AdvACT

AdvACT, short for Advanced ACTPol, is an upgraded program on the Atacama Cosmology Telescope (ACT) in northern Chile, designed to improve measurements of the cosmic microwave background (CMB) polarization and temperature anisotropies. Initiated in the mid-2010s, AdvACT expands and replaces the original ACTPol detector arrays with larger, more sensitive focal planes and broader frequency coverage, enabling deeper maps of the CMB across a range of angular scales.

Technically, AdvACT uses arrays of transition-edge sensor bolometers read out with superconducting multiplexing electronics. The focal planes are designed to observe multiple frequency bands, typically around 90, 150, and 230 GHz, with multi-chroic detectors that separate the sky into polarization-sensitive channels. The combination of higher detector count and broad frequency coverage improves the ability to separate CMB signals from foregrounds such as dust and synchrotron emission.

Observations are conducted as part of ACT's survey program from the Atacama Desert in Chile, produced by the AdvACT collaboration, a consortium of universities and national laboratories. Data products include maps of temperature and polarization, power spectra, and gravitational lensing reconstructions, used in cosmological analyses to constrain parameters including the sum of neutrino masses and the reionization optical depth.

Since its deployment, AdvACT has contributed to the overall ACT science program by delivering improved CMB polarization measurements and by facilitating cross-corroboration with other CMB experiments. The project continues to inform future instrumentation and analysis strategies in observational cosmology.