Air breakdown by avalanche ionization plays an important role in the electron beam and microwave propagations. For high electric fields and short pulse applications one needs avalanche ionization parameters for modeling and scaling of experimental devices. However, the breakdown parameters, i.e., the ionization frequency vs E/p (volt. cm−1. Torr−1) in air is uncertain for very high values of E/P. We review the experimental data for the electron drift velocity, the Townsend ionization coefficient in N2 and O2 and develop the ionization frequency and the collision frequency for momentum transfer in air. We construct the E/p vs Pτ diagram and show that our results are in better agreement with the most recent short pulse air breakdown experiments, compared to those predicted by the expression of Felsenthal & Proud (1965). This is because they extrapolate an expression for the drift velocity, linear in E/p, to high values of E/p. Experimentally the drift velocity varies as (E/p)½ in the region of E/p > 100.

A one-dimensional Lagrangian code is used to model the interaction of laser light with plasma. The equation of state used is a realistic, piecewise analytic fit, which allows simulations starting from normal density and temperature conditions. The atomic physics required in the code (ionization, radiation rate, and opacities) is interpolated from tables generated using a non-LTE hydrogenic atom model. Radiation transport is treated approximately using a new, numerically efficient recursive algorithm. Results from numerical simulations are compared with recent X-ray measurements from Al, Ti, and Fe plasmas. The code is also used to investigate the X-ray conversion efficiency and the effect of radiation transport on the mass ablation rate and ablation pressure.

The synchrotron emission from relativistic electrons in a thermal plasma with large-scale random magnetic fields is considered. In this case, the spectral synchrotron power of a single electron can be given in closed form allowing exact analytical expressions for the synchrotron emissivity, absorption coefficient, intensity and total energy loss of particles to be derived. The influence of various physical parameters such as gas density, magnetic field strength, particle's Lorentz factor on the resulting emissivities, intensities and energy loss is discussed in detail. Below the Razin– Tsytovich frequency vR = 20 Hz (ne/l cm−3) (B/l Gauss)−1, the spectral appearance of synchrotron radiation both in the optically thin and thick case is quite different than the vacuum behaviour. Since in the quasar broad line regions, vR is of the order 1011 Hz the suppression of synchrotron radiation may explain why most quasars are radio quiet. Likewise, the necessary physical conditions for the occurrence of synchrotron masering in the optically thick case are given. We obtain optical depth |τ|>1 for compact nonthermal sources. The total energy loss of a single particle is shown to be exponentially reduced at Lorentz factors less than γR = 2·1. 10−3 (ne/1 cm−3)½ (B/1 Gauss)−1.

The self-radiation characteristics of plasma created under the effect of a powerful laser radiation on a target are considered. The radiation in the spectral range from 1 to 1300 Å is calculated in coherent assumption for given gas-dynamic fields corresponding to various phases of laser target explosion. The source function was determined in accordance with a plasma radiation-collision model with the assumption of its transparency. Calculations show that the contribution of line radiation to the total flux may be from 20 to 60%. Mainly, this paper considers radiation transfer. The effect of self-radiation on level populations and frequency redistribution at resonance scattering is taken into account. The resonance scattering is predominant in the coronal plasma. Exit of photons from deeper layers of the target in comparison with the coherent case increases. Macroscopic plasma motion leading to spectral line shift is taken into consideration in the calculations. Output radiation spectral intensity distribution in oxygen and silicon H-like ions resonance lines has been determined. Spectral line profiles calculated with account of basic broadening mechanisms were used.

The effect of viscosity on the growth reduction of Rayleigh–Taylor modes is studied. It is shown that short wavelength perturbations are strongly damped; however the growth of the most relevant modes in fusion pellets is nearly unaffected.

The coupling of a large amplitude plasmon, generated by the beat-wave process, to ion acoustic waves may lead to modulational or decay instabilities, which are investigated here. A general dispersion relation obtainable from Zakharov equations predicts large growth rates (∼ωpi) for short wavelength modulations. To avoid these, extremely short pulse lengths are required in the beat-wave experiments. Due to the very long wavelength of the beat-plasmon, the decay instability is not likely below the ke V-temperatures.

Radiation characteristics of laser targets are studied in the soft X-ray region where photorecombination, bremsstrahlung and transitions in the discrete spectrum are the basic mechanisms of spectrum formation. The impact-radiational model is employed to describe the states of the laser target plasma. Characteristics obtained from the solution of the kinetic problem are used to compute absorption and emission coefficients. To set the time scale for a given field of gas-dynamic parameters, the transfer equation is solved and detailed information is obtained on the spectral composition of the outgoing radiation and its temporal evolution. Effective emission temperatures and radiation losses are determined. Integral radiation parameters are compared which have been derived from the solution of the transfer equation employing a volume luminescence approximation.

Experiments in the laboratory and in situ measurements in space represent an essential, but often overlooked, key to reliable understanding of our plasma universe. This will be illustrated by discussing several fundamental aspects of matter in the plasma state. They include (1) conduction of electric current, (2) magnetic-field aligned electric fields, (3) acceleration of charged particles to high energy, (4) coupling between magnetic fields and the motion of matter, (5) rapid release of magnetically stored energy, (6) chemical separation, and (7) critical-velocity interaction between plasma and neutral gas.

The flux transport effect on the radiation-induced plasma density profile and ablative flow outside the resonance layer in steady state in one dimensional spherical geometry studied. The numerical predictions conclude the existence of plateau-like plasma density profile rather than overdense bump formation in the underdense plasma. The plasma density profile, though retaining its shape, becomes more pronounced as the heat flux is increased. However, the length of the plasma density plateau is found to be quite small when compared with the isothermal case.

The interaction of light with the intergalactic plasma produces the Hubble red shift versus distance relationship. This interaction also produces an isotopic long wavelength background radiation from the plasma. Intrinsic red shifts in quasars and other objects are similarly explained, showing why they are exceptions to Hubble's law. Because the red shift is not doppler-shifted, big bang cosmological models should be replaced with static models.

Taking into account the emission and absorption of resonance radiation in a recombining laser-produced plasma of intermediate density, the system of rate equations for the population densities coupled with the radiative transfer equation is approximately treated. In the case of spatially varying absorption we derive an approximate form of the rate equation determining the population density of the upper resonance level. By applying this relation to an axially symmetric plasma a simple formula that describes the effect of radiation reabsorption on the spatial behaviour of the population density is obtained.

The paper demonstrates the possibility of the current increase in laser plasma by more than one order at the preaction of low-energy pulse on the target. The conversion effectivity of 0·32% is obtained at the intensity of the principal pulse of a CO2 laser equal to 4 × 109 W/cm2 and at the residual gas pressure of 10−5 torr.

Nd: YAG laser action controlled by a solid target-plasma reflectivity is reported. A quasi-continuous mode-locking pulse train consisting of 26 ± 4 ps pulses was observed using a two-stage laser amplifier and a carbon target. A single pulse energy of 0.2 mJ and a peak power density at the target of about 1011 W/cm2 were measured.

A plasma model of the origin of the light elements and the microwave background is presented. In contrast to the conventional Big Bang hypothesis, the model assumes that helium, deuterium and the microwave background were all generated by massive stars in the early stages of galaxy formation. The microwave background is scattered and isotropized by multi-GeV electrons trapped in the jets emitted by active galactic nuclei. The model produces reasonable amounts of heavy elements, accurately predicts the gamma-ray background intensity and spectrum, and explains the statistics of quasars, compact and extended radio sources.

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.

Focusing processes of a rotating and propagating light ion beam in the drift region are studied numerically by using a 2-dimensional hybrid (particle–fluid) code. An intense ion beam with the current density of 8 kA/cm2 and the total current of 2·5 MA, which is extracted from the diode with the applied voltage of 5·6 MV, is injected into the drift region filled with a low-density plasma. When a radial magnetic field is applied to the neighborhood of entrance, the beam ions start to rotate in the azimuthal direction owing to the Lorentz force. When the pressure of the background plasma is chosen such as the density of the beam becomes comparable with that of the background plasma in the vicinity of the focal spot, the current-neutralization fraction decreases and large self-magnetic fields are induced. The beam is confined by the fields within a small radius, even after passing the focal spot. Because the angular momentum of the beam is conserved, the beam rotation velocity increases up to the same order of the propagation one at a few mm radius. This rotation motion induces the azimuthal magnetic field and stabilizes the beam propagation. In the case where the plasma pressure was 3·0 Torr and the 0·2-Tesla radial magnetic field was applied over the distance of 2·0 cm near the entrance, the maximum beam intensity of 108TW/cm2 in the axial direction was obtained and the half width at half maximum (HWHM) of the focused profile was 3·5 mm.

An investigation into the feasibility of using a laser-generated plasma source of soft X rays as a laboratory based instrument for biological imaging and microlithography is presented. A preliminary characterization of the source has been carried out with carbon, copper and aluminum targets with specific interest in generating a monochromatic source of soft X rays in the ‘water window’. Measurements of X-ray production with respect to angular distribution, effects of cratering and different focusing conditions are reported. Initial conclusions on the optimization of the source for use in biological imaging are drawn.

Three-dimensional plasma simulations of interacting galactic-dimensioned current filaments show bursts of synchroton radiation of energy density 1·2 ×10−13 erg/cm3 which can be compared with the measured cosmic microwave background energy density of 1·5 × 10−13 erg/cm3. However, the synchrotron emission observed in the simulations is not blackbody. In this paper, we analyze the absorption of the synchrotron emission by the current filaments themselves (i.e., self-absorption) in order to investigate the thermalization of the emitted radiation. It is found that a large number of current filaments (>1031) are needed to make the radiation spectrum blackbody up to the observed measured frequency of 100 GHz. The radiation spectrum and the required number of current filaments is a strong function of the axial magnetic field in the filaments.