The Atacama Cosmology Telescope (ACT) is a six meter Microwave telescope on the Atacama Desert, deployed in 2007, aimed a surveying the Cosmic Microwave Background. It is aimable only north-south, across 5 degrees, using the Earth's rotation to scan across the other dimension. Its aim has been identify distant Galaxy Clusters using the Sunyaev-Zel'dovich Effect, e.g., for further study using Sloan Digital Sky Survey, and to gather Polarization information useful for cosmology studies.
Its current receiver, AdvACT (for Advanced ACTPol), is a set of arrays of Transition Edge Sensor Bolometers covering Bands ranging from 27GHz to 230GHz, including some p, and to polarization-sensitive sensors, with up to 1.4 arcminute Angular Resolution. Earlier receivers covered a smaller Frequency range, the original receiver being MBAC (Millimeter bolometer array camera), with three 32 x 32 grids, for 145 GHz, 215 GHz and 280 GHz. In 2013, MBAC was replaced by ACTPol, for mapping CMB Polarization, with receivers for 90 GHz and 150 GHz in its grids, each bolometer sensitive to polarization, and which was used until 2015.
The instruments are designed for surveying, i.e., coverage of fields of hundreds to thousands of square degrees, the surveys sometimes referred to as the ACT Survey, the ACTPol Survey, and the AdvACT Survey. As the telescope is located in Chile, the coverage is generally in the southern hemisphere. Locations were chosen so as to provide complimentary coverage of some of the same regions covered by Visible Light surveys.
CMB Stage-4 (CMB-S4)