The Llano de Chajnantor is located on the western side of the Puna de Atacama, which is another name for the southern part of the Altiplano. The main ridge of the Andes is over 200 kilometres (120 mi) to the east, well into Argentina. The Salar de Atacama basin borders the Puna de Atacama to the west, which in turn is bordered by the Cordillera Domeyko. The western side of the Puna de Atacama is dotted with the volcanoes of the Central Volcanic Zone of the Andean Volcanic Belt. The Llano de Chajnantor site itself is bounded by volcanic peaks of the Purico Complex, which have been active in the Holocene but have not erupted in historic times. Cerro Chajnantor is to the north, Cerro El Chascón to the east, and smaller peaks to the south and west. The Pampa la Bola lies to the northeast, north of Cerro El Chascón and east of Cerro Chajnantor. Llano de Chajnantor has an average elevation of 5,000 m (16,000 ft), while Pampa la Bola averages 4,800 m (15,700 ft). The thin atmosphere makes work difficult for humans, so much of the activity for ALMA will be conducted at a base camp in the Salar de Atacama basin at approximately 2,900 m (9,500 ft) in elevation.
The Cerro Chajnantor Atacama Telescope (CCAT) is a planned 25 m (82 ft) submillimetre radio telescope which will be located on Cerro Chajnantor near the TAO. Originally called the Cornell Caltech Atacama Telescope earlier in the development process, it is now referred to on the project's website by the CCAT acronym. Completion is expected in 2020.
The Cosmic Background Imager (CBI) was a radio telescope interferometer designed to measure the intensity and polarization of the cosmic microwave background radiation. It operated with thirteen 0.9 m (3.0 ft) antennas between 1999 and 2006, and until 2008 with 1.4 m (4.6 ft) antennas. The CBI facility is now used by the QUIET experiment.
The Millimeter-wave Interferometer (MINT) was a heterogenous four-element array that operated on the slopes of Cerro Toco in late 2001. The prototype instrument contained two 0.3 m (12 in) and two 0.45 m (18 in) Cassegrain reflectors. It was designed to measure the cosmic microwave background radiation.
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