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The 12 articles in this special issue focus on space and cosmic plasma. The articles are briefly summarized here.

The concept of a critical ionization velocity (CIV) was first introduced by Alfven (1942, 1954) as a component of his theory for the formation of the solar system. If a neutral gas and magnetized plasma are in relative motion, a rapid ionization of the neutrals takes place if the kinetic energy of the neutrals relative to the plasma exceeds the ionization potential eV i of the neutrals.

Plasma science is rich in distinguishable scales ranging from the atomic to the galactic to the meta-galactic, i.e., the mesoscale. Thus plasma science has an important contribution to make in understanding the connection between microscopic and macroscopic phenomena. Plasma is a system composed of a large number of particles which interact primarily, but not exclusively, through the electromagnetic field. The problem of understanding the linkages and couplings in multiscale processes is a frontier problem of modern science involving fields as diverse as plasma phenomena in the laboratory to galactic dynamics.

Contrary to popular and scientific opinion of just a few decades ago, space is not an ‘empty’ void. It is actually filled with high energy particles, magnetic fields, and highly conducting plasma. The ability of plasmas to produce electric fields, either by instabilities brought about by plasma motion or the movement of magnetic fields, has popularized the term ‘Electric Space’ in recognition of the electric fields systematically discovered and measured in the solar system. Today it is recognized that 99.999% of all observable matter in the universe is in the plasma state and the importance of electromagnetic forces on cosmic plasma cannot be overstated; even in neutral hydrogen regions (∼ 10-4 parts ionized), the electromagnetic force to gravitational force ratio is 107.

One of the earliest predictions about the morphology of the universe is that it be filamentary (Alfven, 1950). This prediction followed from the fact that volumewise, the universe is 99.999% matter in the plasma state. When the plasma is energetic, it is generally inhomogeneous with constituent parts in motion. Plasmas in relative motion are coupled by the currents they drive in each other and nonequilibrium plasma often consists of current-conducting filaments.

Plasma consists of electrically charged particles that respond collectively to electromagnetic forces. The charged particles are usually clouds or beams of electrons or ions, or a mixture of electrons and ions, but also can be charged grains or dust particles. Plasma is also created when a gas is brought to a temperature that is comparable to or higher than that in the interior of stars. At these temperatures, all light atoms are stripped of their electrons, and the gas is reduced to its constituent parts: positively charged bare nuclei and negatively charged free electrons. The name plasma is also properly applied to ionized gases at lower temperatures where a considerable fraction of neutral atoms or molecules are present.

The plasma Universe approach to the structure of the Universe considers space to be filled with a network of currents which can undergo pinch compression. The equilibrium structures of such currents are treated in the same way as the structure in laboratory pinches. The difference, for the galactic case, is that gravitational interaction forces between the particles must be included in the analysis. A simple and straightforward way of achieving this is illustrated. >

Numerical methods are used to investigate absorption of either intense or weak electromagnetic waves obliquely incident on a nonuniform plasma with and without the presence of a dc magnetic field. The numerical formulation includes the full set of Maxwell's equations and three moments of the Boltzmann equation with a ponderomotive-force description. The investigation includes a study of the reflection and absorption of the incident wave as a function of angle of incidence as well as the complex electric and magnetic fields, electron-flow, dc magnetic field generation, and kinetic energy gained by resonant electrons within the plasma. Selected field snapshots are directly compared to particle-simulation predictions where a thousandfold reduction in computation time allows a detailed investigation of the wave-plasma interaction for laser wavelengths.

Cosmic plasma physics and our concept of the universe is in a state of rapid revision. This change started with in-situ measurements of plasmas in Earth's ionosphere, cometary atmospheres, and planetary magnetospheres; the transition of knowledge from laboratory experiments to astrophysical phenomena; discoveries of helical and filamentary plasma structures in the Galaxy and double radio sources; and the particle simulation of plasmas not accessible to in-situ measurement. Because of these, Birkeland (field-aligned) currents, double layers, and magnetic-field aligned electric fields are now known to be far more important to the evolution of space plasma, including the acceleration of charged particles to high energies, than previously thought. This paper reviews the observational evidence for a plasma universe threaded by Birkeland currents and particle beams.

A simple analysis of the dynamic state of a current‐conducting high‐density plasma column, resulting from an exploded wire between the conductors of a rail‐gun accelerator or one or more wires strung between the anode and cathode conductors in a pulsed‐power generator diode, is given on the basis of a one‐dimensional magnetohydrodynamics model. Spatial distributions of the current density, magnetic field, temperature, and particle density are calculated as well as the temporal current, voltage, and impedance histories. The model self‐consistently treats the accelerator load transition through its solid, melt, vapor, and plasma states in the presence of its supply source and feed network. Once formed and accelerated, the plasma state calculations show expansion cooling across the self‐induced magnetic field if the Bennett condition is not satisfied. The model predictions are compared to two experimental situations. The first involves the delivery of some hundreds of Joules of stored energy to the wire load...

In our investigation of the linear theory of waves in plasma and the stability of relativistic beam‐plasma systems, we have been led to consider methods for the evaluation of integrals of the form ∫dχ(χ−ζ)−1 exp(−χ2) and ∫dχ(χ−ζ)−1 exp[(1−χ2)−1/2] for complex ζ. In this work, we report on the evaluation of this integral and its derivative by means of continued fraction expansions. The expressions derived allow the precise calculation of these integrals in previously inaccessible regions. Additionally, applications to non‐Maxwellian particle distributions, such as those found in the analysis of plasma diodes, are included.

Cosmic plasma physics and our concept of the universe is in a state of rapid revision. This change started with in-situ measurements of plasmas in Earth's ionosphere, cometary atmospheres, and planetary magnetospheres; the translation of knowledge from laboratory experiments to astrophysical phenomena; discoveries of helical and filamentary plasma structures in the Galaxy and double radio sources; and the particle simulation of plasmas not accessible to in-situ measurement. Because of these, Birkeland (field-aligned) currents, double layers, and magnetic-field-aligned electric fields are now known to be far more important to the evolution of space plasma, including the acceleration of charged particles to high energies, than previously thought. This paper and its sequel investigate the observational evidence for a plasma universe threaded by Birkeland currents or filaments. This model of the universe was inspired by the advent of three-dimensional fully electromagnetic particle simulations and their application to the study of laboratory z pinches. This study resulted in totally unexpected phenomena in the data post-processed from the simulation particle, field, and history dumps. In particular, when the simulation parameters were scaled to galactic dimensions, the interaction between pinched filaments led to synchrotron radiation whose emission properties were found to share the following characteristics with double radio galaxies and quasars: power magnitude, isophotal morphology, spectra, brightness along source, polarization, and jets. The evolution of these pinched synchrotron emitting plasmas to elliptical, peculiar, and spiral galaxies by continuing the simulation run is addressed in a sequel paper.

Connection formulas relevant to the description of wave conversion in inhomogeneous plasma have been derived.

The effect of laser light having Gaussian spatial and temporal variations upon ion‐acoustic waves is investigated analytically. At high power densities this light can interfere with coherent propagating waves in addition to exciting waves streamers which propagate away from the perturbed region at the ion sound velocity.

The dispersion of ion‐acoustic plasma waves is investigated using pulsed CO2 laser scattering and homodyne detection techniques. Broadening of the scattered spectrum due to spatial wave damping is demonstrated.

Ionized matter—plasma—is the over-whelmingly dominant constituent of the universe as a whole, and matter in the plasma state is characterized by a complexity that vastly exceeds that exhibited in the solid, liquid, and gaseous states. Correspondingly, the physical and especially the electrodynamic properties of the plasma are still far from well understood.; While it is now universally acknowledged that our universe is a plasma universe, the physical understanding of this universe has remained in doubt. This is primarily because interpreting the physical processes from high-energy, optical, infrared, and radio telescope observations critically depend on our understanding of matter in the plasma state.

Approximate expressions describing the Tonks‐Dattner and Buchsbaum‐Hasegawa resonances (at the second electron cyclotron harmonic) in a warm nonuniform plasma are derived by means of a fairly easy analytic continuation technique. Connection formulas are developed for third‐order electric field differential equations derived from kinetic theories and show the coupling of slow and fast waves in the vicinity of a linear turning point. The relatively simple field expressions predict traveling longitudinal waves possessing outwardly directed phase velocities. Internal plasma fields appreciably larger than the excitation field are found when the density nonuniformity supports even mode resonances. The field equations and expressions for the associated impedance variation are compared to numerical integration solutions and show striking similarity to experimental observations.