  In the context of coronal heating, among the zoo of MHD waves that exist in
the solar atmosphere, Alfven waves receive special attention. Indeed, these
waves constitute an attractive heating agent due to their ability to carry over
the many different layers of the solar atmosphere sufficient energy to heat and
maintain a corona. However, due to their incompressible nature these waves need
a mechanism such as mode conversion (leading to shock heating), phase mixing,
resonant absorption or turbulent cascade in order to heat the plasma. New
observations with polarimetric, spectroscopic and imaging instruments such as
those on board of the japanese satellite Hinode, or the SST or CoMP, are
bringing strong evidence for the existence of energetic Alfven waves in the
solar corona. In order to assess the role of Alfven waves in coronal heating,
in this work we model a magnetic flux tube being subject to Alfven wave heating
through the mode conversion mechanism. Using a 1.5-dimensional MHD code we
carry out a parameter survey varying the magnetic flux tube geometry (length
and expansion), the photospheric magnetic field, the photospheric velocity
amplitudes and the nature of the waves (monochromatic or white noise spectrum).
It is found that independently of the photospheric wave amplitude and magnetic
field a corona can be produced and maintained only for long (> 80 Mm) and thick
(area ratio between photosphere and corona > 500) loops. Above a critical value
of the photospheric velocity amplitude (generally a few km/s) the corona can no
longer be maintained over extended periods of time and collapses due to the
large momentum of the waves. These results establish several constraints on
Alfven wave heating as a coronal heating mechanism, especially for active
region loops.
