Exploring Cosmic Origins with CORE: The Instrument
  We describe a space-borne, multi-band, multi-beam polarimeter aiming at a
precise and accurate measurement of the polarization of the Cosmic Microwave
Background. The instrument is optimized to be compatible with the strict budget
requirements of a medium-size space mission within the Cosmic Vision Programme
of the European Space Agency. The instrument has no moving parts, and uses
arrays of diffraction-limited Kinetic Inductance Detectors to cover the
frequency range from 60 GHz to 600 GHz in 19 wide bands, in the focal plane of
a 1.2 m aperture telescope cooled at 40 K, allowing for an accurate extraction
of the CMB signal from polarized foreground emission. The projected CMB
polarization survey sensitivity of this instrument, after foregrounds removal,
is 1.7 {\mu}K$\cdot$arcmin. The design is robust enough to allow, if needed, a
downscoped version of the instrument covering the 100 GHz to 600 GHz range with
a 0.8 m aperture telescope cooled at 85 K, with a projected CMB polarization
survey sensitivity of 3.2 {\mu}K$\cdot$arcmin.
