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  • Ning, Hao  (8)
  • 1
    In: Physics of Plasmas, AIP Publishing, Vol. 28, No. 4 ( 2021-04-01)
    Abstract: Plasma emission (PE), i.e., electromagnetic radiation at the plasma frequency and its second harmonic, is a general process occurring in both astrophysical and laboratory plasmas. The prevailing theory presents a multi-stage process attributed to the resonant coupling of beam-excited Langmuir waves with ion-acoustic waves. Here, we examine another possibility of the fundamental PE induced by the resonant coupling of Z-mode and whistler (W) waves. Earlier studies have been controversial in the plausibility and significance of such process in plasmas. In this study, we show that the matching condition of three-wave resonant interaction (Z + W → O) can be satisfied over a wide regime of parameters based on the magnetoionic theory, demonstrate the occurrence of such process, and further evaluate the rate of energy conversion from the pumped Z or W mode to the fundamental O mode with particle-in-cell simulations of wave pumping. The study presents an alternative form of the fundamental PE, which could possibly play a role in various astrophysical and laboratory scenarios with both Z and W modes readily excited through the electron cyclotron maser instability.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 1472746-8
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  • 2
    Online Resource
    Online Resource
    AIP Publishing ; 2022
    In:  Physics of Plasmas Vol. 29, No. 11 ( 2022-11-01)
    In: Physics of Plasmas, AIP Publishing, Vol. 29, No. 11 ( 2022-11-01)
    Abstract: According to the standard scenario of plasma emission, escaping radiations are generated by the nonlinear development of the kinetic bump-on-tail instability driven by a single beam of energetic electrons interacting with plasmas. Here, we conduct fully-kinetic electromagnetic particle-in-cell simulations to investigate plasma emission induced by the ring-distributed energetic electrons interacting with overdense plasmas. Efficient excitations of the fundamental (F) and harmonic (H) emissions are revealed with radiation mechanism(s) different from the standard scenario: (1) The primary modes accounting for the radiations are generated through the electron cyclotron maser instability [for the upper-hybrid (UH) and Z modes] and the thermal anisotropic instability [for the whistler (W) mode] ; the F emission is generated by the nonlinear coupling of the Z and W modes and the H emission by the nonlinear coupling of the UH modes. This presents an alternative mechanism of coherent radiation in overdense plasmas.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 1472746-8
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  • 3
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 651 ( 2021-07), p. A118-
    Abstract: Context. Electron-cyclotron maser emission (ECME) is the favored mechanism for solar radio spikes and has been investigated extensively since the 1980s. Most studies relevant to solar spikes employ a loss-cone-type distribution of energetic electrons, generating waves mainly in the fundamental X / O mode ( X 1/ O 1), with a ratio of plasma oscillation frequency to electron gyrofrequency ( ω pe /Ω ce ) lower than 1. Despite the great progress made in this theory, one major problem is how the fundamental emissions pass through the second-harmonic absorption layer in the corona and escape. This is generally known as the escaping difficulty of the theory. Aims. We study the harmonic emissions generated by ECME driven by energetic electrons with the horseshoe distribution to solve the escaping difficulty of ECME for solar spikes. Methods. We performed a fully kinetic electromagnetic particle-in-cell simulation with ω pe /Ω ce  = 0.1, corresponding to the strongly magnetized plasma conditions in the flare region, with energetic electrons characterized by the horseshoe distribution. We also varied the density ratio of energetic electrons to total electrons ( n e / n 0 ) in the simulation. To analyze the simulation result, we performed a fast Fourier transform analysis on the fields data. Results. We obtain efficient amplification of waves in Z and X 2 modes, with a relatively weak growth of O 1 and X 3. With a higher-density ratio, the X 2 emission becomes more intense, and the rate of energy conversion from energetic electrons into X 2 modes can reach ∼0.06% and 0.17%, with n e / n 0  = 5% and 10%, respectively. Conclusions. We find that the horseshoe-driven ECME can lead to an efficient excitation of X 2 and X 3 with a low value of ω pe /Ω ce , providing novel means for resolving the escaping difficulty of ECME when applied to solar radio spikes. The simultaneous growth of X 2 and X 3 can be used to explain some harmonic structures observed in solar spikes.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 4
    Online Resource
    Online Resource
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Letters Vol. 924, No. 2 ( 2022-01-01), p. L34-
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 924, No. 2 ( 2022-01-01), p. L34-
    Abstract: Previous studies on the beam-driven plasma emission process were done mainly for unmagnetized plasmas. Here we present fully kinetic electromagnetic particle-in-cell simulations to investigate this process in weakly magnetized plasmas of the solar corona conditions. The primary mode excited is the beam-Langmuir (BL) mode via classical bump-on-tail instability. Other modes include the Whistler (W) mode excited by electron cyclotron resonance instability, the generalized Langmuir (GL) waves that include a superluminal Z-mode component with smaller wavenumber k and a thermal Langmuir component with larger k , and the fundamental (F) and harmonic (H) branches of plasma emission. Further simulations of different mass and temperature ratios of electrons and protons indicate that the GL mode and the two escaping modes (F and H) correlate positively with the BL mode in intensity, supporting that they are excited through nonlinear wave–wave coupling processes involving the BL mode. We suggest that the dominant process is the decay of the primary BL mode. This is consistent with the standard theory of plasma emission. However, the other possibility of a Z + W → O–F coalescing process for the F emission cannot be ruled out completely.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 2006858-X
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  • 5
    Online Resource
    Online Resource
    American Astronomical Society ; 2021
    In:  The Astrophysical Journal Letters Vol. 920, No. 2 ( 2021-10-01), p. L40-
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 920, No. 2 ( 2021-10-01), p. L40-
    Abstract: Electron cyclotron maser emission (ECME) is regarded as a plausible source for coherent radio radiations from solar active regions (e.g., solar radio spikes). In this Letter, we present a 2D3V fully kinetic electromagnetic particle-in-cell simulation to investigate the wave excitations and subsequent nonlinear processes induced by the energetic electrons in the loss-cone distribution. The ratio of the plasma frequency to the electron gyrofrequency ω pe /Ω ce is set to 0.25, adequate for solar active region conditions. As a main result, we obtain strong emissions at the second-harmonic X mode (X2). While the fundamental X mode (X1) and the Z mode are amplified directly via the electron cyclotron maser instability, the X2 emissions can be produced by nonlinear coalescence between two Z modes and between Z and X1 modes. This represents a novel generation mechanism for the harmonic emissions in plasmas with a low value of ω pe /Ω ce , which may resolve the escaping difficulty of explaining solar radio emissions with the ECME mechanism.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 2006858-X
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  • 6
    In: The Astrophysical Journal, American Astronomical Society, Vol. 891, No. 1 ( 2020-03-04), p. L25-
    Type of Medium: Online Resource
    ISSN: 2041-8213
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2020
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 2006858-X
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  • 7
    Online Resource
    Online Resource
    American Astronomical Society ; 2021
    In:  The Astrophysical Journal Letters Vol. 909, No. 1 ( 2021-03-01), p. L5-
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 909, No. 1 ( 2021-03-01), p. L5-
    Abstract: The latest study has reported that plasma emission can be generated by energetic electrons of Dory–Guest–Harris distribution via the electron cyclotron maser instability (ECMI) in plasmas characterized by a large ratio of plasma oscillation frequency to electron gyro-frequency ( ω pe /Ω ce ). In our study, on the basis of the ECMI-plasma emission mechanism, we examine the double plasma resonance (DPR) effect and the corresponding plasma emission at both harmonic (H) and fundamental (F) bands using particle-in-cell simulations with various ω pe /Ω ce . This allows us to directly simulate the feature of the zebra pattern (ZP) observed in solar radio bursts for the first time. We find that (1) the simulations reproduce the DPR effect nicely for the upper hybrid and Z modes, as seen from their variation of intensity and linear growth rate with ω pe /Ω ce , (2) the intensity of the H emission is stronger than that of the F emission by ∼2 orders of magnitude and varies periodically with increasing ω pe /Ω ce , while the F emission is too weak to be significant (therefore, we suggest that it is the H emission accounting for solar ZPs), (3) the peak-valley contrast of the total intensity of H is ∼4, and the peak lies around integer values of ω pe /Ω ce (=10 and 11) for the present parameter setup. We also evaluate the effect of energy of energetic electrons on the characteristics of ECMI-excited waves and plasma radiation. The study provides novel insight on the physical origin of ZPs of solar radio bursts.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 2006858-X
    Location Call Number Limitation Availability
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  • 8
    Online Resource
    Online Resource
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 939, No. 2 ( 2022-11-01), p. 63-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 939, No. 2 ( 2022-11-01), p. 63-
    Abstract: The standard theory of plasma emission is based on kinetic couplings between a single beam of energetic electrons and unmagnetized thermal plasmas, involving multistep nonlinear wave–particle and wave–wave interactions. The theory has not yet been completely verified with fully kinetic electromagnetic particle-in-cell (PIC) simulations. Earlier studies, greatly limited by available computational resources, are controversial regarding whether the fundamental emission can be generated according to the standard theory. To resolve the controversy, we conducted PIC simulations with a large domain of simulations and a large number of macroparticles, among the largest ones of similar studies. We found significant fundamental emission if the relative beam density is small enough (say, ≤0.01), in line with an earlier study with a much smaller domain; the relative intensity (normalized by the total initial beam energy) of all modes, except the mode associated with the beam-electromagnetic Weibel instability, decreases with the increasing relative density of the beam. We also found a significant transverse magnetic component associated with the superluminal Langmuir turbulence, which has been mistakenly regarded as evidence of the F emission in the earlier study. Further investigations are required to reveal their origin.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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