E. D. Gospodchikov

On the influence of 2D inhomogeneity on electromagnetic mode conversion near the cut-off surfaces in magnetized plasmas

Most of the analytical results in the theory of OX conversion are obtained in a slab geometry, in which the magnetic field is uniform and 1D spatial inhomogeneity is related to a constant plasma density gradient. An extended analytical study of the OX wave coupling in 2D geometry has been performed previously in our works, which are briefly summarized in the current communication.

Interpretation of complex patterns observed in the electron-cyclotron instability of a mirror confined plasma produced by an ECR discharge

A specific nonlinear regime of electron-cyclotron instability is discussed aimed at explaining the complex temporal patterns of stimulated electromagnetic radiation from a mirror trap with a non-equilibrium plasma typical of an ECR discharge. This regime is characterized by self-modulation of a plasma cyclotron maser due to coherent interference of two counter-propagating unstable waves with degenerate frequencies resulting in the spatial modulation of the amplification coefficient. The proposed simple theoretical model allows one to reproduce the multi-scale time behavior of quasiperiodic pulses of electromagnetic radiation and related precipitation of energetic electrons detected in a laboratory setup based on a magnetic mirror trap with a plasma sustained by mm-wave gyrotron radiation.

On perfect O–X mode conversion near the cut-off surfaces in magnetized plasmas

Recently the theory of linear coupling between the ordinary (O) and extraordinary (X) electron cyclotron waves in the vicinity of critical (cut-off) plasma density was generalized for two-dimensionally inhomogeneous plasma configurations, in particular taking into account the variation of a magnetic field on flux surfaces in tokamaks and stellarators. One of the new features of two-dimensional mode conversion is the existence of optimal quasi-optical beams of a finite aperture exhibiting perfect (no reflection) transformation instead of an optimal plane wave specific for one-dimensional geometry. In this paper such wave structures are analysed in more detail keeping in mind its importance for experiments on electron cyclotron resonance heating and diagnostics of overdense magnetized plasma based on linear mode conversion in modern stellarators and spherical tokamaks.

On O?X mode conversion near the cut-off surfaces in 3D sheared magnetic field

The linear coupling between ordinary and extraordinary electron cyclotron waves in the vicinity of the cut-off plasma density is discussed, taking into account variation of a magnetic field on flux surfaces in tokamaks and stellarators. Previously developed theory of two-dimensional mode conversion is applied to study the effects of the poloidal magnetic field and its shear, in particular, on the efficiency of penetration of quasi-optical beams through the evanescent layer due to transformation into a cross mode.

On the structure of wave fields in the region of linear interaction between ordinary and extraordinary waves in two-dimensionally inhomogeneous magnetoactive plasmas

The linear interaction between ordinary and extraordinary waves in two-dimensionally inhomogeneous magnetoactive plasmas in the electron-cyclotron frequency range is considered. Exact solutions of the reduced wave equation that describes the wave fields in the region of linear interaction are obtained. A procedure is determined for recalculating the fields that pass through and reflect from the transformation region. The field distributions in the transformed and reflected beams are studied analytically for various incident beams. The results may be considered as a solution of a new standard problem with a wide range of astrophysical and laboratory applications.

Impact of poloidal curvature on linear mode conversion of quasi-optical wave beams in tokamak plasmas

A theory of ordinary and extraordinary wave coupling in the electron cyclotron frequency range in inhomogeneous magnetized plasmas of a toroidal magnetic trap is reconsidered. Reduced wave equations are studied taking into account the poloidal curvature of the magnetic flux surfaces in a tokamak geometry. Based on these equations, the wave field distributions in the vicinity of the coupling region are found in a semi-analytical form. Non-one-dimensional effects of the flux surface curvature on the mode-conversion efficiency in tokamak plasmas are identified and analyzed.

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.

On the determination of the electromagnetic field upon scattering by a small inhomogeneous spherical object

An efficient and fairly simple method of solving the problem of the incidence of a plane electromagnetic wave on an inhomogeneous object with specified spherically symmetric distributions of its electric permittivity and magnetic permeability is presented. The fields inside the object and the integrated scattering and absorption cross sections are found by assuming the object to be small compared to the vacuum wavelength. Since no constraints are imposed on the scales of the fields inside the object, the method is suitable for investigating complex cases, including those associated with the local amplification and absorption of the electromagnetic field in inhomogeneous resonant media.

Effect of Flux Surface Curvature on the Linear Coupling of Electron Cyclotron Waves in Tokamak Plasmas

Specific features of the linear interaction of ordinary and extraordinary electromagnetic waves in the electron cyclotron frequency range in a nonuniform plasma confined in a toroidal magnetic trap are considered. Reduced wave equations taking into account the curvature of the cut-off surfaces in toroidal geometry are formulated. Using these equations, the distributions of the wave fields in the coupling region are analyzed. A method for calculating quasi-optical beams passed through the region of linear wave interaction is proposed.

On Influence of 2D Inhomogeneity on Electromagnetic Mode Conversion Near the Cut_Off Surfaces in Magnetized Plasmas

Most of the analytical results in the theory of OX conversion are obtained in a slab geometry, in which the magnetic field is uniform and 1D spatial inhomogeneity is related to a constant plasma density gradient. An extended analytical study of the OX wave coupling in 2D geometry has been performed previously in our works, which are briefly summarized in the current communication.