Hunting Dark Matter Axions with CAST

The CAST experiment at CERN has been looking for the hypothetical particles of Dark Matter called axions for about 22 years. After setting world-class limits on the axion-photon coupling strength for solar axions as a helioscope, it has been converted into a haloscope looking for Dark Matter axions. By following the Sikivie haloscope principle, microwave cavities have been inserted in the two bores of the CAST dipole magnet. The CAST-CAPP sub-detector is making use of a novel technique called phase-matching which maximizes the detection sensitivity by combining coherently four cavities which allows for future large-scale upgrades. At the same time, each cavity is equipped with a fast frequency tuning mechanism which opens up the possibility of being sensitive also to axion streams and mini-clusters in addition to standard galactic halo axions. Even though axions remain to be discovered, CAST has excluded a significant amount of the available parameter space and has paved the way for future axion searches with next-generation experiments.