On the possibility of terahertz wave generation upon dense gas optical breakdown

The possibility of applying the physical principles underlying the operation of a solid-state terahertz oscillator to plasma gas-discharge media is analyzed. A new method of electromagnetic wave generation in the terahertz frequency range is proposed. It is based on the excitation of plasma-oscillation current by a static electric field in a laser spark produced by an axicon lens, followed by the radiation of an electromagnetic pulse through the Cherenkov mechanism.     

Dynamics of an RF Discharge in a Magnetic Field under Strong Initial Preionization

We demonstrate experimentally the possibility to create and sustain a strongly ionized plasma at low gas pressures by the electromagnetic radiation of the intensity which is below the conventional breakdown level. The conditions of ignition and sustaining the plasma are found, and the plasma parameters are measured. The necessary condition for the discharge formation is strong preliminary ionization of an initial gas. Significant electron heating in the RF field, which ensures the effective gas ionization takes place due to Coulomb collisions with protoplasma ions. Such collisions are much more frequent than the electron-neutral collisions. We propose a qualitative analytical model of the discharge evolution, which describes the effects observed.     

One characteristic property of the commutator subgroup of a painted braid group

Translated from Matematicheskie Zametki, Vol. 45, No. 2, pp. 113–117, February, 1989.     

Third-order effects in the propagation of elastic waves in isotropic solids generation of higher harmonics

The nonlinear interactions of longitudinal and shear waves in an isotropic solid medium are discussed in the nine-constant theory of elasticity. Expressions are obtained describing the generation of second and third harmonics of elastic waves in the approximations of a non-dispersive medium and in the presence of quasistatic elastic fields.     

On the quasioptical approximation in dissipative media with spatial dispersion

A new form of the quasioptical equation is proposed to describe the propagation of an electromagnetic wave beam in a stationary smoothly inhomogeneous medium with spatial dispersion and dissipation. The proposed approach guarantees the positive definiteness of the absorbed power in the locally dissipative medium, which is a nontrivial property for inhomogeneous media with spatial dispersion. An efficient numerical scheme is constructed to solve the derived quasioptical equation.     

On the Effect of Small-Angle Scattering by Density Fluctuations on the Efficiency of Linear Transformation of Ordinary and Extraordinary Waves in a Toroidally Inhomogeneous Plasma

We have analyzed the efficiency of tunneling of quasi-optical wave beams through the evanescent region in the vicinity of plasma cutoff in a randomly inhomogeneous magnetoactive plasma. A new theoretical model proposed here makes it possible to study the effect of a random phase modulation induced by density fluctuations in the wave beam path on the efficiency of the linear transformation of waves in the 2D geometry corresponding to the experimental conditions for heating the overdense plasma in toroidal magnetic systems. We have derived a general analytic expression connecting the wave beam coefficient of transformation averaged over the ensemble of random wave field realizations with its phase correlation function. We have analyzed the dependence of the coefficient of transformation on the correlation length for the random phase distribution in the beam and on the traversed path length to the interaction region. The threshold value of the path length above which the fluctuations produce a dominating effect has been determined. The importance of taking into account the 2D effects has been demonstrated.     

Extreme Ultraviolet Radiation Source Based on a Discharge Sustained by a Radiation Pulse from a Terahertz Free-Electron Laser

Journal of Experimental and Theoretical Physics - We consider the possibility of sustaining a discharge in xenon efficiently emitting light in a wavelength range of 11.2 nm ± 1% by a...     

Quasi-optical simulation of the electron cyclotron plasma heating in a mirror magnetic trap

The resonance microwave plasma heating in a large-scale open magnetic trap is simulated taking into account all the basic wave effects during the propagation of short-wavelength wave beams (diffraction, dispersion, and aberration) within the framework of the consistent quasi-optical approximation of Maxwell’s equations. The quasi-optical method is generalized to the case of inhomogeneous media with absorption dispersion, a new form of the quasi-optical equation is obtained, the efficient method for numerical integration is found, and simulation results are verified on the GDT facility (Novosibirsk).     

Theory of a stationary microwave discharge with multiply charged ions in an expanding gas jet

The formation of a jet of a nonequilibrium multiply charged ion plasma is studied in the inhomogeneous gas jet. It is shown that the geometrical divergence of the jet restricts the maximum ion charge state and results in the spatial localization of the discharge. Stationary solutions corresponding to such regimes are constructed. The model proposed can be used to optimize modern experiments on generation of hard UV radiation due to the line emission of multiply ionized atoms in a gas jet heated by high-power millimeter and submillimeter radiation.     

Focusing of Divergent Cylindrical Waves and the Prospects for Borehole Acoustics

This paper discusses prospects for borehole acoustics associated with the use of focused fields. The possibility of developing efficient borehole methods for testing nonlinear characteristics of natural deposited geological environments is studied. The potential of improving geotechnological processes using focused fields induced by extended borehole antennas is considered. The results of a pilot experiment on acoustic-field stimulation of underground leaching of less-common metals are presented.