POINCARE - cmbpol.uchicago.edu
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Goddard Space Flight Center POINCARE P olarimeter for O bserving In flationary C osmology at the R eionization E poch David T. Chuss NASA Goddard Space Flight Center CMBPol Systematics Workshop Annapolis, MD July 29, 2008
Transcript of POINCARE - cmbpol.uchicago.edu
Goddard Space Flight Center
POINCAREPolarimeter for Observing Inflationary Cosmology at
the Reionization Epoch
David T. ChussNASA Goddard Space Flight Center
CMBPol Systematics WorkshopAnnapolis, MDJuly 29, 2008
Goddard Space Flight Center
TeamJohns Hopkins
Chuck BennettBen GoldJoseph EimerLingzhen Zeng
NASA GSFCGary HinshawEd WollackHarvey MoseleyDavid ChussGeorge VoellmerJames Hinderks
U. British ColumbiaMark Halpern
NIST BoulderKent IrwinKi Won YoonWilliam DuncanSherry ChoGene HiltonMike Niemack
Northwestern U.Giles Novak
U. ColoradoNils Halverson
Goddard Space Flight Center
Experimental DetailsAngular resolution 120’
Frequency Coverage 40-150 GHz
Sky Coverage ~Full Sky
Multipole Coverage ~2-90
Polarization ModulationVariable-delay Polarization
Modulator (VPM)
Types of Detectors Feedhorn-coupled TES
Location Ground
Expected limit on r ~0.01
Status Future
Goddard Space Flight Center
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
Goddard Space Flight Center
Detectors
Goddard Space Flight Center
40 GHz GSFC Detectors
Goddard Space Flight Center
OMT Design
CPW
TESHeater
Gold meander
150 GHz CMB polarimeter fabricated
at NIST
Components designed by NIST, CU-Boulder, University of Chicago and Princeton University
Filter Design
6 mm
Goddard Space Flight Center
Variable-delay Polarization Modulators (VPMs)
Stokes V
Stokes U
Stokes Q
Qdetector = Q cos φ + V sin φ
Goddard Space Flight Center
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.
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Submillimeter VPMs
Voellmer et al. (2006), Krejny et al. (2008)
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•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
Voellmer et al. (2008)
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Data Stream
0 5000 10000 150000
Grid!Mirror Separation (microns)
H
V
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3 mm Laboratory Tests
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Systematics/CalibrationSystematic Mitigation
E → B Ensure cross-calibration is good between Q and U measurements, measuring Q, U independently
∆T → B Front-end modulation- beam shape not changed by modulator
T → B1. Beams underfill VPM so variability in edge illumination is
minimized. 2. This effect is monotonic with separation- signal is oscillatory. 3. Common mode signal is manifest in
unmeasured linear Stokes parameter.
∆TOptics → B Modulator located in front of optics. Modulate faster than temperatures can drift
∆TCold Stage → B Monitor bias, external calibrator, Calibrate using astrophysical standards.
Foregrounds → B Multiple frequencies & operation near the suspected foreground minimum
Goddard Space Flight Center
Systematic Concerns
Concern Mitigation
Beam Walkoff location of VPM at (primary) pupil
Variable Beam Truncation sufficient edge taper; symmetry of system
Variable Grid Emission High polarization isolation; symmetry of system.
Wire Vibrations High resonant frequency (tight wires)
Goddard Space Flight Center
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 2009Cryostat for Pathfinder under developmentViper telescope to be shipped to JHU early Fall.
