Huan%20T.%20Tran%20UC%20Berkeley

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POLARBEAR Polarization of Background Radiation
Huan T. Tran
Huan T. Tran UC Berkeley
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POLARBEAR Collaboration
University of California at Berkeley Kam Arnold
Daniel Flannigan Wlliam Holzapfel Jacob
Howard Zigmund Kermish Adrian Lee
P.I. Marius Lungu Mike Myers Roger
O'Brient Erin Quealy Christian Reichardt Paul
Richards Chase Shimmin Bryan Steinbach Huan
Tran P.M. Oliver Zahn
Lawrence Berkeley National Lab Julian
Borrill Christopher Cantalupo Theodore
Kisner Eric Linder Helmuth Spieler University
of Colorado at Boulder Aubra Anthony Nils
Halverson
University of California at San Diego David
Boettger Brian Keating George Fuller Nathan
Miller Hans Paar Ian Schanning Meir
Shimon Imperial College Andrew Jaffe Daniel
ODea Laboratoire Astroparticule Cosmologie
Josquin Errard Joseph Martino Radek Stompor KEK
Masashi Hasumi Haruki Nishino Takayuki
Tomaru McGill University Peter Hyland Matt
Dobbs Cardiff University Peter Ade Carole Tucker
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POLARBEAR Concept
Polarbear concept
Key Technologies for Sensitivity

• Large Format Antenna-coupled TES bolometer
  arrays
• Frequency-Multiplexed Readout
• Monochromatic switch focal planes for
  different frequencies

Key designs for Systematic Control

• HWP Modulator stepped/continuous
• Low Spurious Polarization Optics
• Stringent Ground Shielding/monolithic primary
• Located in Chile for Sky Rotation

Eric Chauvin-General Dynamics (Vertex)
Test phase in California- Cedar Flat
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POLARBEAR Telescope
3.5m Clear aperture (2.5m active)
Dragone-Gregorian

• 4 at 150 GHz Constrain Lensing
• Large FOV 2.4 deg
• Relatively compact
• Monolithic central primary
• Flat-telecentric focal plane
• Cold Lyot Stop

Cold Reimaging Optics
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POLARBEAR mirrors
Primary RMS 53 micron
Secondary RMS 37 micron
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POLARBEAR Receiver
Cold Reimaging Optics

• Three UHMWPE lenses
• Cold Lyot Stop
• Telcentric Focal Plane

Rotating HWP

• Skyward of lenses
• Field Stop

Cryogenics

• Cryomech Pulse-tube cooler
• Simon-Chase He10 refrigerator
• now demonstrated with APEX/SPT

2m
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POLARBEAR Array

• 7 Hexagonal wafers in Chile
• 2 Wafers at Cedar Flat
• 637 Pixels/1274 bolometers _at_ 150 GHz

Antenna
Filter
Bolometer
Pixel pair
Si Wafer
Si Lenslet
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POLARBEAR Detector performance
Receiver Spectrum
Polarization Purity
Beam map
E-Plane
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POLARBEAR DfMUX Readout
capacitors
inductors
NIST squids
Bolometer wafer
FPGA-based Oscillator-Demodulators
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POLARBEAR HWP rotation mechanism
Idler
Drive

• Single plate Sapphire (not shown)
• AR coated with TMM
• 70K

28cm

• Designed for both continuous and stepped
  rotation
• Ball bearing
• Belt driven / stepper motor
• Optical encoder readout
• Arcsec repeatability (stepped)

Tooth
Pawl
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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
Foregrounds
Polarization Calibration
HWPSS
Band mismatch
Array Temp stability
Scan Strategy
Ghost reflections
HWP
Ground/sidelobes
Small beam size
Telescope flexure
Beam Measurement
Beam Distortions
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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-gt null many effects
• Can choose steps wisely

Step HWP 3 times, once per day
f1 Measure of quad-pole non-uniformity
polarization coverage
f2 dipole and oct-pole non-uniformity
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POLARBEAR Parameter Tolerances
Instrumental leakage
Suppression due to modulation
Diff Pointing
Diff Ellipticity
Diff FWHM
Diff Gain
Diff Rotation
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Beam effect Suppression
Differential gain
Beam constrained 10-3
lensing
Diff Ellipticity
Suppression With sky rot
Suppression w/ stepped HWP
Diff Rotation
Diff Beam Width
small beams gt Peak in leakage at high-l
Diff Pointing
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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 dust
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Experiment Summary
Frequencies 150/220 GHz
Angular resolutions 7 90GHz 4 150GHz 2.7220 Ghz arcmin at each freq
Field centers and sizes Coord w/ QUIET 1000 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. lt10X foreground removal
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POLARBEAR Deployment
Polarbear concept

• Testing phase at Cedar Flat
• Telescope assembly underway
• First light in months

• Test stepped vs continuous HWP
• Test for atmospheric removal