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Proposed Payload Instrument

B-Pol focal plane arrays

Artist's impression of the cryogenic instrument

Example of optical configuration for one of the telescopes of B-Pol

Example of resulting beams (in arbitrary units)

Total spectral transmission of the 143GHz filter stack with the waveguide low pass defining edge. The thicker horizontal lines indicate the science requirement on the level of blocking

Polarimeter scheme. Left: High frequencies (over 70GHz); Right: Low frequencies (45 & 70 GHz)

Left: Achromatic Half-Wave plate example; Right: Planar Ortho-Mode Transducer scheme.

A microstrip coupled, MoCu TES detector for 100GHz. The microstrip line enters bottom left.

Block-diagram of the room temperature instrument electronics

Example of a possible overall cryogenic architecture: shields (grey) and on-axis V-grooves (yellow) provide the first stages for a cryostat (blue) surrounding the optics and the detector assembly

Example of a possible B-Pol cryostat

Hit count for a pixel at 1.6 degrees from the center of the B-pol focal plane for observation lasting 1 day (left), 1 month (center) and 1 year (right). The precession and nutation angles are 45 degrees, the precession period is 0.5 days, the nutation period is 40 min. Only one pixel at a fiducial frequency of 10Hz is represented.

Maps of angular coverage relevant for polarization determination for one year of observation by a pixel at 1.6 degrees from the center of B-pol focal plane. The estimator we chose is $\langle
\cos 2\alpha \rangle^2 + \langle \sin 2\alpha \rangle^2$, where alpha is the angle between the main axis of the polarimeter and a reference direction on the sky. The smaller the better (0=ideal, 1=worst). Compared to Planck (top), B-pol's angular coverage is a factor $10^6$ better without an internal modulator (center), and even $10^9$ with a rotating Half Wave Plate (5Hz, right)