This special issue is devoted to the memory of Professor Padma Kant Shukla, who passed away 26 January 2013 on his travel to New Delhi, India to receive the prestigious Hind Rattan (Jewel of India) award. Padma was born in Tulapur, Uttar Pradesh, India, 7 July 1950, where he grew up and got his education. He received a PhD degree in Physics at the Banaras Hindu University, Varanasi, Uttar Pradesh, India, in 1972, under the supervision of late Prof. R. N. Singh, and a second PhD degree in Theoretical Plasma Physics from Umeå University in Sweden in 1975, under the supervision of Prof. Lennart Stenflo. He worked at the Faculty of Physics & Astronomy, Ruhr-University Bochum, Germany since January 1973, where he was a permanent faculty member and Professor of International Affairs, a position that was created for him to honour his international accomplishments and reputation.

Previous theory for stimulated Brillouin scattering is reconsidered and generalized. We introduce an effective ion sound velocity that turns out to be useful in describing scattering instabilities.

We present results from numerical simulations conducted to investigate a potential method for realizing the required fusion fuel heating in the fast ignition scheme to achieving inertial confinement fusion. A comparison will be made between collisionless and collisional particle-in-cell simulations of the relaxation of a non-thermal electron beam through the two-stream instability. The results presented demonstrate energy transfer to the plasma ion population from the laser-driven electron beam via the nonlinear wave–wave interaction associated with the two-stream instability. Evidence will also be provided for the effects of preferential damping of competing instabilities such as the Weibel mode found to be detrimental to the ion heating process.

It is shown that the two-flavor neutrino oscillation equations admit an exact analytic solution for arbitrarily chosen normalized electron neutrino population, provided the electron plasma density is adjusted in a certain way. The associated formula for the electron plasma density is applied to the cases of exponentially decaying or oscillating electron neutrino populations.

We present a theoretical model for the generation of coherent gamma rays by a free electron laser, where a high-energy electron beam interacts with an electromagnetic wiggler. By replacing the static undulator with a 1-μm laser wiggler, the resulting radiation would go from X-rays currently observed in experiments, to gamma rays. Coherent light in the gamma-ray range would have wide-ranging applications in the probing of matter on sub-atomic scales.

Numerical simulations have been conducted to study the spatial growth rate and emission topology of the cyclotron-maser instability responsible for stellar/planetary auroral magnetospheric radio emission and intense non-thermal radio emission in other astrophysical contexts. These simulations were carried out in an unconstrained geometry, so that the conditions existing within the source region of some natural electron cyclotron masers could be more closely modelled. The results have significant bearing on the radiation propagation and coupling characteristics within the source region of such non-thermal radio emissions.

A stimulated Raman scattering (SRS) on electron plasma waves in underdense plasmas is of a big concern in laser fusion due to an energy loss and target preheating. Complex features of large Backward-SRS (BRS) in experiments and simulations with laser fusion targets are found. Recently, to reach ultra-high intensities at multi-exawatts and beyond, relevant to high-energy physics, Raman amplification based on BRS was proposed; still, with high sensitivity and a narrow operational window. Firstly, we revisit a standard three-coupled mode model of BRS to show that the condition for an absolute instability is readily satisfied in uniform plasmas which excites large Raman signals from a background noise. It sets in for interaction length L0 shorter than, both, the plasma length L and absorption length La. Further, we point out a generic BRS feature, which due to a nonlinear frequency shift in large electron plasma wave (relativistic/trapping effects), instead to a steady state, saturates via intermittent pulsations with incoherent spectral broadening. A ‘break up’ of Manley–Rowe invariants is shown to predict non-stationary BRS. Finally, an intermediate intensity regime is originally proposed for coherent femto-second pulse generation in a thin exploding foil plasma, with scalings investigated by theory and particle simulations.

Asymmetric oscillatory expansion of a cylindrical plasma layer into vacuum is investigated analytically by solving the fluid equations of the electrons and ions together with the Maxwell's equations. For the problem considered, it is found that the asymmetrical flow components are strongly affected by the symmetrical components, but not the vice versa.

It is shown that turbulent interactions of two interpenetrating plasma clouds can cause seeding of the large scale-length magnetic field. This process becomes especially pronounced when clouds have the ions with different Z/M ratios.

The rather general set of fluid equations with full curvature effects (Shukla and Weiland, Phys. Rev. A 40, 341 (1989)) has been modified to apply to the core and generalized to include also microtearing modes.

A kinetic theory of the Debye sheath in the Tonks–Langmuir model of the plasma-wall transition layer with hot neutrals is presented. The plasma, consisting of Boltzmann-distributed electrons and singly charged ions, is in contact with an absorbing negative wall. Dependencies of electric-potential characteristics on neutrals temperature are investigated for the first time. The results can be generalized to other sheath models.

We point the rather unusual existence of a potential embedding in the Lorentz trajectory – charged particle trajectory in a magnetic field – of a one-dimensional matter wave dynamics on the macro-scale as demonstrated through one-dimensional matter wave interference effects on the macro-scale, as well as the observation of a curl-free vector potential in one dimension, also on the macro-scale. Such an embedding is a manifestation of the generation of the quantum modulation of the de Broglie wave of the particle along the magnetic field, arising concomitantly, with a scattering-induced transition across Landau levels in consequence of quantum entanglement between the parallel and perpendicular degrees of freedom.

Tsallis q-non-extensive distributions have recently found favor in describing the presence of energetic particles and their influences on several plasma modes, notably electrostatic solitons. Here attention is drawn to ambiguities and subtleties in the superextensive and subextensive ranges in q, which are not always recognized in the literature, particularly in numerical studies.

Some years ago, a group including the present author and Padma Shukla showed that a suitable non-thermal electron distribution allows the formation of ion sound solitary waves with either positive or negative density perturbations, whereas with Maxwellian electrons only a positive density perturbation is possible. The present paper discusses the qualitative features of this distribution allowing the negative waves and shared with suitable two-temperature distributions.

Supersolitons are a form of soliton characterised, inter alia, by additional local extrema superimposed on the usual bipolar electric field signature. Previous studies of supersolitons supported by three-component plasmas have dealt with ion-acoustic structures. An analogous problem is now considered, namely, dust-acoustic supersolitons in a plasma composed of fluid negative dust grains and two kappa-distributed positive ion species. Calculations illustrating some supersoliton characteristics are presented.

The basic features of dust shear Alfvén (DSA) solitary structures formed in an opposite polarity dust medium (containing positively and negatively charged dust fluids) have been investigated by using the reductive perturbation method. The derivative nonlinear Shrödinger equation and its stationary solitary wave solution are obtained for this investigation. It is shown that the opposite polarity dust medium under consideration supports the compressive DSA solitary structures having new features with new time and length scales. The implications of our results in space environments and laboratory devices are briefly discussed.

The generation of ion-acoustic rogue waves in ultracold neutral plasmas (UNPs) composed of ion fluids and nonextensive electron distribution is investigated. For this purpose, basic equations are reduced to a nonlinear Schrödinger equation (NLSE) using a reductive perturbation technique. The existence region for the rogue waves defined precisely in terms of the critical wavenumber threshold kc. It is found that increasing the nonextensive parameter q would lead to a decrease of kc until q approaches to its critical value qc, then further increase of q beyond qc enhances kc; however, kc shrinks with the increase of the ions effective temperature ratio σ∗. The dependence of the first- and second-order rational solutions profile on the UNP parameters is numerically examined. It is noticed that near to the critical nonextensive parameter qc, the rogue wave amplitude becomes smaller, but it enhances whenever we stepped away from qc. However, the enhancement of the temperature ratio σ∗ and the wavenumber k reduces the envelope rogue wave amplitudes.

The dynamics of solitons is considered in the framework of the extended nonlinear Schrödinger equation (NLSE), which is derived from a system of Zakharov's type for the interaction between high-frequency (HF) and low-frequency (LF) waves, in which the LF field is subject to diffusive damping. The model may apply to the propagation of HF waves in plasmas. The resulting NLSE includes a pseudo-stimulated-Raman-scattering (PSRS) term, i.e. a spatial-domain counterpart of the SRS term, which is well known as an ingredient of the temporal-domain NLSE in optics. Also included is inhomogeneity of the spatial second-order diffraction (SOD). It is shown that the wavenumber downshift of solitons, caused by the PSRS, may be compensated by an upshift provided by the SOD whose coefficient is a linear function of the coordinate. An analytical solution for solitons is obtained in an approximate form. Analytical and numerical results agree well, including the predicted balance between the PSRS and the linearly inhomogeneous SOD.

We consider the excitation and dispersion of ion acoustic waves in expanding ultracold plasmas, taking into account the influence of boundary conditions. A cylindrical plasma geometry is assumed. We show that temporal changes in the medium lead to a wave frequency shift, associated with an evolving radial and standing wave mode structure, and to the temporal change of the background plasma parameters. A non-collisional model for the cylindrical geometry is also proposed.

The Rosetta–Philae mission to comet 67P/Churyumov–Gerasimenko in 2014 will provide a unique opportunity to observe the variable nature of the interaction of a comet with the solar radiation and the solar wind, as the comet approaches the Sun. In this short paper we will focus on the varying global structure of the cometary plasma environment. Specifically we make predictions on the varying locations of the two basic transitions in the global, contaminated solar wind flow toward the comet: the outer bow shock and the ionopause.