Nonlinear theory of beam excitation of azimuthal surface modes in plasma-filled cylindrical metal waveguides

It is shown that electromagnetic surface waves propagating along the azimuthal angle can be excited efficiently by an annular electron beam in a cylindrical metal waveguide partially filled with a magnetoactive plasma. A self-consistent system of differential equations is obtained to describe the nonlinear interaction between the beam particles and an azimuthal surface wave in the single-mode regime. This system of equations is analyzed numerically and the influence of the parameters of this waveguide structure on the development of the resonant beam instability is determined. Zh. Tekh. Fiz. 69, 84–88 (July 1999)     

Degenerate slightly nonideal Bose gas in a parabolic trap

The correction to the energy and the number of particles in excited oscillator states is found in the approximation of a pair interaction between the particles at close to zero temperature. It is shown that in the case of the traps used in experiments the gas starts to differ appreciably from an ideal gas when more than N=1000 particles are trapped. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 228–231 (25 August 1997)     

Analysis of the conditions for ultradeep penetration of powder particles into a metallic matrix

The critical conditions for ultradeep penetration of particles when a flux of high velocity particles interacts with a matrix material are examined from the standpoint of nonequilibrium thermodynamics. The problem of the change in entropy consistent with their deformation during loading is solved qualitatively for the example of aluminum and copper samples. It is shown that ultradeep penetration of particles is a system process of mass and energy transfer owing to a developed instability in the material caused by the shock-wave action of the particle flux. The degree of disequilibrium of the process is described by the dependence of the change in entropy on the deformation of the matrix material. It turns out that the ultradeep particle penetration process occurs only in a region lying beyond a bifurcation point. Zh. Tekh. Fiz. 68, 124–125 (July 1998)     

Multiply-charged magnetoexcitons in low-dimensional structures

The frequencies and intensities of absorption lines of a “hole + Nelectrons” complex in a magnetic field are found. The motion of all particles is assumed to be two-dimensional, and the electron and hole quantum wells are assumed to be spatially separated. It is shown how Kohn’s theorem can be extended to the case of a system with a finite total mass. The energy of a N-electron complex in a quantum ring oscillates as a function of the magnetic flux with a period that depends on N and the ratio of the masses. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 423–427 (25 September 1997)     

Nuclear pumping of a carbon monoxide laser

It is shown that plasma-chemical processes involving ionized and excited particles can make the main contribution to the pumping of energy into vibrations of carbon monoxide molecules. It is noted that the use of helium as a buffer gas in the active laser medium is not optimal. The employment of argon instead of helium permits a 1.5-fold increase in the efficiency of the pumping of energy into carbon monoxide molecules and an order-of-magnitude decrease in the threshold energy for pumping the active medium. Zh. Tekh. Fiz. 68, 80–85 (July 1998)     

Solitons in semiconductor microstructures with a two-dimensional electron gas

Nonlinear waves in a two-dimensional electronic plasma with metal screening gates are investigated. It is shown that solitons described by the KdV equation exist in such a system. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 479–481 (10 October 1999)     

Induction mechanism of cosmic ray production and kinks in the cosmic ray spectrum

Two kinks are observed in the energy spectrum of galactic cosmic rays. It is shown that the entire spectrum can be described, to a good approximation, by a single formula obtained on the basis of the hypothesis that the particles are produced and accelerated in plasma pinches by an induction mechanism under the assumption that three hierarchical groups of currents are present—interstellar, galactic, and metagalactic. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 225–230 (25 August 1996)     

Toward a nonlinear theory of acceleration of charged particles in a linearly polarized EH-ubitron field

The motion of charged particles in a linearly polarized EH-ubitron field with sinusoidal time dependence of the variable component of the magnetic field is investigated. It is shown that, depending on the parameters of the system and the initial conditions of entry of the particle into the EH-field region, three different types of motion are possible: ballistic motion, capture in the vicinity of one of the maxima of the magnetic field, and escape of particles from the EH-field region. An analytical expression is found for the criterion determining the type of motion of the particles, along with analytical solutions for the energy of the particles in the approximation of slow variation of the magnetic field amplitude in time. Peculiarities of the motion of the particles in EH fields with arbitrary rate of change of the magnetic field amplitude in time are investigated numerically. Zh. Tekh. Fiz. 69, 87–93 (January 1999)     

Radiation of slow electromagnetic waves in an isotropic medium with spatial dispersion

This paper discusses the distinctive features of radiation of electromagnetic waves with anomalously large values of the wave vector and small phase velocity that exist near narrow absorption lines. The distribution of radiated energy with respect to angle and frequency is calculated for Čerenkov radiation and bremsstrahlung of the slow waves. It is shown that the angular distribution of the slow-wave bremsstrahlung exhibits a characteristic maximum in the direction perpendicular to the plane of motion of the particles. Zh. éksp. Teor. Fiz. 112, 1557–1562 (November 1997)     

Stochastic heating of plasma at electron cyclotron resonance

It is shown theoretically and experimentally that stochastic heating of plasma electrons is highly efficient. Calculations have shown that over the course of 100 periods of an external microwave field the kinetic energy of the particles reaches values of around 1.0 MeV and the average energy reaches values of the order of 0.3 MeV in the field of two oppositely propagating characteristic (eigen) waves of a cylindrical waveguide, with amplitudes 24 kV/cm in a 1 kG stationary magnetic field. Stochastic instability develops as a result of overlapping of non-linear cyclotron resonances. The experimental results agree with the theory: When these waves are excited by a 0.9 MW external source, above a threshold of 0.45 MW one obtains x rays with a photon energy corresponding to a maximum electron energy of the order of 1 MeV over about 800 periods of the external microwave field. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 806–811 (10 June 1999)     

Some effects of the electrostatic interaction of water drops in the atmosphere

The electric field at the surface of two conducting spherical charged particles and their interaction force are calculated. It is shown that as particles carrying like charge approach each other, the force changes sign and becomes attractive. The case where the charge on each particle varies as the square of its radius is an exception (repulsion at any distance between the particles). Self-similar asymptotic solutions for the interaction force and energy are found for particles of identical size. For a pair of charged water drops falling simultaneously in the atmosphere, a numerical simulation shows that a drop formed by coalescence of the pair may be subject to the Rayleigh instability. Zh. Tekh. Fiz. 69, 12–17 (December 1999)     

A theory of the magnetic susceptibility of composites

The absorption of ac magnetic field energy by nonconducting composites made with fillers consisting of microscopic magnetic inclusions with various shapes is investigated over a wide range of frequencies and temperatures. It is predicted that the temperature dependence of the susceptibility χ(ω,T) of these structures is nonstandard only when the interaction between particles of the finely dispersed phase is included. The effect of the magnetic particles is taken into account by introducing a stochastic force into the Boltzmann equation, and using the resulting equation to calculate the susceptibility χ, which is a complicated function of the concentration p of the added dispersed phase. It is shown that the susceptibility should have a singularity near the point p=p _cr. Fiz. Tverd. Tela (St. Petersburg) 39, 1622–1627 (September 1997)     

Dynamic fractal structure of emulsions due to motion and interaction of the particles: Numerical simulation

The method of numerical simulation is used to study the geometrical structure of micro-emulsions in the plane. It is found that the interaction between the particles leads to the formation of a dynamic homogeneous fractal structure of the micro-emulsion. In the absence of any interaction between the particles the structure of the emulsion is homogeneous. The interaction energy of the particles at which the fractal inhomogeneity arises is close in magnitude to the interaction energy of the particles in real (e.g., aqueous) micro-emulsions. It is also found that the size of the inhomogeneities (correlation radius) depends on the particle density in the system and is largest for the density of the percolation transition. The numerical simulation data qualitatively coincide with the results of measurements in real micro-emulsions. Zh. éksp. Teor. Fiz. 111, 1314–1319 (April 1997)     

Nonexponential temperature dependence of the rate of threshold inelastic processes in dense media

The influence of the density of the medium on the temperature dependence of the rate constants of inelastic processes is investigated. It is shown that besides the effects like lowering of the ionization potential, which accelerate excitation and ionization processes in a nonideal plasma, there is a stronger mechanism for such acceleration, which is associated with the high frequency of collisions between particles and leads to destruction of the one-to-one relation between the energy and momentum of the particles in a dense medium. It is manifested by the presence of power-law tails in the equilibrium momentum distribution of the particles, which leads to a nonexponential temperature dependence of the rates of inelastic reactions in dense gases and nonideal plasmas. A kinetic equation for the generalized energy and momentum distribution function of electrons in an external electric field, which permits investigation of the effect under consideration under nonequilibrium conditions, is presented. Zh. éksp. Teor. Fiz. 113, 1661–1674 (May 1998)     

Choice of conditions of an electrical discharge for generating chemically active particles for the decomposition of impurities in water

An electrical discharge between a liquid surface and an electrode positioned above it is considered. A second electrode, which delivers the output from a high-voltage source, is located at the bottom of the vessel containing the liquid. The conditions that must be met by the electrical discharge in order to efficiently initiate reactions in the liquid phase are analyzed. Under these conditions the number of active particles generated by the discharge turns out to depend on the concentration in the liquid of the substance with which the active particles interact. It is shown that for a corona or spark discharge the reactions can occur in a liquid layer 10–20 mm thick and that for specific reactions there exists an optimum value of the electric field at which the energy expenditures on the initiation of the reaction will be minimum. Zh. Tekh. Fiz. 69, 58–63 (January 1999)     

Electron clouds around charged particulates

Poisson’s equation is used to derive an expression for the characteristics of the Debye electron cloud around a multiply charged particle. It is shown that the limiting dimension of the Debye cloud (for an infinitely large charge of the particles) varies from 0.7 to 2.2 Debye radii, depending on the geometry of the problem. A first-principles modeling of the dynamics of many electrons moving around an immobile charged center is carried out. It is shown that a metastable state which relaxes at least one thousand times more slowly than would follow from the kinetic theory is established. Calculations show that in this metastable state (which is far from thermodynamic equilibrium) there is a detailed balance of electron transitions from a state with one energy to another. The distribution of electrons over kinetic energy has a Maxwellian form, while the distribution over total energy is radically different from the Boltzmann distribution and is close to that which was established previously by the authors for a plasma of singly charged ions. The potential distribution around the immobile charge in the metastable plasma is obtained. Zh. Tekh. Fiz. 69, 53–57 (January 1999)     

Detection of very high energy cosmic rays by the UTR-2 decameter telescope

The author believes that the method of radio detection of 10²²–10²³ eV cosmic rays can be revived. The proof will be the detection of electromagnetic pulses produced by the passage of particles with such energy through the surface of the moon. It is shown that the amplitude of the radio signal attesting to this event will be two orders of magnitude greater than the gallactic noise, if the antenna of the UTR-2 decameter radio telescope (Khar’kov) is used for this purpose. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 639–641 (25 November 1999)     

Quantum kinetic Boltzmann equation taking into account the resonant exchange of excitations

A derivation of the quantum Boltzmann equation is given for identical particles with internal degrees of freedom. It is shown that the off-diagonal (with respect to the internal degrees of freedom) term of the equation contains an energy pole term, which is not present in the most commonly used kinetic equation, known as the Waldmann-Snider equation. The physical conditions underlying the occurrence of the pole term in the quantum kinetic equation are analyzed. Zh. éksp. Teor. Fiz. 111, 831–837 (March 1997)     

Electrostatic energy of a disordered system of metallic granules

Electrostatic interaction energies in a disordered monodisperse system of metallic granules are calculated. The calculation is performed in the dipole approximation for particles that cannot be regarded as point charges. The dependences of the charging energies of the particles on the concentration of the metallic phase as well as the dependences of the interaction energy of the charged particles on the distances between them are obtained. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 100–105 (25 July 1999)     

Formation and magnetic properties of fractal aggregates of cobalt

Macroscopic fractal aggregates of cobalt are obtained by thermal evaporation of cobalt metal in an argon atmosphere and subsequent deposition on a silicon substrate heated to 1000 K. It is established that the fractal structure is formed by diffusion-limited aggregation of cobalt particles. The macroscopic fractal cobalt aggregates are ferromagnetic. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 8, 556–558 (25 October 1997)