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Plasma radio emission from inhomogeneous collisional plasma of a flaring loop  

Heather Ratcliffe   Submitted: 2013-12-16 04:55

The evolution of a solar flare accelerated non-thermal electron population and associated plasma emission is considered in collisional inhomogeneous plasma. Non-thermal electrons collisionally evolve to become unstable and generate Langmuir waves, which may lead to intense radio emission. We self-consistently simulated the collisional relaxation of electrons, wave-particle interactions, and non-linear Langmuir wave evolution in plasma with density fluctuations. Additionally, we simulated the scattering, decay, and coalescence of the Langmuir waves which produce radio emission at the fundamental or the harmonic of the plasma frequency, using an angle-averaged emission model. Long-wavelength density fluctuations, such as are observed in the corona, are seen to strongly suppress the levels of radio emission, meaning that a high level of Langmuir waves can be present without visible radio emission. Additionally, in homogeneous plasma, the emission shows time and frequency variations that could be smoothed out by density inhomogeneities.

Authors: Heather Ratcliffe, Eduard. P. Kontar
Projects: None

Publication Status: Accepted, in press (A & A)
Last Modified: 2013-12-16 16:48
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Density fluctuations and the acceleration of electrons by beam-generated Langmuir waves in the solar corona  

Heather Ratcliffe   Submitted: 2012-11-14 10:22

Non-thermal electron populations are observed throughout the heliosphere. The relaxation of an electron beam is known to produce Langmuir waves which, in turn, may substantially modify the electron distribution function. As the Langmuir waves are refracted by background density gradients and as the solar and heliospheric plasma density is naturally perturbed with various levels of inhomogeneity, the interaction of Langmuir waves with non-thermal electrons in inhomogeneous plasmas is an important topic. We investigate the role played by ambient density fluctuations on the beam-plasma relaxation, focusing on the effect of acceleration of beam electrons. The scattering of Langmuir waves off turbulent density fluctuations is modeled as a wavenumber diffusion process which is implemented in numerical simulations of the one-dimensional quasilinear kinetic equations describing the beam relaxation. The results show that a substantial number of beam electrons are accelerated when the diffusive time scale in wavenumber space au_D is of the order of the quasilinear time scale au_ql, while when au_D << au_ql, the beam relaxation is suppressed. Plasma inhomogeneities are therefore an important means of energy redistribution for waves and hence electrons, and so must be taken into account when interpreting, for example, hard X-ray or Type III emission from flare-accelerated electrons.

Authors: Ratcliffe, H; Bian, N. H.; Kontar, E. P.
Projects: None

Publication Status: Accepted for ApJ
Last Modified: 2012-11-14 16:06
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Plasma radio emission from inhomogeneous collisional plasma of a flaring loop
Density fluctuations and the acceleration of electrons by beam-generated Langmuir waves in the solar corona

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