HR: 17:45h
AN: SH34A-08    [Abstracts]
TI: Angle-averaged Efficiency of Linear Mode Conversion of Langmuir waves into Radiatio
AU: * Cairns, I H
EM: cairns@physics.usyd.edu.au
AF: University of Sydney, School of Physics, Sydney, NSW 2006 Australia
AU: Willes, A J
EM: willes@physics.usyd.edu.au
AF: University of Sydney, School of Physics, Sydney, NSW 2006 Australia
AB: Langmuir waves propagating in density irregularities can have a fraction of their energy converted linearly into radio waves near the plasma frequency. Linear mode conversion (LMC) is potentially relevant to the Langmuir waves and associated radio emissions in planetary foreshocks and the source regions of type II and III solar radio bursts. Recent idealised 2-D calculations show that LMC can have an efficiency of order $50 - 90%$ for optimum choices of parameters. In order to compare the efficiencies of LMC and nonlinear processes it is necessary to average over the Langmuir wavevector spectrum and distribution of density irregularities. Here it is shown analytically and numerically that averaging over 2-D and 3-D density irregularities with a uniform distribution of orientation angles reduces the overall LMC conversion efficiency to values $\approx 10^{-3}$ and $10^{-5}$, respectively, for 1 AU parameters. Moreover, the average efficiency decreases as the square root of the electron temperature. The important qualitative conclusion is that averaging over more realistic source conditions strongly reduces the efficiency of LMC.
DE: 7534 Radio emissions
DE: 7847 Radiation processes
DE: 7871 Waves and instabilities
DE: 2159 Plasma waves and turbulence
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting