HR: 1340h
AN: SH23A-1160    [Abstracts]
TI: Linear Mode Conversion of Langmuir to Electromagnetic Waves at Oblique Density Inhomogeneities
AU: * Cairns, I H
EM: i.cairns@physics.usyd.edu.au
AF: School of Physics, University of Sydney, Sydney, NSW 2006, Australia
AU: Kim, E
EM: ehkim@pppl.gov
AF: School of Physics, University of Sydney, Sydney, NSW 2006, Australia
AU: Kim, E
EM: ehkim@pppl.gov
AF: Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543, United States
AU: Robinson, P A
EM: p.robinson@physics.usyd.edu.au
AF: School of Physics, University of Sydney, Sydney, NSW 2006, Australia
AB: Linear mode conversion (LMC) of waves from one mode to another at constant frequency can occur in plasma irregularities because the natural modes in inhomogeneous plasmas need not be distinct but instead can be connected for restricted ranges of wave vectors k and frequencies f. Previous work suggests that the electrostatic (ES) Langmuir/z mode and free-space electromagnetic (EM) modes have two "radio windows", with multiple possible applications to solar radio bursts, planetary continuum radiation, auroral radio emissions, and ionospheric modification events. The first radio window is for Langmuir/z waves just above the local plasma frequency (f_pe) with k almost aligned with the ambient magnetic field B₀ and the density gradient \nabla n. The second involves upper hybrid/z waves with f ≈ f_UH, the upper hybrid frequency, and k almost perpendicular to B₀ and \nabla n. Here we use numerical simulations of the warm plasma fluid equations to investigate the detailed characteristics of LMC as functions of the outgoing EM o and x modes, k, the angles φ between B₀ and \nabla N, B₀, and the length scale of the density irregularity L. These results extend the recent demonstration that LMC produces both o and x-mode radiation when φ = 0 [Kim et al., Phys. Rev. Lett., 99, 015003, 2007], contrary to previous expectations that only the o mode is produced. Our new results include: (1) Only one radio window exists, smoothly linking the previous two windows as φ, f and k change. (2) Both o and x-mode radiation are produced in the unmagnetized to moderately magnetized regimes, as found for the φ = 0 case. (3) Less than 10% of the incident ES energy is transformed into EM radiation. (4) In weakly magnetized situations almost equal amounts of o and x-mode radiation are produced, but only the o mode is produced for large enough B₀. Applications of these results to natural solar and planetary emissions and to ionospheric modification experiments are also explored.
DE: 2471 Plasma waves and instabilities (2772)
DE: 2772 Plasma waves and instabilities (2471)
DE: 6984 Waves in plasma (7867)
DE: 7534 Radio emissions
DE: 7847 Radiation processes
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting