BICEP3, the successor to BICEP2, was deployed to the Dark Sector Laboratory at Amundsen-Scott South Pole Station in the 2014-2015 Austral summer season. It was upgraded in 2015-2016 to a full 2560 detectors operating at 95 GHz, together with Keck Array, the BICEP/Keck program observe the polarization of the Cosmic Microwave Background from 95GHz to 270GHz.
BICEP3 is a wide-field cryogenic refractor, with a 55cm aperture and fast optics it achieves an order of magnitude increase in throughput compare to previous telescopes in the BICEP series. It is also prototype for the four BICEP3-sized receivers of the BICEP Array, which will replace Keck Array over the next several years and will include a total of over 30,000 detectors in five frequency bands.
BICEP3 is a 520mm aperture, compact two-lens refractor designed to observe the polarization of the cosmic microwave background (CMB) at 95 GHz. Its focal plane consists of modularized tiles of antenna-coupled transition edge sensors (TESs), similar to those used in Bicep 2 and the Keck Array. The increased per-receiver optical throughput compared to Bicep 2/Keck Array, due to both its faster f/1.7 optics and the larger aperture, will more than double the combined mapping speed of the Bicep /Keck program. Figure 1 shows a cutaway view of the BICEP3 CAD model in this state. A PT415 two-stage pulsetube cryocooler provides continuous cooling to < 4 K for all the optical elements. A three-stage (4 He/3 He/3 He) helium sorption fridge is mounted on the 4K stage to cool BICEP3's detector modules from 4K to 250mK and then maintain operating temperatures for more than 48 hours before needing to re-cycle.
Caption: Cross sections of the Keck Array and BICEP3 receivers on a common scale. The paerture is doubled to 55 cm and the optical throughput increased by an order of magnitude.
BICEP3 uses the same antenna-coupled TES bolometer architecture as BICEP2/ Keck, but we adapted a new modular housing design that allows us to ll larger optically illuminated areas and for easier detector repair and replacement.