Charge screening in a plasma with an external ionization source

An asymptotic theory for the screening of the electric field of a dust particle or a spherical probe in a plasma with an external steady and/or internal (proportional to the electron density) gas ionization source has been developed for the first time. It has been established that the screening of the charge of a spherical body adsorbing the charge of the incident plasma particles is described by a superposition of two exponentials with different screening constants. The two exponentials are retained even in the absence of nonequilibrium fluxes on the macroparticle and only in the special case of an isothermal plasma does the screening become Debye one. The screening length is determined by the ratio of the electron-ion, β_ei, and Langevin, β_L = 4πeμ_i (where μ_i is the ion mobility), recombination coefficients. If β_L ? β_ei, then it is much larger than the electron Debye length. The ions in an isothermal plasma have been found to give the same contribution to the screening as the electrons if the electron-ion recombination coefficient exceeds the Langevin ion recombination coefficient by a factor of 2 or more, β_ei ≥ 2β_L. The Vlasov equation is used to analyze the asymptotic behavior of the macroparticle potential in a collisionless plasma.     

Experimental determination of dust-particle charge in a discharge plasma at elevated pressures

The charge of dust particles is determined experimentally in a bulk dc discharge plasma in the pressure range 20-100 Pa. The charge is obtained by two independent methods: one based on an analysis of the particle motion in a stable particle flow and another on an analysis of the transition of the flow to an unstable regime. Molecular-dynamics simulations of the particle charging for conditions similar to those of the experiment are also performed. The results of both experimental methods and the simulations demonstrate good agreement. The charge obtained is several times smaller than predicted by the collisionless orbital motion theory, and thus the results serve as an experimental indication that ion-neutral collisions significantly affect particle charging.     

Screening of a moving charge in a nonequilibrium plasma

The problem of screening a moving charged dust particle is analyzed in the model of point sinks. Typical time scales for the formation of a polarization cloud around the moving macroscopic particle are found using the three-dimensional integral transform with respect to the spatial coordinates and the Laplace transform in time. It is shown that the stationary potential of a moving charge has a dipole component dominating at sufficiently large distances. The force exerted on a moving charged macroscopic particle by the electric field of induced charges is calculated. It is shown that, in general, the direction of this force depends on the ratio between the transfer coefficient and the decay rate of plasma particles in the plasma. In the presence of sinks, a dust particle is accelerated by this force if the Langevin recombination rate for ions, β _iL = 4πeμ _i , exceeds the electron-ion recombination rate β _ei . In the absence of sinks or if β _ei > β _iL this force is antiparallel to the dust-particle velocity.     

Screening of a moving charge in a nonequilibrium plasma

Based on the model of point sinks, we consider the problem on the screening of the charge of a moving macroparticle in a nonequilibrium plasma. The characteristic formation times of the polarization cloud around such a macroparticle have been determined by the method of a three-dimensional integral Fourier transformation in spatial variables and a Laplace transformation in time. The screening effect is shown to be enhanced with increasing macroparticle velocity. We consider the applicability conditions for the model of point sinks and establish that the domain of applicability of the results obtained expands with decreasing gas ionization rate and macroparticle size. We consider the problem of charge screening at low velocities and establish that the stationary potential of the moving charge has a dipole component that becomes dominant at large distances. We show that the direction of the force exerted on the dust particle by the induced charges generally depends on the relationship between the transport and loss coefficients of the plasma particles in a plasma. When the Langevin ion recombination coefficient β _iL = 4πeμ _i exceeds the electron-ion recombination coefficient β _ei , this force will accelerate the dust particles in the presence of sinks. In the absence of sinks or when β _ei > β _iL , this force will be opposite in direction to the dust particle velocity. We also consider the problem on the energy and force of interaction between a moving charged macroparticle and the induced charges.     

Interaction of a plasma source with an ambient plasma

Summary Plasma sources are used to control spacecraft potential and, in general, to improve the electrical contact between a charged body and the space plasma. In the present paper we address the problem of the interaction of a plasma source with the ambient plasma. The source is supposed to be positively charged with respect to the ambient. A self-consistent collisionless one-dimensional fluid model is sketched and some of the results obtained are then presented and discussed. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Effects of external fields on the potential of a test charge in a plasma

This paper considers the far field potential of a stationary test charge in a plasma. It is shown that external fields can have a significant influence on the potential which can be very large when an upper hybrid wave propagates through the plasma.     

Stability in the Yang-Mills system with an external source

We investigate stability of the Coulomb solution in the Yang-Mills system under finite perturbations below the critical coupling strength. The role of recently discovered low-energy solutions is discussed.     

Electron transport and permittivity in a plasma with an arbitrary ionic charge

Based on the solution of a linearized kinetic equation for electrons with a Landau collision integral, we develop a theory of electron transport for small perturbations in a completely ionized plasma with an arbitrary ionic charge that is free from any constraints on the characteristic perturbation time and length scales. We calculate the potential and vortex electron fluxes for an arbitrary electron collision frequency that allow the spatial and temporal nonlocal transport to be described. We also derive expressions for the longitudinal and transverse electron permittivities of a collisional plasma with an arbitrary ionic charge that are suitable for describing the plasma response to small perturbations with an arbitrary frequency and wave vector. Using the transverse permittivity, which allows the absorption of an electromagnetic wave to be described in the entire range of plasma parameters (from the strongly collisional to the collisionless one), as an example, we provide a detailed comparison with previously known models.     

Vacuum polarization and color charge shielding in the external source problem of QCD2 with massless quarks

An approximate treatment of vacuum polarization in the external source problem of two-dimensional QCD with massless quarks is proposed. The static response to a static external source is determined with and without vacuum polarization. In the former case and if the gauge group is SU(2), a static solution is obtained only if the external source is essentially abelian. Complete shielding of the external charge sets in with the screening length equal to the inverse of the Schwinger mass. This shielding is enforced for special, self-screening external charges.     

On existence of the spatial charge layers in plasma with regions of rapid growth of the ionization rate

1D quasi-static self-consistent model of nonequilibrium nitrogen and oxygen plasma with highly non-uniform spatial distribution of the electric field strength is used for analysis of the correlation of ionization rate profile and charged particles profiles. It is shown that inside a region of local increase of the ionization rate the layers with violation of quasi-neutrality can exist. This leads to the appearance of local static electric fields. Special attention is devoted to plasma resonance regions in microwave plasma. The role of negative ions is also studied.     

High-voltage pulsed discharge in an electron source with a plasma cathode

The nature of and mechanism for producing a high-voltage discharge in an electron source with a plasma cathode are investigated. The possibility of generating pulsed electron currents with an amplitude of 10³–10⁴ A and a length of 10^–6 sec is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 117–121, October, 1973.The authors thank B. M. Koval'chuk for help in developing the experimental arrangement and G. A. Mesyates for constant attention to the work and discussion of the results.     

Frequency upshifting by an ionization front in a magnetized plasma

The interaction of a light wave with a relativistic ionization front in the presence of an applied DC magnetic field which is perpendicular or parallel to the incident wave is considered. In both cases, four transmitted modes are generated in the magnetized plasma by an incident linearly polarized wave. The frequency upshifts of the various modes are calculated and compared to the unmagnetized case. The corresponding reflection and transmission coefficients are also obtained. Finally, the density ripple associated with the free streaming mode in a magnetized plasma for the perpendicular case is discussed     

Effect of an external resonator on the space charge dynamics in a semiconductor superlattice

The dynamics of a semiconductor superlattice in an external resonator is studied. It is shown that the external electrodynamic system considerably complicates the behavior of the superlattice by exciting random oscillations and leads to additional negative differential conductivity in the I–V characteristic that is not observed in an autonomous system.     

Seismoelectric waves in a borehole excited by an external explosive source

The conversion of energy between seismic and electromagnetic wave fields has been described by Pride’s coupled equations in porous media. In this paper, the seismoelectric field excited by the explosive point source located at the outside of the borehole is studied. The scattering fields inside and outside a borehole are analyzed and deduced under the boundary conditions at the interface between fluid and porous media. The influences of the distance of the point source, multipole components of the eccentric explosive source, and the receiving position along the axis of vertical borehole, on the converted waves inside the borehole are all investigated. When the distance from the acoustic source to the axis of a borehole is far enough, the longitudinal and coseismic longitudinal wave packets dominate the acoustic and electric field, respectively. The three components of both electric field and magnetic field can be detected, and the radial electric field is mainly excited and converted by the dipole component. Owing to the existence of borehole, the electric fields and magnetic fields in the borehole are azimuthal. The distance from the point where the maximum amplitude of the axial components of electric field is recorded, to the origin of coordinate indicates the horizontal distance from the explosive source to the axis of vertical borehole.