Issue |
A&A
Volume 382, Number 1, JanuaryIV 2002
|
|
---|---|---|
Page(s) | 301 - 311 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361:20011583 | |
Published online | 15 January 2002 |
Temperature isotropization in solar flare plasmas due to the electron firehose instability
Institute of Astronomy, ETH Zentrum, 8092 Zürich, Switzerland
Corresponding author: P. Messmer, messmer@astro.phys.ethz.ch
Received:
7
August
2001
Accepted:
7
November
2001
The isotropization process of a collisionless plasma with an
electron temperature anisotropy along an external magnetic field
(,
and
with respect to the
background magnetic field) and isotropic protons is investigated using a
particle-in-cell (PIC) code. Restricting wave growth mainly parallel to
the external magnetic field, the isotropization mechanism is
identified to be the Electron Firehose Instability (EFI). The free
energy in the electrons is first transformed into left-hand circularly
polarized transverse low-frequency waves by a non-resonant interaction.
Fast electrons can then be scattered towards higher perpendicular
velocities by gyroresonance, leading finally to a complete
isotropization of the velocity distribution. During this phase of the
instability, Langmuir waves are generated which may lead to the
emission of radio waves. A large fraction of the protons is resonant with the
left-hand polarized electromagnetic waves, creating a
proton temperature anisotropy
.
The parameters of the simulated plasma are chosen compatible to
solar flare conditions. The results indicate the significance of this
mechanism in the particle acceleration context: the EFI limits the anisotropy
of the electron velocity distribution, and thus provides the necessary
condition for further acceleration. It enhances the pitch-angle of the
electrons and heats the ions.
Key words: acceleration of particles / instabilities / plasmas / Sun: corona / Sun: flares
© ESO, 2002
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