High Frequency Electric Field Research Articles

Electrohydrodynamic domain patterns in freely suspended layers of nematic liquid crystals with negative dielectric anisotropy

The electrohydrodynamic domain patterns observed in freely suspended layers of nematic liquid crystals with negative dielectric anisotropy are investigated. Two different domain patterns, in low and high frequency electric fields, occur. Both the director lines and the hydrodynamic flow lines associated with these patterns are investigated in detail. The threshold voltage of the instability is measured as a function of thickness and distance between the electrodes. The experimental results agree with a two-dimensional theoretical approach based on the Carr–Helfrich’s model.

Solitary Surface Waves in Plasmas Interacting with a High-Frequency Electric Field

We show that a solitary surface wave can exist at the boundary between a plasma and a dielectric, due to a balance between the nonlinear surface charge terms and the dispersive terms which here are caused by the presence of a high-frequency incident electromagnetic wave. The solitary wave propagation velocity, which depends on the intensity of the incident field, is also calculated.

Low frequency surface waves in the presence of an external high frequency electric field

The problem of surface sound propagation in the presence of external high frequency dipole electric field is investigated using Vlasov-Poisson equations. The structure of the electric field of these surface waves is also determined. It has been found that the ion sound waves that exist in the presence of external high frequency waves are true surface waves while those without the external field are quasi-surface waves as the former waves decay within one wavelength away from the surface.

Multimode theory and simulation of quasioptical gyrotrons and gyroklystrons

Very high power sources for millimeter wavelength radiation are desired for cyclotron heating of magnetic fusion devices. To meet this goal a quasioptical gyrotron has recently been proposed and analysed using a single mode approach. In this work, a more realistic analysis of the quasioptical gyrotron is carried out using multimode time-dependent simulations to study mode competition in a highly overmoded cavity. It is shown that with suitable contouring of the DC magnetic field, single mode operation at 30% or greater efficiency is possible. To further improve on efficiency, an alternative configuration, the quasioptical gyroklystron, is also analysed using multimode dynamic simulations. The gyroklystron is shown to lead to a significant increasing in efficiency (≈ 45%), particularly at moderate values for the high frequency electric field. Similar analyses of the quasioptical gyrotron and gyroklystron operating on the second harmonic have shown promising results ; efficiencies ≈ 30% have been obtained f...

Surface waves in the presence of external high frequency fields

The system equations of a collisionless, unmagnetized plasma, contained in a box where a high frequency (HF) electric field is incident, are solved in the electrostatic approximation. The surface modes of the plasma in the semi-infinite and box geometry are investigated. In thi high frequency limit, the mode frequencies are not significantly changed by the HF field but their group velocities can be quite different. Two long wavelength low frequency modes, which are not excited in the absence of HF field, are found. These modes are true surface modes (decaying on one wavelength from the surface) unlike the only low frequency ion acoustic mode in the zero field case. In the short wavelength limit the low frequency mode occurs at omega i/ square root 2, omega i being the ion plasma frequency, as a result similar to the case of no HF field.

Effect of an ac electric field on normal combustion rate of organic compounds in air

The present study attempts to develop a probable mechanism for the effect of a high frequency electric field on normal combustion rate of organic compounds in air. Several previous experiments were analyzed to concretize the mechanism by which the rate of reaction is changed. The experiments were performed under conditions of electric field strength and nitrogen molecule density such that highly efficient oscillatory excitation is realized. Replacement of nitrogen with argon in the original fuel mixture led to a significant decrease in the rise in combustion rate. Methane/air and methane/oxygen mixtures were tested in an electric field of frequency 6 mHz and intensity 1.67 kV/cm. Selective excitation of oscillatory levels of nitrogen molecules by electrons, with further transfer of oscillatory energy to oxygen molecules explains, in principle, the effect of an AC electric field on normal combustion rate. However, the required experimental and theoretical data for complete proof of the proposed mechanism are absent at present.

Surface instability of a current carrying plasma under the influence of a high frequency electric field

Surface instability of a collisionless semi-infinite current carrying plasma is studied. The semi-infinite plasma bounded by a plane surface is under the influence of a high frequency (hf) field. There are two classes of surface modes. One is a normal extension of zero high frequency field and the other due entirely to the presence ofhf field. As expected, with the increase in thehf field, the growth rates of the surface instabilities decrease. There are regions defined by the electron drift velocityu where the unstable surface and bulk regions overlap. The interesting result is that unlike the bulk plasma, there is a stable region on theu-axis flanked by two unstable regions. The width of this stable region increases with the increase in the field strength.

A differential displacement transducer for measuring relative movement in biological systems

This article describes a modified and improved version of the displacement transducer design originally presented by Sandeman (1968). The present design generates a high frequency electric field in the bathing solution. Relative displacement is detected within this field by measuring the differential voltage between two small diameter wire-sensing electrodes, which can be attached to different biological structures. By placing one of the sensing electrodes at a fixed point within the bath, absolute displacement can also be measured. A brief theoretical discussion and complete design are presented for the differential displacement transducer. The method presented here is more sensitive and versatile than the original approach.

Cellular spin resonance of aging yeast and mouse sarcoma cells

The way in which individual cells may be made to spin by the application of alternating electric fields is examined. The spinning of a given living cell is observed to respond rather sharply and in a resonant manner at several frequencies, hence the term "cellular spin resonance" (CSR). The frequencies of the applied field can be orders of magnitude higher than the actual spin rate. The CSR varies with the conductivity of the medium, with the square of the applied field, with the cell type and with the phase of the yeast cell life cycle. Living cells respond readily and individually are sharply resonant. Dead cells show little such response. From the behavior of the CRS in sinusoidal AC, as compared to pulsed DC, it appears likely that one cause of CSR, at least that in high frequency electric fields, is the presence of natural rf oscillations arising from the cells, and modulated by their high polarizability.

Effect of the Ponderomotive Force on a Plasma with Flow

The effect of the ponderomotive force on a plasma with flow is studied by controlling the velocity. The density of the plasma with flow velocity slower/faster than the ion acoustic velocity respectively decreases/increases by the ponderomotive force of the high frequency field. The density change is proportional to the square of the high frequency electric field intensity. The experimental results are compared with the theoretical ones calculated from the continuity and momentum equations, including a term of the ponderomotive force.

Suppression of localization effects by the high frequency field and the nyquist noise

It is shown that strong inelastic processes are not necessary for suppression of localization effects in disordered conductors. The influence of an external high frequency electric field on quantum corrections to conductivity is considered. Relatively weak fields are found to suppress localization. Thermal electromagnetic fluctuations act in the same way. These fluctuations lead to new dependences of localization effects in films and wires on temperature, impurity concentration and transversal size of the sample.

Influence of High Frequency Electric Field on the Dispersion of Ion-Acoustic Waves in Plasma

The modification of the ion-acoustic wave dispersion under the action of a high frequency electric field was studied experimentally, the wave propagating along and against the plasma stream. The frequency of the field amounted to approximately half the electron plasma frequency. It was found that the phase velocity of the ion wave and the plasma drift velocity decrease as the effective high frequency field power increases

Positron life times in helium gas

The life time of positrons in helium gas has been studied in the presence of high frequency electric and steady magnetic fields. The life time depends upon the frequency and attains a maximum value when the frequency of the electric field equals the cyclotron frequency.

Induction of chromosomal alignment by high frequency electric fields

Induction of chromosomal alignment by high frequency electric fields

Orientational order of triradical spin probes in nematic liquid crystals

The trigonal symmetry of organic triradicals makes them important candidates for spin probes of liquid crystals. Here we develop a lineshape model for such spin probes, within the limit of fast motion, and show how the E.S.R. spectra depend on the orientation of the director with respect to the magnetic field. The theory is employed to study the lineshapes of trisverdazyl radicals in 4,4′-dimethoxyazoxybenzene, aligned by a high frequency electric field. An analysis of the angular-dependent linewidths provides reliable values for the order parameter P 4. They are in good agreement with statistical theories of nematic liquid crystals.

Nonlinear Behaviour of High Frequency Electric Field Just before the Initiation of Beam-Plasma Discharge

The behavior of high frequency electric field nearby electron hybrid frequency, which is excited by electron beam-plasma interaction, is experimentally investigated before sudden buildup of the beam plasma discharge. The experiments are performed with a 2keV-20mA continuous or pulsed electron beam drifting in a partially evacuated region immersed in mirror magnetic field(mirror ratio of 1.4 and a peak field of lOOgauss). As the results, a frequency spread of its electric field is observed, which may be caused by nonlinear three wave interaction. In addition, a nonlinear saturation of its field intensity, which may be due to the formation of sidebands accompanied with the oscillation of the beam electrons trapped in the field potential well, is observed.

Ponderomotive Force in Interaction between Ion Wave and High Frequency Electric Field

We examine experimentally the propagation of an ion wave under the action of a high frequency electric field with frequency close to the electron plasma frequency and an interaction between them. The interaction is characterized by the ponderomotive force. It is proportional to the gradient of a time-averaged high frequency electric field modulated by an ion wave. Experiment confirms that the modulation of a high frequency field increases linearly with the amplitude of the ion wave and with that of the high frequency field. The phase of the modulated wave with respect to the ion wave depends on a frequency of the applied field. Under the action of the ponderomotive force, the phase velocity of ion wave decreases as an injected high frequency power increases in the case where the frequency of the field is lower than the electron plasma frequency.

Broken Ambipolarity of Diffusion in Drift Wave Turbulence

Momentum balance equations for electrons and ions are derived correct to the second order with respect to high frequency electric fields within the framework of the quasilinear theory. In particular, the stress tensor modification due to drift waves is evaluated from the second-moment equation. The ion drift caused by the gradient of the stress tensor breaks the ambipolarity of the diffusion. Strong electric fields across the ambient magnetic field are induced by the broken ambipolarity.

Effects of high frequency electric fields on mammalian chromosomes in vitro

The effect of an alternating electric field in the frequency range 2 to 50 MHz on human and Chinese hamster chromosomes in liquid suspension was studied. Three distinct types of behavior were observed. Above certain threshold field strengths the chromosomes orient themselves with their long axes along the field direction. The dependence of this threshold on frequency was measured and was found to be much larger at low than at high frequencies. At higher field strengths the chromosomes move together and form end-to-end chains along the field direction. When the field is intense and spacially inhomogeneous, translational motion of the chromosomes occurs. There was no marked difference between the response of the human and hamster chromosomes.

Glow Discharge Detection of Long Wavelength Electromagnetic Radiation: Cascade Ionization Process Internal Signal Gain and Temporal and Spectral Response Properties

The mechanism of long wave electromagnetic signal detection by glow-discharge plasma, based upon gas breakdown theory by high frequency electric fields, is developed to include internal signal amplification of the order of that associated with the photomultiplier, upper and lower limits to response linearity, temporal and spectral response properties, and noise in the abnormal glow discharge. Agreement between signal-to-noise expressions in this analysis and measurements involving simple and inexpensive glow discharge indicator lamps exhibiting excellent sensitivity to microwave radiaion is quite good. An inherent ideal limit to speed of response is derived which indicates picosecond-order risetimes are theoretically possible if parasitic reactance effects which limit risetimes of present day devices to microsecond order can be overcome. Sensitivity can be improved further by increasing the number of free electrons. Enhanced diffusion current losses for a subnormal glow yield spectrally flat response which can be useful in radiometric applications.