Issue |
A&A
Volume 371, Number 2, May IV 2001
|
|
---|---|---|
Page(s) | 738 - 747 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361:20010411 | |
Published online | 15 May 2001 |
The relation between cyclotron heating and energetic particles on open coronal field lines
Space Research Laboratory, Department of Physics, 20014 Turku University, Finland
Corresponding author: R. Vainio, rami.vainio@utu.fi
Received:
5
February
2001
Accepted:
16
March
2001
Cyclotron resonance with high-frequency Alfvén waves has been
proposed as an ion heating mechanism for producing high-speed winds and large
ion temperatures in coronal holes. In the simplest version of the model
(cyclotron sweep model), the waves propagate without interacting until they hit
a resonance with the plasma ions at distance, where the ion cyclotron frequency
becomes comparable to the wave frequency. We calculate the energetic
test-particle mean free path λ in solar corona heated by this
mechanism. The primary result of our study is that energetic particles are
efficiently coupled to the high-frequency MHD waves and may, thus, provide
important feed back to wave-heating models. Detailed calculations are presented
for a solar-wind stream of intermediate speed driven by the cyclotron sweep
mechanism applying an extended quasi-linear theory for the mean free path. A
local maximum of λ is located near , but
λ is very small at distances close to the Sun (
) helping the acceleration of particles to high energies on open coronal field
lines there. Another minimum for the mean free path is obtained near
enabling ion acceleration beyond 10 MeV/n in streams of intermediate speeds
by CME shock waves in the test-particle approximation. However, the presence of
high-frequency Alfvén waves in amounts required for the cyclotron sweep heating
has to be limited below ~10
on field lines close to the
ecliptic to avoid discrepancies with the inferred arrival times of solar
energetic particles. Non-linear effects are discussed as a possible mechanism
for removing the wave excess from the plasma.
Key words: Sun: corona / Sun: particle emission / solar wind
© ESO, 2001
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