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$n$ 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.

We construct the model of a quantum spherically symmetric plasma structure based on radial oscillations of ions. We suppose that ions are involved in ion-acoustic plasma oscillations. We find the exact solution of the Schrödinger equation for an ion moving in the self-consistent oscillatory potential of an ion-acoustic wave. The system of ions is secondly quantized and its ground state is constructed. Then, we consider the interaction between ions by the exchange of an acoustic wave. It is shown that this interaction can be attractive. We describe the formation of pairs of ions inside a plasma structure and demonstrate that such a plasmoid can exist in a dense astrophysical medium corresponding to the outer core of a neutron star (NS).

A generic proof has been given that, for the acoustic mode with the highest velocity in a plasma comprising a number of fluid species and one kind of inertialess electrons, even though there can be critical densities (making the coefficient of the quadratic nonlinearity in a Korteweg–de Vries equation vanish), no supercritical densities exist (requiring the simultaneous annulment of both the quadratic and cubic nonlinearities in a reductive perturbation treatment). Similar conclusions hold upon expansion of the corresponding Sagdeev pseudopotential treatment. When there is only one (hot) electron species, the highest-velocity mode is an ion-acoustic one, but if there is an additional cool electron species, with its inertia taken into account, the highest-velocity mode is an electron-acoustic mode in a two-temperature plasma. The cool fluid species can have various polytropic pressure–density relations, including adiabatic and/or isothermal variations, whereas the hot inertialess electrons are modelled by extensions of the usual Boltzmann description that include non-thermal effects through Cairns, kappa or Tsallis distributions. Together, in this way quite a number of plasma models are covered. Unfortunately, there seems to be no equivalent generic statement for the slow modes, so that these have to be studied on a case-by-case basis, which for models with more than three species is far from straightforward, given the parameter ranges to be discussed.

There was an error made in the name of the author in the above published article. The fourth author's name should have appeared as ‘D. P. Potapenko’. This error has now been rectified in the original article.

This study demonstrates a remarkable flexibility of advanced divertor configurations created with the remote poloidal field coils. The emphasis here is on the configurations with three poloidal field nulls in the divertor area. We are seeking the structures where all three nulls lie on the same separatrix, thereby creating two zones of a very strong flux expansion, as envisaged in the concept of Takase’s cusp divertor. It turns out that the set of remote coils can indeed produce a cusp divertor, with additional advantages of: (i) a large stand-off distance between the divertor and the coils and (ii) a thorough control that these coils exert over the fine features of the configuration. In reference to these additional favourable properties acquired by the cusp divertor, the resulting configuration could be called ‘a super-cusp’. General geometrical features of the three-null configurations produced by remote coils are described. Issues on the way to practical applications include the need for a more sophisticated control system and possible constraints related to excessively high currents in the divertor coils.

We examine, in the limit of electron plasma {\it\beta}_{e}\ll 1${\it\beta}_{e}\ll 1$, the effect of an external guide field and current sheet thickness on the growth rates and nature of three-dimensional (3-D) unstable modes of an electron current sheet driven by electron shear flow. The growth rate of the fastest growing mode drops rapidly with current sheet thickness but increases slowly with the strength of the guide field. The fastest growing mode is tearing type only for thin current sheets (half-thickness {\approx}d_{e}${\approx}d_{e}$, where d_{e}=c/{\it\omega}_{pe}$d_{e}=c/{\it\omega}_{pe}$ is the electron inertial length) and zero guide field. For finite guide field or thicker current sheets, the fastest growing mode is a non-tearing type. However, growth rates of the fastest 2-D tearing and 3-D non-tearing modes are comparable for thin current sheets (d_{e}<\text{half thickness}<2\,d_{e}$d_{e}<\text{half thickness}<2\,d_{e}$) and small guide field (of the order of the asymptotic value of the component of magnetic field supporting the electron current sheet). It is shown that the general mode resonance conditions for tearing modes depend on the effective dissipation mechanism. The usual tearing mode resonance condition (\boldsymbol{k}\boldsymbol{\cdot }\boldsymbol{B}_{0}=0$\boldsymbol{k}\boldsymbol{\cdot }\boldsymbol{B}_{0}=0$, \boldsymbol{k}$\boldsymbol{k}$ is the wavevector and \boldsymbol{B}_{0}$\boldsymbol{B}_{0}$ is the equilibrium magnetic field) can be recovered from the general resonance conditions in the limit of weak dissipation. The conditions (relating current sheet thickness, strength of the guide field and wavenumbers) for the non-existence of tearing mode are obtained from the general mode resonance conditions. We discuss the role of electron shear flow instabilities in magnetic reconnection.

The interaction between incident transverse magnetic (TM) waves and nonuniform plasma cylinder is investigated. The forward and backscattering fields of incident TM microwave are calculated and analyzed by using the scattering matrix model. The dependences of the scattering field on plasma electron density, collision frequency, and incident frequency are analyzed, respectively. The electric field distribution across the section of the plasma cylinder is deduced, visually shown, and discussed.

It is widely held that the Nernst effect can drive instability in un-magnetised laser-plasmas by laterally compressing seed B-fields arising from the field-generating thermal instability [Tidman & Shanny, Phys. Fluids, 12:1207 (1974)]. Indeed, for wavelike perturbations, differential compression by the Nernst mechanism is thought to be most pronounced in the limit of low wave-number k → 0, and is considered particularly important given that it can ostensibly lead to instability when the more usual field-generating mechanism is stable. However, as part of a recent article [Bissell et al., New J. Phys., 15:025017 (2013)] we noted some irregularities to the Nernst mechanism which obscure its operation. For example, by taking characteristic density and temperature length-scales ln and lT respectively, we observed that consistent analytical treatment of the instability requires kln,T ≫ 1, preventing the peak-growth limit k → 0. Furthermore, the Nernst term—which compresses magnetic field perturbations—does not couple to a corresponding term acting on thermal perturbations, and as such does not describe an unstable feedback mechanism. In this article we probe the origin of such ambiguities more formally, and in so doing argue (contrary to reports existing elsewhere in the literature) that the Nernst effect does not drive instability in un-magnetised conditions, at least not in the fashion typically cited.

A model for the initial acceleration of electrons of the core of ball lightning is presented, according to which this acceleration occurs on screening of the strong electric field of the positive charge injected into the atmosphere. Several scenarios for such injection, the factors favourable for the formation of ball lightning and possible experiments on such formation are considered.

We present a new model for the generation of thermoelectric currents during laser welding, taking into account sheath effects at both contact points as well as the potential drop within the quasi-neutral plasma generated by the laser. We show that the model is in good agreement with experimentally measured electric potential difference between the hot and the cold parts of the welded workpiece. In particular, all three elements of the model are needed to correctly reproduce the sign of the measured voltage difference. The mechanism proposed relies on the temperature dependence of the electron flux from the plasma to the workpiece and hence does not need thermoemission from the workpiece surface to explain the experimentally observed sign and magnitude of the potential drop.

The theory for the two-stream free-electron laser with the whistler wave as a slow electromagnetic wave wiggler is studied theoretically. The results show that for small values of plasma density, there are seven groups of orbits and the plasma density enhancement leads to increase in the number of trajectories. Also, increasing the plasma density causes growth in the axial velocity for groups (1–4) of orbits and a reduction for groups (6–7). It is shown that for groups (6–7), the effect of plasma is to increase the gain, and for groups (1–4) the effect of plasma is to decrease the gain. For group (1) the effect of plasma is to decrease the maximum frequency and for group (3) it is to increase the maximum frequency.

In this work we numerically demonstrate both significant transient (i.e. non-modal) linear amplification and sustained nonlinear turbulence in a kinetic plasma system with no unstable eigenmodes. The particular system considered is an electrostatic slab with magnetic shear, kinetic electrons and ions, weak collisions and a density gradient, but with no temperature gradient. In contrast to hydrodynamic examples of non-modal growth and subcritical turbulence, here there is no sheared flow in the equilibrium. Significant transient linear amplification is found when the magnetic shear and collisionality are weak. It is also demonstrated that nonlinear turbulence can be sustained if initialized at sufficient amplitude. We prove that these two phenomena are related: when sustained turbulence occurs without unstable eigenmodes, states that are typical of the turbulence must yield transient linear amplification of the gyrokinetic free energy.

In this paper, the effect of the electron collision frequency with background ions on TMmr mode field components, the trajectory and the electron energy gain is studied. The field components of the TMmr mode in the elliptical waveguides are calculated. The ohmic heating for three different value of collision frequency calculated and the power losses is obtained. The deflection angle and acceleration gradient of an electron in the fields associated with a transverse magnetic (TM) wave propagating inside a elliptical waveguide for TMmr mode is studied. The relativistic momentum and energy equations for an electron are solved, which was injected initially along the propagation direction of the microwave. The results for TMmr mode are graphically represented. Finally, the optimum point of acceleration for the even mode TM11 is obtained and it is shown that in a cross section of elliptical waveguide optimum point is center of ellipse.

A one-dimensional model of magnetic relaxation in a pressureless low-resistivity plasma is considered. The initial two-component magnetic field \boldsymbol{b}(\boldsymbol{x},t)$\boldsymbol{b}(\boldsymbol{x},t)$ is strongly helical, with non-uniform helicity density. The magnetic pressure gradient drives a velocity field that is dissipated by viscosity. Relaxation occurs in two phases. The first is a rapid initial phase in which the magnetic energy drops sharply and the magnetic pressure becomes approximately uniform; the helicity density is redistributed during this phase but remains non-uniform, and although the total helicity remains relatively constant, a Taylor state is not established. The second phase is one of slow diffusion, in which the velocity is weak, though still driven by persistent weak non-uniformity of magnetic pressure; during this phase, magnetic energy and helicity decay slowly and at constant ratio through the combined effects of pressure equalisation and finite resistivity. The density field, initially uniform, develops rapidly (in association with the magnetic field) during the initial phase, and continues to evolve, developing sharp maxima, throughout the diffusive stage. Finally it is proved that, if the resistivity is zero, the spatial mean \langle (\boldsymbol{b}\boldsymbol{\cdot }\boldsymbol{{\rm\nabla}}\times \boldsymbol{b})/b^{2}\rangle$\langle (\boldsymbol{b}\boldsymbol{\cdot }\boldsymbol{{\rm\nabla}}\times \boldsymbol{b})/b^{2}\rangle$ is an invariant of the governing one-dimensional induction equation.

In this paper, a method of processing argon plasma images, obtained from the DC pseudo glow discharge technique, using two- and multiple-beam interference is suggested. This method is based on measuring the image fringe shift from the background interference fringes. Hence, this mapping of intensity shift is related to the electron density distribution of the argon plasma. Also, the refractive index of the plasma is computed from the electron density values. The contrast of the interferometer images in presence of plasma shift is investigated in both cases of two- and multiple-beam interference.

We present a theoretical investigation on the propagation of surface waves on the magnetized degenerate electron plasma half-space with spin effects. Using magnetohydrodynamic model with quantum effects due to the Bohm potential, Fermi degenerate pressure and electron spin, the dispersion relations of surface plasmon polaritons (SPPs) are derived. The dispersion relation of electrostatic surface waves is also obtained by taking electrostatic limit.

The authors would like to correct several misprints in the original article (Sulem and Passot 2014).

The generation and propagation of a small-amplitude Langmuir pulse excited by a planar grid electrode in a spatially uniform collisionless plasma with a constant flow velocity is studied by solving the linearized Vlasov–Poisson equations. The electrode is transparent to the flow of particles, like a screen or a wire mesh. The particles are assumed to have a Kappa velocity distribution, a reasonable approximation for electron distribution functions in the solar wind. Exact, closed-form solutions are obtained for {\it\kappa}=1${\it\kappa}=1$ , the Lorentzian distribution, and for {\it\kappa}=2${\it\kappa}=2$ . The explicit form of the solution in the case {\it\kappa}=2${\it\kappa}=2$ has not, to our knowledge, appeared in the literature before. The properties of the solutions are investigated and a practical technique for measuring the bulk flow velocity in plasma experiments is proposed that may be useful for high-accuracy, high-time-resolution measurements of the bulk flow velocity in the solar wind.

Kinetic magnetohydrodynamics refers usually to the hybrid fluid and kinetic description of a zero-Larmor-radius collisionless plasma, originally formulated in the classic papers of Kruskal and Oberman (1958) (Kruskal, M. D. and Oberman, C. R. 1958 Phys. Fluids1, 275), Rosenbluth and Rostoker (1959) (Rosenbluth, M. N. and Rostoker, N. 1959 Phys. Fluids2, 23), and Kulsrud (1962) (Kulsrud, R. 1962 Phys. Fluids5, 192). Such a theory is revisited here, as a special limit of the more general description put forward in Ramos (2010, 2011) (Ramos, J. J. 2010 Phys. Plasmas, 17, 082502; Ramos, J. J. 2011 Phys. Plasmas, 18, 102506). The present approach has the advantage of fulfilling the quasineutrality condition and avoiding the redundancy between the fluid and kinetic parallel force balance conditions with a built-in, rigorous account of the parallel electric field, thus affording a clear-cut handling of these issues. At zero-frequency marginal stability, the Rosenbluth–Rostoker fluid closures for the parallel and perpendicular pressures are obtained, in a solution with vanishing parallel electric field and non-zero parallel fluid displacement that satisfies exactly the desired quasineutrality and parallel force balance.

Plasma stabilization due to a nearby conducting wall can provide access to better performance in some scenarios in tokamaks. This was proved by experiments with an essential gain in {\it\beta}${\it\beta}$ and demonstrated as a long-lasting effect at sufficiently fast plasma rotation in the DIII-D tokamak (see, for example, Strait et al., Nucl. Fusion, vol. 43, 2003, pp. 430–440). The rotational stabilization is the central topic of this review, though eventually the mode rotation gains significance. The analysis is based on the first-principle equations describing the energy balance with dissipation in the resistive wall. The method emphasizes derivation of the dispersion relations for the modes which are faster than the conventional resistive wall modes, but slower than the ideal magnetohydrodynamics modes. Both the standard thin wall and ideal-wall approximations are not valid in this range. Here, these are replaced by an approach incorporating the skin effect in the wall. This new element in the stability theory makes the energy sink a nonlinear function of the complex growth rate. An important consequence is that a mode rotating above a critical level can provide a damping effect sufficient for instability suppression. Estimates are given and applications are discussed.