BICEP Array: a multi-frequency degree-scale CMB polarimeter
  BICEP Array is the newest multi-frequency instrument in the BICEP/Keck Array
program. It is comprised of four 550 mm aperture refractive telescopes
observing the polarization of the cosmic microwave background (CMB) at 30/40,
95, 150 and 220/270 GHz with over 30,000 detectors. We present an overview of
the receiver, detailing the optics, thermal, mechanical, and magnetic shielding
design. BICEP Array follows BICEP3's modular focal plane concept, and upgrades
to 6" wafer to reduce fabrication with higher detector count per module. The
first receiver at 30/40 GHz is expected to start observing at the South Pole
during the 2019-20 season. By the end of the planned BICEP Array program, we
project $\sigma(r) \sim 0.003$, assuming current modeling of polarized Galactic
foreground and depending on the level of delensing that can be achieved with
higher resolution maps from the South Pole Telescope.
