Corrected Formula for the Polarization of Second Harmonic Plasma Emission

1980 ◽  
Vol 4 (1) ◽  
pp. 50-53 ◽  
Author(s):  
D. B. Melrose ◽  
G. A. Dulk ◽  
D. E. Gary
Keyword(s):  
Transverse Wave ◽  
Second Harmonic ◽  
Plasma Emission ◽  
Langmuir Waves

Second harmonic plasma emission is attributed to the coalescence of two Langmuir waves into a transverse wave.

scholarly journals 'Plasma Emission' without Langmuir Waves

1982 ◽  
Vol 35 (1) ◽  
pp. 67 ◽  
Author(s):  
DB Melrose
Keyword(s):  
Second Harmonic ◽  
Parametric Instability ◽  
The Other ◽  
Plasma Emission ◽  
Sound Waves ◽  
S Wave ◽  
Langmuir Waves ◽  
Transverse Waves ◽  
Type Iii ◽  
T Wave

Recent observations have confirmed that the level of Langmuir waves associated with type III streams of electrons in the interplanetary medium is usually too low to account for the observed radio emission by the accepted 'plasma emission' processes, and it has been suggested that emission mechanisms which do not require Langmuir waves should be explored. Four such mechanisms are discussed. One is a parametric instability leading directly to second-harmonic emission; it is found inapplicable under conditions of interest here. The other three processes all involve ion-sound turbulence. One which is known in a different context is turbulent bremsstrahlung. Turbulent bremsstrahlung of transverse waves is found to compare unfavourably with the other two processes, which are scattering of an ion-sound (s) wave into a transverse (t) wave and double emission of both waves simultaneously. These latter two processes are related by a crossing symmetry and are treated together with the following results: (i) The processes become greatly enhanced when the beat (w�w', k�k') between the t wave and the s wave nearly satisfies the dispersion relation for Langmuir (I) waves. (ii) A bump-in-the-tail instability (due to electrons with dF(v)/dv > 0) can cause the transverse waves to grow due to double emission; this growth has been likened to a freeelectron maser. (iii) The familiar bump-in-the-tail instability for resonant I waves can be suppressed by the ion-sound waves, and the double-emission instability then takes over with about the same growth rate as the original I-wave instability. (iv) The conditions for the double-emission instability to occur are probably satisfied at least some of the time for type III streams. It is concluded that although 'plasma emission' without Langmuir waves may be possible in principle, it is unlikely to play any role in type III bursts.

scholarly journals The effects of density inhomogeneities on the radio wave emission in electron beam plasmas

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Xin Yao ◽  
Patricio A. Muñoz ◽  
Jörg Büchner ◽  
Xiaowei Zhou ◽  
Siming Liu
Keyword(s):  
Magnetic Reconnection ◽  
Radio Wave ◽  
Solar Flares ◽  
Electron Beams ◽  
Distribution Functions ◽  
Plasma Emission ◽  
Langmuir Waves ◽  
Radio Emissions ◽  
Density Inhomogeneities ◽  
Effects Of Density

Type III radio bursts are radio emissions associated with solar flares. They are considered to be caused by electron beams travelling from the solar corona to the solar wind. Magnetic reconnection is a possible accelerator of electron beams in the course of solar flares since it causes unstable distribution functions and density inhomogeneities (cavities). The properties of radio emission by electron beams in an inhomogeneous environment are still poorly understood. We capture the nonlinear kinetic plasma processes of the generation of beam-related radio emissions in inhomogeneous plasmas by utilizing fully kinetic particle-in-cell code numerical simulations. Our model takes into account initial electron velocity distribution functions (EVDFs) as they are supposed to be created by magnetic reconnection. We focus our analysis on low-density regions with strong magnetic fields. The assumed EVDFs allow two distinct mechanisms of radio wave emissions: plasma emission due to wave–wave interactions and so-called electron cyclotron maser emission (ECME) due to direct wave–particle interactions. We investigate the effects of density inhomogeneities on the conversion of free energy from the electron beams into the energy of electrostatic and electromagnetic waves via plasma emission and ECME, as well as the frequency shift of electron resonances caused by perpendicular gradients in the beam EVDFs. Our most important finding is that the number of harmonics of Langmuir waves increases due to the presence of density inhomogeneities. The additional harmonics of Langmuir waves are generated by a coalescence of beam-generated Langmuir waves and their harmonics.

Second harmonic electromagnetic emission via beam-driven Langmuir waves

2005 ◽  
Vol 12 (1) ◽  
pp. 012103-012103-15 ◽  
Author(s):  
B. Li ◽  
A. J. Willes ◽  
P. A. Robinson ◽  
I. H. Cairns
Keyword(s):  
Second Harmonic ◽  
Electromagnetic Emission ◽  
Langmuir Waves

scholarly journals A Relationship Between the Brightness Temperatures for Type III Bursts

1974 ◽  
Vol 57 ◽  
pp. 285-287
Author(s):  
D. B. Melrose
Keyword(s):  
Fundamental Frequency ◽  
Solar Phys ◽  
Second Harmonic ◽  
Intermediate Stage ◽  
Langmuir Waves ◽  
Type Iii ◽  
Brightness Temperatures ◽  
Two Stages

(Solar Phys.). The widely accepted emission mechanisms for type III bursts involve at least two stages. The first stage is the generation of Langmuir waves by the inferred stream of electrons. Emission at the fundamental frequency arises when these waves are scattered by thermal ions. Emission at the second harmonic arises when two Langmuir waves coalesce; however, the coalescence is possible only after an intermediate stage in which the distribution of Langmuir waves evolves towards isotropy due to scattering by thermal ions.

scholarly journals A new hydrodynamic analysis of double layers

1987 ◽  
Vol 5 (2) ◽  
pp. 269-286 ◽  
Author(s):  
M. P. Goldsworthy ◽  
F. Green ◽  
H. Hora
Keyword(s):  
Electric Fields ◽  
Second Harmonic ◽  
Fluid Model ◽  
Inhomogeneous Plasma ◽  
Macroscopic Model ◽  
Double Layers ◽  
Astrophysical Plasmas ◽  
Langmuir Waves ◽  
Hydrodynamic Description ◽  
Very High

A Genuine two-fluid model of plasmas with collisions permits the calculation of dynamic electric fields and double layers inside plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser produced plasmas showing very high dynamic electric fields in nonlinear force produced cavitons and inverted layers, in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. We find the rotation of plasmas in magnetic fields and a new second harmonic resonance. Explanation of inverted double layers, second harmonic emission from laser produced plasmas, and laser acceleration of charged particles by the very high fields of the double layers is given.

scholarly journals Plasma Emission Processes in a Magnetoactive Plasma

1972 ◽  
Vol 25 (4) ◽  
pp. 387 ◽  
Author(s):  
DB Melrose ◽  
WN Sy
Keyword(s):  
Magnetic Field ◽  
Second Harmonic ◽  
Magnetoactive Plasma ◽  
Plasma Waves ◽  
Weak Field ◽  
Type I ◽  
Plasma Emission ◽  
Weak Field Limit ◽  
Electron Cyclotron Waves ◽  
The Magnetic Field

Plasma emission (i.e. emission at about the plasma frequency and twice this frequency) is treated taking into account the effects of the magnetic field on the electron plasma waves, on the conversion processes, and on the escaping radiation. The expected degrees of polarization of the fundamental and second harmonic are calculated in the weak field limit. The results are used to estimate the magnetic field strength B at the 80 MHz level from the observed polarization of type III bursts; the result B < 0�04 G is smaller than previous estimates. The possible importance of electron-cyclotron waves in an application to type I bursts is noted.

Two Alternative Mechanisms for Very Bright Radio Emission from Flare Stars

1993 ◽  
Vol 10 (3) ◽  
pp. 254-257 ◽  
Author(s):  
D.B. Melrose
Keyword(s):  
Radio Emission ◽  
Brightness Temperature ◽  
Second Harmonic ◽  
Temporal Variations ◽  
Plasma Emission ◽  
High Brightness ◽  
Circular Polarisation ◽  
Cyclotron Maser ◽  
Flare Stars ◽  
High Degree

AbstractThe bright radio emission from flare stars has three characteristic properties: high brightness temperature, high degree of circular polarisation and rapid temporal variations. Two proposed emission mechanisms, electron cyclotron maser emission (ECME) and plasma emission, are compared and contrasted. It is argued that although the important features of the emission can be explained in terms of either ECME or plasma emission, all three favor ECME. However, the escapes of the radiation through the second harmonic absorption layer remains inadequately understood, and as a consequence doubts about the ECME interpretation remain.

scholarly journals Characterization of Microcrack Orientation Using the Directivity of Secondary Sound Source Induced by an Incident Ultrasonic Transverse Wave

Materials ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3318
Author(s):  
Jishuo Wang ◽  
Caibin Xu ◽  
Youxuan Zhao ◽  
Ning Hu ◽  
Mingxi Deng
Keyword(s):  
Transverse Wave ◽  
Sound Source ◽  
Second Harmonic ◽  
Directivity Pattern ◽  
Fe Model ◽  
Driving Frequency ◽  
Stress Strain ◽  
Contact Acoustic Nonlinearity ◽  
Strain Model

In this paper, characterization of the orientation of a microcrack is quantitatively investigated using the directivity of second harmonic radiated by the secondary sound source (SSS) induced by the nonlinear interaction between an incident ultrasonic transverse wave (UTW) and a microcrack. To this end, a two-dimensional finite element (FE) model is established based on the bilinear stress–strain constitutive relation. Under the modulation of contact acoustic nonlinearity (CAN) to the incident UTW impinging on the microcrack examined, the microcrack itself is treated as a SSS radiating the second harmonic. Thus, the directivity of the second harmonic radiated by the SSS is inherently related to the microcrack itself, including its orientation. Furthermore, the effects of the stiffness difference between the compressive and tensile phases in the bilinear stress–strain model, and the UTW driving frequency, as well as the radius of the sensing circle on the SSS directivity are discussed. The FE results show that the directivity pattern of the second harmonic radiated by the SSS is closely associated with the microcrack orientation, through which the microcrack orientation can be characterized without requiring a baseline signal. It is also found that the SSS directivity varies sensitively with the driving frequency of the incident UTW, while it is insensitive to the stiffness difference between the compressive and tensile phases in the bilinear stress–strain model and the radius of the sensing circle. The results obtained here demonstrate that the orientation of a microcrack can be characterized using the directivity of the SSS induced by the interaction between the incident UTW and the microcrack.

scholarly journals Detection of Langmuir Solitons: Implications for Type III Burst Emission Mechanisms at 2ωPE

1996 ◽  
Vol 154 ◽  
pp. 195-198
Author(s):  
G. Thejappa ◽  
R.G. Stone ◽  
M.L. Goldstein
Keyword(s):  
Second Harmonic ◽  
Theoretical Models ◽  
Burst Source ◽  
Langmuir Waves ◽  
Type Iii ◽  
Source Regions ◽  
Envelope Solitons ◽  
Turbulence Regime ◽  
Solar Type ◽  
Langmuir Solitons

AbstractWe present the experimental verification of existing theoretical models of emission mechanisms of solar type III bursts at the second harmonic of the plasma frequency, ωpe. This study is based on the detection of Langmuir and envelope solitons by the Ulysses spacecraft inside three type III burst source regions. We show that the oscillating-two-stream instability, coherent radiation by Langmuir solitons and stochastic phase mixing of the Langmuir waves in the strong turbulence regime are the appropriate emission mechanisms at 2ωpe.

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