Weibel instability in the field of a short laser pulse

The growth rate of Weibel instability in a plasma interacting with a high-frequency pulse with a duration less or comparable with the electron mean free time is determined. The growth rate is shown to decrease with decreasing pulse duration. It is found that instability can develop after the short pulse is switched off and the generated magnetic field no longer affects electron motion in the high-frequency field.     

Generation of terahertz radiation from a low-density plasma slab irradiated by a laser pulse

The generation of terahertz electromagnetic radiation when a laser pulse propagates through a low-density plasma slab is considered. It is shown that terahertz waves are excited because of the growth of a weakly damped, antisymmetric leaking mode of the plasma slab. The spectral, angular, and energy parameters of the terahertz radiation are investigated, as well as the spatiotemporal structure of the emitted waves. It is demonstrated that terahertz electromagnetic wave fields are generated most efficiently when the pulse length is comparable to the slab thickness.     

Analytical and numerical treatment of resistive drift instability in a plasma slab

An analytic approach combining the effect of equilibrium diamagnetic flows and the finite ionsound gyroradius associated with electron?ion decoupling and kinetic Alfvén wave dispersion is derived to study resistive drift instabilities in a plasma slab. Linear numerical computations using the NIMROD code are performed with cold ions and hot electrons in a plasma slab with a doubly periodic box bounded by two perfectly conducting walls. A linearly unstable resistive drift mode is observed in computations with a growth rate that is consistent with the analytic dispersion relation. The resistive drift mode is expected to be suppressed by magnetic shear in unbounded domains, but the mode is observed in numerical computations with and without magnetic shear. In the slab model, the finite slab thickness and the perfectly conducting boundary conditions are likely to account for the lack of suppression.     

Quasilinear theory of the ion Weibel instability in the Earth's magnetospheric tail

The quasilinear equation for the ion Weibel instability is solved for waves propagating along the magnetic field. The energy of the excited waves is estimated and the moments of the ion distribution function in the saturation stage are determined as functions of the current velocity for parameters characteristic of the neutral sheet of the Earth's magnetotail. The question is studied of whether the current disruption at the beginning of the explosive phase of a substorm can be explained as being due to the onset of the ion Weibel instability.     

Dependence of radiation from a laser-produced plasma on the plasma composition

Results are reported from calculations of how the radiation spectrum from a laser-produced plasma depends on the gold concentration in a target made of a gold-copper alloy. Calculations were carried out with the SND code by using the photon absorption coefficients obtained from the THERMOS code. The experimental data are interpreted by comparing them with the calculated results.     

Impurity radiation from a tokamak plasma

In tokamak operating modes, energy balance is often governed by impurity radiation. This is the case near the divertor plates, during impurity pellet injection, during controlled discharge disruptions, etc. The calculation of impurity radiation is a fairly involved task (it is sometimes the most difficult part of the general problem) because the radiation power is determined by the distribution of ions over the excited states and by the rate constants of elementary processes of radiation and absorption. The objective of this paper is to summarize in one place all the approximate formulas that would help investigators to describe radiation from the most often encountered impurities in a fairly simple way in their calculations accounting for plasma radiation, without reference to special literature. Simple approximating formulas describing ionization, recombination, and charge-exchange processes, as well as radiative losses from ions with a given charge, are presented for five impurity species: beryllium, carbon, oxygen, neon, and argon. Estimating formulas that allow one to take into account plasma opacity for resonant photons in line impurity radiation are also presented.     

Effect of the plasma electron motion on the development of Cherenkov instability in a waveguide

A linear theory of the Cherenkov amplification in a transversely nonuniform waveguide in an infinitely strong magnetic field is constructed with allowance for both ordered and thermal motions of plasma electrons. The effect of these electron motions on the threshold for the onset of Cherenkov instability is investigated. The amplification coefficients and the conditions for the onset of the instability are determined.     

Development of beam-plasma instability during the injection a low-energy electron beam into the ionospheric plasma

Results are presented from an active experiment on the injection of charged particle beams into the ionospheric plasma. The experiment was carried out in 1992 onboard the Intercosmos-25 satellite and the Magion-3 daughter satellite (APEX). A specific feature of this experiment was that both the ion and electron beams were injected upward, in the same direction along the magnetic field. The most interesting results are the excitation of HF and VLF-LF waves and the generation of fast charged particle flows, which were recorded on both satellites.     

Mechanisms of trinucleotide repeat instability during human development

Trinucleotide expansion underlies several human diseases. Expansion occurs during multiple stages of human development in different cell types, and is sensitive to the gender of the parent who transmits the repeats. Repair and replication models for expansions have been described, but we do not know whether the pathway involved is the same under all conditions and for all repeat tract lengths, which differ among diseases. Currently, researchers rely on bacteria, yeast and mice to study expansion, but these models differ substantially from humans. We need now to connect the dots among human genetics, pathway biochemistry and the appropriate model systems to understand the mechanism of expansion as it occurs in human disease.     

Granulocytopoiesis during the development of radiation injury from prolonged intake of tritium oxide

During chronic exposure to tritium oxide (a dose rate of 0.125 Gy/day-1, and a cumulative-absorbed dose of 22.1 Gy) different granulocytopoiesis compartments (i.e. polypotent CFUs, committed CFUc; proliferating, maturing, and functional pools) were differently damaged by radiation. In the course of the development of tritium oxide-induced affection granulocytopoiesis proceeds at an intense pace.     

Experimental studies of the behavior of the ion plasma component during disruptive instability in a tokamak

Results are presented from experimental studies of the behavior of the plasma ion component during disruptive instability in the TVD and DAMAVAND tokamaks. It is shown that the ion temperature increases during a major disruption by a factor of 1.5–2. The ions are accelerated predominantly across the magnetic field near the rational magnetic surfaces. Results on the ion acceleration along the magnetic field indicate that disruptions are accompanied by the generation of longitudinal electric fields that are aligned in opposite directions at the plasma periphery and near the plasma axis.     

Interaction of an ion bunch with a plasma slab

Charge neutralization of a short ion bunch passing through a plasma slab is studied by means of numerical simulation. It is shown that a fraction of plasma electrons are trapped by the bunch under the action of the collective charge separation field. The accelerated electrons generated in this process excite beam?plasma instability, thereby violating the trapping conditions. The process of electron trapping is also strongly affected by the high-frequency electric field caused by plasma oscillations at the slab boundaries. It is examined how the degree of charge neutralization depends on the parameters of the bunch and plasma slab.     

On the instability of a two-dimensional plane plasma crystal

A study is made of the transverse instability of two-dimensional plane dust crystals with a simple (one particle per primitive cell) and a complex (two particles per primitive cell) lattice structure. The instability criteria (crystal melting conditions) are obtained for an arbitrary, spherically symmetric intergrain interaction potential. It is shown that, for simple lattices, the instability develops in the short-wavelength limit, whereas, for complex lattices, the instability growth rate is maximum in the long-wavelength limit. The structural instability of a square lattice is also considered.     

Electromagnetically induced transparency in a magnetized plasma during oblique propagation of radiation

The parametric effect of electromagnetically induced transparency (EIT) is studied in the case of quasi-transverse propagation of an extraordinary wave in the vicinity of the upper hybrid resonance in a cold plasma. The question is investigated of whether the waves that propagate in a smoothly inhomogeneous medium (from the transparency region in the vicinity of the upper hybrid resonance into vacuum or in the opposite direction) can reach the EIT region. The features of the quasi-transverse propagation of an extraordinary wave at the electron cyclotron resonance frequency in the quasi-EIT regime are also considered. It is shown that, in this situation, the parametric effects modify the polarization of the wave, with the result that its absorption increases substantially (by one to two orders of magnitude).     

Kelvin-Helmholtz instability in a bounded plasma flow

Kelvin-Helmholtz instability in a three-layer plane geometry is investigated theoretically. It is shown that, in a three-layer system (in contrast to the traditionally considered case in which instability develops at the boundary between two plasma flows), instability can develop at an arbitrary ratio of the plasma flow velocity to the ion-acoustic velocity. Perturbations with wavelengths on the order of the flow thickness or longer can increase even at a zero temperature. The system can also be unstable against long-wavelength perturbations if the flow velocity at one of the boundaries is lower than the sum of the Alfvén velocities in the flow and the ambient plasma. The possibility of applying the results obtained to interpret the experimental data acquired in the framework of the CLUSTER multisatellite project is discussed. It follows from these data that, in many cases, the propagation of an accelerated particle flow in the plasma-sheet boundary layer of the Earth’s magnetotail is accompanied by the generation of magnetic field oscillations propagating with a velocity on the order of the local Alfvén velocity.     

Photoionization two-stream instability in a collisional plasma

An analysis is made of how electron collisions influence the development of photoionization two-stream instability of a plasma produced in the irradiation of matter by a short X-ray pulse from a free-electron laser. The cases of a weakly ionized and a completely ionized plasma are discussed.     

Electromagnetic wave in a relativistic magnetized plasma

Results are presented from a theoretical investigation of the dispersion properties of a relativistic plasma in which an electromagnetic wave propagates along an external magnetic field. The dielectric tensor in integral form is simplified by separating its imaginary and real parts. A dispersion relation for an electromagnetic wave is obtained that makes it possible to analyze the dispersion and collisionless damping of electromagnetic perturbations over a broad parameter range for both nonrelativistic and ultrarelativistic plasmas.     

Electromagnetic absorption in a multilayered slab model of tissue under near-field exposure conditions

The electromagnetic energy deposited in a semi-infinite slab model consisting of skin, fat, and muscle layers is calculated for both plane-wave and near-field exposures. The plane-wave spectrum (PWS) approach is used to calculate the energy deposited in the model by fields present due to leakage from equipment using electromagnetic energy. This analysis applies to near-field exposures where coupling of the target to the leakage source can be neglected. Calculations were made for 2,450 MHz, at which frequency the layered slab adequately models flat regions of the human body. Resonant absorption due to layering is examined as a function of the skin and fat thicknesses for plane-wave exposure and as a function of the physical extent of the near-field distribution. Calculations show that for fields that are nearly constant over at least a free-space wavelength, the energy deposition (for the skin, fat, and muscle combination that gives resonant absorption) is equal to or less than that resulting from plane-wave exposure, but is appreciably greater than that obtained for a homogeneous muscle slab model.     

Generation of terahertz radiation in the reflection of a laser pulse from a dense plasma

The generation of low-frequency (terahertz) electromagnetic radiation in the reflection of a laser pulse from the boundary of a dense plasma is considered. Low-frequency wave electromagnetic fields in vacuum are excited by a vortex electric current that is induced at the plasma boundary by the ponderomotive force of the laser pulse. The spectral, angular, and energy parameters of the low-frequency radiation, as well as the spatiotemporal structure of the emitted waves, are investigated. It is shown that for typical parameters of present-day laser plasma experiments, the power of terahertz radiation can amount to tens of megawatts.     

Electromagnetic instability of an anisotropic relativistic plasma in the context of the evolution of galactic and intergalactic high-energy particle sources

The electromagnetic instability of a relativistic space plasma is considered. The instability manifests itself during transverse oscillations in an anisotropic plasma either when the wavelength is sufficiently long and the velocity distribution is fixed or when the plasma is strongly anisotropic and the wavelength is fixed. The critical wavenumber is estimated for a velocity distribution in the form of an oblate ellipsoid of revolution.