Reflection of Magnetoionic Waves from a Steep Density Gradient. I. Incident Extraordinary Mode

Hayes, L. M.

doi:10.1071/ph850687

Cited by 4 publications

(6 citation statements)

References 2 publications

(3 reference statements)

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“…In fact, the reflected intensity is likely to be much smaller. For a simple 1‐D problem in which radiation is incident normally on an interface between two media with indices of refraction n 1 and n 2 , application of the continuity conditions to Maxwell's equations at the boundary [ Hayes , 1985] yields an expected reflected electric field of relative amplitude R = ( n 1 − n 2 )/( n 1 + n 2 ). For extraordinary mode waves with frequency near Ω e and assuming k ∥ = 0, the dispersion relation has the approximate form [ Le Quéau et al , 1984; Pritchett , 1986a]

where A involves an integration in velocity space of a differential operator acting on the electron velocity distribution function but is otherwise linear in the plasma density.…”

Section: Driven Simulation Resultsmentioning

confidence: 99%

Generation and propagation of cyclotron maser emissions in the finite auroral kilometric radiation source cavity

et al. 2002

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The properties of the electron‐cyclotron maser radiation produced in the auroral kilometric radiation (AKR) source cavity are investigated by means of two‐dimensional particle‐in‐cell simulations and observations made by the Fast Auroral SnapshoT (FAST) Explorer. The simulations assume a population of primary auroral electrons with a downgoing shell distribution. Driven simulations in a meridional plane with a finite magnetic field gradient demonstrate that the maser radiation builds up very rapidly with decreasing altitude and that bursts of radiation with timescales of the order of 0.5 ms are produced at only 5–6 km below the injection level. Initial value simulations in a longitudinal plane show that the radiation component striking the cavity boundary at normal incidence is damped away via particle absorption and conversion to the Z mode. In contrast, the longitudinally propagating component is able to be amplified along an extended path length. The FAST observations of the electric field in the source region reveal that the polarization in the plane perpendicular to the ambient magnetic field varies between being approximately isotropic to having a substantial (as much as a factor of 100) enhancement of the “along‐track” polarization. No evidence is found that the “across‐track” polarization is ever dominant, and thus the AKR emissions do not form a standing wave structure between the cavity boundaries.

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where A involves an integration in velocity space of a differential operator acting on the electron velocity distribution function but is otherwise linear in the plasma density.…”

Section: Driven Simulation Resultsmentioning

confidence: 99%

Generation and propagation of cyclotron maser emissions in the finite auroral kilometric radiation source cavity

et al. 2002

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“…Mode coupling theory cannot be valid when reflection leads to two reflected modes, which is the case of interest in explaining depolarization. The transition from reflection-like refraction to true reflection cannot be treated within the framework of mode-coupling theory, and requires a full-wave theory (Budden 1961;Hayes 1985a).…”

Section: Qualitative Discussion Of Mode Couplingmentioning

confidence: 99%

“…The parameter r may be interpreted as the sine of the angle of incidence times the initial refractive index. It follows that the plasma frequency much change over a distance of order the free-space wavelength in order for reflection rather than refraction to apply (Budden 1961;Hayes 1985a).…”

Section: Separation Of Reflection Pointsmentioning

confidence: 99%

“…The requirement for reflection to lead to depolarization is discussed in section 2: existing arguments that the boundary can be no more than about a wavelength (a few meters) thick (Budden 1961;Hayes 1985a) are supported by an argument based on mode-coupling theory. The simplified form of magnetoionic theory is introduced in section 3 and used to calculate a depolarization coefficient for reflection off a sharp boundary.…”

Section: Introductionmentioning

confidence: 99%

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Depolarization of Radio Bursts Due to Reflection off Sharp Boundaries in the Solar Corona

Melrose

2006

ApJ

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Depolarization of solar radio bursts requires reflection off boundary layers no thicker than about a wavelength (a few meters at most) between regions with large density ratios. The implied inhomogeneities suggest that the corona is much more highly and sharply structured than can be resolved from observations at other wavelengths. A simplified version of magnetoionic theory is used to derive a depolarization coefficient; the effect of the magnetic field is ignored in treating the dispersion, but taken into account in treating the (circular) polarization. Plots of the depolarization coefficient are used to infer conditions under which effective depolarization occurs, and it is concluded that favorable conditions require total internal reflection. For type I sources away from the central meridian, effective depolarization requires reflection off an overdense structure with a density ratio % 10. For type III bursts, a density ratio % 2 suffices, with at least two reflections off walls of ducts at %20 to the radial.

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“…We employ the approximation of an infinitely sharp density discontinuity. The validity of this assumption has been investigated by Hayes [1985], who found that it was justified if the distance over which the density varies is of the order of a wavelength or less. For the case of AKR this is of the order of a kilometer.…”

Section: Propagation Out Of Source Regionmentioning

confidence: 99%

Cyclotron maser radiation from a source structure localized perpendicular to the ambient magnetic field

Pritchett¹

1986

J. Geophys. Res.

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The plasma cavity in which the auroral kilometric radiation (AKR) is generated is known to contain localized density enhancements, and the cavity itself is surrounded by regions of much higher plasma density. Particle simulations are used to investigate the effects of such a source structure perpendicular to a uniform magnetic field on the generation and propagation of electromagnetic radiation produced by the cyclotron maser instability. It is found that the efficiency of radiation production is significantly increased in comparison to the uniform geometry case. The radiation is observed to consist of wave packets which travel at speeds of the order of 0.1c-0.2c, which is consistent with the X mode group velocity near cutoff. The reflection of these structures at the edge of a density enhancement is quite weak, with less than 0.1% of the incident energy being reflected in a typical case. The radiation with frequency ro •< tl e produced in the cavity region and emitted perpendicular to the magnetic field is observed to penetrate through regions of high-density cold plasma with little diminution. The mechanism for this propagation is identified as mode conversion of the original X mode waves into Z mode waves at the edge of the plasma •avity and subsequent conversion to the R-X mode as the plasma density decreases again. The implications of these results for theories concerning the generation and propagation of AKR are discussed.

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Reflection of Magnetoionic Waves from a Steep Density Gradient. I. Incident Extraordinary Mode

Cited by 4 publications

References 2 publications

Generation and propagation of cyclotron maser emissions in the finite auroral kilometric radiation source cavity

Generation and propagation of cyclotron maser emissions in the finite auroral kilometric radiation source cavity

Depolarization of Radio Bursts Due to Reflection off Sharp Boundaries in the Solar Corona

Cyclotron maser radiation from a source structure localized perpendicular to the ambient magnetic field

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