1. B-Pol L. Piccirillo Jodrell Bank Centre for Astrophysics (University of Manchester) A European mission to get a CMB polarization measurement limited only by natural foreground sources was proposed in response to the ESA Cosmic-Vision call. The mission is based on the availability of large format arrays of ultra-sensitive bolometric detectors, cooled at 0.1K, and fed by cold corrugated feedhorns and low polarization telecentric telescopes. Polarization modulation is obtained by means of rotating waveplates.

2. Countries involved: Canada Denmark France Germany Ireland Italy Netherland Norway Portugal Romania Spain Sweden Switzerland United Kingdom United States PI: P. De Bernardis (Italy) Instrument Group: L. Piccirillo (UK) Science Group: M. Bucher (Fr) Foreground Group: C. Burigana (Italy)

3. Service Module V-Grooves Cryostat Telescope 2.7 m 3.3 m

4. Optical system: Wide field, low cross-pol, low emissivity Possible solution: modified telecontric telescope HWP

5. L1 L2 Focal plane Dilution Lenses (telecentric telescope) Array of Horns and Bolometers (0.1K) 8K 2K Spinning half-wave plate Sub-K cooler

6. Sensitivity and frequency coverage: the focal plane Baseline technology: TES bolometers arrays Sub-K, 600 mm Corrugated feedhorns for polarization purity and beam symmetry

7. Sensitivity

12.  9

14. Mesh Half Wave Plate Space qualified already bc identical technology to mesh filters Prototypes built and tested @ 30 and 90 GHz Excellent agreement with theory

16. END