Conceptual design of the International Axion Observatory (IAXO)

Abstract

The International Axion Observatory (IAXO) will be a forth generation axion\nhelioscope. As its primary physics goal, IAXO will look for axions or\naxion-like particles (ALPs) originating in the Sun via the Primakoff conversion\nof the solar plasma photons. In terms of signal-to-noise ratio, IAXO will be\nabout 4-5 orders of magnitude more sensitive than CAST, currently the most\npowerful axion helioscope, reaching sensitivity to axion-photon couplings down\nto a few $\\times 10^{-12}$ GeV$^{-1}$ and thus probing a large fraction of the\ncurrently unexplored axion and ALP parameter space. IAXO will also be sensitive\nto solar axions produced by mechanisms mediated by the axion-electron coupling\n$g_{ae}$ with sensitivity $-$for the first time$-$ to values of $g_{ae}$ not\npreviously excluded by astrophysics. With several other possible physics cases,\nIAXO has the potential to serve as a multi-purpose facility for generic axion\nand ALP research in the next decade. In this paper we present the conceptual\ndesign of IAXO, which follows the layout of an enhanced axion helioscope, based\non a purpose-built 20m-long 8-coils toroidal superconducting magnet. All the\neight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able\nto focus the signal photons into $\\sim 0.2$ cm$^2$ spots that are imaged by\nultra-low-background Micromegas x-ray detectors. The magnet is built into a\nstructure with elevation and azimuth drives that will allow for solar tracking\nfor $\\sim$12 h each day.\n