Institut de recherche sur les lois fondamentales de l'Univers

The CAST (CERN Axion Solar Telescope) experiment is searching for solar axions by their conversion into photons inside the magnet pipes of an LHC dipole magnet. The expected converted photons can be measured by four independent X-ray detectors installed at each end of the magnet. We will briefly present results of the first phase (2003-2004) of the experiment with vacuum in the conversion region which resulted in an upper limit on the axion-photon coupling that supersedes the best limits derived from stellar energy-loss arguments. Since 2005, CAST entered in its second phase where it operates with a buffer gas in the conversion region in order to extend the sensitivity of the experiment to higher axion masses. The first results on the 4He data taking will be presented. During 2007 major system upgrades that have been made in the last year in order to adapt the experiment for the 3He data taking, including replacement of two of the detectors with new technology Micromegas, and datataking started on April 2008. Furthermore CAST has already started exploring the sub-keV axion energy region, which is favored by several observed solar mysteries.