Roles of hot electrons in generating upper-hybrid waves in the earth's radiation belt

Hwang, Junga; Shin, Dong-Ho; Yoon, Peter H.; Kurth, W. S.; Larsen, B.; Reeves, G. D.; Lee, D. Y.

doi:10.1063/1.4984249

Cited by 12 publications

(56 citation statements)

References 51 publications

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“…The plasma frequency can be deduced from the upper‐hybrid and cyclotron frequency measurement, which directly gives the electron density. In a recent pair of papers, it was pointed out that the measured upper‐hybrid frequency fluctuations may also contain information on the underlying hot electron properties (Hwang et al, ; Yoon et al, ). The electron contents in the Earth's inner magnetosphere are composed of different electron populations occupying distinct energy ranges.…”

Section: Application To Radiation Belt Environment: Spontaneously Emimentioning

confidence: 99%

“…Relativistic electrons (> 100 keV) characterize the radiation belt, but their number density is extremely low such that they do not influence average plasma characteristics (see, e.g., Baker et al, , and references therein). Combining the VAP data analysis and electrostatic spontaneous emission theory in magnetized plasmas, Hwang et al () showed that it is possible to deduce the information on the hot electron temperature from upper‐hybrid wave analysis in addition to the background cold electron density.…”

Section: Application To Radiation Belt Environment: Spontaneously Emimentioning

confidence: 99%

“…Electric field power spectrum corresponding to the 8 May 2013 event, where the time interval centered around 15:55 UT as analyzed by Hwang et al (), is highlighted with the rectangular box. Note how quiet the low‐frequency portion of the spectrum is throughout the entire time interval, thus indicating that this particular time period corresponds to the quiet time interval with no whistler chorus wave activity.…”

Section: Application To Radiation Belt Environment: Spontaneously Emimentioning

confidence: 99%

“…Other planetary magnetospheres also feature such fluctuations (Meyer‐Vernet et al, ; Moncuquet et al, ). Traditional theoretical explanations, whether they are based upon coherent emissions by unstable (i.e., loss cone) electron distribution functions (Ashour‐Abdalla & Kennel, , ; Hubbard & Birmingham, ; Rönnmark et al, ) or are based upon spontaneous emission theory (Hwang et al, ; Issautier et al, ; Meyer‐Vernet et al, ; Moncuquet et al, ; Sentman, ; Yoon et al, ), basically assume electrostatic formalism. This is because the measurements of these high‐frequency fluctuations are generally done with electric field detectors only.…”

Section: Introductionmentioning

confidence: 99%

“…The purpose of this paper is to address this problem in a quantitative manner and to calculate the predicted level of electric versus magnetic field fluctuation intensities. By employing the data‐theory comparison analysis as recently carried out by Hwang et al (), who assumed electrostatic formalism, we make a quantitative prediction on the expected level of the magnetic field intensity spectrum that, when combined with the antenna geometric factor (Meyer‐Vernet et al, ), may be used as a tool for electromagnetic quasi‐thermal spectroscopy. The potential significance of the present findings in broader astrophysical contexts will also be discussed.…”

Section: Introductionmentioning

confidence: 99%

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Electromagnetic Thermal Noise in Upper‐Hybrid Frequency Range

et al. 2018

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The inner magnetosphere including the radiation belt and ring current environment is replete with high‐frequency fluctuations with peak intensity occurring near upper‐hybrid frequency and/or multiple harmonic electron cyclotron frequencies above and below the upper‐hybrid frequency. Past and contemporary spacecraft missions, including the Van Allen Probes, were designed to detect the electric field spectrum only for these high‐frequency fluctuations. Making use of the recently formulated generalized theory of electromagnetic spontaneous emission in thermal magnetized plasmas, it is shown that upper‐hybrid/multiple harmonic electron cyclotron emissions are characterized by a significant magnetic field component, even in the high‐frequency regime. Such a prediction may potentially be tested by upcoming spacecraft missions including the Solar Probe Orbiter and Parker Solar Probe. The present finding may also have a potentially significant ramification for the broader astrophysical contexts.

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Section: Application To Radiation Belt Environment: Spontaneously Emimentioning

confidence: 99%

Section: Application To Radiation Belt Environment: Spontaneously Emimentioning

confidence: 99%

Section: Application To Radiation Belt Environment: Spontaneously Emimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electromagnetic Thermal Noise in Upper‐Hybrid Frequency Range

et al. 2018

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High‐Frequency Thermal Fluctuations and Instabilities in the Radiation Belt Environment

Hwang

Yoon

2018

JGR Space Physics

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This paper overviews the electrostatic and electromagnetic theories of spontaneous emission in magnetized plasma as they relate to measured electric and magnetic field fluctuations in quiet time radiation belt and ring current region. The pervasively detected high-frequency fluctuations in the upper-hybrid frequency range as well as the background low-frequency range spectral profile in the whistler mode range are explained within the context of the spontaneous emission theory. The quasilinear calculation of loss cone instability is also carried out in order to validate the assumption of spontaneous emission model. It is shown that the saturated wave amplitudes associated with the upper-hybrid and multiple-harmonic cyclotron instability are quite low, indicating that the theoretical explanation based upon the assumption of spontaneous emission theory may be adequate for understanding the observed background fluctuations during quiet times. Plain Language SummarySince hot electrons constitute only a small fraction of the total electron number density in the space plasma, the general thought has been that the upper-hybrid fluctuations are useful only as a tool for indirectly measuring the cold electron number density. However, the data from the Van Allen Probes showed that upper-hybrid electrostatic fluctuations pervasively and ubiquitously exist in the radiation belts. From there, we proved that the presence of hot electrons and upper-hybrid fluctuations are mutually related phenomenon. We believe that it is the high-frequency electrostatic fluctuations that are constantly emitted and reabsorbed by the hot electrons, which allow these radiation belt electrons to remain inside the outer radiation belt for such a long time.n 0 e 2 ∕( m e ) and f c = eB 0 ∕(2 m e c) are the plasma frequency and electron cyclotron frequency, respectively. Here e, n 0 , B 0 , m e , and c represent the unit electric charge, ambient number density, ambient magnetic field intensity, electron rest mass, and the speed of light in vacuo, respectively. The multiple harmonic cyclotron emissions are also known in the literatures as the (n + 1∕2)f c emissions, and such emissions have been detected by the GEOTAIL and the Van Allen Probes.

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Simulation and Quasi‐linear Theory of Magnetospheric Bernstein Mode Instability

et al. 2018

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Multiple‐harmonic electron cyclotron emissions, often known in the literature as the (n + 1/2)fce emissions, are a common occurrence in the magnetosphere. These emissions are often interpreted in terms of the Bernstein mode instability driven by the electron loss cone velocity distribution function. Alternatively, they can be interpreted as quasi‐thermal emission of electrostatic fluctuations in magnetized plasmas. The present paper carries out a one‐dimensional relativistic electromagnetic particle‐in‐cell simulation and also employs a reduced quasi‐linear kinetic theoretical analysis in order to compare against the simulation. It is found that the Bernstein mode instability is indeed excited by the loss cone distribution of electrons, but the saturation level of the electrostatic mode is quite low, and that the effects of instability on the electrons is rather minimal. This supports the interpretation of multiple‐harmonic emission in the context of the spontaneous emission and reabsorption in quasi‐thermal magnetized plasma in the magnetosphere.

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Roles of hot electrons in generating upper-hybrid waves in the earth's radiation belt

Cited by 12 publications

References 51 publications

Electromagnetic Thermal Noise in Upper‐Hybrid Frequency Range

Electromagnetic Thermal Noise in Upper‐Hybrid Frequency Range

High‐Frequency Thermal Fluctuations and Instabilities in the Radiation Belt Environment

Simulation and Quasi‐linear Theory of Magnetospheric Bernstein Mode Instability

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