Broadband wide-angle absorption enhancement due to mode conversion in cold unmagnetized plasmas with periodic density variations

Yu, Dae Jung; Kim, Kihong

doi:10.1063/1.4943872

Cited by 6 publications

(2 citation statements)

References 23 publications

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“…In the presence of an infinitesimally small amount of damping in the resonance region, a large absorption of the EM wave energy occurs. This strong resonant absorption arises due to the mode conversion of incident p-polarized EM waves into longitudinal plasma oscillations at the resonance region [1,5,[15][16][17][18][19][20][21][22][23]. In this paper, we study theoretically similar phenomena occurring in transition anisotropic media with unequal values of the transverse and longitudinal components of the permittivity tensor, using the invariant imbedding theory of wave propagation.…”

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confidence: 99%

Resonant absorption of electromagnetic waves in transition anisotropic media

Kim

2017

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We study the mode conversion and resonant absorption phenomena occurring in a slab of a stratified anisotropic medium, optical axes of which are tilted with respect to the direction of inhomogeneity, using the invariant imbedding theory of wave propagation. When the tilt angle is zero, mode conversion occurs if the longitudinal component of the permittivity tensor, which is the one in the direction of inhomogeneity in the non-tilted case, varies from positive to negative values within the medium, while the transverse component plays no role. When the tilt angle is nonzero, the wave transmission and absorption show an asymmetry under the sign change of the incident angle in a range of the tilt angle, while the reflection is always symmetric. We calculate the reflectance, the transmittance and the absorptance for several configurations of the permittivity tensor and find that resonant absorption is greatly enhanced when the medium from the incident surface to the resonance region is hyperbolic than when it is elliptic. For certain configurations, the transmittance and absorptance curves display sharp peaks at some incident angles determined by the tilt angle.

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Section: Introductionmentioning

confidence: 99%

Resonant absorption of electromagnetic waves in transition anisotropic media

Kim

2017

Preprint

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“…The mode conversion coefficient, which denotes the ratio of energy transformation from one mode to another mode, has a maximum value of about 0.5 for the linear or parabolic density profile. When the density profile is more complex, the scaling behavior is broken and the conversion coefficient can vary greatly [39][40][41][42]. While this scaling behavior is well-known in planar geometry, its behavior in cylindrical geometry was unknown until recently.…”

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confidence: 99%

Universal scaling behavior of resonant absorption

Doorsselaere

2019

Physics of Plasmas

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Mode conversion and resonant absorption are crucial mechanisms for wave transport and absorption. Scaling behavior of mode conversion or resonant absorption is well-known for electromagnetic and MHD waves in planar geometry. Our recent study showed that such a scaling behavior of resonant absorption could also exist for coronal loop oscillations with cylindrical geometry, but it was only tested for one density profile. Here we generalise our previous study on the scaling behavior of resonant absorption by considering multiple density profiles. Applying an invariant imbedding method to the ideal MHD wave equations, we show that the scaling behavior also exists for these density models. We thus generalise our earlier results and show that such a universal scaling exists in cylindrical geometry, too. Given these results and the earlier results in planar geometry, we formulate a hypothesis that a universal scaling behavior exists regardless of the type of mode conversion or resonant absorption.Mode conversion and resonant absorption can often occur in inhomogeneous plasmas such that two different waves are coupled with an exchange of energy. This mechanism has been considered as crucial for plasma heating and transport [4, 5, 14-17, 23, 28-31, 35]. The previous literature is mainly concerned with mode conversion between electromagnetic waves and electrostatic waves or between magnetoacoustic waves and Alfvén waves [e.g., 23, 44]. From theoretical and numerical studies, it is well established that a scaling behavior exists for the mode conversion coefficient in a planar geometry [8, 10-13, 17, 19, 20, 23, 27, 33, 38, 43]. The scaling parameter has in general a certain relation with the density gradient, wave vector, and wave frequency [see, e.g., 17, 19, 20, 33, 38]. The mode conversion coefficient, which denotes the ratio of energy transformation from one mode to another mode, has a maximum value of about 0.5 for the linear or parabolic density profile. When the density profile is more complex, the scaling behavior is broken and the conversion coefficient can vary greatly [39][40][41][42]. While this scaling behavior is well-known in planar geometry, its behavior in cylindrical geometry was unknown until recently. In our recent study, we considered kink modes in coronal loops, where the coronal loop was assumed as a infinitely long, straight, and axisymmetric cylinder with a radial inhomogeneity. We found that resonant absorption of the kink modes in the Alfvén resonance also show a certain scaling behavior. We called this behavior sub-universal therein. However, we only considered a sinusoidal density profile in the transitional layer [44]. Given that it was studied only for a particular density profile, it was unclear whether this behavior would be generally valid, as it is for planar geometry. This motivates the question if the results from our * djyu79@gmail.com previous paper can be generalised to other density profiles. If they can be generalised, it would imply that the scaling behavior is universal in inhomo...

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Mode conversion of extraordinary waves in stratified plasmas with an external magnetic field perpendicular to the directions of inhomogeneity and wave propagation

Kim

2021

J. Korean Phys. Soc.

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Broadband wide-angle absorption enhancement due to mode conversion in cold unmagnetized plasmas with periodic density variations

Cited by 6 publications

References 23 publications

Resonant absorption of electromagnetic waves in transition anisotropic media

Resonant absorption of electromagnetic waves in transition anisotropic media

Universal scaling behavior of resonant absorption

Mode conversion of extraordinary waves in stratified plasmas with an external magnetic field perpendicular to the directions of inhomogeneity and wave propagation

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