The Keck Array is a new set of five receivers which constitute a powerful upgrade to the single BICEP2 telescope. The first three Keck Array receivers were deployed to the South Pole during the 2010/2011 Austral summer season, and are currently staring deep into the same patch of sky as BICEP1 and BICEP2, collecting powerful data. The Keck Array leverages the success of BICEP1 and BICEP2, combining cutting-edge technology and unprecedented throughput, aiming to measure the polarization of the cosmic microwave background (CMB) with better sensitivity than ever before.
Each Keck Array telescope is a small aperture, refracting telescope, allowing for good control of systematics. The telescope optics are cooled to 4K using a pulse tube cooler. The heart of each Keck Array receiver is very similar to BICEP2, with 512 antenna-coupled TES bolometers in each focal plane, for a total of 2560 detectors in the entire array. The focal plane is kept at 250 mK for CMB observations. Gaining detector sensitivity is critical in the search for "B-mode" polarization, and the Keck Array will have 5 times as many detectors as its predecessor.