Parametric Instability of Surface Waves on the Second Harmonic of Electron Cyclotron Frequency in a Plasma Layer

The parametric instability of surface waves on the second harmonic of electron cyclotron frequency (SWCF) in a plasma filled dielectric wave guide is examined in a kinetic approximation. The studied surface waves are extraordinary polarized modes and propagate across the external steady magnetic field. The amplitude of the electrical pump wave is assumed to be small. Simple expressions for increments of the parametric instability of the SWCF are calculated. The otained results can be used in controlled fusion researches in order to avoid undesirable regimes of plasma periphery heating in that fusion devices which use the resonance electron cyclotron heating method.     

Instability of Electromagnetic Ion Cyclotron Harmonic Waves in Plasmas

The stability of electromagnetic ion cyclotron harmonic waves propagating normal to an external magnetic field is studied for plasmas whose ions possess loss cone type velocity distributions. It is found that, if the ions are stationary, no instability develops except in the extreme case when the ratio of parallel to perpendicular "temperatures" of the ions is of the order mi/me, where mi and me are the ion and electron masses respectively. However, for the case of two counterstreaming ion beams in a neutralizing background of electrons, instability at zero frequency and near the first several ion cyclotron harmonics can occur if the streaming velocity is of the order of the electron thermal speed.     

Finite Temperature and Wall Effects on the Absorption of Electron Cyclotron Waves in an EBT Plasma

The absorption of electron cyclotron waves propagating along an externally applied magnetic field in a uniform plasma surrounded by a cylindrical metallic cavity wall is studied. In the model, the cavity wall, the vacuum-plasma interface, and the effects of finite electron temperature are considered, and the dispersion relation for the wave propagation is derived. The results are then applied to the ELMO Bumpy Torus (EBT-I) plasma, and the propagation characteristics are computed. The wave absorption in the ordinary mode is found to be a result of the wall effects, which cannot be predicted with the infinite plasma theory. The loaded quality factor QL is also estimated from the model to be about 14, which is in good agreement with the experimentally observed value.     

Low-Threshold Parametric Excitation of Electron Plasma Waves Localized in the Edge Transport Barrier of a Tokamak during Electron Cyclotron Resonance Heating of a Plasma

JETP Letters - The possibility of the localization of longitudinal waves in the intermediate frequency range in the edge transport barrier of a toroidal nuclear fusion facility is discovered. It is...     

Electrostatic Waves in the Warm Magnetoplasma at the Cyclotron Harmonic Frequencies

Mode conversion and collisionless absorption of electromagnetic wave at the cyclotron harmonic frequencies in an inhomogeneous non-Maxwellian magnetoplasma have been studied. Under suitable energy transfer condition the converted electrostatic wave (plasma wave) either grows or damps. The expressions for the growth/damping rates of this wave have been derived and studied at the cyclotron harmonic frequencies. The effect of the temperature anisotropy on the growth/damping rate of the electrostatic wave at the second cyclotron harmonic frequency has been shown. Growth of such electrostatic waves at ionospheric heights may explain the observed upper hybrid resonance (UHR) echoes and noise bands at the second cyclotron harmonic frequency.     

An Experimental Investigation of Second Harmonic Generation in a Cyclotron and Upper Hybrid Resonant Plasma

An experiment is described in which an electromagnetic wave (extraordinary mode) is propagated across a magnetized plasma and second harmonic generation is detected. The generation of the plasma and the second harmonic wave is associated with resonant conditions of electron cyclotron resonance and upper hybrid resonance. By adjusting the intensity of axial magnetic field, the second harmonic generation can be made solely due to the electron cyclotron resonance, the upper hybrid resonance or both. The experiment is qualitatively in agreement with previous similar experiments and can be explained in terms of the spatial variations of the magnetic field intensity and the electron number density. A technique for diagnosing peak number density is developed from the observed second harmonic power characteristics.     

Electromagnetic Excitation of the Discharge and Optical Absorption in Sulfur Vapor

The light emission spectra of a discharge excited by the high-frequency and microwave radiation sources in mixtures of sulfur with buffer gas (argon or neon) were experimentally studied. Various stages of changing the characteristic spectra in the process of discharge development were revealed. The temperature dependences of the absorption spectra of sulfur saturated vapor were measured up to 1000 K. A linear shift of the absorption line from the violet to the green region with temperature was found. The absorptivity rises steeply and reaches of 3 cm^-1 at T=1000 K. The analysis shows that the same temperature dependence is observed for the maximum of the emission line. The filtering of light by colder sulfur vapor in the vicinity of the walls is supposedly responsible for the increase in the optical absorption at shorter wavelength. This explains the nontrivial increase in the wavelength of maximum of the spectral radiant intensity with temperature.     

On the Possibility of Strong Anomalous Absorption of Microwaves in Experiments on Electron Cyclotron Plasma Heating at the Second Resonance Harmonic

JETP Letters - It has been shown that more than two thirds of the pumping power can be transmitted to the upper hybrid waves localized near the local maximum of the plasma density as a result of...     

A Numerical Study on Current Drive by Electron Cyclotron Waves in a Toroidal Plasma Device

A survey of the main features of ECR current driving in toroidal plasmas is presented. Numerical calculations are performed in order to obtain the spatial profiles of the ECT energy deposition and of the correlated current density as a function of temperature and of the direction of the wave vector with respect to the toroidal magnetic field. The results indicate a very strong dependence of the ECR absorption profiles and of the driven current densites on the direction of launching of the wave.     

Plasma Maser Theory of Whistler Waves in the Presence of Ion Cyclotron Turbulence

In this paper we consider the plasma maser theory of whistler waves in the presence of ion cyclotron waves in a magnetized plasma. In a plasma with low frequency ion cyclotron turbulence and a high frequency test whistler wave, growth of the whistler wave takes place because of the turbulent bremsstrahlung interaction between the resonant electrons and the modulated electric fields. The growth rate of the whistler wave is calculated and the results discussed.     

Impurity Driven Linear and Nonlinear MHD Cylindrical Waves in a Three Species Plasma

The propagation of axisymmetric linear and nonlinear dispersive waves in a three species plasma to include the thermoelectrostatic effects together with the dissipative effects of main ions has been discussed. The impurity driven MHD fluid modes have been examined when the electrostatic drift has been taken into account. We have discussed the linear propagation of dispersive cylindrical waves in the plasma system for different ion thermal phase number. The thermal force resulting from the collisions between main ion and impurity ion densities (i.e. α_iI = 0) has been neglected. The shock waves and the soliton solutions are obtained for two different cases of the non-collisional plasma and the non-dissipative plasma.     

Excitation of Electron Plasma Waves by Beating Two Self-Trapped Laser Beams

This paper presents the detailed studies of the focusing of pump beams and the excited electron plasma waves(EPW) in a PBWA(Paema-Beat-Wave-Accelerator) by beating two self-trapped laser beams. The equations governing the saturated amplitude of EPW in nonuniform pump beams have been derived analytically. With these the condition for self-trapping of pump beams has been studied self-consistently. The optimum frequency mismatch parameter and the corresponding optimum initial plasma density as well as the maximum amplitude of the EPW have been obtained analytically. The transverse distributions of the EPW for Gaussian pump profile have been calculated numerically and show peculiar characteristics for certain frequency mismatch parameters. In addition, the effect of the radial component of the EPW on the bunch of accelerated particles in PBWA has been briefly discussed.     

Optical Fiber Excitation of Fano Resonances in a Silicon Microsphere

In this article, Fano lineshape whispering gallery modes were observed in the light scattering spectrum of a silicon microsphere in near-infrared telecommunication wavelengths. A simple model is presented to explain the transition from Lorentzian lineshape to the Fano lineshape resonances with the coupled-mode theory of multiple whispering gallery modes. Polar mode spacing of 0.23 nm is observed in the spectra, which correlates well with the calculated value. The quality factor of the Lorentzian and Fano resonances are on the order of 10⁵. By using an appropriate interface design for the microsphere coupling geometries, Fano lineshape optical resonances herald novel device applications for silicon volumetric lightwave circuits.     

Scattering and Absorption of Electromagnetic Waves in the Case of Excitation of Dipole Modes of a Spherical Particle

Radiophysics and Quantum Electronics - We compare the solution to the problem of scattering and absorption of a plane electromagnetic wave by a small spherical particle in the quasistatic dipole...     

The Generation of Current in Tokamaks by the Absorption of Waves in the Electron Cyclotron Frequency Range

The theory of current generation due to the absorption of high-frequency waves is developed for the case in which the propagation of the waves is described in the geometrical optics approximation. An expression for the current generated is obtained which is similar in fornn to the expression for the rate of energy deposition. This expression is incorporated in a toroidal ray tracing code to study current generation due to the absorption of waves in the electron cyclotron frequency range. The dependence of the current generated on temperature and angle of injection for the joint Naval Research Laboratory-Oak Ridge National Laboratory experiment on ISXB is studied.     

Excitation of the Potential Relaxation Instability in a Weakly Magnetized Discharge Plasma by a Voltage Step

An instability is triggered in a weakly magnetized discharge plasma by the application of a positive voltage step to a planar collector immersed into the plasma column with its surface perpendicular to the magnetic field lines. Time developement of the plasma density after the application of the pulse is measured by a Langmuir probe. Radial and axial velocity of the plasma density perturbation are measured. Radial velocity is consistent with the increase of the plasma potential in the current channel. Axial velocity is very high. It is interpreted as phase velocity of radial quasiperiodic motion of the plasma in and out of the current channel. Response time of the collector current to the applied voltage step is measured versus different parameters. Experimental results are in agreement with a qualitative model presented in previous work [1] where the observed instability is modeled as a two dimensional potential relaxation instability (PRI). Minor improvements of the previous model are proposed. A rarefaction pulse that moves towards the collector is found as the initial stage of the instability.     

Excitation of Nonsymmetric Waves by Given Sources in a Magnetoplasma in the Presence of a Cylindrical Plasma Channel

We consider the problem of excitation of electromagnetic field by spatially bounded, arbitrary given sources in a magnetoplasma in the presence of a cylindrical plasma channel aligned with an external magnetic field. We obtain a rigorous solution for the total field comprising both the discrete and continuous parts of the spatial spectrum of excited waves. Expressions for the radiation pattern and total radiation power of given sources are analyzed. For the whistler range, we calculate the radiation power of a ring electric current located in a channel with enhanced plasma density. It is shown that in this range, the presence of such a channel can lead to a significant increase in the radiation power of ring currents as compared with the case where the considered sources are immersed in a uniform background magnetoplasma, regardless of their orientation.