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Nonlinear trapping and self-guiding of magnetized Langmuir waves due to thermal plasma filamentation
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10.1063/1.2822161
/content/aip/journal/pop/14/12/10.1063/1.2822161
http://aip.metastore.ingenta.com/content/aip/journal/pop/14/12/10.1063/1.2822161

Figures

Image of FIG. 1.
FIG. 1.

Schematic view of the experimental setup.

Image of FIG. 2.
FIG. 2.

Wave index surfaces in the upper hybrid frequency range: (a), (b) Cold plasma approximation; (c) plasma with a finite electron temperature. Ordinary-polarized mode ( mode) and quasi-electrostatic extraordinary-polarized UH mode ( mode) are indicated as “” and “,” respectively.

Image of FIG. 3.
FIG. 3.

Field patterns of a small electric dipole at different plasma densities in the UH range. ; ; . The resonance cone structure is observed throughout the UH range.

Image of FIG. 4.
FIG. 4.

The dynamics of the UH field pattern in the afterglow plasma at different amplitudes of the input signal applied to the emitting antenna. ; ; . Resonance cones are registered for all input signals. The appearance of the new radiation component is observed as the amplitude of the input signal increases (b), (c). This component propagates along the ambient magnetic field, when the radiation frequency is equal to the plasma frequency . The decrease of plasma density in the afterglow is indicated by dimensionless parameter . The UH range lies between . The distance between the emitter and the receiver is .

Image of FIG. 5.
FIG. 5.

Amplitude of the new radiation component as a function of the amplitude of the input signal incident to the emitting antenna . The new radiation component exhibits a threshold, fast growth, and saturation, which are typical for the instabilities. Curve 1 corresponds to the initially uniform plasma column; curve 2 is measured with a small ( diameter) obstacle introduced at from the exciting antenna.

Image of FIG. 6.
FIG. 6.

2D plot of the new component of the antenna radiation in the surface. The radiation penetrates into the plasma volume as a narrow channel without radial divergence with the characteristic velocity . .

Image of FIG. 7.
FIG. 7.

Schematic view of the microwave resonator probe.

Image of FIG. 8.
FIG. 8.

(a) Electron temperature measured with a Langmuir probe. (b) Plasma density profile measured with a microwave resonator probe. A narrow, magnetic-field-aligned density depletion is formed due to the thermal nonlinearity. Measurements are performed at .

Image of FIG. 9.
FIG. 9.

(a) Electron temperature measured with a Langmuir probe. (b) Plasma density profile measured with a microwave resonator probe. A narrow, magnetic-field-aligned density depletion is formed due to the thermal nonlinearity. Measurements are performed at .

Image of FIG. 10.
FIG. 10.

Trapping of probe waves inside the density channel. (a) Field pattern of a probe wave radiated by a small antenna located inside a preformed density channel. The channel is formed by the pump wave: , . Trapping of a probe wave inside the channel is observed at . Distance between the emitter and the receiver is . (b)–(e) Dynamics of the radial distribution of the trapped probe wave measured at from the emitting antenna.

Image of FIG. 11.
FIG. 11.

Amplitude of the trapped wave as a function of the ratio . Suppression of the wave trapping is observed in the vicinity of the gyroharmonics. .

Image of FIG. 12.
FIG. 12.

Amplitude of UH waves propagating along the ambient magnetic field as a function of time in afterglow. Trapped waves are observed as a narrow peak at (a), (c). Suppression of the trapped waves are observed in the vicinity of second gyroharmonics (b). .

Image of FIG. 13.
FIG. 13.

Threshold of nonlinear wave trapping measured as a function of . The threshold amplitude is highest in the vicinity of each harmonic of the electron gyrofrequency ; it sharply decreases when goes beyond , gets its lowest value just above the gyroharmonics, and slowly increases with increasing . When approaches to the next gyroharmonic , the threshold amplitude sharply grows and gets very high again at .

Image of FIG. 14.
FIG. 14.

Qualitative model of Langmuir wave trapping inside a magnetic-field-aligned density depletion: Profile of the depletion (a) and corresponding wave index surfaces (b). Propagation of an eigenmode with is considered. Directions of its group velocities are marked with arrows. The Langmuir wave is excited in the center of the depletion and propagates toward the periphery of the depletion, where the plasma density is higher. The angle between the group velocity of the excited wave and the ambient magnetic field diminishes and vanishes at a particular density , whereupon the wave gets reflected toward the center of the depletion. Corresponding ray tracing inside the density depletion is also shown qualitatively.

Tables

Generic image for table
Table I.

Typical reduced plasma parameters in the ionospheric heating experiments and in the present laboratory modeling.

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/content/aip/journal/pop/14/12/10.1063/1.2822161
2007-12-19
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Nonlinear trapping and self-guiding of magnetized Langmuir waves due to thermal plasma filamentation
http://aip.metastore.ingenta.com/content/aip/journal/pop/14/12/10.1063/1.2822161
10.1063/1.2822161
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