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Axions are well motivated particles proposed in an extension of the SM as asolution to the strong CP problem. Also, there is the category of Axion-LikeParticles (ALPs) which appear in extensions of the SM and share the samephenomenology of the axion. Axions and ALPs are candidates to solve the DarkMatter problem. CAST, the CERN Axion Solar Telescope is looking for solaraxions since 2003. CAST exploit the helioscope technique using a decommissionedLHC dipole magnet in which solar axions could be reconverted into photons.Three of the four detectors operating at CAST are of the Micromegas type. Theanalysis of the data of the three Micromegas detectors during the 2011 datataking campaign at CAST is presented in this thesis, obtaining a limit on thecoupling constant of g$_{a \gamma}$ < 3.90 $\times$ 10$^{-10}$ GeV$^{-1}$ at a95$\%$ of confidence level, for axion masses from 1 to 1.17 eV. CAST Micromegasdetectors exploit different strategies developed for the reduction of thebackground level. Moreover, different test benches have been developed in orderto understand the origin of the background. The state of art in low backgroundtechniques is shown in the upgrades of the Micromegas detectors at CAST, whichhas led to a reduction of the background in a factor $\sim$6. It translates inan improvement of the sensitivity of CAST in a factor $\sim$2.5. Beyond CAST anew generation axion helioscope has been proposed: IAXO-the International AxionObservatory. IAXO will enhance the helioscope technique by exploiting all thesingularities of CAST implemented into a large superconducting toroidal magnet,dedicated X-ray optics and ultra-low background detectors. A description of theIAXO proposal and the study of the sensitivity of IAXO are presented in thisthesis. IAXO will surpass CAST in more than one order of magnitude, enteringinto an unexplored parameter space area.

Solar Axion search with Micromegas detectors in the CAST Experiment with $^{3}$He as buffer gas