A Cryogenic Bolometer Observatory for Cosmic Microwave Background Polarisation: Detector Count and Mapping Depth from Photon Noise

A ground-based cosmic microwave background observatory is designed from the photon noise of its own optical loading. For a 6 m telescope at a high dry site with 4.5 pW of loading per detector in a 150 GHz band, the photon noise-equivalent power is 43.2 attowatts per root hertz and the noise-equivalent temperature of one detector is 121 microK root second. An array of 30,000 such detectors within a 60,000-detector focal plane reaches an array sensitivity of 0.70 microK root second, which over five years on 40 percent of the sky gives a polarisation depth of 0.01 microK per square-degree pixel and 0.38 microK per 1.4 arcminute beam. The facility is estimated at 210 tonnes and 260 kW. All performance figures are computed from the stated loading model; the design is simulated, not measured.