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.

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.

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.

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.

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.

A four-dimensional systematic mathematical approach for investigating propagation and coupling of wave modes in a slowly varying (in all space directions and time) anisotropic, absorbing plasma is represented. The formalism is especially useful for energy considerations of the waves. It is applicable to general cases of mode couplings in plasmas with general geometries of space–time and magnetic field configurations. A simple example of how this formalism can be applied to practical cases is given.

A large-amplitude upper-hybrid wave in a plasma cylinder is susceptible to parametric decay into a lower-hybrid wave and an upper-hybrid wave. The perpendicular and parallel motions of electrons play equally important roles in the nonlinear interaction. The coupled-mode equations are solved using a perturbation technique. The growth rate of the instability is less sensitive to the radial mode number of the sideband. However, for higher-order radial modes it falls off as the overlap of the interacting wave functions decreases.

The velocity distribution functions of newly born (t=0) charged fusion products (protons in DD and alpha particles in DT plasmas) of tokamak discharges can be approximated by a monoenergetic ring distribution with a finite v∥ such that v⊥≈v∥ ≈Vj, where ½MjV2j =Ej, the directed birth energy of the charged fusion-product species j of mass Mj. As the time t progresses, these distribution functions will evolve into a Gaussian in velocity (i.e. a drifting Maxwellian type), with thermal spreads given by the perpendicular and parallel temperatures T⊥j(t) =T∥j(t), with Tj(t) increasing as t increases and finally reaching an isotropic saturation value of

formula here

Here Td is the temperature of the background deuterium plasma ions, M is the mass of a triton or a neutron for j=protons and alpha particles respectively, and τj≈¼τsj is the thermalization time of the fusion product species j in the background deuterium plasma, with τsj the slowing-down time. For times t of the order of τj, the distributions can be approximated by a Gaussian in the total energy (i.e. a Brysk type). Then, for times t[ges ]τsj, the velocity distributions of the fusion products will relax towards their appropriate slowing-down distributions. Here we shall examine the radiative stability of all these (i.e. a monoenergetic ring, a Gaussian in velocity, a Gaussian in energy, and the slowing-down) distributions.

The weakly nonlinear dynamics of fast magnetosonic waves ducted by a region of density enhancement in a cold plasma is considered. A self-consistent 2D quasi-hyperbolic equation with quadratic and cubic nonlinearities is derived for perturbations of the transverse component of the plasma velocity. For a wave package with a narrow spectrum, the governing equation is reduced to the nonlinear Schrödinger equation, whose structure is independent of the detailed density profile provided that it has a maximum (to be a potential well for the waves). The derived equation allows us to take into account the effect of the shape and steepness of the density profile on the wave dynamics.

Some aspects of plasma dynamics with electron-inertia effects are considered. The behaviour of (i) one-dimensional steady current sheets, (ii) two-dimensional steady reconnection models, (iii) one-dimensional current-sheet evolution, (iv) linear tearing-mode evolution and (v) nonlinear magnetic-island evolution in this regime is investigated. Stability of the two-dimensional plasma in this regime is then discussed, and necessary conditions for linear stability in the Liapunov sense for steady states are then given.

The effect of a beam of radio waves of very high brightness passing through a cold, magnetized, electron–positron plasma is discussed. The properties of the natural wave modes in such a plasma are summarized, and approximate forms for the nonlinear response tensor are written down. Photon-beam-induced instabilities of low-frequency waves in the pair plasma are analysed in the random-phase approximation. When three-wave interactions involve two high-frequency waves in the same mode and a low-frequency wave in a different mode, wave–wave interactions are similar to wave–particle interactions in that photons act like particles that emit and absorb low-frequency waves. The absorption coefficients for various low-frequency waves due to a photon beam are evaluated. In a pure electron–positron plasma, photon-beam-induced instabilities can be effective only when either the high-frequency or the low-frequency waves are strongly modified by the magnetic field. The growth of the low-frequency waves is most effective when the high-frequency photon beam has a frequency close to the cyclotron frequency.

Staged pinch implosions provide a means to couple energy to a small-diameter fibre on an extremely fast time scale, circumventing the limitations of conventional pinches. In this scheme the generator current initially traverses an intermediate hollow plasma shell, which compresses onto the fibre placed coaxially and transfers the current to the fibre with a significantly reduced risetime. The results are impressive, since the delivered peak power is increased by several orders of magnitude, the coupling efficiency improves, and the most dangerous plasma instabilities that commonly plague high-density/high-temperature pinches are eliminated. This technique can be fielded on both fast and slow generators (i.e. tens of nanoseconds to microseconds), making it feasible to extend the concept to a wide range of presently assembled systems. Staging may therefore present a dramatically new means of pulsed-energy conversion, which could find many applications. In addressing the requirements for thermonuclear fusion in a staged Z pinch, our preliminary calculations based on zero-D models suggest the potential for a significant thermonuclear burn with generator currents of the order of a few megaamperes and one microsecond risetime. Studies are actively underway at various places around the world (England, France, Germany and Russia) as well as in the USA (UCI/UCR) to investigate different aspects of staged pinching and its applications, particularly those leading to controlled thermonuclear fusion.

In a recent study Tsytovich et al. [J. Plasma Phys. 56, 127 (1996)] claimed to obtain new expressions for electron–ion bremsstrahlung in plasmas. It is shown, however, that they interpreted earlier work incorrectly and simply reproduced well-known results.