Linear mode conversion of Langmuir/z-mode waves to radiation: Scalings of conversion efficiencies and propagation angles with temperature and magnetic field orientation

Schleyer, Fiona; Cairns, Iver H.; Kim, Eun Hwa

doi:10.1063/1.4793726

Cited by 13 publications

(24 citation statements)

References 29 publications

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“…We assume that type III bursts are produced by quasi‐linear and nonlinear processes involved in plasma emission [e.g., Melrose , ; Cairns , , ; Bastian et al , ; Robinson and Cairns , ]. Other mechanisms such as linear mode conversion [ Kim et al , ; Schleyer et al , ], antenna radiation from Langmuir eigenmodes [ Malaspina et al , , ], and nongyrotropic beam‐driven emission [ Tsiklauri , ; Pechhacker and Tsiklauri , , ] are assumed to be less important and are not included. The injection of energetic electrons produced during a flare onto an open magnetic field line embedded in a plasma whose waves are treated using unmagnetized theory is represented by adding a source term G to the quasi‐linear electron transport equation [e.g., Li et al , , ]:

\frac{\partial f_{e}}{∂t} + v \frac{\partial f_{e}}{∂x} = \frac{\partial}{∂v} (A f_{e}) + \frac{\partial}{∂v} ((), D \frac{\partial f_{e}}{∂v}) + G (t, x, v),

where

G (t, x, v) = \frac{F_{inj}}{\sqrt{π} δt} I (v) exp ([], - \frac{{(t - t_{0})}^{2}}{{(δt)}^{2}} - \frac{{(x - x_{0})}^{2}}{{(δx)}^{2}}) .

Here f e = f e ( t , x , v ) is the electron distribution function at time t and radial distance x = r − R ⊙ above the photosphere ( r = R ⊙ ), v is the electron speed, and f e is normalized to the plasma density n e .…”

Section: Simulation Modelmentioning

confidence: 99%

“…[8] We assume that type III bursts are produced by quasilinear and nonlinear processes involved in plasma emission [e.g., Melrose, 1980;Cairns, 1987aCairns, , 1987bBastian et al, 1998;Robinson and Cairns, 1998a]. Other mechanisms such as linear mode conversion [Kim et al, 2008;Schleyer et al, 2013], antenna radiation from Langmuir eigenmodes [Malaspina et al, 2010[Malaspina et al, , 2012, and nongyrotropic beamdriven emission [Tsiklauri, 2011;Tsiklauri, 2012a, 2012b] are assumed to be less important and are not included. The injection of energetic electrons produced during a flare onto an open magnetic field line embedded in a plasma whose waves are treated using unmagnetized theory is represented by adding a source term G to the quasi-linear electron transport equation [e.g., Li et al, 2003Li et al, , 2011a:…”

Section: Introductionmentioning

confidence: 99%

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Type III bursts produced by power law injected electrons in Maxwellian background coronal plasmas

Cairns

2013

JGR Space Physics

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[1] Simulations are presented for coronal type III bursts produced by injection of energetic electrons with power law speed spectra onto open magnetic field lines embedded in an otherwise unmagnetized Maxwellian background coronal plasma, including quasi-linear wave-particle interactions and nonlinear wave-wave processes. The simulations show that although fast electrons with speeds > 0.3c are injected, they are important only to the onset and not to the peak of f p emission, where f p is the local electron plasma frequency. Instead, slower beam electrons are the major drivers of the peak f p emission. Therefore, the type III beam speeds derived from the drift rates of peak f p emission are less than the typical speeds of c/3 observed for coronal type III bursts. This occurs mainly because the number of fast beam electrons with speeds > 0.3c is much less than the slower ones, causing weaker f p emission from these fast beam electrons. Comparisons are made with injected electrons having Maxwellian spectra. We find that type III beams are faster when the injection has power law spectra, since there are more fast electrons injected than for Maxwellian spectra. These results suggest that type III beams produced in the corona with Maxwellian background particle distributions and either power law or Maxwellian spectra can account only for the lower half of the observed range 0.1-0.6c of type III beam speeds but not for the upper half.Citation: Li, B., and I. H. Cairns (2013), Type III bursts produced by power law injected electrons in Maxwellian background coronal plasmas,

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\frac{\partial f_{e}}{∂t} + v \frac{\partial f_{e}}{∂x} = \frac{\partial}{∂v} (A f_{e}) + \frac{\partial}{∂v} ((), D \frac{\partial f_{e}}{∂v}) + G (t, x, v),

where

G (t, x, v) = \frac{F_{inj}}{\sqrt{π} δt} I (v) exp ([], - \frac{{(t - t_{0})}^{2}}{{(δt)}^{2}} - \frac{{(x - x_{0})}^{2}}{{(δx)}^{2}}) .

Section: Simulation Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Type III bursts produced by power law injected electrons in Maxwellian background coronal plasmas

Cairns

2013

JGR Space Physics

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“…As the density decreases with the distance to the Sun, the plasma frequency decreases, and the type III exhibits their characteristic time-frequency drift. Several wave conversion processes have been discussed from linear mode conversion in inhomogeneous density profiles [Field, 1956;Kim et al, 2008;Schleyer et al, 2013] to nonlinear processes including nonlinear beam instability [Yoon, 1995], wave coupling (electrostatic parametric decay [Cairns, 1987b;Henri et al, 2009], or electromagnetic coupling [Cairns, 1987a]). …”

Section: Introductionmentioning

confidence: 99%

Inhibition of type III radio emissions due to the interaction between two electron beams: Observations and simulations

2014

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International audienceWe report the peculiar interaction of two type III bursts observed in the solar wind. As electronbeams propagating on the same magnetic field lines cross, a spectacular depletion of the type III radioemission is observed. We combine observations from the WAVES experiment on board the STEREO missiontogether with kinetic plasma simulations to study the extinction of type III radio emission resulting fromthe interaction between two electron beams. The remote observations enable to follow the electron beamsin the interplanetary medium and show that the level of radiated radio waves is recovered after the beamcrossing. The in situ observations of beam-driven Langmuir waves give evidence for Langmuir decay. Thedensity fluctuations are extracted from in situ observations. The velocity of the beams is independentlyevaluated from in situ observations of decaying Langmuir waves and remote radio observations. The kineticsimulations show that the level of beam-driven Langmuir waves is reduced as the two beams cross. Weshow that the slow beam induced a strong reduction of the quasilinear relaxation of the fast beam, limitingthe amplitude of the generated Langmuir waves. Moreover, in the case of two electron beams, the lack ofLangmuir wave coherence reduces the efficiency of the Langmuir parametric decay. We thus conclude thatthe observed depletion of the type III radio emission is independent of the radio emission mechanism, aslong as it depends on the Langmuir amplitude and coherence

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“…Previous analytical and numerical studies of LMC have targeted the conversion of Langmuir/ z mode waves to electromagnetic (EM) free‐space radiation. The mode conversion efficiencies, the fraction of energy or power transferred from one wave mode to another, depend upon a range of parameters including the incoming wave vector k ES [ Forslund et al , ; Mjolhus , ; Budden , ; Willes and Cairns , ], the orientation and length scale of the density gradient ∇ N 0 [ Forslund et al , ; Budden , ; Hinkel‐Lipsker et al , ; Willes and Cairns , ; Schleyer et al , ], the ambient magnetic field strength and orientation B 0 [ Yin et al , ; Kim et al , , , ; Schleyer et al , ], and the plasma temperature T e [ Forslund et al , ; Cairns and Willes , ; Kim et al , , ; Schleyer et al , ]. They also depend weakly on the functional form of the monotonic density profile [ Hinkel‐Lipsker et al , ; Forslund et al , ; Willes and Cairns , ] and random density fluctuations [ Yu and Kim , ].…”

Section: Introductionmentioning

confidence: 99%

“…Subsequently, Schleyer et al [] performed simulations of LMC for Langmuir/ z mode and EM waves under arbitrary orientations of the density gradient ∇ N 0 . They found that the energy conversion efficiencies depend on γ β and also that both the energy and power conversion efficiencies depend on the angle between ∇ N 0 and B 0 ; however, Kim et al [] found that for sufficiently weak magnetized plasmas, the power conversion efficiency may be independent of the angle between ∇ N 0 and B 0 .…”

Section: Introductionmentioning

confidence: 99%

Linear mode conversion of Langmuir/z mode waves to radiation: Averaged energy conversion efficiencies, polarization, and applications to Earth's continuum radiation

2014

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Linear mode conversion (LMC) is the linear transfer of energy from one wave mode to another in a density gradient. It is relevant to planetary continuum radiation, type II and III radio bursts, and ionospheric radio emissions. This paper analyzes LMC by calculating angle‐averaged energy (ε) and power (εp) conversion efficiencies in both 2‐D and 3‐D for Langmuir/z mode waves (including upper hybrid waves for perpendicular wave vectors) converting to free‐space radiation in turbulent plasmas. The averages are over the distributions of the incoming Langmuir/z mode wave vectors k, density scale lengths L, and angles α and δ, where α is the angle between k and the background magnetic field B0 and δ is the angle between the density gradient ∇N0 and B0. The results show that the averaged and unaveraged conversion efficiencies are dependent on γβ, where γ is the adiabatic index and β is related to the electron temperature Te by β = Te/mec2. The averaged energy conversion efficiencies are proportional to γβ in 2‐D and to (γβ)3/2 in 3‐D, whereas the power conversion efficiencies are proportional to (γβ)1/2 in 2‐D and γβ in 3‐D. The special case of a perpendicular density gradient (δ≈90°) is considered and used to predict the conversion efficiencies of terrestrial continuum radiation (TCR) in three known source regions: the plasmapause, magnetopause, and the plasma sheet. The observed energy conversion efficiencies are estimated and are found to be consistent with the 2‐D and 3‐D predicted efficiencies; importantly, these results imply that LMC is a possible generation mechanism for TCR. The polarization of TCR is also predicted: TCR should be produced primarily in the o mode at the plasmapause and in both the o and x modes at the magnetopause and plasma sheet. These predictions are consistent with previous independent predictions and observations.

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Linear mode conversion of Langmuir/z-mode waves to radiation: Scalings of conversion efficiencies and propagation angles with temperature and magnetic field orientation

Cited by 13 publications

References 29 publications

Type III bursts produced by power law injected electrons in Maxwellian background coronal plasmas

Type III bursts produced by power law injected electrons in Maxwellian background coronal plasmas

Inhibition of type III radio emissions due to the interaction between two electron beams: Observations and simulations

Linear mode conversion of Langmuir/z mode waves to radiation: Averaged energy conversion efficiencies, polarization, and applications to Earth's continuum radiation

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