scholarly journals DENSITY FLUCTUATIONS AND THE ACCELERATION OF ELECTRONS BY BEAM-GENERATED LANGMUIR WAVES IN THE SOLAR CORONA

2012 ◽  
Vol 761 (2) ◽  
pp. 176 ◽  
Author(s):  
H. Ratcliffe ◽  
N. H. Bian ◽  
E. P. Kontar
Keyword(s):  
Solar Corona ◽  
Density Fluctuations ◽  
Langmuir Waves

Solar type III radio burst fine structure from Langmuir wave motion through turbulent plasma

2021 ◽  
Author(s):  
Eduard Kontar ◽  
Hamish Reid
Keyword(s):  
Fine Structure ◽  
Solar Corona ◽  
Interplanetary Space ◽  
Langmuir Wave ◽  
Turbulent Medium ◽  
Density Fluctuations ◽  
Solar Radio Emission ◽  
Langmuir Waves ◽  
Type Iii ◽  
Diagnostic Potential

<div>The Sun frequently accelerates near-relativistic electron beams that travel out through the solar corona and interplanetary space. Interacting with their plasma environment, these beams produce type III radio bursts, the brightest astrophysical radio sources detected by humans. The formation and motion of type III fine frequency structures is a puzzle but is commonly believed to be related to plasma turbulence in the solar corona and solar wind. Combining a theoretical framework with kinetic simulations and high-resolution radio type III observations, we quantitatively show that the fine structures are caused by the moving intense clumps of Langmuir waves in a turbulent medium. Our results show how type III fine structure can be used to remotely analyse the intensity and spectrum of compressive density fluctuations, and can infer ambient temperatures in astrophysical plasma, both significantly expanding the current diagnostic potential of solar radio emission.</div><div> </div>

scholarly journals Electron beam relaxation in inhomogeneous plasmas

2013 ◽  
Vol 31 (8) ◽  
pp. 1379-1385 ◽  
Author(s):  
A. Voshchepynets ◽  
V. Krasnoselskikh
Keyword(s):  
Electron Beam ◽  
Beam Energy ◽  
Electron Beams ◽  
Inhomogeneous Plasma ◽  
Density Fluctuations ◽  
Langmuir Waves ◽  
Wave Trapping ◽  
Beam Plasma ◽  
Beam Plasma Instability ◽  
Accelerated Particles

Abstract. In this work, we studied the effects of background plasma density fluctuations on the relaxation of electron beams. For the study, we assumed that the level of fluctuations was so high that the majority of Langmuir waves generated as a result of beam-plasma instability were trapped inside density depletions. The system can be considered as a good model for describing beam-plasma interactions in the solar wind. Here we show that due to the effect of wave trapping, beam relaxation slows significantly. As a result, the length of relaxation for the electron beam in such an inhomogeneous plasma is much longer than in a homogeneous plasma. Additionally, for sufficiently narrow beams, the process of relaxation is accompanied by transformation of significant part of the beam kinetic energy to energy of accelerated particles. They form the tail of the distribution and can carry up to 50% of the initial beam energy flux.

STATISTICS OF DENSITY FLUCTUATIONS DURING THE TRANSITION FROM THE OUTER SOLAR CORONA TO THE INTERPLANETARY SPACE

2009 ◽  
Vol 706 (1) ◽  
pp. 238-243 ◽  
Author(s):  
D. Telloni ◽  
R. Bruno ◽  
V. Carbone ◽  
E. Antonucci ◽  
R. D'Amicis
Keyword(s):  
Solar Corona ◽  
Interplanetary Space ◽  
Density Fluctuations

scholarly journals Analysis of Observations near the Fourth Electron Gyrofrequency Heating Experiment in EISCAT

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 191
Author(s):  
Zeyun Li ◽  
Hanxian Fang ◽  
Hongwei Gong ◽  
Zhe Guo
Keyword(s):  
Electron Temperature ◽  
Electron Density ◽  
Parametric Instability ◽  
Density Fluctuations ◽  
Lower Hybrid ◽  
Langmuir Waves ◽  
Ionospheric Heating ◽  
Superthermal Electron ◽  
Temperature Electron ◽  
Electron Gyrofrequency

We present the observations of the artificial ionospheric heating experiment of EISCAT (European Incoherent Scatter Scientific Association) on 22 February 2012 in Tromsø, Norway. When the pump is operating near the fourth electron gyrofrequency, the UHF radar observation shows some strong enhancements in electron temperature, electron density, ion line, and the outshifted plasma lines. Based on some existing theories, we find the following: first, Langmuir waves scattering off lower hybrid density fluctuations and strong Langmuir turbulence (SLT) in the Zakharov model cannot completely explain the outshifted plasma lines, but the data suggest that this phenomenon is related to the cascade of the pump wave and should be researched further; second, the spatiotemporal consistency between the enhancement in electron density/electron temperature reaches up to three to four times that of the undisturbed state and HF-enhanced ion lines (HFILs) suggest that SLT excited by parametric instability plays a significant role in superthermal electron formation and electron acceleration; third, some enhancements in HFILs and HF-induced plasma lines (HFPLs) are generated by parametric decay instability (PDI) during underdense heating in the third cycle, we suggest that this is due to the existence of a second cut-off in the upper hybrid dispersion relation as derived from a kinetic description.

scholarly journals Stimulated Raman scattering in active galactic nuclei

1986 ◽  
Vol 119 ◽  
pp. 419-420
Author(s):  
V. Krishan ◽  
P. J. Wiita
Keyword(s):  
Raman Scattering ◽  
Active Galactic Nuclei ◽  
Stimulated Raman Scattering ◽  
Galactic Nuclei ◽  
Density Fluctuations ◽  
Time Variability ◽  
Langmuir Waves ◽  
Spatially Periodic ◽  
Modulational Instabilities ◽  
Stimulated Raman

Stimulated Raman scattering (SRS) processes offer an attractive and efficient method for producing both essentially the entire non-thermal continuum as well as fast electrons in active galactic nuclei (AGN). In this picture, electrons are accelerated by Langmuir waves which are generated by Raman forward scattering (RFS); these electrons then rapidly radiate their energy by means of Raman back scattering (RBS) off of spatially periodic magnetic fields. Such periodic fields can be produced by magnetic modulational instabilities of the Langmuir field The emission is envisaged to arise from an expanding region, with the highest frequency radiation originating from the smallest volumes at the core of the AGN. Time variability is dominated by density fluctuations in these magnetohydrodynamic flows.

scholarly journals Fundamental Electromagnetic Emissions by a Weak Electron Beam in Solar Wind Plasmas with Density Fluctuations

2022 ◽  
Vol 924 (2) ◽  
pp. L24
Author(s):  
C. Krafft ◽  
P. Savoini
Keyword(s):  
Electron Beam ◽  
Electromagnetic Radiation ◽  
Inhomogeneous Plasma ◽  
Langmuir Wave ◽  
Density Fluctuations ◽  
Electromagnetic Energy ◽  
Langmuir Waves ◽  
Harmonic Emission ◽  
Electromagnetic Emissions ◽  
Weak Electron

Abstract The generation of Langmuir wave turbulence by a weak electron beam in a randomly inhomogeneous plasma and its subsequent electromagnetic radiation are studied owing to two-dimensional particle-in-cell simulations in conditions relevant to type III solar radio bursts. The essential impact of random density fluctuations of average levels of a few percents of the background plasma on the characteristics of the electromagnetic radiation at the fundamental plasma frequency ω p is shown. Not only wave nonlinear interactions but also processes of Langmuir waves’ transformations on the density fluctuations contribute to the generation of such emissions. During the beam relaxation, the amount of electromagnetic energy radiated at ω p in a plasma with density fluctuations strongly exceeds that observed when the plasma is homogeneous. The fraction of Langmuir wave energy involved in the generation of electromagnetic emissions at ω p saturates around 10−4, i.e., one order of magnitude above that reached when the plasma is uniform. Moreover, whereas harmonic emission at 2ω p dominates over fundamental emission during the time evolution in a homogeneous plasma, fundamental emission is strongly dominant when the plasma contains density fluctuations, at least during several thousands of plasma periods before being overcome by harmonic emission when the total electromagnetic energy begins to saturate.

scholarly journals LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse

2021 ◽  
Author(s):  
Aoife Maria Ryan ◽  
Peter T. Gallagher ◽  
Eoin P. Carley ◽  
Michiel A. Brentjens ◽  
Pearse C. Murphy ◽  
...  
Keyword(s):  
Solar Corona ◽  
Spatial Resolution ◽  
Solar Eclipse ◽  
Electromagnetic Waves ◽  
Imaging Techniques ◽  
Active Regions ◽  
Density Fluctuations ◽  
Source Size ◽  
Interferometric Imaging ◽  
Low Frequencies

<p>The solar corona is a highly-structured plasma which can reach temperatures of more than 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations, due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120–180 MHz using baselines of up to 3.5 km (corresponding to a resolution of 1–2’) during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (0.6’) than that attainable via standard interferometric imaging (2.4’). This provides a means of studying the contribution of scattering to apparent source size broadening. This study shows that the de-occultation technique can reveal a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be 4’ using both de-occultation and standard imaging. This may be explained by increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.</p><p><br><br></p>

Connection between ambient density fluctuations and clumpy Langmuir waves in type III radio sources

1992 ◽  
Vol 387 ◽  
pp. L101 ◽  
Author(s):  
P. A. Robinson ◽  
I. H. Cairns ◽  
D. A. Gurnett
Keyword(s):  
Density Fluctuations ◽  
Radio Sources ◽  
Langmuir Waves ◽  
Type Iii
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