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