This special issue marks the 65th birthday of John Dougherty, the founding father of this Journal and its Editor for the first 27 years of its life. Since the Journal is so much John's creation, we thought that it would not be appropriate to let this occasion pass without recognition, and we are pleased that a number of John's former students and a selection of people who have contributed regularly to the Journal or have been Associate Editors have agreed to contribute to this issue.

Most plasma physicists will probably associate John with at least three major contributions to the subject. The first is his classic work with Don Farley on scattering of electromagnetic waves from a plasma, and we are very pleased that Don has written a short note about the genesis of this work and about his collaboration with John. The second is his book on plasma physics written with P. C. Clemmow, which, some 30 years after its publication, is still one of the best available texts on some advanced aspects of the subject. It received the rare accolade of being reprinted in the Addison-Wesley Advanced Book Classics series 21 years after its first publication. Finally, there is his editorship of this Journal, which he continued long after his own interests had shifted from plasma physics to fundamental aspects of statistical mechanics. Under John's stewardship, the Journal published papers on all aspects of plasma physics, but perhaps became specially noted for thoughtful contributions to basic aspects of the subject.

All readers who know John, whether as authors, visitors to Cambridge or in any other capacity, will be aware of his friendliness and willingness to help others. On behalf of the plasma physics community, we would like to pass on to him our appreciation of his contribution, our congratulations on the occasion of his 65th birthday and our best wishes for the future.

The collective kinetic interaction of a neutrino distribution with electrostatic waves propagating in a dense plasma is considered. A Klimontovich-type kinetic equation for the neutrino gas in a plasma is derived, and the resulting kinetic description is applied to study the processes of the neutrino Landau damping and the neutrino-beam–plasma instability.

On the basis of kinetic fluctuation theory, the relaxation process between the electron and ion temperatures in a magnetized inhomogeneous plasma is considered when an external pump wave parametrically decays into lower-hybrid and electron drift waves. In the region above the instability threshold, the inverse relaxation time is calculated, and its dependence on the density gradient and the pump-wave intensity and frequency is obtained. It is shown that the presence of the parametric instability leads to a decrease of the relaxation time.

The hydrodynamic expansion of plasmas produced by laser beams focused on thin-foil targets is studied using a self-similar approach. The model is useful for studying long-scale-length plasmas, produced by uniform laser irradiation, which become fully underdense during the laser pulse. An essentially qualitative analysis of the hydrodynamics system in Cartesian geometry is given. In particular, a useful expression is obtained by integration of the thermal energy equation.

It is proposed to add a Rapid Communications section to the Journal of Plasma Physics. Papers submitted to this section should be restricted to no more than five printed pages in length, and should contain new and important ideas that warrant rapid dissemination amongst the plasma physics community. Submissions may be sent to any of the Editors or Associate Editors, who will obtain an assessment of the suitability of the paper as quickly as possible. We hope that readers and authors will find this a valuable addition to the journal.

Relativistic and non-relativistic particle acceleration along and across a magnetic field, and the generation of an electric field transverse to the magnetic field, both induced by almost perpendicularly propagating electrostatic waves in a relativistic magnetized plasma, are investigated theoretically on the basis of relativistic quasilinear transport equations. The electrostatic waves accelerate particles via Landau or cyclotron damping, and the ratio of parallel and perpendicular drift velocities vs||/vd can be proved to be proportional to k||/k⊥. Simultaneously, an intense cross-field electric field E0 = B0 × vd/c is generated via the dynamo effect owing to perpendicular particle drift to satisfy the generalized Ohm's law, which means that this cross-field particle drift is identical to E × B drift. The relativistic quasilinear transport equations for relativistic cross-field particle acceleration are derived by Lorentz transformation of the relativistic quasilinear momentum-space diffusion equation in the moving frame of reference without the electric field and the cross-field particle drift. They can be applied to the investigation of the relativistic perpendicular particle acceleration that may possibly occur in space plasmas.

It is shown that the asymptotic evolution of finite-amplitude magnetosonic waves propagating obliquely to an external uniform magnetic field in a warm homogeneous plasma is governed by a Kadomtsev–Petviashvili equation having an extra dispersive term. The dispersion is provided by finite-Larmor-radius (FLR) effects in the momentum equation and by the Hall-current and electron-pressure corrections in the generalized Ohm's law. A double-layer-type solution of the equation is obtained, and the equation is shown to reduce to a KdV–Burgers equation under certain assumptions.

The model of time-dependent Petschek-type reconnection is extended to take into account first-order corrections with respect to the reconnection rate. The plasma velocity inside the outflow region turns out to be smaller than the zero-order Alfvén velocity, and therefore strong reconnection is less effective in plasma acceleration. The model is also applied to study the effect of incoming waves on reconnection. We show that incoming waves of Alfvén type, carrying an electric current that is antiparallel to the initial current in the sheet, increase the reconnection rate and cause additional acceleration of the plasma, so that this wave can be considered as a potential trigger.

What follows are some personal recollections of John that I thought might be of interest to some readers of this special issue of the Journal of Plasma Physics.

The dynamics of a free electron gas interacting with neutral and excited atoms whose populations are assumed fixed is considered in the case of a three-dimensional model. An analytical form of the time-dependent electron distribution function for arbitrary initial conditions is obtained when interactions are only inelastic and superelastic between two atomic levels. It is shown that this electron gas reaches a stationary state. We deduce an experimental method for the measurement of the population of excited atoms in a neutral gas by injecting a dilute electron beam into the gas.

Reduced two-fluid equations governing the nonlinear dynamics of drift–Alfvén waves in dusty plasmas with non-zero ion temperature are derived. In the linear limit, we find a dispersion relation that shows the coupling between the ion-drift–Shukla–Varma mode, and electron-drift (magnetostatic) and (inertial or kinetic) Alfvén waves due to the finite collisionless electron skin depth or Larmorradius corrections. In contrast to the case of an electron–ion plasma, when the nonlinear drift–Alfvén vortices are weakly localized, i.e. decrease at infinity as r−1, the presence of the charged dust grains makes exponential localization possible. The physical meaning of such a localization is connected with the fact that charged massive dust granules provide an additional screening that results in stronger localization of the vortex. In several intermediate-β plasmas with 1 [Gt ] β [Gt ] me/mi (me,i is the electron or ion mass), the localization length approaches a minimum value when the vortex velocity is of the order of the ion diamagnetic drift. It then reaches the value ρiδ−1/4d where ρi is the ion Larmor radius and δd is the ratio of the dust to ion densities multiplied by the dust charge number Zd. In the case of very low plasma pressure, β [Lt ] me/mi, the vortex is localized with typical scale (λeρi)1/2δ−1/4d where λe is the electron skin depth. Our investigation can thus predict the velocities of coherent nonlinear structures in space plasmas.

This paper concerns experiments on the turbulence of a toroidal magnetoplasma in the presence of a radial electric field. The possibility of reduction of turbulence through the application of an external biasing potential has been evaluated by measuring the electrostatic fluctuations and main plasma parameters.

Generalized dispersion relations for Alfvén waves are derived, accounting for arbitrary values of ω/ωci, k⊥ρi, and k⊥λe, where ω(ωci) is the wave (ion gyro) frequency, k⊥ = 2π/λ⊥ the perpendicular (to the external magnetic field line) wavenumber, and ρi(λe) the ion gyroradius (electron skin depth). Our dispersion relations are appropriate for deducing the relationships of the dispersive (inertial and kinetic) Alfvén waves with other plasma modes. The present results can be considered as a prerequisite for understanding some salient features of the broadband electromagnetic/electrostatic waves that are frequently observed by the Freja and FAST spacecraft in the auroral zone of the Earth's ionosphere.

We study the magnetic field and plasma parameters downstream of a fast shock as functions of normalized upstream parameters and the rate of pressure anisotropy (defined as the ratio of perpendicular to parallel pressure). We analyse two cases: with the shock (i) perpendicular and (ii) inclined with respect to the magnetic field. The relations on the fast shock in a magnetized anisotropic plasma are solved taking into account the criteria for the mirror instability and firehose instability bounding the pressure anisotropy downstream of the shock. Our analysis shows that the parallel pressure and the parallel temperature as well as the tangential component of the velocity are the parameters that are most sensitive to the rate of pressure anisotropy. The variations of the other parameters, namely density, normal velocity, tangential component of the magnetic field, perpendicular pressure, and perpendicular temperature are much less pronounced, in particular when the perpendicular pressure exceeds the parallel pressure. The variations of all parameters increase substantially for a very low rate of anisotropy, which is bounded by the firehose instability in the case of inclined shocks. Using the criterion for mirror instability as a closure relation for the jump conditions at the fast shock, we obtain the plasma parameters and the magnetic field downstream of the shock as functions of the Alfvén Mach number. For each Alfvén Mach number, the criterion for mirror instability determines the minimum jumps in such parameters as density, tangential magnetic field component, parallel pressure, and temperature, and determines the maximum values of the velocity components and the perpendicular temperature. Ideal anisotropic magnetohydrodynamics (MHD) has wide applications for space plasma physics. Observations of the field and plasma behaviour in the solar wind as well as in the Earth's magnetosheath have highlighted the need for an MHD model where the plasma pressure is treated as a tensor.

The evolution of magnetic flux ropes in a sheared plasma flow is investigated. When the magnetic field outside the flux rope lies parallel to the axis of the flux rope, a flux rope of circular cross-section, whose centre is located at the midpoint of the shear layer, has its shape distorted, but remains in the shear layer. Small displacements of the flux-rope centre above or below the midpoint of the shear layer lead to the flux-rope being expelled from the shear layer. This motion arises because small asymmetries in the plasma pressure around the flux-rope boundary leads to a force that forces the flux rope into a region of uniform flow. When the magnetic field outside the flux rope lies in a plane perpendicular to the flux-rope axis, the flux rope and external magnetic field reconnect with each other, leading to the destruction of the flux rope.

The theory of resonant nonlinear magnetohydrodynamic (MHD) waves in dissipative steady plasmas developed by Ballai and Erdélyi is used to study the effect of steady flows on nonlinear resonant heating of MHD waves in (a) linear, (b) weakly and (c) strongly nonlinear approximations. Nonlinear connection formulae for slow MHD waves are derived. This nonlinear theory of driven MHD waves is then used to study the interaction of sound waves with one-dimensional isotropic steady plasmas. We find that a steady equilibrium flow can significantly influence the efficiency of resonant absorption in the considered limits. In the case of strong nonlinearity, the efficiency of the resonant coupling is found to be proportional to the counterpart obtained in linear theory. The factor of proportion is approximately of the order of unity, justifying the commonly applied linear approximations.

The dielectric tensor for a multicomponent magnetized dusty plasma, including the effect of capture of plasma electrons and ions by the dust particles, is rewritten in order to provide expressions more suitable for applications. We use this tensor to study the spatial absorption of a magnetosonic wave, including effects up to second order in the Larmor radius. We analyse the absorption of the wave due to the presence of dust particles with variable charge and the modification of this absorption due to finite-Larmor-radius effects.

This paper reports the results of computations to obtain the spatial distributions of the charged particles in a bounded active plasma dominated by negative ions. Using the fluid model with a constant collision frequency for electrons, positive ions and negative ions the cases of both detachment-dominated gases (such as oxygen) and recombination-dominated gases (such as chlorine) are examined. It is concluded that it is valid to use a Boltzmann relation ne = ne0exp(eV/kT) for the electrons of density ne, where the temperature T is approximately the electron temperature Te, and that the density nn of the negative ions at low pressures obeys nn = nn0exp(eV/kTn), where Tn is the negative-ion temperature. However, at high pressure in detachment-dominated gases where the ratio of negative-ion density to electron density is constant and greater than unity, and when the attachment rate is larger than the ionization rate, the negative ions are distributed with the same effective temperature as the electrons. In all other cases there is no simple relationship. Thus to put nn/ne = const, nn = ne0exp(eV/kTe) and nn = nn0exp(eV/kTn) simultaneously is mathematically inconsistent and physically unsound. Accordingly, expressions deduced for ambipolar diffusion coefficients based on these assumptions have no validity. The correct expressions for the situation where nn/ne = const are obtained without invoking a Boltzmann relation for the negative ions.

Dispersion in an intrinsically relativistic, one-dimensional, electron–positron pair plasma (a pulsar plasma) is treated exactly, generalizing earlier results that applied in the low-frequency limit and that neglected the cyclotron resonance. The general theory involves two additional relativistic plasma dispersion functions, evaluated at the normal and anomalous Doppler resonances. These two functions are associated with the non-gyrotropic and gyrotropic parts of the response respectively. The functions are evaluated for bell-type and Jüttner distributions. Wave dispersion is discussed for a non-gyrotropic pulsar plasma with a highly relativistic Alfvén speed. Emphasis is placed on crossings of the light line, defined in terms of the parallel phase velocity. Subluminal waves exist only for sufficiently small angles of propagation, and are confined to frequencies below about the mean gyrofrequency of the relativistic particles.

Nonlinear resonant slow magnetohydrodynamic (MHD) waves are studied in weakly dissipative isotropic plasmas for a cylindrical equilibrium model. The equilibrium magnetic field lines are unidirectional and parallel with the z axis. The nonlinear governing equations for resonant slow magnetoacoustic (SMA) waves are derived. Using the method of matched asymptotic expansions inside and outside the narrow dissipative layer, we generalize the connection formulae for the Eulerian perturbation of the total pressure and for the normal component of the velocity. These nonlinear connection formulae in dissipative cylindrical MHD are an important extention of the connection formulae obtained in linear ideal MHD [Sakurai et al., Solar Phys. 133, 227 (1991)], linear dissipative MHD [Goossens et al., Solar Phys. 175, 75 (1995); Erdélyi, Solar Phys. 171, 49 (1997)] and in nonlinear dissipative MHD derived in slab geometry [Ruderman et al., Phys. Plasmas4, 75 (1997)]. These generalized connection formulae enable us to connect the solutions at both sides of the dissipative layer without solving the MHD equations in the dissipative layer. We also show that the nonlinear interaction of harmonics in the dissipative layer is responsible for generating a parallel mean flow outside the dissipative layer.