In this work we outline an approach to the problem of local equilibrium in non-axisymmetric configurations that adheres closely to Miller's original method for axisymmetric plasmas (Miller et al. 1998 Phys. Plasmas5, 973). Importantly, this method is novel in that it allows not only specification of 3D shape, but also explicit specification of the shear in the 3D shape. A spectrally-accurate method for solution of the resulting nonlinear partial differential equations is also developed. We verify the correctness of the spectral method, in the axisymmetric limit, through comparisons with an independent numerical solution. Some analytic results for the two-dimensional case are given, and the connection to Boozer coordinates is clarified.

We consider the limits of validity of ray tracing and ray diffusion equations, for short wavelength waves propagating in a turbulent plasma background. We derive an improved transport equation for the electric field autocorrelation function, where first order diffraction effects associated with these waves are included. We apply this description to the case of lower hybrid (LH) waves propagating in non-stationary plasma where density perturbations can occur due to drift wave turbulence, as well as magnetic field perturbations due to MHD turbulence. This is relevant to the problem of LH current drive.

Runaway electrons in tokamaks can cause serious damage to the first wall of the reactor and decrease its life time. Also, hard x-ray emission generated from high energy runaway electrons lead to the plasma energy loss. Therefore, suggesting methods to minimize runaway electron in tokamaks are very important. Applying external resonant field is one of the methods for controlling the Magneto Hydrodynamic (MHD) activity. Relation between the MHD activity and runaway electrons has already been studied (Jaspers et al. 1994; Ghanbari et al. 2012) Jaspers, R., et al. 1994 Phys. Rev. Lett.72, 4093; Ghanbari, M. R., et al. 2012a Phys. Scr.83, 055501. Present study attempts to investigate the effects of limiter biasing and Resonant Helical magnetic Field (RHF) on the generation of runaway electrons. For this purpose, plasma parameters such as plasma current, MHD oscillation, loop voltage, emitted hard x-ray intensity, Halpha impurity, safety factor in the presence and absence of external fields, were measured. Frequency activity was investigated with FFT analysis. The results show that applying resonant fields can control the MHD activity, and then hard x-ray emitted from the runaway electrons.

A large-amplitude plasma beat-wave driven by two lasers (differing in frequencies equal to the plasma frequency) can accelerate the plasma electrons to a higher energy level. As the plasma beat-wave grows, it becomes susceptible to oscillating two-stream instability. The decayed sideband plasma wave couples with the pump wave to divert its energy by the instability, and saturates it. The saturated amplitude of the plasma beat-wave traps the electrons more effectively to accelerate them to higher energy. The saturation of plasma beat-wave amplitude is shown to have a significant effect in an electron energy gain.

The transient, growth and nonlinear saturation stages in the evolution of the electrostatic two-stream instabilities as described by the Vlasov–Poisson system are reconsidered by numerically following the evolution of the total wave energy of the plasma oscillations excited from (numerical) noise. Except for peculiarities related to the necessarily finite (even though very small) magnitude of the perturbations in the numerical simulation, the existence and initial growth properties of the instabilities from the numerical results are found to be consistent with those from linear normal mode analysis and the Penrose criteria. However, contradictory to the traditional point of view, the growth of instability before saturation is not always linear. The initial stage of the growth can exhibit fine structures that can be attributed to the harmonics of the excited plasma oscillations, whose wavelengths are determined by the system size and the numerical noise. As expected, saturation of the unstable oscillations is due to electron trapping when they reach sufficiently large amplitudes.

We investigate the transformation process of longitudinal Langmuir wave into the transverse electromagnetic wave in turbulent plasma subjected to an upper hybrid pump. The case, when upper hybrid pump wave decays into daughter and ion – sound waves is considered. The transformation of the Langmuir wave into electromagnetic one is considered as the possible mechanism of energy radiation from the plasma. It is shown that the frequency of such radiation is chosen to be near double electron Langmuir frequency 2ωpe. These results give us the possibility to explain the nature of radiation from the laboratory and cosmic plasmas (particularly, from the solar crown).

Fluid simulations are used to investigate a multi-component magnetized dusty plasma sheath. The model consists of positive ions, dust grains, and two species of electron populations. These electrons are assumed to be a sum of two Maxwellian distributions with two different temperatures (cold and hot). According to multi-fluid equations and some dimensionless variables, the dimensionless equations are obtained and solved numerically. The effect of the presence of the hot electrons in the sheath is examined. A significant change is observed in the quantities characterizing the sheath with respect to one species electrons (cold) assumption.

A plasma target for highly efficient neutralization of powerful negative ion beams is considered. The plasma is confined within a magnetic trap with multipole magnetic walls. It is proposed to use inverse magnetic mirrors to limit plasma outflow through the inlet and outlet holes in the trap. Using the particle-in-cell method, mathematical simulation of plasma dynamics in the trap has been performed. The estimates of plasma distribution and particle confinement efficiency in the region of the magnetic mirrors has been obtained. Simulation results were compared with experimental data.

This paper presents an explicit proof that, in the kinetic magnetohydrodynamics framework, the squared frequencies of normal-mode perturbations about a static equilibrium are real. This proof is based on a quadratic form for the square-integrable normal-mode eigenfunctions and does not rely on demonstrating operator self-adjointness. The analysis is consistent with the quasineutrality condition without involving any subsidiary constraint to enforce it, and does not require the assumption that all particle orbits be periodic. It applies to Maxwellian equilibria, spatially bounded by either a rigid conducting wall or by a plasma-vacuum interface where the density goes continuously to zero.

Upon crossing the shock front, ions begin to gyrate. The ion distribution just behind the ramp is manifestly non-gyrotropic. The gyration of the ion distribution as a whole results in spatially periodic oscillations of the ion pressure. The magnetic pressure must oscillate in the opposite phase to ensure the maintenance of the pressure balance throughout the shock front. The ion non-gyrotropy and the pressure oscillations gradually damp due to the collisionless gyrophase mixing. The rate of this relaxation depends on the basic shock parameters. The most influential are the angle between the shock normal and the magnetic field, the upstream ion temperature and the magnetic compression.

The probe intended for the characterization of cold plasma is introduced. The probe allows the estimation of Debye length of cold plasma. The probe is based on the pronounced modification of surface properties (wettability) of polymer films by cold plasmas. The probe was tested with the cold radiofrequency inductive air plasma discharge. The Debye length and the concentration of charge carriers were estimated for various gas pressures. The reported results coincide reasonably with the corresponding values established by other methods. The probe makes possible measurement of characteristics of cold plasmas in closed chambers.

The Jeans self-gravitational instability is studied for dense quantum viscous plasma with Hall term and intrinsic magnetization generated by collective electron spin. The quantum magnetohydrodynamic model is employed to formulate the basic equations of the problem. The dispersion relation is obtained using the normal mode analysis, and further reduced for both transverse and longitudinal modes of propagation. The transverse mode of propagation is found to be unaffected by the Hall term but affected by quantum effect, viscosity, and magnetization parameters. The Jeans criterion of instability in the transverse direction is modified by Alfven velocity, magnetization parameter, and quantum effect. The non-gravitating magnetized mode is obtained in the longitudinal direction, which is modified by Hall parameter and is not affected by quantum term, whereas the gravitational mode is unaffected by the magnetization parameter but affected by viscosity and quantum parameters. It is observed that the Jeans condition of instability is affected by the quantum term. The growth rate of Jeans instability is plotted for various values of magnetization, quantum, and viscosity parameters of the quantum plasma medium.

The betatron radiation in the bubble regime is studied in the presence of resonant interaction between the accelerated electrons and the driver laser pulse tail. The calculations refer to experimental parameters available at the FLAME laser facility at the National Laboratories of Frascati (LNF), and represent the radiation spectra and spatial distributions to be expected in forthcoming experiments.

Nonlinear interaction between Langmuir waves and Electron Acoustic Wave (EAW) is being studied in a warm magnetized plasma in presence of two intermingled fluids, hot electrons, and cold electrons while ions forming static background. Two-fluid, two-timescale theory is performed to derive modified Zakharov's equations in a magnetized plasma. These coupled equations describe low-frequency response of electron density due to high-frequency electric field along with magnetic field perturbations. Linear analysis shows coupling between acoustic mode, upper hybrid mode, and cyclotron modes. These modes are found to be modified due to the presence of two electron components. These equations are significant in the context of weak and strong turbulence.

The origin of the 22-year solar magnetic cycle lies below the photosphere where multiscale plasma motions, due to turbulent convection, produce magnetic fields. The most powerful intensity and velocity signals are associated with convection cells, called granules, with a scale of typically 1 Mm and a lifetime of a few minutes. Small-scale magnetic elements (SMEs), ubiquitous on the solar photosphere, are passively transported by associated plasma flows. This advection makes their traces very suitable for defining the convective regime of the photosphere. Therefore the solar photosphere offers an exceptional opportunity to investigate convective motions, associated with compressible, stratified, magnetic, rotating and large Rayleigh number stellar plasmas. The magnetograms used here come from a Hinode/SOT uninterrupted 25-hour sequence of spectropolarimetric images. The mean-square displacement of SMEs has been modelled with a power law with spectral index ${\it\gamma}$ . We found ${\it\gamma}=1.34\pm 0.02$ for times up to ${\sim}2000~\text{s}$ and ${\it\gamma}=1.20\pm 0.05$ for times up to ${\sim}10\,000~\text{s}$ . An alternative way to investigate the advective–diffusive motion of SMEs is to look at the evolution of the two-dimensional probability distribution function (PDF) for the displacements. Although at very short time scales the PDFs are affected by pixel resolution, for times shorter than ${\sim}2000~\text{s}$ the PDFs seem to broaden symmetrically with time. In contrast, at longer times a multi-peaked feature of the PDFs emerges, which suggests the non-trivial nature of the diffusion–advection process of magnetic elements. A Voronoi distribution analysis shows that the observed small-scale distribution of SMEs involves the complex details of highly nonlinear small-scale interactions of turbulent convective flows detected in solar photospheric plasma.

The nonlinear propagation of dust ion-acoustic (DIA) waves in a unmagnetized collisionless degenerate dense plasma (containing degenerate electron and positron, and classical ion fluids) has been theoretically investigated. The K-dV equation has been derived by employing the reductive perturbation method and by taking into account the effect of different plasma parameters in plasma fluid. The stationary solitary wave solution of K-dV equation is obtained, and numerically analyzed to identify the basic properties of DIA solitary structures. It has been shown that depending on plasma parametric values, the degenerate plasma under consideration supports compressive or rarefactive solitary structures. It has been also found that the effect of pressures on electrons, ions, and positrons significantly modify the basic features of solitary waves that are found to exist in such a plasma system. The relevance of our results in astrophysical objects such as white dwarfs and neutron stars, which are of scientific interest, is discussed briefly.

In this research, the effect of inserting deuterated solid target in plasma focus device ‘SBUMTPF1’ on neutron yield has been investigated. The deuterated target with the diameter of 2.5 cm was placed at different heights relative to the anode tip. In each height, the best place of target (where the ion density is highest) was found from observing the effects of ions struck on the aluminum samples. Also for each height, 20 shots were performed at the optimum pressure of deuterium working gas and operating voltage, which are equal to 1.5 mbar and 24 kV, respectively. The neutron production was measured with two activation counters, which placed in 0○ and 90○ relative to the anode axis. Neutron scattering from two activation counters was calculated with MCNP4C code and the results showed that this effect is negligible. In this article, the probability of implanting deuterium ions into the titanium target was also investigated. Deviation angle of the ion emission relative to the anode axis was measured experimentally in this research and it was about 3.1○.

The formation and propagation characteristics of small-amplitude magnetoacoustic dark/grey solitons are investigated in a semi relativistic degenerate magnetoplasma whose constituents are electrons and singly ionized positive ions. For this purpose, the electrons are assumed to follow the degeneracy pressure law through the Chandrasekhar equation of state, while the inertial cold ions are taken as non-degenerate and magnetized. By solving the one-fluid quantum magnetohydrodynamic (QMHD) model with the aid of a reductive perturbation technique, a nonlinear Schrödinger (NLS) equation is derived for weakly nonlinear envelope magnetoacoustic solitons. The NLS equation admits the existence of stable excitations, e.g. dark and grey solitons for which the condition $P/Q<0$ holds. Numerical results reveal that the variation of plasma number density, magnetic field strength, relativistic parameter $({\it\eta}_{e0})$ and the quantum parameter $(H)$ significantly modify the profiles of the envelope magnetoacoustic solitons. The present results are important to understanding of the nonlinear dynamics of magnetoacoustic solitons in astrophysical dense magnetoplasmas (viz., white dwarfs, magnetars, neutron stars, etc.), where the relativistic degeneracy effects play a vital role in collective interactions.

The paper reports a new electrostatic-confinement-based fusion approach, where a new non-equilibrium distribution function for an ion-beam compressed by an external electric force has been derived. This distribution function allows the system to possess appreciably low and insignificant thermal energy irrespective of the energy per particle. The spread of energy among particles in the non-equilibrium state is attributed to collisions in the presence of external force, whereas for equilibrium, the spreading of energy is due to the absence of force. The reactivity for a deuterium--deuterium fusion, using the proposed distribution function, has been computed. It is shown that for initiating fusion among the particles, the fusion time is comparable with the energy confinement time of ions for beam energy greater than 160 keV. The estimated energy gain factor Q (ratio of the output fusion power to the power consumed by the system) is around 12 for beam energy 170 keV and ion density 1015 cm−3. The energy loss due to particle scattering is estimated and is taken into consideration for the estimation of energy gain. An outline of a conceptual model of a device is proposed in accordance with the proposed theory and the device is not similar to the one used conventionally in Inertial Electrostatic Confinement systems based on collisions of a beam with a reflex beam or with background gas or plasma.

In this paper we study transport features of a one-dimensional beam–plasma system in the presence of multiple resonances. As a model description of the general problem of a warm energetic particle beam, we assume $n$ cold supra-thermal beams and investigate the self-consistent evolution in the presence of the complete spectrum of nearly degenerate Langmuir modes. A qualitative transport estimation is obtained by computing the Lagrangian Coherent Structures of the system on given temporal scales. This leads to the splitting of the phase space into regions where the local transport processes are relatively faster. The general theoretical framework is applied to the case of the nonlinear dynamics of two cold beams, for which numerical simulation results are illustrated and analysed.