Nonlinear nonstationary Alfvén resonance in a finite-pressure plasma

A nonlinear equation for a resonant Alfvén disturbance in a finite-pressure plasma is derived and matching conditions for a fast magnetosonic wave are obtained. The evolution of the resonant disturbance and the rate of resonant energy absorption are calculated for two cases: when the source is switched-on exponentially and instantaneously. It is shown that the evolution to a nonlinear regime is accompanied by the stratification of the resonant disturbance and the average plasma parameters at a progressively decreasing spatial scale. Essential properties of the nonlinear resonant disturbance are the nonlinear saturation of its amplitude, the displacement of the resonance layer, and the disappearance of resonant energy absorption.     

Resonance of the Larmor drift with plasma oscillations

Resonance phenomena arising when the Larmor drift velocity is locally equal to the phase velocity of plasma oscillations are analyzed. It is shown that, in a plasma with a nonuniform temperature, the wavelength of the oscillations sharply reduces at the resonant point, so that the oscillations convert into small-scale waves. In a plasma with a uniform temperature, Coulomb collisions cause the oscillations to dissipate at the resonant point. It is noted that a resonance with the Larmor drift can be used to heat the plasma.     

Effect of Resonant Radiation Transport on the Parameters of RF and DC Discharges in a He-Ar-Xe Mixture

A study is made of the effect of the transport of Xe 147-nm resonant radiation on the parameters of a low-temperature plasma of DC and RF discharges in gas mixtures used as the working medium in lasers based on infrared transitions in xenon. RF discharges are treated in the planar geometry typical of slab lasers. DC discharges in tubes are treated in cylindrical geometry. The trapping of resonant radiation is described using different approximate models: the decay time approximation for a plasma slab (the Holstein approximation) and the effective lifetime approximation (the Biberman approximation). The transport equation for resonant radiation is solved numerically. The effect of the radiation transport on both the current-voltage characteristics of a discharge and the spatial distribution of the excited Xe atoms is investigated. The current-voltage characteristics calculated for a DC discharge with allowance for the resonant radiation transport agree well with the experimental characteristics. It is found that, for an RF discharge, the effective lifetime approximation overestimates the density of the excited Xe atoms near the electrodes by several times and underestimates this density at the midplane of the discharge gap.     

Influence of resonant charge exchange on the viscosity of partially ionized plasma in a magnetic field

The influence of resonant charge exchange for ion-atom interaction on the viscosity of partially ionized plasma embedded in the magnetic field is investigated. The general system of equations used to derive the viscosity coefficients for an arbitrary plasma component in the 21-moment approximation of Grad’s method is presented. The expressions for the coefficients of total and partial viscosities of a multicomponent partially ionized plasma in the magnetic field are obtained. As an example, the coefficients of the parallel and transverse viscosities for the ionic and neutral components of the partially ionized hydrogen plasma are calculated. It is shown that the account for resonant charge exchange can lead to a substantial change of the parallel and transverse viscosity of the plasma components in the region of low degrees of ionization on the order of 0.1.     

Resonant Laser-Assisted Process of Ultrarelativistic Electrons Bremsstrahlung in the Field of a Nucleus

Plasma Physics Reports - The scrutiny of the resonant laser-assisted bremsstrahlung (LAB) of ultrarelativistic electrons within the laser plasma ambience in the field of a nucleus is presented. The...     

Broadband Wide-Angle Second Harmonic Generation in Magnetized Plasma: Double Resonant Effect

Conditions for the phase synchronism between high-frequency electromagnetic waves with frequencies ω and 2ω propagating in magnetized plasma are investigated. The variety of the values of the plasma density and magnetic field, as well as of wave polarizations, obeying the synchronism conditions are shown to provide resonant broadband wide-angle nonlinear generation of the second harmonic of the pumping wave. Special attention is given to oblique propagation of interacting waves. The coupling strengths for the resonant mode conversion in magnetized collisional plasma are obtained. The double resonance ensuring efficient nonlinear generation of extraordinary mode in the vicinity of the electron cyclotron resonance (ω(2k) = ω _ce ) is considered. Examples illustrating these nonlinear phenomena for some plasma and radiation parameters are presented.     

Theory of the ICR heating of a plasma column: Methodological note

A set of wave equations is derived that describes electromagnetic waves at frequencies on the order of the ion gyrofrequency in a plasma column with an arbitrary electron temperature. This set takes into account, in particular, the resonant interaction of electrons with waves in the transit-time magnetic pumping regime. The effect of the amplification of the electromagnetic fields of current-carrying antennas by the plasma is analyzed. The evolution of the fields with an increase of plasma density from a zero value (vacuum) is considered. The main parameters are determined for minority ion cyclotron resonance heating in the planned EPSILON system.     

A possible mechanism for the generation and motion of blobs in tokamaks

A possible mechanism for the generation and motion of so-called blobs—peculiar perturbations that are observed in a tokamak edge plasma—is proposed. It is suggested that blobs are self-contracting plasma filaments generated either by the thermal-radiative instability of a plasma with impurities or by the nonradiative resonant charge-exchange instability resulting from the presence of neutral hydrogen atoms near the tokamak wall. Instability occurs in a narrow temperature range in which pressure is a decreasing function of density. Under these conditions, the most typical perturbations are the local ones that originate spontaneously in the form of separate growing hills and wells in the density. The temperature at the centers of the hills is lower than that in the surrounding plasma, but they are denser and, consequently, brighter than the background. The (denser) hills should move (“sink”) toward the separatrix, while the (less dense) wells should “rise” in the opposite direction, as is observed in experiments. It may even be said that they behave in accordance with a peculiar Archimedes' principle.     

Resonant effect of the noncircular shape of the plasma surface on the dispersion properties of extraordinary azimuthal surface modes in magnetoactive waveguides

A theoretical study is made of the resonant effect of the shape of the cross section of the plasma column on the propagation of a packet of extraordinary electromagnetic waves with a zero axial wavenumber in a circular-cross-section cylindrical metal waveguide in an axial magnetic field. The waveguide is assumed to be partially filled with a plasma. The effect of the noncircular shape of the plasma cross section on the dispersion properties of surface eigenmodes propagating strictly transverse to the external magnetic field is investigated by the method of successive approximations for the case in which the angular period of the wave perturbations is twice the ripple period of the interface between the plasma and the dielectric. In this resonant case, the fields and eigenfrequencies of the eigenmodes are determined to second order in the small parameter describing the rippling of the plasma-dielectric interface.     

The Role of Resonance Frequency of the Plasmons in Electromagnetic Wave Scattering Process from a Dielectric Covered Metallic Rod Placed in a Plasma Antenna

The electromagnetic wave scattering due to excitation of surface plasmons from a metallic rod with dielectric layer embedded in the long plasma column is investigated. In the first part, for short-wavelength waves by investigating the variations of surface polarized charge density on the boundaries, the resonance frequencies and the effective factors on it such as the geometrical dimensions, the radius of the metal, the dielectric thickness, and the plasma radius will be analyzed. In the second part, for presenting an exact analysis and categorizing types of resonant frequency to the dominant resonant frequency and subsidiary resonant frequency of the plasmons, the scattering of long-wavelength waves from the mentioned object will be reviewed. In both cases, the backscattering cross section which is a scale of the scattered power in the direction of incident will be presented.     

Excitation of growing wake waves by an electron bunch in a plasma in an intense pump wave

A study is made of the excitation of wake waves by a one-dimensional electron bunch in an electron plasma in the presence of an intense monochromatic pump wave with circular polarization. In the main state (in the absence of a bunch), the interaction between a pump wave and a plasma is described by Maxwell's equations and the nonlinear relativistic hydrodynamic equations for a cold plasma. The excitation of linear waves by a one-dimensional bunch is investigated against a cold plasma background. It is shown that, in a certain range of parameter values of the bunch, pump wave, and plasma, the excitation is resonant in character and the amplitude of the excited wake waves increases with distance from the bunch.     

Ca2+ ion transport through patch-clamped cells exposed to magnetic fields

The total current of Ca²⁺ ions through patch-clamped cell membranes was measured while exposing clonal insulin-producing β-cells (RINm5F) to a combination of DC and AC magnetic fields at so-called cyclotron resonance conditions. Previous experimental evidence supports the theory that a resonant interaction between magnetic fields and organisms can exist. This experiment was designed to test one possible site of interaction: channels in the cell membrane. The transport of Ca²⁺ ions through the protein channels of the plasma membrane did not show any resonant behavior in the frequency range studied. © 1995 Wiley-Liss, Inc.     

Normal Doppler effect in experiments on the interaction of relativistic electron beams with plasma: Plasma relativistic microwave amplifier

The Cherenkov interaction of a high-current relativistic electron beam with a spatially bounded plasma was studied experimentally. In the generation of electromagnetic radiation, an important role is played by the counterpropagating plasma wave produced due to the reflection from the end of the plasma column. It is shown that, at the resonant value of the magnetic field, the normal Doppler effect occurs and the amplitude of the counterpropagating wave decreases. This effect was used to design and create a plasma relativistic microwave amplifier in which 10% of the beam energy is converted into radiation. The radiation frequency is 9.1 GHz, and the radiation spectrum width (±0.17%) is determined by the microwave-pulse duration. The maximum radiation power is 100 MW, the gain factor being 32 dB.     

Error field amplification near the stability boundary of the modes interacting with a conducting wall

The effect is considered of the amplification of an external resonant error field near the stability boundary of the so-called resistive wall modes observed in the DIII-D tokamak. The analysis is performed in a standard cylindrical approximation. The model is based on Maxwell’s equations and Ohm’s law; therefore, the results of the analysis are valid for any large-scale modes interacting with a conducting wall. In contrast to earlier approaches, the model considers the resonant field amplification as a dynamic effect. It is shown that, when the effect is the strongest, the stationary solutions proposed earlier are inapplicable. The problem of plasma response to a probing pulse of the resonant field of a given amplitude and duration is analyzed. The relationships obtained explain the basic features of the observed phenomena in the DIII-D tokamak and allow direct experimental verification.     

Electron density modulation in magnetic islands in the TUMAN-3M tokamak

MHD oscillations with m/n = 4/1 and 3/1 that arise at the periphery of the TUMAN-3M tokamak in the initial stage of a discharge are investigated. It is found that these oscillations lead to a significant modulation of the electron density n _e , which is attributable to the accumulation of plasma within a magnetic island. Numerical simulations of the modulation structure made it possible to determine the radius of the resonant surface and the radial width of the island and to evaluate the characteristic density gradient in the island. The gradient was found to be ten times larger than that of the unperturbed profile of n _e (r) near the resonant surface. This points to reduced plasma transport within the magnetic island.     

On the minimal set of plasma parameters to determine the dispersion law of electron whistler waves

The minimal sufficient set of plasma parameters is presented to describe the dispersion properties of electron whistler waves (helicons) in a wide frequency range above the ion cutoff frequency, provided that the wave frequency is significantly lower than the electron plasma frequency. When the gyrofrequency of the lightest ions is much higher than those of heavier ions, it is sufficient to know the relative content of the lightest ions, the highest ion cutoff frequency, the lower hybrid resonance frequency, and the electron gyro- and plasma frequencies. In this case, the frequency of electron whistler waves is determined by the upper root of the biquadratic equation derived, whereas the lower root corresponds to a resonant mode with its refractive index increasing when the frequency tends toward the highest ion gyrofrequency from below. The developed approach is also efficient in plasmas containing a substantial amount of negative ions and/or heavy dust particulates. The accuracy of the approximate solution of the total cold plasma dispersion relation is illustrated graphically.     

The linear model and experimentally observed resonant field amplification in tokamaks and reversed field pinches

A review is given of the experimentally observed effects related to the resonant field amplification (RFA) and the Resistive Wall Mode (RWM) instability in tokamaks and reversed field pinches (RFPs). This includes the feedback rotation of RWM in RFX-mod RFP, dependence of the RWM growth rate on the plasma-wall separation observed in JT-60U, appearance of the slowly growing RWM precursors in JT-60U and similar phenomena in other devices. The experimental results are compared with theoretical predictions based on the model comprising the Maxwell equations, Ohm’s law for the conducting wall, the boundary conditions and assumption of linear plasma response to the external magnetic perturbations. The model describes the plasma reaction to the error field as essentially depending on two factors: the plasma proximity to the RWM stability threshold and the natural rotation frequency of the plasma mode. The linear response means that these characteristics are determined by the plasma equilibrium parameters only. It is shown that the mentioned effects in different devices under different conditions can be described on a common basis with only assumption that the plasma behaves as a linear system. To extend the range of the model validation, some predictions are derived with proposals for experimental studies of the RFA dynamics.     

Present status of the theory of relativistic plasma microwave electronics

Theoretical research on high-power microwave sources based on stimulated emission from relativistic election beams in plasma waveguides and resonators is reviewed. Both microwave amplifiers and oscillators are investigated. Two mechanisms for stimulated emission—resonant Cherenkov emission from a relativistic electron beam in a plasma and nonresonant Pierce emission arising from the onset of a high-frequency Pierce instability—are studied theoretically. The theory developed here is motivated by recent experiments carried out at the Institute of General Physics of the Russian Academy of Sciences and is aimed at creating high-power pulsed plasma microwave sources [both narrowband (Δω/ω<0.1) and broadband (or noisy, Δω/ω≈1)] based on high-current relativistic electron beams. Although the paper is devoted to theoretical problems, all analytic estimates and numerical calculations are made with real experiments in mind and theoretical results are compared with reliable experimental data. Special attention is paid to the opportunity to progress to short (millimeter) and long (decimeter) wavelength ranges. Some factors that influence the formation of the wave spectra excited by relativistic electron beams in plasma sources are discussed.     

Physical plasma in biological solids: a possible mechanism for resonant interactions between low intensity microwaves and biological systems

Observed semiconductor properties of biological material in vitro indicate possible involvement of semiconduction in biological processes. Since in inorganic semiconductors solid-state plasma occurs, it is hypothesized that in organic semiconductors solid-state plasma similarly occurs. Some results of experimental investigation of resonant effects of microwaves in biological systems are considered in the light of that hypothesis. The conditions necessary for the existence of physical plasma in biological solid structures are discussed, and certain parameters of physical plasma in these structures are evaluated. Its is proposed that microwave radiation may support or damp plasma oscillations, thereby stimulating or suppressing biological functions.     

Determination of the resonant harmonics of the error field from dynamic magnetic measurements in a tokamak

The possibility is discussed of determining the amplitude and phase of a static resonant error field in a tokamak by means of dynamic magnetic measurements. The method proposed assumes measuring the plasma response to a varying external helical magnetic field with a small (a few gauss) amplitude. The case is considered in which the plasma is probed by square pulses with a duration much longer than the time of the transition process. The plasma response is assumed to be linear, with a proportionality coefficient being dependent on the plasma state. The analysis is carried out in a standard cylindrical approximation. The model is based on Maxwell’s equations and Ohm’s law and is thus capable of accounting for the interaction of large-scale modes with the conducting wall of the vacuum chamber. The method can be applied to existing tokamaks.