Excitation of Low-Frequency Ion Acoustic Perturbations in the Presence of Stationary Lower Hybrid Turbulence

1978 ◽  
Vol 33 (2) ◽  
pp. 121-123
Author(s):  
I. Zhelyazkov ◽  
S. G. Tagare
Keyword(s):  
Low Frequency ◽  
Lower Hybrid ◽  
Ion Acoustic

scholarly journals Studies of Spectral Broadening of the Lower Hybrid Wave Line in the Current-Drive Regimes and Ion Heating at the FT-2 Tokamak

2021 ◽  
Vol 47 (4) ◽  
pp. 329-336
Author(s):  
V. V. Dyachenko ◽  
A. B. Altukhov ◽  
E. Z. Gusakov ◽  
L. A. Esipov ◽  
A. N. Konovalov ◽  
...  
Keyword(s):  
Electromagnetic Waves ◽  
Low Frequency ◽  
Current Drive ◽  
Lower Hybrid ◽  
Ion Heating ◽  
Lower Hybrid Wave ◽  
Acoustic Instability ◽  
Ion Acoustic ◽  
Lower Hybrid Current Drive ◽  
High Frequency Waves

Abstract The experiments at the FT-2 tokamak are described that were focused on clearing up the role of the parametric decay instabilities in decreasing the generation efficiency of the non-inductive current excited by the electromagnetic waves in the lower hybrid frequency range. The most discussed instability of such kind is the decay of the pump wave into the daughter high-frequency waves and the low-frequency ion–acoustic quasi-modes. The studies performed have shown that, under conditions of the FT-2 experiment, the ion–acoustic instability has no decisive effect on the decrease in the efficiency of the lower hybrid current drive.

scholarly journals Lower-hybrid (LH) oscillitons evolved from ion-acoustic (IA)/ion-cyclotron (IC) solitary waves: effect of electron inertia

2010 ◽  
Vol 17 (3) ◽  
pp. 245-268 ◽  
Author(s):  
J. Z. G. Ma ◽  
A. Hirose
Keyword(s):  
Solitary Waves ◽  
Power Spectra ◽  
Low Frequency ◽  
Lower Hybrid ◽  
Electron Inertia ◽  
Background Density ◽  
Ion Acoustic ◽  
Ion Cyclotron ◽  
Cartesian Geometry ◽  
General Dispersion

Abstract. Lower-hybrid (LH) oscillitons reveal one aspect of geocomplexities. They have been observed by rockets and satellites in various regions in geospace. They are extraordinary solitary waves the envelop of which has a relatively longer period, while the amplitude is modulated violently by embedded oscillations of much shorter periods. We employ a two-fluid (electron-ion) slab model in a Cartesian geometry to expose the excitation of LH oscillitons. Relying on a set of self-similar equations, we first produce, as a reference, the well-known three shapes (sinusoidal, sawtooth, and spiky or bipolar) of parallel-propagating ion-acoustic (IA) solitary structures in the absence of electron inertia, along with their Fast Fourier Transform (FFT) power spectra. The study is then expanded to illustrate distorted structures of the IA modes by taking into account all the three components of variables. In this case, the ion-cyclotron (IC) mode comes into play. Furthermore, the electron inertia is incorporated in the equations. It is found that the inertia modulates the coupled IA/IC envelops to produce LH oscillitons. The newly excited structures are characterized by a normal low-frequency IC solitary envelop embedded by high-frequency, small-amplitude LH oscillations which are superimposed upon by higher-frequency but smaller-amplitude IA ingredients. The oscillitons are shown to be sensitive to several input parameters (e.g., the Mach number, the electron-ion mass/temperature ratios, and the electron thermal speed). Interestingly, whenever a LH oscilliton is triggered, there occurs a density cavity the depth of which can reach up to 20% of the background density, along with density humps on both sides of the cavity. Unexpectedly, a mode at much lower frequencies is also found beyond the IC band. Future studies are finally highlighted. The appendices give a general dispersion relation and specific ones of linear modes relevant to all the nonlinear modes encountered in the text.

Scattering of electromagnetic waves by hybrid waves in a two-electron-temperature plasma

1991 ◽  
Vol 46 (1) ◽  
pp. 99-106 ◽  
Author(s):  
S. K. Sharma ◽  
A. Sudarshan
Keyword(s):  
Growth Rate ◽  
Electron Temperature ◽  
High Frequency ◽  
Electromagnetic Waves ◽  
Low Frequency ◽  
Lower Hybrid ◽  
Stimulated Scattering ◽  
Coupled Modes ◽  
Temperature Plasma ◽  
Electrostatic Perturbation

In this paper, we use the hydrodynamic approach to study the stimulated scattering of high-frequency electromagnetic waves by a low-frequency electrostatic perturbation that is either an upper- or lower-hybrid wave in a two-electron-temperature plasma. Considering the four-wave interaction between a strong high-frequency pump and the low-frequency electrostatic perturbation (LHW or UHW), we obtain the dispersion relation for the scattered wave, which is then solved to obtain an explicit expression for the growth rate of the coupled modes. For a typical Q-machine plasma, results show that in both cases the growth rate increases with noh/noc. This is in contrast with the results of Guha & Asthana (1989), who predicted that, for scattering by a UHW perturbation, the growth rate should decrease with increasing noh/noc.

Scattering of electromagnetic waves by anomalous fluctuations of a magnetized plasma

1990 ◽  
Vol 43 (2) ◽  
pp. 165-172 ◽  
Author(s):  
V. N. Pavlenko ◽  
V. G. Panchenko
Keyword(s):  
Cross Section ◽  
Electromagnetic Waves ◽  
Pump Wave ◽  
Density Fluctuations ◽  
Scattering Cross Section ◽  
Magnetized Plasma ◽  
Lower Hybrid ◽  
Scattering Cross ◽  
Parametric Decay ◽  
Ion Acoustic

Fluctuations and scattering of transverse electromagnetic waves by density fluctuations in a magnetized plasma in the presence of parametric decay of the pump wave are investigated. The spectral density of electron-density fluctuations is calculated. It is shown that the differential scattering cross-section has sharp maxima at the ion-acoustic and lower-hybrid frequencies when parametric decay of the lower-hybrid pump wave occurs. We note that scattering at the ion-acoustic frequency is dominant. When the pump-wave amplitude tends to the threshold strength of the electric field the scattering cross-section increases anomalously, i.e. there is critical opalescence.

Local kinetic analysis of low-frequency electrostatic modes in tokamaks

1991 ◽  
Vol 69 (2) ◽  
pp. 102-106
Author(s):  
A. Hirose
Keyword(s):  
Dispersion Relation ◽  
Kinetic Analysis ◽  
Low Frequency ◽  
Acoustic Mode ◽  
Landau Damping ◽  
Trapped Electrons ◽  
Ion Acoustic ◽  
Transit Frequency

Analysis, based on a local kinetic dispersion relation in the tokamak magnetic geometry incorporating the ion transit frequency and trapped electrons, indicates that modes with positive frequencies are predominant. Unstable "drift"-type modes can have frequencies well above the diamagnetic frequency. They have been identified as the destabilized ion acoustic mode suffering little ion Landau damping even when [Formula: see text].

scholarly journals Anomalous Transport in Current Sheets

1985 ◽  
Vol 107 ◽  
pp. 315-328
Author(s):  
J. D. Huba
Keyword(s):  
Anomalous Transport ◽  
Lower Hybrid ◽  
Diffusion Region ◽  
Transport Mechanisms ◽  
Current Sheets ◽  
Nonlinear Properties ◽  
Acoustic Instability ◽  
Ion Acoustic ◽  
Linear And Nonlinear ◽  
Drift Instability

A review of several microinstabilities that have been suggested as possible anomalous transport mechanisms in current sheets is presented. The specific application is to a ‘field reversed plasma’ which is relevant to the so-called ‘diffusion region’ of a reconnection process. The linear and nonlinear properties of the modes are discussed, and each mode is assessed as to its importance in reconnection processes based upon these properties. It is concluded that the two most relevant instabilities are the ion acoustic instability and the lower-hybrid-drift instability. However, each instability has limitations as far as reconnection is concerned, and more research is needed in this area.

Excitation of lower hybrid waves by electron beams in finite geometry plasmas. Part 2. Surface waves

1978 ◽  
Vol 19 (2) ◽  
pp. 295-299
Author(s):  
Réal R. J. Gagné ◽  
Magdi M. Shoucri
Keyword(s):  
Electron Beam ◽  
Surface Waves ◽  
Electron Beams ◽  
Low Frequency ◽  
Finite Geometry ◽  
Dispersion Relations ◽  
Lower Hybrid ◽  
Small Density ◽  
Hybrid Waves ◽  
Lower Hybrid Waves

The dispersion relations for the quasi-static lower hybrid surface waves are derived. Conditions for their existence and their linear excitation by a small density electron beam are discussed. Instabilities appearing in low-frequency surface waves are also discussed.

scholarly journals Ray tracing of whistler-mode chorus elements: implications for generation mechanisms of rising and falling tone emissions

2013 ◽  
Vol 31 (4) ◽  
pp. 665-673 ◽  
Author(s):  
K. Yamaguchi ◽  
T. Matsumuro ◽  
Y. Omura ◽  
D. Nunn
Keyword(s):  
Ray Tracing ◽  
Low Frequency ◽  
Equatorial Region ◽  
Lower Hybrid ◽  
Wave Pulse ◽  
Generation Region ◽  
Field Lines ◽  
Generation Mechanisms ◽  
Tone Generation ◽  
Lower Hybrid Resonance

Abstract. Using a well-established magnetospheric very-low-frequency (VLF) ray tracing method, in this work we trace the propagation of individual rising- and falling-frequency elements of VLF chorus from their generation point in the equatorial region of the magnetosphere through to at least one reflection at the lower-hybrid resonance point. Unlike recent work by Bortnik and co-workers, whose emphasis was on demonstrating that magnetospheric hiss has its origins in chorus, we here track the motion in the equatorial plane of the whole chorus element, paying particular regard to movement across field lines, rotation, and compression or expansion of the wave pulse. With a generation point for rising chorus at the equator, it was found the element wave pulse remained largely field aligned in the generation region. However, for a falling tone generation point at 4000 km upstream from the equator, by the time the pulse crosses the equator the wavefield had substantial obliquity, displacement, and compression, which has substantial implications for the theory of falling chorus generation.

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