Dust-acoustic and dust-lower-hybrid diamagnetic drift wave instabilities have been examined in a collisional non-uniform quantum dusty magnetoplasma. The dust-acoustic drift instability arises through the Fermi degenerate pressure of electrons for a high-density plasma, while for a relatively low-density collisional quantum plasma and short wavelength consideration, the instability is dominated by the Bohm potential effect exciting a new quantum dust-acoustic wave. In the long-range wavelength limit, dust-lower-hybrid waves are found to be unstable because of the diamagnetic drift of magnetized ions. Various possible instability conditions are found for diamagnetic drift instability.

Laser acceleration of particles is currently a very active area of research in Plasma Physics, with an emphasis on acceleration of electrons and ions using short but intense laser pulses. In this special issue we access the current status of this field by inviting leading researchers all over the world to contribute their original works here. Many of these results were first presented at the recent Laser-Particle Acceleration Workshop (LPAW 2011) held in Wuzhen, China in June 2011. In addition to the laser wakefield acceleration (LWFA) of electrons (Tzoufras et al.) and laser acceleration of ions (Tsung et al.), there were exciting new proposals for a proton-driven plasma wakefield accelerator (Xia et al.) and for a dielectric-structure-based two-beam accelerator (Gai et al.) presented at this workshop, and we are very pleased to have the authors' contributions on these included here.

Stability of the resistive wall mode in cylindrical plasmas confined by surface currents is investigated for the δ-function and step-function equilibrium surface-current profiles. For the former, it is shown that the perturbations oscillate and even decay for all locations of the initial perturbation. The entire system is stable and the plasma flow has little effect. For the step-function surface-current distribution, it is found that the thicker the surface current layer, the more stable is the system even if the largest initial perturbation is located on the rational surface, but the plasma flow also has little effect on the system.

The structure of magnetohydrodynamic (MHD) modes has always been an interesting study in tokamaks. The mode number of tokamak plasma is the most important parameter, which plays a vital role in MHD instabilities. If it could be predicted, then the time of exerting external fields, such as feedback fields and Resonance Helical Field, could be obtained. Autoregressive Integrated Moving Average (ARIMA) and Seasonal Autoregressive Integrated Moving Average are useful models to predict stochastic processes. In this paper, we suggest using ARIMA model to forecast mode number. The ARIMA model shows correct mode number (m = 4) about 0.5 ms in IR-T1 tokamak and equations of Mirnov coil fluctuations are obtained. It is found that the recursive estimates of the ARIMA model parameters change as the plasma mode changes. A discriminator function has been proposed to determine plasma mode based on the recursive estimates of model parameters.

A previous stability condition (see Throumoulopoulos and Tasso, Phys. Plasmas 14, 122104 (2007)) for incompressible plasmas with field-aligned flows is extended to gravitating plasmas, including self-gravitation. It turns out that the stability condition is affected by gravitation through the equilibrium values only.

A possibility of relaxation of relativistically hot electron and positron (e − p) plasma with a small fraction of hot or cold ions has been investigated analytically. It is observed that a strong interaction of plasma flow and field leads to a non-force-free relaxed magnetic field configuration governed by the triple curl Beltrami (TCB) equation. The triple curl Beltrami (TCB) field composed of three different Beltrami fields gives rise to three multiscale relaxed structures. The results may have the strong relevance to some astrophysical and laboratory plasmas.

A well-optimized design of an ion cyclotron resonance heating (ICRH) antenna is very important for steady-state plasma heating with high radio frequency (RF) power of several tens of megawatts. However, a sharp decrease in the coupling RF power because of impedance mismatch of ICRH system is an issue that must be resolved for present-day fusion reactors and International Thermonuclear Experimental Reactor. This paper has theoretically analyzed the ICRH antenna's impedance matching for ELMy plasmas on experimental advanced superconducting tokamak (EAST) by the transmission line theory. The results indicate that judicious choice of the optimal feeder location is found useful for adjustable capacitors' tolerance to the variations of the antenna input impedance during edge-localized mode (ELM) discharge, which is expected to be good for the design of ICRH antenna system and for real-time feedback control during ELM discharge on EAST.

One-dimensional Particle in Cell simulations of a dust–dust counterstreaming instability in a plasma containing dust grains of opposite charge polarity are presented. This dust–dust instability has potentially the lowest threshold drift for a dust wave instability in an unmagnetized dusty plasma. The linear and nonlinear development of this instability is investigated, including the effects of collisions with background neutrals, and a background electric field that acts as a driver to impart the drift velocities of the counter-streaming oppositely charged dust particles. The saturation of the linear instability appears to be due to dust heating related to dust trapping. Potential double layer formation from dust–dust instability turbulence is observed in cases with a high neutral collision rate. A comparative study is done with varying collision rates and background electric fields to explore the nonlinear development as a function of collision rate and background electric field. Applications to possible dusty plasma experimental parameters are discussed.

The Kadomtsev–Petviashvili equation is derived for two-dimensional propagations of electrostatic solitons in unmagnetized dense pair-plasmas. The reductive perturbation method is employed and two-dimensional electrostatic potential hump structures are obtained. The conditions for a stable two-dimensional solitary structure are discussed using energy consideration method. The numerical results are also presented by considering the parameters for the outer layers of white dwarfs/neutron stars.

Solid state nuclear track detectors have been used for measuring axially emitted protons from a 2.2-kJ energy plasma focus device. The flux of the protons emerging out from the pinched plasma column of the plasma focus device has been found to saturate the CR-39 detectors. Aluminum filters have been used to avoid the saturation effect. By varying the aluminum filter thickness as well as the etching time of CR-39 detectors, proton tracks have been analyzed. Proton energy above 200 keV to about 1 MeV has been measured by using different thicknesses of aluminum filters. On increasing the etching hours, the most probable track diameter is found to be shifted from lower to higher values. The track number density decreases on increase of the filter thickness, whereas the track diameters increase linearly with respect to the etching time.

The paper is devoted to the theory of electromagnetic surface waves propagating along the azimuthal direction in cylindrical metal waveguides, which are filled with current-carrying plasmas. The problem is solved by the method of successive approximation. Adequacy of this method application is proved here. To study the coupling of ordinary (O-) and extraordinary (X-) azimuthal modes, the linear theory of the eigenazimuthal X- and O-modes is applied as zero approximation. Plasma particles are described in the framework of magneto-hydrodynamics, electromagnetic fields of the coupled azimuthal modes are determined from Maxwell equations. Spatial distribution of electromagnetic field of these coupled modes and their damping caused for different reasons are studied. Possibility to observe experimentally the phenomena, which accompany propagation of these coupled modes, is estimated numerically. Branches of their possible utilization are discussed as well.

One of the main limitations of energy gain in laser wakefield accelerators is the electron dephasing, In order to resolve the dephasing problem, a tapered plasma channel is proposed and tested numerically. The tapered density is created by means of a laser heating, combining an axially increased external magnetic field. The locally strong magnetic field prevents the thermal energy transport crossing the field lines, and leads to a pressure buildup. The pressure gradient expels the plasma radially and tapers the density axially. A tapered plasma with a density contrast of 2.2 within a 6-cm channel is established. Propagating in the tapered plasma channel, the energy of an accelerated electron is expected to be enhanced greatly.

A study on the generation of unstable electromagnetic wave through nonlinear wave–particle interactions in an inhomogeneous plasma has been presented. Drift wave turbulence, which is one of the common features of inhomogeneous plasma, is found to be strongly in phase relation with thermal particles. The plasma particles, accelerated by drift wave turbulence field, may transfer their energy to electromagnetic O-mode through a modulated field. This process has been described by Vlasov Maxwell system of equations. From the nonlinear dispersion relation for O-mode the growth rate has been estimated. It has been observed that growth of unstable O-mode may predict magnetospheric electromagnetic radiation phenomena.

The nonlinear propagation characteristics of Gardner solitons (GSs) in a non-planar (cylindrical and spherical) two-ion-temperature unmagnetized dusty plasma, whose constituents are inertial negative dust, Boltzmann electrons and ions with two distinctive temperatures, are investigated by deriving the modified Gardner (mG) equation. The standard reductive perturbation method is employed to derive the mG equation. The basic features of non-planar dust-acoustic (DA) GSs are analyzed. It has been found that the basic characteristics of GSs, which are shown to exist for the values of ni10/Zdnd0 around 0.311, for ni20/Zdnd0 = 0.5, Ti1/Te = 0.07, and Ti1/Ti2 = 0.05 [where ni10 (ni20) is the lower (higher) temperature ion number density at equilibrium, Ti1 (Ti2) is the lower (higher) temperature of ions, Te is the electron temperature, Zd is the number of electrons residing on the dust grain surface, and nd0 is the equilibrium dust number density] are different from those of Korteweg-de Vries solitons, which do not exist around ni10/Zdnd0 ≃ 0.311. It has been found that the propagation characteristics of non-planar DA GSs significantly differ from those of planar ones.

In this work we present an experimental study where energetic ions were produced in an underdense 2.5 × 1019 cm−3 plasma created by a 50 fs Ti:Sapphire laser with 5 TWs of power. The plasma comprises 95% He and 5% N2 gases. Ionization-induced trapping of nitrogen K-shell electrons in the laser-induced wakefield generates an electron beam with a mean energy of 40 MeV and ~1 nC of charge. Some of the helium ions at the wake–vacuum interface are accelerated with a measured minimum ion energy of He1+ ions of 1.2 MeV and He2+ ions of 4 MeV. The physics of the interaction is studied with 2D particle-in-cell simulations. These reveal the formation of an ion filament on the axis of the plasma due to space charge attraction of the wakefield-accelerated high-charge electron bunch. Some of these high-energy electrons escape the plasma to form a sheath at the plasma–vacuum boundary that accelerates some of the ions in the filament in the forward direction. Electrons with energy less than the sheath potential cannot escape and return to the plasma boundary in a vortex-like motion. This in turn produces a time-varying azimuthal magnetic field, which generates a longitudinal electric field at the interface that further accelerates and collimates the ions.

Electric interaction between two negatively charged particles of different sizes on a mixed background of positive, negative, and neutral particles is complex and has relevance both to dusty plasmas and to transports in ionized fluids in general. We consider particularly effects during interaction that particle velocity and neutrals in the background may have on the well-known “dressing” and electric shielding that is due to the charged part of the background and how the interaction energy is modified because of this. Without such effects earlier works show the interaction becomes attractive when the distance between the two particles is a bit larger than the Debye length. We use a model where one of the two interacting particles has a radius much larger than the Debye length and the other a radius shorter than the Debye length. Then, the complex interaction may be more easily determined for particle separation up to a few Debye lengths. We consider the larger particle as stationary while the smaller may move. We find quite simple analytic expressions for the dressed particle interaction energy over the whole range of speed of the incoming smaller particle, assumed coming head on the larger particle, and the whole range of neutral particle densities. We also derive a distance of closest approach of small and large particles for all such parameter values. This distance is important for excluded volume estimations for moving small charged particles in media populated by large charged particles on a background as described above, and hence, important for determining the speed of flow of the smaller particles through such media.

Recent numerical studies of the Polar Mesosphere Summer Echo (PMSE) Overshoot Effect predict the basic shape of the Overshoot Characteristic Curve (OCC) to undergo dramatic changes as the frequency of the radar decreases. Principally, this may render earlier modeling, which assumed near-instantaneous diffusion of electrons and ions, moot and exacerbate algebraic analysis of OCC obtained in the future with, e.g. the MORRO-radar (56 MHz) and a synchronized radio wave emitter, both at or near the European Incoherent Scatter (EISCAT) Scientific Association's site in Ramfjordmoen near Tromsø, Norway. Since, however, by far the most observational results on the PMSE Overshoot Effect have been assembled with the help of the Very High Frequency (VHF, 224 MHz) radar and the an Ultra High Frequency (UHF, 929 MHz) radar, both at the EISCAT site, we examine more closely whether near-instantaneous diffusion is a valid assumption for these particular frequencies. We show that, indeed, the earlier less complex and analytically more accessible model can still be considered sufficient for most, if not all, existing experimental data.

Non-planar (cylindrical and spherical) double layers (DLs) in two-ion-temperature dusty plasma, whose constituents are inertial negative dust, ions with two distinctive temperatures, and Boltzmann electrons, are studied by employing the reductive perturbation method. The modified Gardner equation describing the nonlinear propagation of dust-acoustic (DA) waves is derived, and its non-planar double layer solutions are analyzed numerically. The parametric regimes for the existence of DA DLs, which are found to be associated with positive potential only, are obtained. The basic features of non-planar DA DLs, which are found to be different from planar ones, are also identified. The implications of our results to different space and laboratory dusty plasma situations are discussed.

This paper presents an experimental investigation on the role of return current in excitation of electronmagnetohydrodynamic (EMHD) structures. It is shown that only when return currents are excited parallel or anti-parallel to the background magnetic field the EMHD structures can be excited by a biased electrode in the plasma.

Arbitrary amplitude and small amplitude ion-acoustic solitary waves (IASWs) have been investigated in a relativistic, collisionless, unmagnetized, and degenerate dense electron–positron–ion plasma. The arbitrary amplitude IASWs have been studied by using the Sagdeev-type pseudo-potential approach. Along with approximate solution, the exact amplitude solitary structure has also been studied numerically. The electrons and positrons are assumed to follow the corresponding Fermi distribution function and the ions are described by the hydrodynamic equations. A new dispersion relation for the ion-acoustic wave has been derived for the relativistic Thomas–Fermi plasma. An energy balance-like equation involving the Sagdeev-type pseudo-potential has been investigated and it has been shown that the concentration of plasma particles has significant effect on the permitted Mach number range of IASWs. Also, it has been pointed out that the only compressional supersonic IASWs can propagate in the relativistic Thomas–Fermi plasma. The present work would be helpful to understand the excitation of the nonlinear ion-acoustic waves in a degenerate plasma, such as in superdense white dwarfs and in the cores of massive planets.