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.

Understanding the origin and nature of turbulent transport in tokomak plasmas is one of the major challenges of a successful magnetic confinement fusion. The aim of this work is to study instability associated with the ion-temperature gradient (ITG)-driven turbulence in the core of the plasma, which is the seat of fusion reactions. We used a low degree of freedom model composed of 18 ordinary differential equations. When the system is slightly above the stability threshold of the ITG mode, it is considered to be in the convection regime and convective heat transport of the system is time-independent, or oscillates periodically. As ITG is increased further, the system bifurcates to the turbulent regime. In a strongly turbulent regime, intermittent bursts (the so-called avalanches) are observed. This intermittency is a result of the competition among the following three factors: generation of sheared flows and suppression of ITG turbulence, gradual reduction of the sheared flows due to viscosity, and rapid regrowth of ITG modes due to reduction of sheared flows.

Energetic divergent proton beams can be generated in the interaction of ultra-intense laser pulses with solid-density foil targets via target normal sheath acceleration (TNSA). In this paper, a scheme using a capillary to reduce the proton beam divergence is proposed. By two-dimensional particle-in-cell (PIC) simulations, it is shown that strong transverse electric and magnetic fields rapidly grow at the inner surface of the capillary when the laser-driven hot electrons propagate through the target and into the capillary. The spontaneous magnetic field collimates the electron flow, and the ions dragged from the capillary wall by hot electrons neutralize the negative charge and thus restrain the transverse extension of the sheath field set up by electrons. The proton beam divergence, which is mainly determined by the accelerating sheath field, is therefore reduced by the transverse limitation of the sheath field in the capillary.

This paper is concerned to give a definitive account of a physical situation of current practical interest by examining the plasma solution for a plasma in coaxial geometry with an applied axial magnetic field. It builds on earlier work concerned with plasma diamagnetism and concentrates on the parameters involved at low pressures and low collisionalities but can be extended to situations where the ions are magnetized.

Laser guiding through an axially non-uniform collisional magnetoplasma channel formed by ionizing laser prepulse has been investigated. Self-defocusing of the ionizing prepulse leads to an axial non-uniform plasma channel. Due to the propagation of second laser beam through such preformed plasma channel, non-uniform heating of electrons takes place on account of non-uniform intensity distribution of laser beam. Non-uniform heating diffuses the electrons away from the axis and thereby enhances the plasma channel. Due to the competition between diffraction and refraction phenomenon through such an axial non-uniform collisional magnetoplasma channel, there is a periodic beam width variation with the distance of propagation. Second order ordinary differential equations for the beam width parameter of prepulse and the guided beam have been set up using the moment theory approach. Effect of axial non-uniformity, intensity of guided beam and magnetic field has been seen on the propagation of the second guided beam in the plasma channel.

We are exploring a new parameter space of the two-beam acceleration (TBA) scheme based on an ultra-short (~20 ns) rf pulse in a dielectric TBA. All two-beam accelerators (TBAs) use an electron drive beam to generate high-power rf in a decelerator and extract this power to drive an accelerating structure to high gradient. Typically, the rf pulse is on the order of hundreds of ns or greater in order to maintain good rf-to-beam efficiency. However, recent scaling arguments show that the rf breakdown threshold improves with decreasing rf pulse length, so it desirable to find a way to run at short-pulse length with good efficiency. In this paper, we discuss how we chose the design parameters of a short-pulse TBA for a TeV linear collider module. We then present plans for an experimental program to demonstrate TBA at Argonne wakefield accelerator (AWA) facility including high-power rf generation, high-gradient acceleration, and staging.

Dispersion characteristics of electromagnetic waves with radial and azimuthal polarization in a rotating relativistic electron beam guided by an ion channel are investigated. Ion-channel electrostatic field and self-fields of relativistic electron beam were included in the formalism. It is shown that the wave with radial polarization is unstable in two regions due to coupling with fast space charge wave. The behaviors of the instability magnitude and spread are analyzed as a function of equilibrium parameters. The introduced instability can be used for amplification and production of high-intensity laser pulse with radial polarization.

The linear propagation of the low-frequency (compared to the electron gyrofrequency) electromagnetic (EM) waves in a self-gravitating, strongly coupled magnetized plasma with ultra-relativistic degenerate electron fluid is investigated. It is found that the dispersion properties of the EM waves and stability criteria for such a degenerate plasma are significantly modified by the effects of the ultra-relativistic degenerate electron pressure, strong co-relation among extremely dense ion fluid, and the direction of the EM wave propagation relative to the ambient magnetic field direction. The relevance of our investigation to stability of white dwarf stars is briefly discussed. It is particularly seen here that the cores of such stars are stable for the class of gravito-electrodynamic waves that are analyzed for the characteristic ranges of relevant physical parameters.

An atmospheric pressure plasma jet is generated with a cold arc discharge in ambient air. The current-voltage characteristics and optical emission spectra of plasma discharges are investigated. The molecular nitrogen (N2), hydroxyl radical (OH), and oxygen atom (O) are observed and analyzed. Based on the best fit of the simulated spectra of N2 (C3∏u+ − B3∏g+) band and OH (A2∑+ − X2∏) band transition and the experimentally recorded spectra, the rotational temperature and the vibrational temperature of atmospheric pressure cold arc plasma jet (APCAPJ) are estimated.

Beam–plasma interaction is investigated in a model of plasma microwave oscillator: waveguide with spatially separated plasma and beam layers of finite thicknesses. Investigation is carried out in general form without specifying shape of the waveguide in cross section. Approach is based on perturbation theory over wave coupling. Spatial separation implies weak beam–plasma interaction that exhibits many specific features. Developing instability is caused by the growth of the negative energy beam wave. It is shown that upon weak coupling presence, dissipation leads to a new type of dissipative beam instability. Its maximal growth rate is inversely proportional to collision frequency in plasma. The growth rate of this instability is obtained for an arbitrary level of dissipation. Basic parameters of instability show that its properties cannot be neglected upon design of high-power, high-frequency plasma-filled generators/amplifiers based on relativistic e-beams.

The propagation of dust-lattice waves in two-dimensional hexagonal dusty plasma crystals in the presence of an external weak magnetic field is considered. Linear and nonlinear properties of the longitudinal dust-lattice waves are investigated. Dispersion relation, group velocity and evolution equation are found. The influence of the magnetic field on the propagation of dust-lattice waves is studied. We obtain the envelope evolution equation for longitudinal modes in the presence of a weak magnetic field, which is in the form of the Gross–Pitaevskii equation.

Linear electrostatic waves in a magnetized four-component, two-temperature electron–positron plasma are investigated, with the hot species having the Boltzmann density distribution and the dynamics of cooler species governed by fluid equations with finite temperatures. A linear dispersion relation for electrostatic waves is derived for the model and analyzed for different wave modes. Analysis of the dispersion relation for perpendicular wave propagation yields a cyclotron mode with contributions from both cooler and hot species, which in the absence of hot species goes over to the upper hybrid mode of cooler species. For parallel propagation, both electron-acoustic and electron plasma modes are obtained, whereas for a single-temperature electron–positron plasma, only electron plasma mode can exist. Dispersion characteristics of these modes at different propagation angles are studied numerically.

Dust ion-acoustic solitary structures have been investigated in an unmagnetized non-thermal plasma consisting of negatively charged dust grains, adiabatic positive ions, and non-thermal electrons. Whenever the non-thermal parameter exceeds a critical value, the present system supports negative potential double layer solution. However, this double layer solution is unable to restrict the occurrence of negative potential solitary waves of the present system. As a result, the occurrence of one type of negative potential solitary wave is restricted by Mc < M < MD, whereas the second type of solitary wave exists for all M > MD, where Mc is the lower bound of the Mach number M and MD (> Mc) is the Mach number corresponding to a negative potential double layer. A finite jump between the amplitudes of negative potential solitary waves at M = MD − ϵ1 and M = MD + ϵ2 has been observed, where 0 < ϵ1 < MD − Mc and ϵ2 > 0. Depending on the analytical theory presented in this paper, a numerical scheme has been provided to find the value of the Mach number at which double layer solution exists, and also the amplitude of that double layer. Although the occurrence of coexistence of solitary structures of both polarities is restricted by Mc < M ≤ Mmax, only negative potential solitary wave still exists for all M > Mmax, where Mmax is the upper bound of M for the existence of positive potential solitary waves only. Qualitatively different compositional parameter spaces showing the nature of existing solitary structures of the energy integral have been found. These solution spaces are capable of producing new results and physical ideas for the formation of solitary structures whenever one can move the solution spaces through the family of curves parallel to the curve M = Mc.

The operation of the quantum free-electron lasers (QFELs) with a helical wiggler and in the presence of ion-channel guiding is considered. The quantum Hamiltonian of single particle has been derived in the Bambini-Renieri (BR) frame. Time dependent wave function and three constants of motion are obtained. The Raman-Nath equation (RNE) and its approximation solution have been calculated, and then the resulted solution has been employed to obtain the quantum gain, photon statistics parameter and squeezing parameter. A quantum approach has been used to get quantum statistical properties of the FEL and the photon gain formula for the small signal gain limit. It is found that the ion-channel guiding decreases the squeezing. Also, the conditions for positive (bunching) and negative (antibunching) gain have been studied numerically.

A large amplitude modulated Gaussian electromagnetic beam propagating in a dusty plasma with dust charge fluctuations has been studied. The electrons are heated non-uniformly by the electromagnetic beam. For non-steady state, we obtain nonlinear current density in the presence of dust grains. This expression has been used to study the non-stationary self-focusing and resulting self-distortion of the amplitude modulated electromagnetic beam. It has been observed that the dust charge fluctuation increases the self-focusing of electromagnetic beam. It is also found that the effect of dust charge fluctuations is significant on the modulation index.

The proton bunch-driven plasma wakefield acceleration (PWFA) has been proposed as an approach to accelerate an electron beam to the TeV energy regime in a single plasma section. An experimental program has been recently proposed to demonstrate the capability of proton-driven PWFA by using existing proton beams from the European Organization for Nuclear Research (CERN) accelerator complex. At present, a spare Super Proton Synchrotron (SPS) tunnel, having a length of 600 m, could be used for this purpose. The layout of the experiment is introduced. Particle-in-cell simulation results based on realistic SPS beam parameters are presented. Simulations show that working in a self-modulation regime, the wakefield driven by an SPS beam can accelerate an externally injected ~10 MeV electrons to ~2 GeV in a 10-m plasma, with a plasma density of 7 × 1014 cm−3.

By using the standard reductive perturbation technique, a nonlinear Schrödinger equation is derived to study the stability of finite amplitude ion-acoustic waves in an unmagnetized plasma consisting of warm positive and negative ions and non-thermal electrons. The effect of relative temperature of positive and negative ions, their charge and mass ratios, density ratios and non-thermally distributed electrons on modulational instability of fast and slow ion-acoustic mode is investigated. It is found that these parameters significantly change the domain of modulation instability. Both, envelope and dark solitons appear in different regions of parameter space.

A theoretical investigation of the basic characteristics of cylindrical and spherical dust-ion-acoustic (DIA) solitary waves (SWs) is made in a dusty non-thermal plasma, whose constituents are non-thermal electrons, inertial ions, and arbitrarily charged stationary dust. The reductive perturbation method is used to derive the modified Gardner equation. The latter is numerically analyzed for both positively and negatively charged dust. The basic features of cylindrical and spherical DIA SWs, which are found to exist in such a dusty non-thermal plasma, are identified. The implications of our results to both space and laboratory plasma situations are also discussed briefly.

In this paper, intense laser pulse guiding through a weakly ionized plasma channel is studied numerically. The radial profile of the channel refractive index is assumed to be top-hat. The propagating intense laser pulses are Gaussian TEM00 and Laguerre–Gaussian LG01 modes. The analysis includes the effects of plasma density inhomogeneity, diffraction, further ionization by the propagating laser pulse and nonlinearity arising from the nonlinear Kerr effect. Matched conditions are obtained for both TEM00 and LG01 laser modes for a top-hat refractive index profile. It is seen that the electron density profile changes the matched condition in the transmission of the laser pulse through the plasma channel. It is also shown that the nonlinear Kerr effect changes the matched condition and becomes the dominant effect in intense laser pulse propagation through the weakly ionized plasma channel.

Many experimental data along with their theoretical interpretations on the rf low-temperature cylindrical plasma have been issued until today. Our Laboratory has contributed to that research by publishing results and interpretative mathematical models. With the present paper, two issues are being examined; firstly, the estimation of electron drift caused by the rf field gradient, which is the initial reason for the plasma behaviour, and secondly, many new experimental results, especially the electron-neutral collision frequency effect on the other plasma parameters and quantities. Up till now, only the plasma steady state was taken into consideration when a theoretical elaboration was carried out, regardless of the cause and the effect. This indicates the plasma's complicated and chaotic configuration and the need to simplify the problem. In the present work, a classification about the causality of the phenomena is attempted; the rf field gradient electron drift is proved to be the initial cause.