The Next Generation of Axion Helioscopes: The International Axion Observatory (IAXO)

Abstract The International AxionObservatory (IAXO) is a proposed 4 th -generation axion helioscopewith the primary physics research goal to search for solar axionsvia their Primakoff conversion into photons of 1 – 10 keV energies in a strong magnetic field. IAXO will achieve a sensitivity to the axion-photon coupling g aγ down to a few ×10 −12 GeV −1 for a wide range of axionmasses up to ∼ 0 . 25 eV. This is an improvement over the currently best (3rd generation) axion helioscope, the CERN Axion Solar Telescope(CAST), of about 5 orders of magnitude in signal strength, corresponding to a factor ∼ 20 in the axionphoton coupling. IAXO's sensitivity relies on the construction of a large superconducting 8-coil toroidal magnet of 20 m length optimized for axionresearch. Each of the eight 60 cm diameter magnet bores is equipped with x-ray opticsfocusing the signal photons into ∼ 0 . 2 cm2 spots that are imaged by very low background x-ray detectors. The magnet will be built into a structure with elevation and azimuth drives that will allow solar tracking for 12 hours each day. This contribution is a summary of our papers [1] , [2] , [3] and we refer to these for further details.