Huan T. Tran UC Berkeley
POLARBEAR: Polarization of Background Radiation
Huan T. Tran
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University of California at BerkeleyKam Arnold Daniel FlanniganWlliam Holzapfel Jacob HowardZigmund Kermish Adrian Lee P.I. Marius Lungu Mike Myers Roger O'Brient Erin Quealy Christian Reichardt Paul Richards Chase Shimmin Bryan SteinbachHuan Tran P.M. Oliver Zahn Lawrence Berkeley National LabJulian BorrillChristopher CantalupoTheodore KisnerEric Linder Helmuth Spieler University of Colorado at Boulder Aubra AnthonyNils Halverson
University of California at San DiegoDavid BoettgerBrian KeatingGeorge Fuller Nathan Miller Hans Paar Ian SchanningMeir ShimonImperial College Andrew Jaffe Daniel O’DeaLaboratoire Astroparticule & Cosmologie Josquin ErrardJoseph MartinoRadek Stompor KEK Masashi HasumiHaruki NishinoTakayuki TomaruMcGill University Peter Hyland Matt DobbsCardiff University Peter AdeCarole Tucker
POLARBEAR Collaboration
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• Large Format Antenna-coupled TES bolometer arrays• Frequency-Multiplexed Readout• Monochromatic – switch focal planes for different frequencies
Polarbear conceptPOLARBEAR Concept
• HWP Modulator stepped/continuous
• Low Spurious Polarization Optics
• Stringent Ground Shielding/monolithic primary
• Located in Chile for Sky Rotation
Key designs for Systematic Control
Test phase in California- Cedar Flat
Key Technologies for Sensitivity
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Eric Chauvin-General Dynamics (Vertex)
POLARBEAR Telescope
• 4’ at 150 GHz: Constrain Lensing
• Large FOV: 2.4 deg
• Relatively compact
• Monolithic central primary
• Flat-telecentric focal plane
• Cold Lyot Stop
3.5m Clear aperture (2.5m active) Dragone-Gregorian
Cold Reimaging Optics
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POLARBEAR mirrors
Primary: RMS 53 micron
Secondary: RMS 37 micron
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POLARBEAR Receiver
• Three UHMWPE lenses
• Cold Lyot Stop
•Telcentric Focal Plane
Cold Reimaging Optics
• Cryomech Pulse-tube cooler
• Simon-Chase ‘He10’ refrigerator
• now demonstrated with APEX/SPT
Cryogenics
2m
Rotating HWP
• Skyward of lenses
• Field Stop
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POLARBEAR Array
• 7 Hexagonal wafers in Chile• 2 Wafers at Cedar Flat• 637 Pixels/1274 bolometers @ 150 GHz
Si Lenslet Si Wafer
Pixel pair
Antenna Filter
Bolometer
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Polarization Purity Receiver Spectrum
POLARBEAR Detector performance
Beam map
E-Plane
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POLARBEAR DfMUX Readout
capacitors
inductors
Bolometer wafer
FPGA-basedOscillator-Demodulators
NIST squids
POLARBEAR HWP rotation mechanism
28cm
Drive Idler
Pawl
• Designed for both continuous and stepped rotation• Ball bearing • Belt driven / stepper motor• Optical encoder readout• ~Arcsec repeatability (stepped)
• Single plate Sapphire (not shown)• AR coated with TMM• ~70K
Tooth 11
POLARBEAR Groundshielding
•Goal: Ground must be suppressed by ~109 •Cylindrically symmetric•Curved panels•Extra tall to shield mountains
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Systematic errors
Atmosphere
Ground/sidelobes
Polarization Calibration
Beam Distortions
Foregrounds
Band mismatch
Telescope flexure
Ghost reflections
Beam Measurement
Scan Strategy
Small beam size
HWP
HWPSS
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Array Temp stability
Scan Strategy
• Scan in AZ, fixed EL ~ 1 hour
• Re-center scan each hour
• Choose centers for uniformity
• Choose HWP stepping scheme
• Maps ground pickup template each hour
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Scan Strategy: optimizing polarization uniformity
• Sky rotation gives some uniformity• Continuous HWP is ideal-> null many effects• Can choose steps wisely
f1 : Measure of quad-pole non-uniformity polarization coverage
f2 : dipole and oct-pole non-uniformity
Step HWP 3 times, once per day
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Diff Diff GainGain
Diff Diff FWHMFWHM
Diff Diff PointingPointing
Diff Diff EllipticityEllipticity
Diff Diff RotationRotation
POLARBEAR Parameter Tolerances
Instrumental leakage Suppression due to modulation
Beam effect Suppression
Differential gain
Diff Rotation
Suppression w/stepped HWP
Suppression With sky rot
Diff Beam Width
Diff Ellipticity
small beams => Peak in leakage at high-l
Diff Pointing
lensing
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Beam constrained10-3
Foregrounds and Scan Regions
Scan is targeted at low dust contrast regions as low as ~2uK intensity
150,220 GHz bands
Patches chosen to match QUIET
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POLARBEAR Performance
Red error bars: Includes noise increase from subtracting 220 GHz to remove mid lat dustRed error bars: Includes noise increase from subtracting 220 GHz to remove mid lat dust19
Experiment Summary
Frequencies 150/220 GHz
Angular resolutions 7’ :90GHz4’ :150GHz 2.7’:220 Ghz
arcmin at each freq
Field centers and sizes Coord w/ QUIET1000 sq-Deg total
Ra/Dec/Sq-Deg
Telescope type Gregorian/lenses Refractor, Gregorian, Compact-range etc
Polarization Modulations HWP, sky rot Waveplate, boresight rot., sky rot., scan etc. – list all that apply
Detector type Bolometer/TES
Location Atacama
Instrument NEQ/U 360/sqrt(1288/4) =20 K s1/2 for both Q and U
Observation start date 2010
Planned observing time 1000/250 Elapsed/effective days
Projected limit on r 0.025 95% c.l. <10X foreground removal 20
Polarbear conceptPOLARBEAR Deployment
Testing phase at Cedar Flat
Telescope assembly underway
First light in months
Test stepped vs continuous HWP
Test for atmospheric removal21