Conceptual Design of the International Axion Observatory (IAXO)

The International Axion Observatory (IAXO) will be a forthgeneration axion helioscope. As its primary physics goal, IAXO willlook for axions or axion-like particles (ALPs) originating in theSun via the Primakoff conversion of the solar plasma photons. Interms of signal-to-noise ratio, IAXO will be about 4–5 orders ofmagnitude more sensitive than CAST, currently the most powerfulaxion helioscope, reaching sensitivity to axion-photon couplingsdown to a few × 10−12 GeV−1 and thus probing a largefraction of the currently unexplored axion and ALP parameterspace. IAXO will also be sensitive to solar axions produced bymechanisms mediated by the axion-electron coupling gae withsensitivity — for the first time — to values of gae notpreviously excluded by astrophysics. With several other possiblephysics cases, IAXO has the potential to serve as a multi-purposefacility for generic axion and ALP research in the next decade. Inthis paper we present the conceptual design of IAXO, which followsthe layout of an enhanced axion helioscope, based on a purpose-built20 m-long 8-coils toroidal superconducting magnet. All the eight60cm-diameter magnet bores are equipped with focusing x-ray optics,able to focus the signal photons into ~ 0.2 cm2 spots thatare imaged by ultra-low-background Micromegas x-ray detectors. Themagnet is built into a structure with elevation and azimuth drivesthat will allow for solar tracking for ~ 12 h each day