Upper-hybrid Waves Research Articles

Energy behavior of spin electron cyclotron wave in a spin polarized plasma

In degenerate quantum plasma the energy behavior of electrostatic modes propagating perpendicular to the external magnetic field is studied by employing the separated spin evolution quantum hydrodynamic (SSE-QHD) model. This model reveals that spin electron cyclotron wave (SECW) appears additionally with the upper hybrid wave (UHW). In case of SECW, the curves for the energy flow speed at different levels of spin polarization effect flip over at a particular value of wave number. The spin polarization effect enhances the energy flow speed before this value of wave number and then suppresses it afterward. The energy flow speed is enhanced by spin polarization effect in the entire range of wave number for the propagation of UHW. The Bohm potential effect drastically increases the energy flow speed at high wave number domain in both the waves. This study may find its applications to understand the energy behavior inspin polarized solid state plasmas

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

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 saturation of the low-threshold two-plasmon decay instability of a microwave beam. This nonlinear effect can significantly change the power deposition profile during electron cyclotron resonance heating of plasma in toroidal traps and, thus, explain its significant broadening, often observed in experiments.

High‐Frequency Wave Generation in Magnetotail Reconnection: Linear Dispersion Analysis

AbstractPlasma and wave measurements from the NASA Magnetospheric Multiscale mission are presented for magnetotail reconnection events on 3 July and 11 July 2017. Linear dispersion analyses were performed using distribution functions comprising up to six drifting bi‐Maxwellian distributions. In both events electron crescent‐shaped distributions are shown to be responsible for upper hybrid waves near the X‐line. In an adjacent location within the 3 July event a monodirectional field‐aligned electron beam drove parallel‐propagating beam‐mode waves. In the 11 July event an electron distribution consisting of a drifting core and two crescents was shown to generate upper‐hybrid and beam‐mode waves at three different frequencies, explaining the observed broadband waves. Multiple harmonics of the upper hybrid waves were observed but cannot be explained by the linear dispersion analysis since they result from nonlinear beam interactions.

Crescent‐Shaped Electron Distributions at the Nonreconnecting Magnetopause: Magnetospheric Multiscale Observations

AbstractCrescent‐shaped electron distributions perpendicular to the magnetic field are an important indicator of the electron diffusion region in magnetic reconnection. They can be formed by the electron finite gyroradius effect at plasma boundaries or by demagnetized electron motion. In this study, we present Magnetospheric Multiscale mission observations of electron crescents at the flank magnetopause on 20 September 2017, where reconnection signatures are not observed. These agyrotropic electron distributions are generated by electron gyromotion at the thin electron‐scale magnetic boundaries of a magnetic minimum after magnetic curvature scattering. The variation of their angular range in the perpendicular plane is in good agreement with predictions. Upper hybrid waves are observed to accompany the electron crescents at all four Magnetospheric Multiscale spacecraft as a result of the beam‐plasma instability associated with these agyrotropic electron distributions. This study suggests electron crescents can be more frequently formed at the magnetopause.

Investigating Transport and Dissipation in the Subauroral E Region With Ionospheric Modification Experiments and Very High Frequency Radar Backscatter

AbstractIonospheric modification experiments have been performed at the High‐Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska, using a Very High Frequency (VHF) coherent scatter radar in Homer, Alaska, for experimental diagnostics. The experiments were intended to determine the threshold pump electric field required to initiate thermal parametric instability in the E region. The pump power level was ramped systematically to determine the threshold, and the experiment was repeated at four closely spaced pump frequencies. This provided threshold estimates at four E region altitudes. The theory for thermal parametric instability based on the work of Dysthe et al. (1983, https://doi.org/10.1063/1.863993) has been modified for application in the E region. The theory considers magneto‐ionic effects on the pump mode, linear mode conversion theory for upper hybrid wave generation, wave heating, and the effects of transport and dissipation based on fluid theory. The theory amounts to an eigenvalue problem where the eigenvalue is the threshold pump electric field for instability. The theory shows how the threshold depends on ionospheric transport coefficients and on the fractional cooling rate for inelastic electron‐neutral collisions. The theoretical predictions for threshold are roughly consistent with experimental values although the latter are probably affected by excess ionospheric absorption.

Growth Rates of the Upper-Hybrid Waves for Power-Law and Kappa Distributions with a Loss-Cone Anisotropy

Fine structures of radio bursts play an important role in diagnostics of the solar flare plasma. Among them the zebras, which are prevalently assumed to be generated by the double plasma resonance instability, belong to the most important. In this paper we compute the growth rate of this instability for two types of the electron distribution: a) for the power-law distribution and b) for the kappa distribution, in the both cases with the loss-cone type anisotropy. We found that the growth rate of the upper-hybrid waves for the power-law momentum distribution strongly depends on the pitch-angle boundary. The maximum growth rate was found for the pitch-angle $\theta_\mathrm{c} \approx$ 50$^\circ$. For small angles the growth rate profile is very flat and for high pitch-angles the wave absorption occurs. Furthermore, analyzing the growth rate of the upper hybrid waves for the kappa momentum distribution we found that a decrease of the characteristic momentum $p_\kappa$ shifts the maximum of the growth rate to lower values of the ratio of the electron-plasma and electron-cyclotron frequencies, and the frequency widths of the growth rate peaks are very broad. But, if we consider the kappa distribution which is isotropic up to some large momentum $p_m$ and anisotropic with loss-cone above this momentum then distinct peaks of the growth rate appear and thus distinct zebra stripes can be generated. It means that the restriction for small momenta for the anisotropic part of distributions is of principal importance for the zebra stripes generation. Finally, for the 1 August 2010 zebra stripes, the growth rates in dependence on radio frequency were computed. It was shown that in this case the growth rate peaks are more distinct than in usually presented dependencies of growth rates on the ratio of the plasma and cyclotron frequencies.

Anomalous absorption in ECRH experiments due to the parametric low-threshold excitation of localized UH waves

We describe the theoretical model which interprets the anomalous phenomena, i.e. the generation of backscattering signal observed in the ECRH experiments at TEXTOR, TCV, TJ-II, ASDEX-UG, LHD and FTU, as a consequence of the excitation of the parametric decay instability (PDI) leading to anomalous damping of the pump wave. The PDI power-threshold is shown to be extremely low due to the localization of both or one daughter upper hybrid (UH) waves in presence of a nonmonotonic (hollow) density profile, which is often observed in the ECRH experiments due to the magnetic island or the density pump-out effect. In the case of the extraordinary wave pump the model predicts substantial (up to 25%) anomalous absorption in the electron channel and explains the anomalous ion acceleration by the generation of secondary low frequency waves which directly transfer the pump power to the ion component. The possibility of anomalous absorption of the O-mode pump in the ECRH experiment due to the parametric excitation of trapped UH wave is also discussed and the anomalous absorption rate at the 10% level is predicted.

Low-threshold absolute parametric decay instability in the monotonous density profile region in O1-mode ECRH experimental conditions

The possibility of the low-threshold absolute parametric decay instability excitation by the ordinary wave in the presence of a monotonous plasma density profile is analyzed. It is shown that in the cases of daughter upper hybrid and ion Bernstein waves the energy circulation between two nearby decay points can lead to an absolute instability at the pump power of less than half a megawatt. The instability saturation due to the ion Bernstein wave amplitude-dependent stochastic damping effect is considered and the rate of anomalous pump absorption is estimated. This scenario can explain the observations of anomalous scattering in the O1-mode electron cyclotron resonance heating (ECRH) experiments at the FTU (Frascati Tokamak Upgrade) tokamak in the presence of a monotonous density profile.

On the dispersion characteristics of relativistic obliquely propagating Bernstein wave in a degenerate electron plasma

The dispersion characteristics of obliquely propagating electrostatic Bernstein wave in a relativistic degenerate electron plasma is markedly different from perpendicular one. Employing linearized Vlasov-Maxwell model, the dispersion relation of obliquely propagating Bernstein wave in a relativistic degenerate electron plasma is derived. In particular, the results are obtained in the propagation range kz > kx with kx≠0. In the high frequency (ω > > k.v) and weak propagation (Ω>>k.v or k → 0) limiting cases, the generalized results reduce to the Upper hybrid wave for θ′ = 00 and Langmuir wave for θ′ = 900 (where Ω is the gyro-frequency and θ′ is the propagation angle of k with respect to x-axis). Graphical analysis is also performed to highlight the new trends in wave spectra.

Enhanced Escape of Spacecraft Photoelectrons Caused by Langmuir and Upper Hybrid Waves

AbstractThe spacecraft potential is often used to infer rapid changes in the thermal plasma density. The variations in spacecraft potential associated with large‐amplitude Langmuir and upper hybrid waves are investigated with the Magnetospheric Multiscale (MMS) mission. When large‐amplitude Langmuir and upper hybrid waves are observed, the spacecraft potential increases. The changes in spacecraft potential are shown to be due to enhanced photoelectron escape from the spacecraft when the wave electric fields reach large amplitude. The fluctuations in spacecraft potential follow the envelope function of the Langmuir and upper hybrid waves. Comparison with the high‐resolution electron moments shows that the changes in spacecraft potential associated with the waves are not due to density perturbations. Indeed, using the spacecraft potential as a density probe leads to unphysically large density fluctuations. In addition, the changes in spacecraft potential are shown to increase as density decreases: larger spacecraft potential changes are observed in the magnetosphere, than in the magnetosheath and solar wind. These results show that external electric fields can lead to unphysical results when the spacecraft potential is used as a density probe. The results suggest that fluctuations in the spacecraft potential alone cannot be used to determine whether nonlinear processes associated with Langmuir and upper hybrid waves, such as the ponderomotive force and three‐wave decay, are occurring.

Modulational and three wave decay instabilities in degenerate electron-ion dense plasmas

A formalism for nonlinear interaction of degenerate upper-hybrid waves (DUHWs) with degenerate ion-cyclotron waves (DICWs) and degenerate Alfven waves (DAWs) is revisited to account for quantum corrections owing to quantum Bohm potential, quantum exchange-correlations, and quantum statistical pressure. For this purpose, different nonlinear dispersion relations are derived with quantum settings. By using the phasor matching techniques, the growth rates of three wave decay and modulational instabilities are analyzed by identifying the nonlinear coupling of high-frequency DUHWs with low-frequency DICWs and DAWs. Numerically, it is revealed that parametric three wave decay and modulational instabilities are significantly influenced by the impact of Fermi pressure and exchange-correlation in a degenerate magnetoplasma. The present results are important to understand the dispersive properties of nonlinear waves and their mutual couplings at quantum scales in degenerate environments like white dwarfs, neutron stars, and magnetars.

Coherent terahertz radiation from beam-driven upper hybrid wave in magnetostatic plasma

ABSTRACTA scheme for generating tunable terahertz radiation using relativistic electron beam-induced upper hybrid wave immersed in a magnetized plasma is investigated. The ponderomotive force applied to the beam electrons because of electromagnetic radiation wave and pump wave generates the non-linear current density in the high-frequency regime. For an appropriate pump wave frequency, under the condition of phase matching the THz radiation wave is obtained. The enhancement in the radiation power occurs along the axial direction in the vicinity of Cerenkov resonance. Our analytical expression shows that the growth rate in the unstable modes of the THz radiation wave increases with beam density (beam current) and the modulation index. In addition, the growth rate of the instability decreases with an increase in radiation wave frequency and scales as the inverse cube root of radiation frequency. An interesting result obtained from our model is that an increase in cyclotron frequency causes the growth decrement in THz radiation emission, while the efficiency of THz radiation emission increases with the growth rate and the modulation index. Also, the emission of the THz radiation wave becomes larger as the modulation index approaches unity.

Saturation of the low-threshold parametric decay of the O-mode pump in the fundamental harmonic ECRH experiment

The saturation regime of the low-power-threshold ordinary (O) wave parametric decay instability leading to the excitation of a localized upper hybrid (UH) wave and a low-hybrid wave is analysed. The cascade of secondary decays of a daughter UH wave to a localized UH wave and ion Bernstein wave is considered as presumably the most important nonlinear mechanism responsible for the transition to a saturation regime. A set of equations describing this nonlinear frequency down-conversion is derived and then solved both analytically and numerically under the conditions typical of the on-axis fundamental harmonic ordinary mode (O1-mode) electron cyclotron resonance heating experiments at the FTU tokamak.

Kinematics of electrostatic 3-wave decay of generalized Langmuir waves in magnetized plasmas

The decay of generalised Langmuir waves L into backscattered (generalised) Langmuir waves L and ion acoustic waves S or ion cyclotron waves IC, represented by L→L′+S and L→L′+IC, is a fundamental nonlinear process relevant to beam-plasma instabilities in space and laboratory plasmas and to multiple solar system radio emissions. Both magnetization and arbitrary wavevector directions are included for the generalised Langmuir waves, thereby naturally encompassing both conventional Langmuir waves and upper hybrid waves. A recent 1D analysis for L waves with wavevectors closely parallel to the ambient magnetic field B0 in weakly magnetized plasma (angular electron cyclotron frequency Ωe much less than the angular electron plasma frequency ωp) showed that the electrostatic (ES) decay L→L′+S persists for kL<k0, reversing the old prediction based on the unmagnetized dispersion relation. Here, the kinematics for the processes L→L′+S and L→L′+IC are derived in 2 dimensions for approximately electrostatic waves in arbitrary magnetized plasmas and for all wavevector orientations relative to B0. ES decay processes are shown to exist in both weakly and strongly magnetized plasmas and, under most circumstances, for arbitrary L-wavevector directions, including close to perpendicular to B0, and wavenumbers. For L-wavenumbers kL≳2k0, the decay process is very similar to the standard unmagnetized decay for kL close to parallel with B0, proceeding primarily as a backscatter to kL′≈(kL−k0)kL/kL and a trivial forward-scatter solution with kL≈kL. (Here, k0=2ωpvS/3Ve2, VS is the ion acoustic speed, and Ve is the electron thermal speed.) In addition, the decay persists for kL<k0 to very small kL′≈k*=(ωp/c)(1+fp/fce)−1/2 for arbitrary magnetizations and orientations of kL relative to B0, at least for sufficiently large ion-to-electron temperature ratios Ti/Te. Thus, once magnetization effects are included, the decay is kinematically allowed for essentially all initial wavevectors and can proceed for the very fast beams (with kL<k0) for which modulational instability and not ES decay was previously expected to dominate the nonlinear evolution.

A Comparative Study of ULF Waves' Role in the Dynamics of Charged Particles in the Plasmasphere: Van Allen Probes Observation

AbstractBy analyzing observations from Van Allen Probes in its inbound and outbound orbits, we present evidence of coherent enhancement of cold plasmaspheric electrons and ions due to drift‐bounce resonance with ultralow frequency (ULF) waves. From 18:00 UT on 28 May 2017 to 10:00 UT on 29 May 2017, newly formed poloidal mode standing ULF waves with significant electric field oscillations were observed in two consecutive orbits when Probe B was traveling inbound. In contrast to observations during outbound orbits, the cold (<150 eV) electrons measured by the HOPE instrument were characterized by flux enhancements several times larger and bidirectional pitch angle distributions during inbound orbits. The electron number density inferred from upper hybrid waves is twice as larger as during inbound orbits, which were also confirmed by an increase of spacecraft potential. The observed ULF waves are identified as second harmonic modes that satisfy the drift‐bounce resonant condition of N = 1 with cold electrons. An enhancement of the plasmaspheric ion number density to restore charge neutrality of plasmas in inbound orbits is observed, which is associated with an increase of ULF wave periods. The observations suggest that the dynamics of plasmaspheric electrons is modified by ULF waves through drift‐bounce resonance and that plasmaspheric ions are indirectly impacted.

Saturation of low-threshold two-plasmon parametric decay leading to excitation of one localized upper hybrid wave

We analyze the saturation of the low-threshold absolute parametric decay instability of an extraordinary pump wave leading to the excitation of two upper hybrid (UH) waves, only one of which is trapped in the vicinity of a local maximum of the plasma density profile. The pump depletion and the secondary decay of the localized daughter UH wave are treated as the most likely moderators of a primary two-plasmon decay instability. The reduced equations describing the nonlinear saturation phenomena are derived. The general analytical consideration is accompanied by the numerical analysis performed under the experimental conditions typical of the off-axis X2-mode ECRH experiments at TEXTOR. The possibility of substantial (up to 20%) anomalous absorption of the pump wave is predicted.

Artificial Ionospheric GPS Phase Scintillation Excited During High‐Power Radiowave Modulation of the Ionosphere

AbstractArtificial ionospheric GPS phase scintillation effects excited during the fourth gyroharmonic (4fce) heating at the High Frequency Active Auroral Research Program along with a theoretical model for the associated ionospheric irregularities are presented in this paper. The generation mechanism and time evolution of artificial GPS phase scintillation have been investigated using the simultaneous collected data including GPS scintillation, wideband stimulated electromagnetic emissions (WSEE), and ionosonde. The generation of the broad upshifted maximum, a WSEE spectral line associated with super small striation, through the four‐wave decay instability is studied using a theoretical model. The possible role of decameter‐scale irregularities within the Fresnel zone as well as super small striation in the GPS phase scintillation is investigated using the correlation of WSEE features with the scintillation data. Time evolution of slant total electron content (STEC) data and modulation of GPS phase and amplitude are compared with the theoretical model to study the plasma waves involved in the scintillation process. The similarity of theoretical and previously developed computational results, with the observations, is discussed. Specifically, the time evolution of STEC fluctuations including an initial growth period and subsequent saturation has been compared with the estimated growth rate of upper hybrid and electron Bernstein waves using the theoretical calculations as well as previous computational results. The damping process associated with the decay of STEC fluctuations after the initial growth has been investigated by considering the nonlinear behavior of electron Bernstein waves obtained from the computational model.

On the upper hybrid wave instability in a spin polarized degenerate plasma

Applying the separate spin evolution-quantum hydrodynamic model incorporating Coulomb exchange interaction, the instabilities of upper hybrid mode and beam driven mode due to passing of electron beam in a spin polarized degenerate plasma are studied. It is found that the electron spin not only changes the growth rate of these modes but also gives birth to a new spin-dependent wave (spin electron acoustic wave) in the real frequency spectrum. Further, the Bohm potential and exchange interaction effects significantly affect the frequency spectra of upper hybrid mode. Other parameters like streaming speed of beam electron and beam density are also found to influence the growth rate of these modes. These consequential effects may have a strong bearing on the wave and instability phenomena in the solid state plasmas.

Combined effects of density ripples and transverse magnetic field on the suppression of stimulated Raman scattering of X- mode laser in a plasma

The present study shows that stimulated Raman Scattering of X-mode lasers may be suppressed significantly due to the presence of density ripples and transverse magnetic field in plasma. A laser propagating in magnetized plasma excites a primary upper hybrid wave and a sideband electromagnetic wave. Primary upper hybrid wave couples with density ripples and excites a secondary upper hybrid of same frequency but of longer wave number. Secondary wave is strongly Landau damped and diverts the energy available in feedback mechanism of Raman process. As a consequence, the growth rate of SRS reduces significantly. The growth rate of Raman process also decreases with applied magnetic field. The growth of Raman process is reduced ∼ 40% when the ripple wave number is twice the propagation constant of pump laser (intensity 1015 W/ cm2 at 1μm wavelength) in a 10% critical density plasma having electron temperature 1 keV.

Double plasma resonance instability as a source of solar zebra emission

Context. The double plasma resonance (DPR) instability plays a basic role in the generation of solar radio zebras. In the plasma, consisting of the loss-cone type distribution of hot electrons and much denser and colder background plasma, this instability generates the upper-hybrid waves, which are then transformed into the electromagnetic waves and observed as radio zebras. Aims. In the present paper we numerically study the double plasma resonance instability from the point of view of the zebra interpretation. Methods. We use a 3-dimensional electromagnetic particle-in-cell (3D PIC) relativistic model. We use this model in two versions: (a) a spatially extended “multi-mode” model and (b) a spatially limited “specific-mode” model. While the multi-mode model is used for detailed computations and verifications of the results obtained by the “specific-mode” model, the specific-mode model is used for computations in a broad range of model parameters, which considerably save computational time. For an analysis of the computational results, we developed software tools in Python. Results. First using the multi-mode model, we study details of the double plasma resonance instability. We show how the distribution function of hot electrons changes during this instability. Then we show that there is a very good agreement between results obtained by the multi-mode and specific-mode models, which is caused by a dominance of the wave with the maximal growth rate. Therefore, for computations in a broad range of model parameters, we use the specific-mode model. We compute the maximal growth rates of the double plasma resonance instability with a dependence on the ratio between the upper-hybrid ωUH and electron-cyclotron ωce frequency. We vary temperatures of both the hot and background plasma components and study their effects on the resulting growth rates. The results are compared with the analytical ones. We find a very good agreement between numerical and analytical growth rates. We also compute saturation energies of the upper-hybrid waves in a very broad range of parameters. We find that the saturation energies of the upper-hybrid waves show maxima and minima at almost the same values of ωUH∕ωce as the growth rates, but with a higher contrast between them than the growth rate maxima and minima. The contrast between saturation energy maxima and minima increases when the temperature of hot electrons increases. Furthermore, we find that the saturation energy of the upper-hybrid waves is proportional to the density of hot electrons. The maximum saturated energy can be up to one percent of the kinetic energy of hot electrons. Finally we find that the saturation energy maxima in the interval of ωUH∕ωce = 3–18 decrease according to the exponential function. All these findings can be used in the interpretation of solar radio zebras.