The propagation of a localized beam (cloud) of hot electrons and generation of Langmuir waves are investigated using numerical simulation of the quasi-linear equations in the presence of collisional effects for electrons and beam-driven Langmuir waves. It is found that inclusion of the collisional damping of Langmuir waves has remarkable effects on the evolution of the electron distribution function and the spectral density of Langmuir waves, while the effect of collision term for electrons is almost negligible. It is also found that in the presence of collisional damping of Langmuir waves, the relaxation of the beam distribution function in velocity space is retarded and the Langmuir waves are strongly suppressed. The average propagation velocity of the beam is not constant and is larger when collisional damping of Langmuir waves is considered. The collisional damping for electrons does not affect the upper boundary of the plateau but the collisional damping of Langmuir waves pushes it towards small velocities. It is also found that the local velocity of the beam and its width decrease when the collisional damping of Langmuir waves is included.

Time-dependent cylindrical and spherical dust-acoustic (DA) solitary and shock waves propagating in a strongly coupled dusty plasmas (containing strongly correlated negatively charged dust grains and weakly correlated adiabatic electrons and ions) are investigated. It is shown that cylindrical and spherical DA solitary and shock waves exist with negative potential, and that the strong correlation between the charged dust grains is a source of dissipation, and is responsible for the formation of cylindrical or spherical DA shock structures. It is also shown that the effects of a non-planar geometry (cylindrical and spherical) significantly modify the basic features (e.g. amplitude, width, speed, etc.) of DA solitary and shock waves. The implications of our results in laboratory experiments are briefly discussed.

Nonlinear z-independent solutions to a generalized Grad–Shafranov equation (GSE) with up to quartic flux terms in the free functions and incompressible plasma flow non-parallel to the magnetic field are constructed quasi-analytically. Through an ansatz, the GSE is transformed to a set of three ordinary differential equations and a constraint for three functions of the coordinate x, in Cartesian coordinates (x,y), which then are solved numerically. Equilibrium configurations for certain values of the integration constants are displayed. Examination of their characteristics in connection with the impact of nonlinearity and sheared flow indicates that these equilibria are consistent with the L–H transition phenomenology. For flows parallel to the magnetic field, one equilibrium corresponding to the H state is potentially stable in the sense that a sufficient condition for linear stability is satisfied in an appreciable part of the plasma while another solution corresponding to the L state does not satisfy the condition. The results indicate that the sheared flow in conjunction with the equilibrium nonlinearity plays a stabilizing role.

Using the multi-fluid model of plasmas, we have analytically obtained a generalized Bohm criterion in the plasma, including hot electrons and multiply charged ions, and have numerically examined its validity. The new Bohm-sheath criterion shows that increasing the charge number of positive ions and decreasing the charge number of negative ions would increase the minimum ion speed that is required for the Bohm criterion to satisfy.

High-speed imaging is a powerful tool for studying dusty plasmas. The recorded trajectories of dust particles can provide direct information about the physical processes involved in dust-plasma and dust–dust interactions. A review of some experiments and their imaging techniques employed for tracking dust particles immersed in low-ionized gases and in high-density plasma jets is presented. Digital cameras are used to record the motion of slow or hypervelocity dust particles dragged by plasma jets, or to evidence single or collective dust particle oscillations and vibrations in the plasma sheath.

The nonlinear solitary and freak waves in a plasma composed of positive and negative ions, superthermal electrons, ion beam, and stationary dust particles have been investigated. The reductive perturbation method is used to obtain the Korteweg-de Vries (KdV) equation describing the system. The latter admits solitary wave solution, while the dynamics of the modulationally unstable wavepackets described by the KdV equation gives rise to the formation of freak/rogue excitation described by the nonlinear Schrödinger equation. In order to show that the characteristics of solitary and freak waves are influenced by plasma parameters, relevant numerical analysis of appropriate nonlinear solutions are presented. The results from this work predict nonlinear excitations that may associate with ion jet and superthermal electrons in Herbig–Haro objects.

In this paper, the theoretical analysis regarding potential structure on the inertial electrostatic confinement fusion devices has been carried out. Negatively biased grid as cathode placed at the center of the device surrounded by anode is assumed. The device is an ion-injection system and electrons may be emitted from the surface of the cathode. So the existence of both ion and electron currents inside the cathode is considered. Dependence of radial potential well structure on some important parameters as the spreads in the normalized total and angular electron and ion energies, the ratio of ion circulating current to electron circulating current, ion perveance, and grid transparency are investigated by solving Poisson equation.

The head-on collision between two magneto-acoustic solitons in spin-1/2 fermionic quantum plasma is studied in the framework of the model proposed by Marklund et al. (Marklund, M., Eliasson, B. and Shukla, P. K. 2007 Phys. Rev. E. 76, 067401). The extended Poincare–Lighthill–Kuo method is used to obtain the phase shifts and the trajectories during the head-on collision of two solitons. The effect of the Zeeman energy for different speeds of the waves, the effect of the total mass density of the charged plasma particles for different strengths of magnetic field, the effect of the speed of the wave for different values of the Zeeman energy, and that of the ratio of the sound speed to Alfven speed for different values of Zeeman energ on the phase shift are studied. It is observed that the phase shifts are significantly affected in all the cases. The most interesting observation of this paper is that the phase shifts increase as well as decrease, and also they may be positive as well as negative depending upon the domain of the chosen parameters.

The Electron Cyclotron Emission (ECE) radiation has been investigated, passing through plasma column with concerning absorption effect on the IR-T1 tokamak. The intensity of second harmonic X-mode is used to investigate changes in electron temperature profile. The results show that radiation temperature (Trad) detected outside the plasma column is less than the electron temperature (Te) in the core. The radiation temperature can be directly interpreted as Te to about 3–10% reduction. This implies that optical thickness and electron density effects are more considerable at lower temperatures.

Supersonic plasma flow around an object large compared with the Debye distance is treated using an isothermal gas dynamics model. The case of (initially) subsonic flow has been studied previously using this model, the motivation then being the use of Langmuir probes. In supersonic plasma flow Mach cones describing weak discontinuities rather than shock waves are predicted. A comparison has been made with particle-in-cell simulations carried out by Willis et al. (Willis, C. T. N., Allen, J. E., Coppins, M. and Bacharis, M. 2011 Phys. Rev. E, 84, 046410), where such Mach cones are observed. Other features cannot be explained by the isothermal gas dynamics model, these include the appearance, at high supersonic velocities, of an ion-free region downstream.

The paper considers the erosion mechanism of operation of nano- and microsecond plasma opening switches (POSs). For this purpose, postulates of the well-known erosion model of the POS operation are reviewed and some remarks on its individual statements are discussed. A voltage scaling for a nanosecond switch with rarefied plasma (~1013 cm−3) is derived. It is shown that the peak voltage across the nanosecond switch on its opening is proportional to the switch conduction current. The formation of an erosion gap in a microsecond switch with high-density plasma (~1015 cm−3) is put to phenomenological analysis and a voltage scaling for the switch is obtained. It is found that in the microsecond switch, unlike the nanosecond switch, the peak voltage is inversely proportional to the switch conduction current.

An attempt is made to explain dark energy and dark matter of the expanding universe in terms of the zero point vacuum energy. This analysis is mainly limited to later stages of an observable nearly flat universe. It is based on a revised formulation of the spectral distribution of the zero point energy, for an ensemble in a defined statistical equilibrium having finite total energy density. The steady and dynamic states are studied for a spherical cloud of zero point energy photons. The ‘antigravitational’ force due to its pressure gradient then represents dark energy, and its gravitational force due to the energy density represents dark matter. Four fundamental results come out of the theory. First, the lack of emitted radiation becomes reconcilable with the concepts of dark energy and dark matter. Second, the crucial coincidence problem of equal orders of magnitude of mass density and vacuum energy density cannot be explained by the cosmological constant, but is resolved by the present variable concepts, which originate from the same photon gas balance. Third, the present approach becomes reconcilable with cosmical dimensions and with the radius of the observable universe. Fourth, the deduced acceleration of the expansion agrees with the observed one. In addition, mass polarity of a generalized gravitation law for matter and antimatter is proposed as a source of dark flow.

We have built a code to numerically solve the Riemann problem in ideal magnetohydrodynamics (MHD) for an arbitrary initial condition to investigate a variety of solutions more thoroughly. The code can handle not only regular solutions, in which no intermediate shocks are involved, but also all types of non-regular solutions if any. As a first application, we explored the neighborhood of the initial condition that was first picked up by Brio and Wu (1988) (Brio, M. and Wu, C. C. 1988 An upwind differencing scheme for the equation of ideal magnetohydrodynamics. J. Comput. Phys. 75, 400–422) and has been frequently employed in the literature as a standard problem to validate numerical codes. Contrary to the conventional wisdom that there will always be a regular solution, we found an initial condition for which there is no regular solution but a non-regular one. The latter solution has only regular solutions in its neighborhood and actually sits on the boundary of regular solutions. This implies that the regular solutions are not sufficient to solve the ideal MHD Riemann problem and suggests that at least some types of non-regular solutions are physical. We also demonstrate that the non-regular solutions are not unique. In fact, we found for the Brio and Wu initial condition that there are uncountably many non-regular solutions. This poses an intriguing question: Why a particular non-regular solution is always obtained in numerical simulations? This has important ramifications to the discussion of which intermediate shocks are really admissible.