Loss cone‐driven cyclotron maser instability

Lee, Sang-Yun; Yi, So Jeong; Lim, Daye; Kim, Hee‐Eun; Seough, Jungjoon; Yoon, Peter H.

doi:10.1002/2013ja019298

Cited by 25 publications

(19 citation statements)

References 59 publications

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“…In addition, most earlier studies focused on the variation of the growth rate with the plasma-cyclotron frequency ratio, and did not pay much attention to other critical parameters such as the propagation angles (θ max ) and the frequencies (ω r max ) at which the instability develops at the maximum growth rate. Lee et al (2013) conducted a parameter study on the electron cyclotron maser instability which directly excites the escaping X and ordinary (O) modes (Wu & Lee 1979) and checked the variation of both parameters for the regime of ω pe Ω ce ≤ 5. Yi et al (2013) extends the study to investigate the variations of the two parameters of Z-mode instability.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Temperature of Background Plasma and the Energy of Energetic Electrons on Z-mode Excitation

Chen

Kong

et al. 2019

ApJ

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It has been suggested that the Z-mode instability driven by energetic electrons with a loss-cone type velocity distribution is one candidate process behind the continuum and zebra pattern of solar type-IV radio bursts. Both the temperature of background plasma (T 0 ) and the energy of energetic electrons (v e ) are considered to be important to the variation of the maximum growth rate (γ max ). Here we present a detailed parameter study on the effect of T 0 and v e , within a regime of the frequency ratio (10 ≤ ω pe Ω ce ≤ 30). In addition to γ max , we also analyze the effect on the corresponding wave frequency (ω r max ) and propagation angle (θ max ). We find that (1) γ max in-general decreases with increasing v e , while its variation with T 0 is more complex depending on the exact value of v e ; (2) with increasing T 0 and v e , ω r max presents step-wise profiles with jumps separated by gradual or very-weak variations, and due to the warm-plasma effect on the wave dispersion relation ω r max can vary within the hybrid band (the harmonic band containing the upper hybrid frequency) and the band higher; (3) the propagation is either perpendicular or quasi-perpendicular, and θ max presents variations in line with those of ω r max , as constrained by the resonance condition. We also examine the profiles of γ max with ω pe Ω ce for different combinations of T 0 and v e to clarify some earlier calculations which show inconsistent results.

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Section: Introductionmentioning

confidence: 99%

Effect of the Temperature of Background Plasma and the Energy of Energetic Electrons on Z-mode Excitation

Chen

Kong

et al. 2019

ApJ

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“…Note that one cannot make a direct comparison between Figs.4, 5 and the panels (g), (h) of Figs.6, 7, respectively, since intensity in Figs.4 and 5 also contain the electrostatic electric fields. For example, the O mode is electrostatic around its cutoff frequency ω pe (Lee et al 2013). Fig.8 shows anisotropy of the spectrogram of differently polarized escaping waves.…”

Section: Polarization Propertiesmentioning

confidence: 99%

Wave Excitation by Energetic Ring-distributed Electron Beams in the Solar Corona

Zhou

Muñoz

Büchner

et al. 2020

ApJ

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We re-considered the properties of electromagnetic waves excited by ring-distributed, in the magnetic-field-perpendicular velocity space, electron beams in the solar atmosphere as they are caused by magnetic reconnection. Ring-beam electrons contain additional free energy due to the positive gradient of their velocity space distribution in the direction perpendicular to the magnetic field, i.e., d f /du ⊥ > 0 in addition to the beam-related free energy u ·d f /du > 0 in the direction parallel to the magnetic field. As a result, not only beam instability but also so called electron cyclotron maser (ECM) instability can be excited, which may generate escaping electromagnetic waves. In order to understand the properties of the waves generated in the course of the propagation of such beams, we investigated the intensity and polarization properties of these excited waves in dependence on the evolving beam density and coronal magnetic field strength. For this sake, we utilized 2.5-dimensional particle-in-cell (PIC) code Corresponding author: X. Zhou zhouxw@pmo.ac.cn arXiv:1907.12958v1 [physics.plasm-ph] 28 Jul 2019 2 Zhou et al.numerical simulations. We separated the intensities of the different wave modes according to their dispersion properties. We found that predominantly electrostatic plasma waves are generated but also highly anisotropic and polarized electromagnetic whistler, Z, O and X-mode waves. Their intensity anisotropy strongly depends on the number density of the ring-beam electrons compared to the density of the background electrons. Circular polarization degree (CPD) and spectrogram of the escaping electromagnetic waves with ω > ω pe and |ck/ω| < 1 are also strongly anisotropic, but becoming more symmetric about the wave propagation direction θ = 90 • for denser ring-beam electron population. Meanwhile, with denser ring-beam electron population, escaping waves are predominantly left-handed polarized over a wide range of propagation directions. We discuss the consequences of our findings for using the solar radio burst observations to diagnose the beam and plasma conditions at the sites of their generation.

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“…The essential details of the theoretical formalism are described in a companion paper [ Lee et al , ]. For the sake of completeness, we briefly outline the theoretical formalism, but we restrict ourselves to Z mode exclusively.…”

Section: Narrowband and Broadband Z‐mode Instabilitiesmentioning

confidence: 99%

Z‐mode maser instability

Lee

Kim

et al. 2013

JGR Space Physics

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[1] Although the cyclotron maser instability customarily involves the extraordinary (X ) and ordinary (O) fast transverse electromagnetic wave modes, which directly escape and propagate long distances from the source region, the instability also excites the Z mode for a wide range of parameters. Even though Z mode is a nonescaping mode, it may convert to O mode in an inhomogeneous medium and be detected by remote means. This process is believed to explain radio emissions near cyclotron harmonics emitted both upward and downward from Earth's auroral ionosphere, as well as analogous emissions detected near Saturn. A more general analysis of the electron loss cone driven Z-mode maser instability than previously reported reveals that for certain plasma-to-cyclotron-frequency ratios, the unstable waves split into broadband and narrowband ranges of unstable modes and that these two bands are characterized by distinct polarizations. In previous studies of the Z-mode maser, the maximum growth rate was considered without distinguishing the two bands. Although the maximum temporal growth rate sometimes corresponds to the narrowband feature, the broadband feature with a significant O-mode-like polarization may be of importance, since it can more easily convert to an escaping radiation. This paper presents analysis of maximum growth rates, wave propagation angles, and wave frequencies for the two band features of the loss cone driven Z-mode maser instability as a function of the ratio of plasma-to-electron cyclotron frequency. The results are relevant to auroral radio emission phenomena, especially those observed near cyclotron harmonics at both Earth and Saturn.

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Loss cone‐driven cyclotron maser instability

Cited by 25 publications

References 59 publications

Effect of the Temperature of Background Plasma and the Energy of Energetic Electrons on Z-mode Excitation

Effect of the Temperature of Background Plasma and the Energy of Energetic Electrons on Z-mode Excitation

Wave Excitation by Energetic Ring-distributed Electron Beams in the Solar Corona

Z‐mode maser instability

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