Many astrophysical disks, such as protoplanetary disks, are in a regime where non-ideal, plasma-specific magnetohydrodynamic (MHD) effects can significantly influence the behaviour of the magnetorotational instability (MRI). The possibility of studying these effects in the plasma Couette experiment (PCX) is discussed. An incompressible, dissipative global stability analysis is developed to include plasma-specific two-fluid effects and neutral collisions, which are inherently absent in analyses of Taylor–Couette flows (TCFs) in liquid metal experiments. It is shown that with boundary driven flows, a ion-neutral collision drag body force significantly affects the azimuthal velocity profile, thus limiting the flows to regime where the MRI is not present. Electrically driven flow (EDF) is proposed as an alternative body force flow drive in which the MRI can destabilize at more easily achievable plasma parameters. Scenarios for reaching MRI relevant parameter space and necessary hardware upgrades are described.

We briefly review some aspects of magnetic turbulence intermittency observed in space plasmas. Deviation of statistical characteristics of a system (e.g. its high statistical momenta) from the Gaussian can manifest itself as domination of rare large intensity peaks often associated with the intermittency in the system's dynamics. Thirty years ago, Zeldovich stressed the importance of the non-Gaussian appearance of the sharp values of vector and scalar physical parameters in random media as a factor of magnetic field amplification in cosmic structures. Magnetic turbulence is governing the behavior of collisionless plasmas in space and especially the physics of shocks and magnetic reconnections. Clear evidence of intermittent magnetic turbulence was found in recent in-situ spacecraft measurements of magnetic fields in the near-Earth and interplanetary plasma environments. We discuss the potentially promising approaches of incorporating the knowledge gained from spacecraft in-situ measurements into modern models describing plasma dynamics and radiation in various astrophysical systems. As an example, we discuss supernova remnants (SNRs) which are known to be the sources of energy, momentum, chemical elements, and high-energy cosmic rays (CRs) in galaxies. Supernova shocks accelerate charged particles to very high energies and may strongly amplify turbulent magnetic fields via instabilities driven by CRs. Relativistic electrons accelerated in SNRs radiate polarized synchrotron emission in a broad range of frequencies spanning from the radio to gamma-rays. We discuss the effects of intermittency of magnetic turbulence on the images of polarized synchrotron X-ray emission of young SNRs and emission spectra of pulsar wind nebula.

A spectacular phenomenon of intermittency, i.e. a progressive growth of higher statistical moments of a physical field excited by an instability in a random medium, attracted the attention of Zeldovich in the last years of his life. At that time, the mathematical aspects underlying the physical description of this phenomenon were still under development and relations between various findings in the field remained obscure. Contemporary results from the theory of the product of independent random matrices (the Furstenberg theory) allowed the elaboration of the phenomenon of intermittency in a systematic way. We consider applications of the Furstenberg theory to some problems in cosmology and dynamo theory.

This issue commemorates an outstanding scientist of the twentieth century, Yakov Borisovich Zeldovich, in connection with the centenary of his birth (8 March 1914), with a collection of reviews and research articles broadly related to large-scale random phenomena in astrophysical plasmas.

In this paper, we investigate the evolution of braided solar coronal loops. We assume that coronal loops consist of several internal strands which twist and braid about each other. Reconnection between the strands leads to small flares and heating of the loop to x-ray temperatures. Using a method of generating and releasing braid structure similar to a forest fire model, we show that the reconnected field lines evolve to a self-organised critical state. In this state, the frequency distributions of coherent braid sequences as well as flare energies follow power law distributions. We demonstrate how the presence of net helicity in the loop alters the distribution laws.

Electron–positron (e–p) plasmas are widely thought to be emitted, in the form of ultra-relativistic winds or collimated jets, by some of the most energetic or powerful objects in the Universe, such as black-holes, pulsars, and quasars. These phenomena represent an unmatched astrophysical laboratory to test physics at its limit and, given their immense distance from Earth (some even farther than several billion light years), they also provide a unique window on the very early stages of our Universe. However, due to such gigantic distances, their properties are only inferred from the indirect interpretation of their radiative signatures and from matching numerical models: their generation mechanism and dynamics still pose complicated enigmas to the scientific community. Small-scale reproductions in the laboratory would represent a fundamental step towards a deeper understanding of this exotic state of matter. Here we present recent experimental results concerning the laser-driven production of ultra-relativistic e–p beams. In particular, we focus on the possibility of generating beams that present charge neutrality and that allow for collective effects in their dynamics, necessary ingredients for the testing pair-plasma physics in the laboratory. A brief discussion of the analytical and numerical modelling of the dynamics of these plasmas is also presented in order to provide a summary of the novel plasma physics that can be accessed with these objects. Finally, general considerations on the scalability of laboratory plasmas up to astrophysical scenarios are given.

The necessity for compact table-top x-ray sources with higher brightness, shorter wavelength and shorter pulse duration has led to the development of complementary sources based on laser-plasma accelerators, in contrast to conventional accelerators. Relativistic interaction of short-pulse lasers with underdense plasmas results in acceleration of electrons and in consequence in the emission of spatially coherent radiation, which is known in the literature as betatron radiation. In this article, we report on our recent results in the rapidly developing field of secondary x-ray radiation generated by high-energy electron pulses. The betatron radiation is characterized with a novel setup allowing to measure the energy, the spatial energy distribution in the far-field of the beam and the source size in a single laser shot. Furthermore, the polarization state is measured for each laser shot. In this way, the emitted betatron x-rays can be used as a non-invasive diagnostic tool to retrieve very subtle information of the electron dynamics within the plasma wave. Parallel to the experimental work, 3D particle-in-cell simulations were performed, proved to be in good agreement with the experimental results.

Experimental evidence supporting the theory of hot tail runaway electron (RE) generation has been identified in TEXTOR disruptions. With higher temperature, more REs are generated during the thermal quench. Increasing the RE generation by increasing the temperature, an obvious RE plateau is observed even with low toroidal magnetic field (1.7 T). These results explain the previously found electron density threshold for RE generation.

In a tokamak, trapped electrons subject to a strong electric field cannot run away immediately, because their parallel velocity does not increase over a bounce period. However, they do pinch toward the tokamak center. As they pinch toward the center, the trapping cone becomes more narrow, so eventually they can be detrapped and run away. When they run away, trapped electrons will have a very different signature from circulating electrons subject to the Dreicer mechanism. The characteristics of what are called trapped-electron runaways are identified and quantified, including their distinguishable perpendicular velocity spectrum and radial extent.

We examine the impact of several factors on electron acceleration by a laser pulse and the resulting electron energy gain. Specifically, we consider the role played by: (1) static longitudinal electric field, (2) static transverse electric field, (3) electron injection into the laser pulse, and (4) static longitudinal magnetic field. It is shown that all of these factors lead, under certain conditions, to a considerable electron energy gain from the laser pulse. In contrast with other mechanisms such as wakefield acceleration, the static electric fields in this case do not directly transfer substantial energy to the electron. Instead, they reduce the longitudinal dephasing between the electron and the laser beam, which then allows the electron to gain extra energy from the beam. The mechanisms discussed here are relevant to experiments with under-dense gas jets, as well as to experiments with solid-density targets involving an extended pre-plasma.

We report the observation of two isolated clouds of positrons inside an active thunderstorm. These observations were made by the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of six gamma-ray detectors, which flew on a Gulfstream V jet aircraft through the top of an active thunderstorm in August 2009. ADELE recorded two 511 keV gamma-ray count rate enhancements, 35 s apart, each lasting approximately 0.2 s. The enhancements, which were approximately a factor of 12 above background, were both accompanied by electrical activity as measured by a flat-plate antenna on the underside of the aircraft. The energy spectra were consistent with a source mostly composed of positron annihilation gamma rays, with a prominent 511 keV line clearly visible in the data. Model fits to the data suggest that the aircraft was briefly immersed in clouds of positrons, more than a kilometre across. It is not clear how the positron clouds were created within the thunderstorm, but it is possible they were caused by the presence of the aircraft in the electrified environment.

The second half of the 20th century can be characterized and named as the ‘plasma era’, as the plasma gathered scientific interest because of its special physical behaviour. Thus, it was considered as the fourth material state and the plasma physics began to form consequently. In addition to this, many important applications of plasma were discovered and put to use. Especially, in last few decades, there has been an increased interest in the use of cold atmospheric plasma in bio-chemical applications. Until now, thermal plasma has been commonly used in many bio-medical and other applications; however, more recent efforts have shown that plasma can also be produced at lower temperature (close to the environment temperature) by using ambient air in an open space (in atmospheric pressure). However, two aspects remain neglected: firstly, low-temperature plasma production with a large area, and secondly, acquiring the necessary knowledge and understanding the relevant interaction mechanisms of plasma species with microorganisms. These aspects are currently being investigated at the ‘Demokritos’ Plasma Laboratory in Athens, Greece with radio frequency (27.12 MHz and it integer harmonics)-driven sub-atmospheric pressure plasma (100 Pa). The first aspect was achieved with atmospheric plasma being produced at a low temperature (close to the environment temperature) and in a large closed space systems. Regarding the plasma effect on living microorganisms, preliminary experiments and findings have already been carried out and many more have been planned for the near future.

The equivalence between the Laplace transform (Landau, J. Phys. USSR10 (1946), 25) and Hermite transform (Zocco and Schekochihin, Phys. Plasmas18, 102309 (2011)) solutions of the linear collisionless Landau damping problem is proven.

We find that the electron in an electron–cyclotron maser (ECM) of Nc = n1/3λ ≫ 1, where n and λ are the electron density and the maser wavelength, respectively, can only lower its energy through masing transition. From this fact and the application of Heisenberg's uncertainty principle on photon emission, we infer that until the electron energy becomes lower to pass through the width of uncertainty in the electron energy, the interval time Tint between two successive radiative transitions is zero. Hence, we find that if the number Nt of radiative transitions during the laser period T under the assumption of Tint = 0 is far larger than the number Nu of radiative transitions required to pass through the half-width ΔE of uncertainty in the electron energy, the radiation power from an electron is equal to ΔE/T. We deduce that the shift in the energy level of an average electron is predominantly produced by the density-deviation mode driven by the laser field so as to be spatially sinusoidal with period λw and amplitude $\mathcal W$. We recognize that the uncertainty in the z position of an electron emitting a laser photon through free-electron two-quantum Stark (FETQS) radiation is the wavelength λe of the electric wiggler. Thus, if λw ≪ λe, then ΔE is equal to $\mathcal W$. Based on the above findings, we identify electron–cyclotron masing in a high-density ECM as a gyration-driven FETQS radiation whose power is given by P = ΔE/T, where ΔE is not caused by gyration but rotation around the waveguide axis. The gain calculated based on this identification agrees with the measured one.

We construct nonlinear toroidal equilibria of fixed diverted boundary shaping with reversed magnetic shear and flows parallel to the magnetic field. The equilibria have hole-like current density and the reversed magnetic shear increases as the equilibrium nonlinearity becomes stronger. Also, application of a sufficient condition for linear stability implies that the stability is improved as the equilibrium nonlinearity correlated to the reversed magnetic shear gets stronger with a weaker stabilizing contribution from the flow. These results indicate synergetic stabilizing effects of reversed magnetic shear, equilibrium nonlinearity and flow in the establishment of Internal Transport Barriers (ITBs).

In this paper, the shape, sound, and current of an electrical discharge in the air between a metal pin and an electrolyte solution are studied. Two different situations are considered: (A) without, and, (B) with inclusion of a dielectric wall in the discharge circuit. It is found that: (1) the discharge A has a cylindrical shape rather than a branched shape in discharge B, (2) the sound and current of discharge in case A are coherent and deterministic but those of case B are incoherent and stochastic. These differences along with the simulation results of a simple model demonstrate that the discharge in case A is glow, but, that in case B is spark.

The lifetimes, volume densities of energy, electron and ion densities and other parameters of ball lightning cores with the nonrelativistic electrons are estimated. The model according to which the motion of the electrons of the ball lightning core is the superposition of the oscillatory motion and the thermal motion in the directions perpendicular to those of the oscillations is proposed. Some problems related to isolation of the ball lightning core from the atmosphere and the transfer of the atmospheric pressure on it are considered.

The behavior of waves in a one-dimensional (1D) dusty plasma lattice where the dust interacts via Yukawa and electric dipole interactions is discussed theoretically. This study is motivated by recent reports on electrorheological dusty plasmas (e.g. Ivlev et al. 2008Phys. Rev. Lett.100, 095003) where the dipole interaction arises due to an external uniaxial AC electric field that distorts the Debye sphere surrounding each grain. Application to possible dusty plasma experimental parameters is discussed.