Coronal ion-cyclotron beam instabilities within the multi-fluid description

Free access article

Issue		A&A Volume 474, Number 2, November I 2007


Page(s)		609 - 615
Section		The Sun
DOI		http://dx.doi.org/10.1051/0004-6361:20077648

A&A 474, 609-615 (2007)
DOI: 10.1051/0004-6361:20077648

Coronal ion-cyclotron beam instabilities within the multi-fluid description

R. Mecheri and E. Marsch

Max-Planck Institut für Sonnensystemforschung, Max-Planck Strasse 2, 37191 Katlenburg-Lindau, Germany
e-mail: mecheri@mps.mpg.de

(Received 15 April 2007 / Accepted 26 June 2007 )

Abstract
Context.Spectroscopic observations and theoretical models suggest resonant wave-particle interactions, involving high-frequency ion-cyclotron waves, as the principal mechanism for heating and accelerating ions in the open coronal holes. However, the mechanism responsible for the generation of the ion-cyclotron waves remains unclear. One possible scenario is that ion beams originating from small-scale reconnection events can drive micro-instabilities that constitute a possible source for the excitation of ion-cyclotron waves.
Aims.We use the multi-fluid model in the low- $\beta$ coronal plasma to study ion beam-driven electromagnetic instabilities. By neglecting the electron inertia this model allows one to take into account ion-cyclotron wave effects that are absent from the one-fluid magnetohydrodynamics (MHD) model. Realistic models of density and temperature as well as a 2-D analytical magnetic field model are used to define the background plasma in the open-field funnel region of a polar coronal hole.
Methods.Taking into account the WKB (Wentzel-Kramers-Brillouin) approximation, a Fourier plane-wave linear mode analysis is employed to derive the dispersion relation. The ray-tracing theory is used to compute the ray path of the unstable wave as well as the evolution of the growth rate of the wave while propagating in the coronal funnel.
Results.We demonstrate that in typical coronal hole conditions and assuming realistic values of the beam velocity, the free energy provided by the ion beam propagating parallel to the ambient field can drive micro-instabilities through resonant ion-cyclotron excitation.

Key words: Sun: corona -- waves -- instabilities

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.