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Transcript
POLARBEAR: Polarization of Background Radiation
Huan T. Tran
Huan T. Tran UC Berkeley
1
POLARBEAR
University of California at Berkeley
Kam Arnold
Daniel Flannigan
Wlliam Holzapfel
Jacob Howard
Zigmund Kermish
Adrian Lee
Marius Lungu
Mike Myers
Roger O'Brient
Erin Quealy
Christian Reichardt
Paul Richards
Chase Shimmin
Bryan Steinbach
Huan Tran
Oliver Zahn
P.I.
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 O’Dea
Laboratoire Astroparticule & Cosmologie
Josquin Errard
Joseph Martino
Radek Stompor
P.M.
Lawrence Berkeley National Lab
Julian Borrill
Christopher Cantalupo
Theodore Kisner
Eric Linder
Helmuth Spieler
University of Colorado at Boulder
Aubra Anthony
Nils Halverson
Collaboration
KEK
Masashi Hasumi
Haruki Nishino
Takayuki Tomaru
McGill University
Peter Hyland
Matt Dobbs
Cardiff University
Peter Ade
Carole Tucker
2
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
Eric Chauvin-General Dynamics (Vertex)
• Stringent Ground Shielding/monolithic
primary
Test phase in California- Cedar Flat
• Located in Chile for Sky Rotation
3
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
Cold Reimaging Optics
•
Flat-telecentric focal plane
•
Cold Lyot Stop
4
5
POLARBEAR
mirrors
Primary: RMS 53 micron
Secondary: RMS 37 micron
6
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
2m
• now demonstrated with APEX/SPT
7
POLARBEAR Array
Antenna
Filter
• 7 Hexagonal wafers
in Chile
• 2 Wafers at Cedar
Flat
• 637 Pixels/1274
bolometers @ 150 GHz
Bolometer
Pixel pair
Si Lenslet
Si Wafer
8
POLARBEAR
Detector performance
Receiver Spectrum
Polarization Purity
Beam map
9
POLARBEAR
DfMUX Readout
capacitors
inductors
NIST squids
Bolometer wafer
FPGA-based
Oscillator-Demodulators
10
POLARBEAR
Drive
HWP rotation mechanism
Idler
• Single plate Sapphire (not
shown)
• AR coated with TMM
• ~70K
28cm
Tooth
• Designed for both
continuous and stepped
rotation
• Ball bearing
• Belt driven / stepper motor
• Optical encoder readout
• ~Arcsec repeatability
(stepped)
Pawl
11
POLARBEAR
Groundshielding
•Goal: Ground must be
suppressed by ~109
•Cylindrically symmetric
•Curved panels
•Extra tall to shield mountains
12
Systematic errors
Foregrounds
Atmosphere
Polarization Calibration
HWPSS
Band mismatch
Array Temp stability
Ghost reflections
Ground/sidelobes
Telescope flexure
Beam Distortions
Scan Strategy
HWP
Small beam size
Beam Measurement
13
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
14
Scan Strategy:
optimizing polarization uniformity
• Sky rotation gives some uniformity
• Continuous HWP is ideal-> null many effects
• Can choose steps wisely
Step HWP 3 times, once per day
f1 : Measure of quad-pole nonuniformity polarization coverage
f2 : dipole and oct-pole non-uniformity
15
POLARBEAR
Parameter Tolerances
Instrumental leakage
Diff
Gain
Suppression due to modulation
Diff
FWHM
Diff
Diff
Diff
Pointing Ellipticity Rotation
Beam effect Suppression
Differential gain
Beam constrained
10-3
Diff Ellipticity
Suppression
With sky rot
Suppression w/
stepped HWP
Diff Rotation
Diff Beam Width
Diff Pointing
small beams =>
Peak in leakage at high-l
17
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
18
POLARBEAR
Performance
Red error bars: Includes noise increase from subtracting 220 GHz to remove mid lat dust
19
Experiment Summary
Frequencies
150/220
GHz
Angular resolutions
7’ :90GHz
4’ :150GHz
2.7’:220 Ghz
Field centers and sizes
Coord w/ QUIET
1000 sq-Deg total
Ra/Dec/Sq-Deg
Telescope type
Gregorian/lenses
Refractor, Gregorian, Compactrange etc
Polarization Modulations
HWP, sky rot
Detector type
Bolometer/TES
Location
Atacama
Instrument NEQ/U
360/sqrt(1288/4) =20
Observation start date
2010
Planned observing time
1000/250
Projected limit on r
0.025 95% c.l.
arcmin at each freq
Waveplate, boresight rot., sky rot.,
scan etc. – list all that apply
K s1/2 for both Q and U
Elapsed/effective days
<10X foreground
removal
20
POLARBEAR
PolarbearDeployment
concept
Testing phase at Cedar Flat
Test stepped vs continuous HWP
Telescope assembly underway
Test for atmospheric removal
 First light in months
21