HF Electric Field Research Articles

Models of HF Interference over Cyprus

Interference from other users, due to the long-distance propagation of HF signals, causes spectral congestion, which is considered a primary detrimental effect on HF (3–30 MHz) communication systems. More than a year of HF electric field measurements from a calibrated monopole HF antenna collected by a dedicated measurement system installed in Cyprus have been used to compare neural networks and non-linear regression for the development of single-allocation congestion models in the HF spectrum. These models can be used to advise operators on typical interference spectral congestion levels and assist in the planning and management of frequency usage by assessing the interference level to alleviate spectral congestion in the HF band over Cyprus. The performance of these alternative modeling approaches is discussed in the context of their ability to successfully capture the diurnal variability of HF interference at a certain incident field strength threshold.

Experimental Determination of Threshold Powers for the Onset of HF-Enhanced Plasma Lines and Artificial Ionization in the Lower F-Region Ionosphere

HF heating experiment, with linear power ramp from 50 to 92 dBW, was conducted to determine the HF threshold power levels for the onset of detectable plasma waves and the onset of artificial ionization inferred from HF-enhanced plasma lines (HFPLs). The threshold free-space electric field at 200-km altitude, where HFPLs were detected, is about 53 mV/m. However, the HF electric field near the reflection height is enhanced by a swelling factor ~ 3.76 and also conversion to a linear dipole pump mode ( $\surd 2$ ); the actual threshold field is about 281 mV/m that is consistent with theory. Artificial ionization in the lower region was detectable via UHF radar. Short wavelength upper-hybrid waves, which were excited parametrically by the HF heating wave at higher threshold, implement Doppler shifted harmonic-cyclotron resonance interaction, via finite Larmour radius effect, to effectively accelerate electrons. Monitoring the spectral power of the parametric decay instability (PDI) line in the HFPLs by radar was shown to determine the artificial ionization onset time more precisely than that by observing the start of a sharp downward trend in the altitude of the HFPLs; at this time, the HF free-space electric field slightly below 200-km altitude is about 550 mV/m. Langmuir cascade lines in the HFPLs are separated by intervals about double the ion-acoustic frequency (about 4–5 kHz) generated by the PDI. These lines, observed at lower power facilities, were not observed. The upper-hybrid OTSI and PDI excited at HighPower Active Auroral Research Program (HAARP) and the mode competition nonlinear-damping mechanism are suggested as the processes, suppressing cascade enhanced HFPLs.

High-Q piezoelectric resonators with a lateral electric field and their potential applications

It is shown for the first time that suppressing parasitic oscillations in a piezoelectric resonator with a lateral electric field by applying a damping coating or by spatially separating the HF electric field source from the resonating plate allows us to achieve record-high Q values for parallel and series resonances. The potential to fabricate an array of acoustically decoupled resonators on a single piezoelectric substrate, and to design microdisplacement sensors with temperature compensation, is also demonstrated for the first time.

Composite lateral electric field excited piezoelectric resonator

The novel method of suppression of parasitic oscillations in lateral electric field excited piezoelectric resonator is suggested. Traditionally such resonator represents the piezoelectric plate with two electrodes on one side of the plate. The crystallographic orientation of the plate is selected so that the tangential components of electric field excite bulk acoustic wave with given polarization travelling along the normal to the plate sides. However at that the normal components of field excite the parasitic Lamb waves and bulk waves of other polarization which deteriorate the resonant properties of the resonator. In this work we suggest to separate the source of the HF electric field and resounded piezoelectric plate by air gap. In this case the tangential components of the field in piezoelectric plate do not practically weaken but normal components significantly decrease. This method is realized on the composite resonator having the structure “glass plate with rectangular electrodes – air gap – plate of 128 Y-X lithium niobate.” It has been shown that there exist the optimal value of the width gap which ensure the good quality of series and parallel resonances in frequency range 3–4MHz with record values of Q-factor of ∼15,000 in both cases.

Simultaneous Multi-angle Observations of Strong Langmuir Turbulence at HAARP

We report results from a recent series of experiments employing the HF transmitter of the High Frequency Active Auroral Research Program (HAARP) to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. The Modular UHF Ionospheric Radar (MUIR) located at the HAARP facility is used as the primary diagnostic. Short pulse, low duty cycle experiments are used to avoid generation of artificial field-aligned irregularities and isolate ponderomotive plasma turbulence effects. The HF pump frequency is close to the 3rd gyro-harmonic frequency and the HF pointing angle and MUIR look angle are between the HF Spitze angle and Magnetic Zenith angle. Plasma line spectra measured simultaneously in different spots of the interaction region display differences dependent on the aspect angle of the HF pump beam in the boresight direction and the pointing angle of the MUIR diagnostic radar. Outshifted Plasma Lines, cascade, collapse, coexistence, spectra are observed in agreement with existing theory and simulation results of Strong Langmuir Turbulence in ionospheric interaction experiments. It is found that SLT at HAARP is most readily observed at a HF pointing angle of 11° and UHF observation angle of 15°, which is consistent with the magnetic zenith effect as documented in previous works and optimal orientation of the refracted HF electric field vector.

Separation Method in the Problem of a Beam-Plasma Interaction in a Cylindrical Warm Plasma Waveguide

The stabilization effect of a strong HF electric field on beam-plasma instability in a cylindrical warm plasma waveguide is discussed. A mathematical technique “separation method” applied to the two-fluid plasma model to separate the equations, which describe the system, into two parts, temporal and space parts. Plasma electrons are considered to have a thermal velocity. It is shown that a HF electric field has no essential influence on dispersion characteristics of unstable surface waves excited in a warm plasma waveguide by a low-density electron beam. The region of instability only slightly narrowing and the growth rate decreases by a small parameter and this result has been reduced compared to cold plasma. Also, it is found that the plasma electrons have not affected the solution of the space part of the problem.

Modeling of dual frequency capacitively coupled plasma sources utilizing a full-wave Maxwell solver: I. Scaling with high frequency

Dual frequency capacitively coupled plasma (DF-CCP) tools for etching and deposition for microelectronics fabrication typically use a high frequency (HF, tens to hundreds of MHz) to sustain the plasma and a low frequency (LF, a few to 10 MHz) for ion acceleration into the wafer. With an increase in both the HF and wafer size, electromagnetic wave effects (i.e. propagation, constructive and destructive interference) can affect the spatial distribution of power deposition and reactive fluxes to the wafer. In this paper, results from a two-dimensional computational investigation of a DF-CCP reactor, incorporating a full-wave solution of Maxwell's equations, are discussed. As in single frequency CCPs, the electron density transitions from edge high to center high with increasing HF. This transition is analyzed by correlating the spatial variation of the phase, magnitude and wavelength of the HF electric field to the spatial variation of the electron energy distributions and ionization sources. This transition is sensitive to the gas mixture, particularly those containing electronegative gases due to the accompany change in conductivity. The consequences of these wave effects on the ion energy distributions incident onto the wafer are also discussed.

Modeling of dual frequency capacitively coupled plasma sources utilizing a full-wave Maxwell solver: II. Scaling with pressure, power and electronegativity

The trend in dielectric etching in microelectronics fabrication with capacitively coupled plasmas is the use of multiple frequencies where a high frequency (HF, tens to hundreds of MHz) dominates ionization and a low frequency (LF, a few to tens MHz) is used to control ion energy distributions to the wafer. Process parameters, such as pressure, gas mixture and LF and HF power deposition, are important to determining the uniformity of the plasma and properties of ions incident on the wafer. In this paper, we report on a computational investigation of the consequences of these parameters on uniformity and ion energy distributions to the wafer in a dual frequency capacitively coupled plasma reactor sustained in Ar/CF4 gas mixtures. Due to the coupling of finite wavelength, electromagnetic skin, electrostatic edge and electronegative effects, there are no simple scaling laws for plasma uniformity. The plasma uniformity is ultimately a function of conductivity and energy relaxation distance of electrons accelerated by electric fields in and near the sheath. There is a strong second-order effect on uniformity due to feedback from the electron energy distributions (EEDs) to ionization sources. The trends from our parametric study are correlated with the spatial variation of the HF electric field, to the total power deposition and to the spatial variation of EEDs and ionization sources.

Relativistic warm plasma waveguide under the effects of plasma electrons and HF electrical field on Buneman instability

Abstract The stabilization effect of a strong HF (pump) electrical field and plasma electrons on a two-stream (Buneman) instability in a plane relativistic warm plasma waveguide is investigated; using the separation method to solve the two-fluid plasma model we separate the problem into two parts. The “temporal” (dynamical) part enables us to determine the frequencies and growth rates of unstable waves; this part within the redefinition of natural frequencies coincides with the system describing HF suppression of Buneman instability in uniform unbounded plasma. Natural frequencies of oscillations and spatial distribution of the amplitude of the self-consistent electrical field are determined from the solution of a boundary-value problem (“space part”) taking into account specific spatial distribution of plasma density. Plasma electrons are considered to have a relativistic thermal velocity. It is shown that the growth rate of instability in relativistic warm plasma is reduced compared to non-relativistic (cold or warm) plasma and relativistic cold plasma. In addition, it is found that the plasma electrons have no effect on the solution of the space part of the problem.

Demeter high resolution observations of the ionospheric thermal plasma response to magnetospheric energy input during the magnetic storm of November 2004

Abstract. High resolution Demeter plasma and wave observations were available during one of the geomagnetic storms of November 2004 when the ionospheric footprint of the plasmasphere was pushed below 64 degrees in the midnight sector. We report here onboard observations of thermal/suprathermal plasma and HF electric field variations with a temporal resolution of 0.4 s, which corresponds to a spatial resolution of 3 km. Local perturbations of the plasma parameters at the altitude of 730 km are analysed with respect to the variation of the field-aligned currents, electron and proton precipitation and large-scale electric fields, measured in-situ by Demeter and by remote optical methods from the IMAGE/Polar satellites. Flow monitoring in the 21:00 and 24:00 MLT sectors during storm conditions reveals two distinct regions of O+ outflow, i.e. the region of the field-aligned currents, which often comprises few layers of opposite currents, and the region of velocity reversal toward dusk at sub-auroral latitudes. Average upward O+ velocities are identical in both local time sectors and vary between 200 and 450 m s−1, with an exception of a few cases of higher speed (~1000 m s−1) outflow, observed in the midnight sector. Each individual outflow event does not indicate any heating process of the thermal O+ population. On the contrary, the temperature of the O+, outflowing from auroral latitudes, is found to be even colder than that of the ambient ion plasma. The only ion population which is observed to be involved in the heating is the O+ with energies a few times higher than the thermal energy. Such a population was detected at sub-auroral latitudes in the region of duskward flow reversal. Its temperature raises up to a few eV inside the layer of sheared velocity. A deep decrease in the H+ density at heights and latitudes, where, according to the IRI model, these ions are expected to comprise ~50% of the positive charge, indicates that the thermospheric balance between atomic oxygen and hydrogen was re-established in favour of oxygen. As a consequence, the charge exchange between oxygen and hydrogen does not effectively limit the O+ production in the regions of the electron precipitation. According to Demeter observations, the O+ concentration is doubled inside the layers with upward currents (downward electrons). Such a density excess creates the pressure gradient which drives the plasma away from the overdense regions, i.e. first, from the layers of precipitating electrons and then upward along the layers of downward current. In addition, the downward currents are identified to be the source regions of hiss emissions, i.e. electron acoustic mode excited via the Landau resonance in the multi-component electron plasma. Such instabilities, which are often observed in the auroral region at 2–5 Earth radii, but rarely at ionospheric altitudes, are believed to be generated by an electron beam which moves through the background plasma with a velocity higher than its thermal velocity.

Electrical conductivity of dense non-ideal plasmas in external HF electric field

In this work, the previously developed method for calculation of HF electroconductivity of non-ideal plasma is applied to the area of high electron densities: 10 21 ≤ N e ≤ 10 23 cm -3 and in the temperature range 20000 K ≤ T ≤ 1000000 K. This is enabled by the improvement of the numerical procedure. The real and imaginary parts of the HF conductivity are parametrized in the Drude-Lorentz form. One of the parameters is the static conductivity σ 0 . The computations are carried out in the frequency range [0, 0.05ω p ], ω p being the plasma frequency.

Optical HF electrical permeability, refractivity and reflectivity of dense non-ideal plasmas

On the basis of numerically calculated values for the dense plasma dynamic conductivity in an external HF electric field, we determine the electrical permeability and the coefficients of refractivity and reflectivity of dense non-ideal plasmas. We consider electronic number density and temperature in the ranges of 1021 ≤ Ne ≤ 1023 cm−3 and 20 kK ≤ T ≤ 1 MK, respectively. The parametrized form of representation of the results is suitable for experimental verification and further usage. The examined range of frequencies covers the IR, visible and near UV regions.

Relaxation phenomena of polar non-polar liquid mixtures under low and high frequency electric field

Simultaneous calculation of the dipole moment μj and the relaxation time τj of a certain number of non-spherical rigid aliphatic polar liquid molecules (j) in non-polar solvents (i) under 9.8 GHz electric field is possible from real e′ij and imaginary e″ij parts of the complex relative permittivity e*ij. The low frequency and infinite frequency permittivities e0ij and e∞ij measured by Purohitet al [1,2] and Srivastava and Srivastava [3] at 25, 35 and 30°C respectively are used to obtain static μs. The ratio of the individual slopes of imaginary σ″ij and real σ′ij parts of high frequency (hf) complex conductivity σ*ij with weight fractionsw jatw j → 0 and the slopes of σ″ij— σ′ij curves for differentw js [4] are employed to obtain τjs. The former method is better in comparison to the existing one as it eliminates polar-polar interaction. The hf μjs in Coulomb metre (C m) when compared with static and reported μs indicate that μs s favour the monomer formations which combine to form dimers in the hf electric field. The comparison among μs shows that a part of the molecule is rotating under X-band electric field [5]. The theoretical μtheos from available bond angles and bond moments of the substituent polar groups attached to the parent molecules differ from the measured μjs and μs to establish the possible existence of mesomeric, inductive and electromeric effects in polar liquid molecules.

Analytical model of a dual frequency capacitive sheath

In recent years, there has been an increased interest in capacitively coupled plasma discharges which are operated with two frequencies. An analytical sheath model for a capacitively coupled radio-frequency plasma discharge operated with two frequencies is proposed and studied under the assumptions of a time-independent, collisionless ion motion. Expressions are obtained for the time-average electric potential within the sheath, nonlinear motion of the electron sheath boundary and nonlinear instantaneous sheath voltage. The derived model is valid under the condition that the low frequency (lf) electric field Elf in the sheath is much higher than the high frequency (hf) electric field Ehf. This condition is fulfilled within typical dual frequency conditions. It is shown, however, that the hf electric field modifies the sheath structure significantly because of the electron response to Ehf. This model has been compared to particle-in-cell plasma simulations, finding good quantitative agreement. We present the dependence of the maximum sheath width and the dc sheath voltage drop on the hf/lf current ratio and on the hf/lf frequency ratio.

Double relaxation phenomena of monosubstituted anilines in benzene under high frequency electric field

The intercept and slope of a derived linear equation: (χoij - χij′)/χij′ = ω (τ1+τ2) χij″/χij′ - ω2τ1τ2 for different weight fractions wj's of monosubstituted anilines (j) in benzene(i) at 35°C under different electric field frequencies are used to yield the double relaxation times τ1 and τ2 of the flexible parts and the whole molecules. χij′ and χij″ are the real and imaginary parts of hf complex dielectric orientational susceptibility χij∗ and χoij is the low frequency dielectric susceptibility which is real. τj's obtained from the ratio of the individual slopes of variations of χij∥ and χij′ with wj's at wj→0 are compared with Murthy et al (Indian J Phys 63 B 1989 491) and Gopalakrishna (Trans Faradey. Soc. 53 1957 767). The theoretical weighted contributions c1 and c2 for τ1 and τ2 from Fröhlichs' equations are compared with the experimental ones from the graphically fitted curves of χij′/χoij and χij″/χoij with wj's in the limit wj=0. The values of (χij′/χoij)wj→0 and (χij″/χoij)wj→0 are again employed to get symmetric and asymmetric distribution parameters γ and δ, the latter one is from the curve of 1/ϕ log Cosϕ against ϕ0, to yield the symmetric and characteristic relaxation times τs and τcs respectively, only to show that symmetric relaxation behaviour is obeyed by the molecules. The dipole moments μ1 and μ2 for the rotation of flexible parts and the whole molecules are measured from τ1 and τ2 and linear coefficient ß's of the variations of χij′ and hf conductivity σij with wj's. The measured μ1 and μ2 are compared with the reported μ's and μtheo's of available bond angles and bond moments of the substituent polar groups of the parent molecules. The slight disagreement of measured μ's from μtheo's indicates the existence of inductive, mesomeric and electromeric effects suffered by the polar groups under hf electric field.

Stabilization effect of a strong HF electrical field on beam–plasma interaction in a relativistic plasma waveguide

The influence effect of a strong HF electrical field on the excitation of surface waves by an electron beam under the development of instability of low-density electron beam passing through plane relativistic plasma is investigated. Starting from the two fluid plasma model we separate the problem into two parts. The “temporal” (dynamical) part enables us to find the frequencies and growth rates of unstable waves. This part within the redefinition of natural (eigen) frequencies coincides with the system describing HF suppression of the Buneman instability in a uniform unbounded plasma. Natural frequencies of oscillations and spatial distribution of the amplitude of the self-consistent electrical field are obtained by solving a boundary-value problem (“spatial” part) considering a specific spatial distribution of plasma density. Plasma electrons are considered to have a relativistic velocity. It is shown that a HF electric field has no essential influence on dispersion characteristics of unstable surface waves excited in a relativistic plasma waveguide by a low-density electron beam. The region of instability only slightly narrowing and the growth rate decreases by a small parameter and this result has been reduced compared to nonrelativistic plasma. Also, it is found that the plasma electrons have not affected the solution of the space part of the problem.

HF Electric Field Effect on Buneman's Instability in a Relativistic Plasma Waveguide

The stabilizing effect of a strong HF (pump) electric field on the Buneman instability in a plane relativistic plasma waveguide is investigated. A new mathematical technique (“separation method”) is applied to the two-fluid plasma model to separate the equations, which describe the system, into two parts: temporal and space parts. The “temporal” dynamical part enables us to determine the frequencies and growth rates of unstable modes; this part within the redefinition of natural frequencies coincides with the system describing, HF suppression of Buneman instability in a uniform unbounded plasma. The natural frequencies of the oscillations and the spatial distribution of the amplitude of the self-consistent electric field are determined from the solution of a boundary-value problem (“space part”) taking into account the specific spatial distribution of the Plasma density. The plasma electrons are considered to have a relativistic velocity. It is shown that the growth rate of the instability in a relativistic plasma has been reduced compared to that of a nonrelativistic plasma. Also, it is found that the relativistic part of the plasma electrons has not affected the solution of the space part of the problem.

The Effect of a HF Electric Field on the Propagation of anElectrostatic Wave in a Nonuniform Plasma Waveguide

An analytical study of the reflection of an electrostatic wavepropagating along a magnetized nonuniform plasma slab subject to anintense HF electric field is presented. It is found that when thefrequency of the incident wave ωg is close to theelectron plasma frequency ωPe, the plasma is lessreflective due to the presence of the HF field. On the other hand, fora low-frequency incident wave(ωg ∼ ωPi), the reflectioncoefficient is directly proportional to the amplitude of the HFfield.

Energy losses of a charged particle in a plasma in an external field allowing for the field action on plasma and particle motion

In this paper we present polarization losses of a charged particle in a Maxwell plasma placed in an external HF electric field allowing for oscillations under the action of an external field of both the particle and plasma electrons. Deriving the expressions for particle losses, we assumed that the vector of translational motion of the particleu is directed at an arbitrary angle with respect to the external HF field vector.

Suprathermal electrons associated with a plasma discharge on an active sounding rocket experiment

Electrons with energies up to 600 eV are observed with the retarding potential analyzer (RPA) instrument aboard the Several Compatible Experiments (SCEX) III sounding rocket. The electrons are concomitant with high‐energy (2–6 keV) electron gun injections and also evidence themselves by luminosity observed with 3805 Å and 3914 Å photometers. Both the collected electron flux and luminosity measurements are strongly nonlinear with gun injection current. For a typical event, the electron distribution is similar to laboratory beam‐plasma discharge (BPD) distributions reported by Sharp (1982) and when backed by HF electric field observations (Goerke et al., 1992; Llobet et al., 1985), the BPD mechanism becomes a most likely explanation. Strong turbulence theories of BPD predict a power law tail in the electron distribution, and we compare our spectral index with some previous observations.