Time damping of non-adiabatic MHD waves in an unbounded partially ionised prominence plasma

Departament de Física, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain e-mail: [pep.forteza;ramon.oliver;joseluis.ballester]@uib.es

Received: 11 June 2008
Accepted: 12 September 2008

Abstract

Aims. We study the joint effect of ion-neutral collisions and thermal mechanisms on the damping of MHD waves in a partially ionised prominence plasma.

Methods. Thermal conduction, radiation, and heating were included in the energy equation of the one-fluid MHD set of equations we derived earlier for an adiabatic, partially ionised plasma. Then, assuming small perturbations, these equations were linearised and the dispersion relation for magnetoacoustic, Alfvén, and thermal waves obtained.

Results. Compared with the non-adiabatic, fully ionised, and the adiabatic, partially ionised cases, the main result is that there is an increase in the efficiency of the damping of magnetoacoustic waves in prominence oscillations within the observed range of wavelengths for the magnetoacoustic waves. On the other hand, the Alfvén wave is only damped by the ion-neutral collision mechanism, and this damping becomes important for almost neutral plasmas.

Conclusions. The coupling of non-adiabatic mechanisms with the ion-neutral collisions mechanism offers a more complete model for the damping of magnetoacoustic waves with those values compatible with those observed in prominence oscillations. Furthermore, the ion-neutral collisions mechanism is able to damp the Alfvén wave in an efficient way.