POINCARE. Polarimeter for Observing Inflationary Cosmology at the Reionization Epoch

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1 POINCARE Polarimeter for Observing Inflationary Cosmology at the Reionization Epoch David T. Chuss NASA Goddard Space Flight Center CMBPol Systematics Workshop Annapolis, MD July 29, 2008

2 Team Johns Hopkins Chuck Bennett Ben Gold Joseph Eimer Lingzhen Zeng NASA GSFC Gary Hinshaw Ed Wollack Harvey Moseley David Chuss George Voellmer James Hinderks NIST Boulder Kent Irwin Ki Won Yoon William Duncan Sherry Cho Gene Hilton Mike Niemack Northwestern U. Giles Novak U. Colorado Nils Halverson U. British Columbia Mark Halpern

3 Experimental Details Angular resolution 120 Frequency Coverage Sky Coverage GHz ~Full Sky Multipole Coverage ~2-90 Polarization Modulation Types of Detectors Location Variable-delay Polarization Modulator (VPM) Feedhorn-coupled TES Ground Expected limit on r ~0.01 Status Future

4 Instrument Architecture VPM is the first element Fastest modulation is in Polarization (~3 Hz modulator cycle) Q and U are measured in separate optical paths Multiple observatories deployed to cover full sky

5 Detectors

6 40 GHz GSFC Detectors

7 150 GHz CMB polarimeter fabricated at NIST CPW Filter Design OMT Design TES Heater 6 mm Gold meander Components designed by NIST, CU-Boulder, University of Chicago and Princeton University

8 Variable-delay Polarization Modulators (VPMs) Stokes V Stokes Q Stokes U Q detector = Q cos φ + V sin φ

9 Systematic Advantages of VPMs Allows for spectropolarimetry Used in reflection- no dielectrics to introduce differential loss Employs small linear motions rather than large circular ones - a potential reliability advantage for space mission More flexibility in size than HWP Allows symmetry for hiding systematics in unmeasured Stokes parameter.

10 Submillimeter VPMs Voellmer et al. (2006), Krejny et al. (2008)

11 Voellmer et al. (2008) Goddard Space Flight Center Wire diameter = 67 µm Wire spacing = 200 µm Grid diameter = 50 cm Flatness < 50 µm Wire resonant frequency > 128 Hz 2 miles of wire 2 Tons of force on the frame 50 cm

12 Data Stream H V Grid!Mirror Separation (microns)

13 3 mm Laboratory Tests

14 Systematics/Calibration Systematic E B T B T B TOptics B TCold Stage B Foregrounds B Mitigation Ensure cross-calibration is good between Q and U measurements, measuring Q, U independently Front-end modulation- beam shape not changed by modulator 1. Beams underfill VPM so variability in edge illumination is minimized. 2. This effect is monotonic with separationsignal is oscillatory. 3. Common mode signal is manifest in unmeasured linear Stokes parameter. Modulator located in front of optics. Modulate faster than temperatures can drift Monitor bias, external calibrator, Calibrate using astrophysical standards. Multiple frequencies & operation near the suspected foreground minimum

15 Systematic Concerns Concern Mitigation Beam Walkoff location of VPM at (primary) pupil Variable Beam Truncation Variable Grid Emission Wire Vibrations sufficient edge taper; symmetry of system High polarization isolation; symmetry of system. High resonant frequency (tight wires)

16 Status Pathfinder for POINCARE (single optical path) is being proposed to NSF this fall 40 GHz Detector components in fabrication at NASA/GSFC 150 GHz Detector components in fabrication at NIST/Boulder VPM grid fabricated; VPM expected early 2009 Cryostat for Pathfinder under development Viper telescope to be shipped to JHU early Fall.