  The CAST (CERN Axion Solar Telescope) experiment is searching for axions, an
hypothetical particle that emerges as a possible solution to the well known CP
violation problem in strong interactions. CAST is using a decommissioned LHC
dipole magnet able to track the Sun as a possible source of solar axions, and
to convert them to X-rays photons detectable with low background X-ray
detectors. CAST continues its data taking period scanning masses up to 1eV.
This thesis presents the data obtained with a Micromegas detector for the
scanned axion mass range up to 0.64eV. The working principle, characterization
and analysis of the Micromegas detectors operating in CAST are detailed in this
work. Moreover, the last detector data corresponding to the new data taking
period, with 3He gas inside the bores, was used to obtain a preliminar and
conservative upper limit on the axion-photon coupling for the new axion mass
range explored, g_{a\gamma} < 2.44 10^{-10} GeV^{-1}.
