Linear mode conversion of Langmuir/z-mode waves to radiation in plasmas with various magnetic field strength
- Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)
- School of Physics, University of Sydney, Sydney, New South Wales 2002 (Australia)
Linear mode conversion of Langmuir/z waves to electromagnetic radiation near the plasma and upper hybrid frequency in the presence of density gradients is potentially relevant to type II and III solar radio bursts, ionospheric radar experiments, pulsars, and continuum radiation for planetary magnetospheres. Here, we study mode conversion in warm, magnetized plasmas using a numerical electron fluid simulation code when the density gradient has a wide range of angle, δ, to the ambient magnetic field, B{sub 0}, for a range of incident Langmuir/z wavevectors. Our results include: (1) Left-handed polarized ordinary (oL) and right-handed polarized extraordinary (xR) mode waves are produced in various ranges of δ for Ω{sub 0} = (ωL/c){sup 1/3}(ω{sub ce}/ω) < 1.5, where ω{sub ce} is the (angular) electron cyclotron frequency, ω is the angular wave frequency, L is the length scale of the (linear) density gradient, and c is the speed of light; (2) the xR mode is produced most strongly in the range, 40° < δ < 60°, for intermediately magnetized plasmas with Ω{sub 0} = 1.0 and 1.5, while it is produced over a wider range, 0° ≤ δ ≤ 90°, for weakly magnetized plasmas with Ω{sub 0} = 0.1 and 0.7; (3) the maximum total conversion efficiencies for wave power from the Langmuir/z mode to radiation are of order 50%–99% and the corresponding energy conversion efficiencies are 5%–14% (depending on the adiabatic index γ and β = T{sub e}/m{sub e}c{sup 2}, where T{sub e} is the electron temperature and m{sub e} is the electron) for various Ω{sub 0}; (4) the mode conversion window becomes wider as Ω{sub 0} and δ increase. Hence, the results in this paper confirm that linear mode conversion under these conditions can explain the weak total circular polarization of interplanetary type II and III solar radio bursts because a strong xR mode can be generated via linear mode conversion near δ ∼ 45°.
- OSTI ID:
- 22218313
- Journal Information:
- Physics of Plasmas, Vol. 20, Issue 12; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTROPHYSICS
ELECTRON TEMPERATURE
ELECTRONS
ENERGY CONVERSION
ION TEMPERATURE
MAGNETIC FIELDS
MODE CONVERSION
NUMERICAL ANALYSIS
PLANETARY MAGNETOSPHERES
PLASMA DENSITY
PLASMA SIMULATION
POLARIZATION
POTENTIALS
PULSARS
SOLAR RADIO BURSTS
VISIBLE RADIATION