Phys.62, 425–439 (1999)].

Application of lower-hybrid (LH) power in short, intense pulses in the 5–10 GW range should overcome the limiting effects of Landau damping, and thereby permit the penetration of LH power into the interior of large-scale plasmas. We show that, under such very intense LH pulses, wave coupling may deteriorate because of nonlinear density changes due to the ponderomotive force effects in front of the grill. Ponderomotive forces are also likely to induce strong plasma bias and consequent poloidal and toroidal plasma rotation. Although backward electric currents, created in the plasma by intense LH pulses, dissipate a large portion of the radio frequency power absorbed, the current drive efficiency is acceptable. We use a numerical simulation of wave–particle interactions to analyse the applicability of standard quasilinear theory to the case of large energy flux densities. The initial results indicate the existence of important restrictions on the use of the quasilinear approximation. The results of the present paper also indicate that some of the effects considerably alter some ideas of Cohen et al.

Beam instabilities that arise in the compression zone of a gyrotron oscillator can degrade the beam quality and hence adversely affect the operating characteristics of the device. This paper investigates a class of space-charge instabilities that are related to unstable Bernstein modes. These are investigated both by simulations with a 2½-dimensional fully electromagnetic particle-in-cell code and by solving the linear dispersion equation (obtained with kinetic theory). Use of the code makes it possible to study effects that cannot be taken into account in the linear dispersion relation, such as the effect of static self-fields. The simulation strongly suggests that the instability is convective. The dependence of growth rate and frequency spectrum on beam parameters is calculated both with simulation and the analytical method, and the results show good agreement. A detailed analysis of the electromagnetic fields calculated in the simulation shows that the unstable waves are not (as has frequently been assumed in the past) purely electrostatic.

The correspondence between the forced magnetic reconnection induced by perturbing the boundary of the simple Taylor model and the surface-wave-induced magnetic reconnection given by Alfvén resonance theory is pointed out explicitly by showing that the theory of forced magnetic reconnection is actually embedded in the Alfvén resonance theory. The advantages of viewing the forced reconnection as surface-wave-induced reconnection are briefly discussed in the context of the formation of small-scale structures at the magnetospheric boundary and solar coronal heating.

A recent study on axisymmetric ideal magnetohydrodynamic equilibria with incompressible flows [H. Tasso and G. N. Throumoulopoulos, Phys. Plasmas5, 2378 (1998)] is extended to the generic case of helically symmetric equilibria with incompressible flows. It is shown that the equilibrium states of the system under consideration are governed by an elliptic partial differential equation for the helical magnetic flux function containing five surface quantities along with a relation for the pressure. The above-mentioned equation can be transformed to one possessing a differential part identical in form to the corresponding static equilibrium equation, which is amenable to several classes of analytical solutions. In particular, equilibria with electric fields perpendicular to the magnetic surfaces and non-constant-Mach-number flows are constructed. Unlike the case in axisymmetric equilibria with isothermal magnetic surfaces, helically symmetric T = T(ψ) equilibria are overdetermined, i.e. in this case the equilibrium equations reduce to a set of eight ordinary differential equations with seven surface quantities. In addition, the non-existence is proved of incompressible helically symmetric equilibria with (a) purely helical flows and (b) non-parallel flows with isothermal magnetic surfaces and with the magnetic field modulus a surface quantity (omnigenous equilibria).

The method of matched asymptotic expansions is used to examine the structure of the plasma sheath of the positive column at low pressure in electronegative gases using the fluid model to describe the positive-ion motion. It is shown that at low negative-ion concentrations, and at high concentrations, the structure is that of a plasma joined to a thin sheath, but that for the electron/negative-ion temperature ratio Te/Tn ≡ ε > 5 + √24, and for a well-defined range of A ≡ nn0/ne0 (the central negative ion to electron density ratio) and for small Debye length, there is a more complex structure with a central negative-ion-dominated plasma surrounded by a quasiplasma in which density oscillations may occur before joining to a sheath. This is in agreement with recent computations using the same model.

The temporal evolution of weakly nonlinear, plane, linearly polarized Alfvén pulses in a cold homogeneous plasma is investigated. A static initial pulse-like disturbance in transverse velocity produces two Alfvén pulses that travel in opposite directions along the magnetic field. The ponderomotive force of the two pulses produces a static shock in longitudinal velocity at the starting position. The travelling pulses form a shock front that is governed by the scalar Cohen–Kulsrud equation. We find good agreement between the analytical solutions we derive and the results from a fully nonlinear numerical MHD code.

Streaming instabilities are studied for an inhomogeneous distribution of dust particles. Such situations are characteristic of stellar neighbourhoods, where the star's plasma wind ploughs through a surrounding dust shell. This should result in the acceleration of dust particles at the expense of the plasma momentum, which may throw light on certain dynamical features of the dust cloud vis-à-vis the plasma dynamical features. Streaming instabilities are a first step towards such a study. Various cases of the relative magnitudes of the plasma and dust velocities are analysed, and the role of inhomogeneities is highlighted.

A new mechanism for the formation of pinching plasma instability related to a tangential discontinuity is discussed. With this in mind we use a simple model of the Davydov–Zakharov class. It appears that there is a strong dependence of the instability increment on current density, resulting from the corresponding dispersion relation. Modulation of a current pulse is shown to be a possible way of stabilizing powerful discharges.

Mode coupling takes place in a small, but non-zero, region around the coupling point. A general formula for the size of this coupling region is given. This formula is valid for anisotropic absorbing media with the inhomogenity in one direction and for a linear system of wave equations with an arbitrary number of fields and of arbitrary order; i.e. an arbitrary number of waves can couple and an arbitrary number of coupling points can coalesce. It is shown that the size is dependent on the number of modes that exist in the medium and the number of coupling points that coalesce. The formula is applied to some examples. A peculiar result that the formula shows is that as the temperature approaches infinity, the size of the mode-coupling region approaches a constant finite value, and in certain cases this size approaches zero; i.e. in these cases of extremely high temperature, mode coupling eventually vanishes.

The properties of a relativistic plasma dispersion function (RPDF) for an intrinsically extremely relativist, strongly magnetized, one-dimensional, electron–positron plasma are discussed in detail. For a plasma with a mean Lorentz factor 〈γ〉 [Gt ] 1 in its rest frame, the RPDF has a large peak >〈γ〉 at a phase speed a fraction of order 1/〈γ〉 below the speed of light, and the asymptotic value (infinite phase speed) is 〈γ−3〉 ∼ 1/〈γ〉. These features are not particularly sensitive to the choice of distribution function. The RPDF is used to discuss the properties of waves in such plasmas. Particular points discussed are the implications of the RPDF for the maximum frequency for parallel Langmuir waves, and for the reconnection between the Langmuir mode and the Alfvén mode.

A class of relativistic dispersion functions for unmagnetized thermal plasmas is defined by generalizing functions first defined by Trubnikov in 1958. Recursion relations are derived that allow one to generate explicit expressions for the class of functions in terms of the relativistic plasma dispersion function T(z, ρ) introduced by Godfrey et al. in 1975. These functions are relevant to the description of the response of a weakly mangetized, highly relativistic, thermal plasma.