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Einstein Polarization Interferometer for Cosmology
(EPIC)
Peter Timbie
University of Wisconsin - Madison
Beyond Einstein SLAC May 12-14 2004
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EPIC Mission Concept Study Team
University of Wisconsin - Madison
Peter Timbie, Shafinaz Ali Peter Hyland, Siddharth Malu, Dan van der Weide
Brown University Greg Tucker, Andrei Korotkov, Jaiseung Kim
University of Richmond Ted Bunn
Cardiff University Lucio Piccirillo, Carolina Calderon
UW Space Science and Engineering Center
Fred Best
Spectrum Astro Dominic Conte
Ball Aerospace Rod Oonk
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CMB Power Spectrum
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Josh Gundersen,
POLAR Upper Limit
Reionization Peak
Zre ~ 30
C
C Farese et al.(2003)
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CMB Polarization Detections!
WMAP TT/10
WMAP TE
DASI EE
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Experimental Challenges
•Sensitivity
•Angular resolution
•Modulation - spatial “chop”- polarization (Q--U)
•Atmosphere
•Temperature stability
•Instrumental polarization
•Antenna sidelobes
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Sensitivity of CMB Detector Systems vs Epoch
rsDet'RMS
N)1(T sΔ
Dicke
Inflation Probe
1.00E-01
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1940 1960 1980 2000 2020
Years
MicroKelvinPlanck
Penzias & Wilson
Maxipol
WMAP
COBE
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Detectors
•bolometers are capable of reaching background limit from CMB
•cooled to < 100 mK
•superconducting transition-edge thermistors (TES)
•readout with SQUID multiplexers
Waveguide-coupled bolometer from MSAM balloon-borne telescope
micromachined Si legs
waveguide x-section
Si frame at 100 mK
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Angular Resolution
DASI interferometer
PLANCK telescope
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Why use an interferometer for CMB?
•simple optics – no reflectors, which can polarize light
•correlation measurement is stable, measures Stokes U directly on a single detector (no differencing)
•instantaneous differencing of sky signals without scanning
•angular resolution ~ 2X better than filled dish of same dia
•measures both Temp and Polarization anisotropy
Systematics!
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Stokes Parameters
yyxx eEeEE ˆˆ +=r )(
,,tkzi
yxyx eaE ϖ−=
yx
yx
yx
EEU
EEQ
EEI
2
22
22
=
−=
+=
For a linearly polarized wave,
where
Stokes parameters are: -additive -coordinate-dependent
Consider rotations:
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎠
⎞⎜⎝
⎛−
=⎟⎟⎠
⎞⎜⎜⎝
⎛
y
x
y
x
E
E
E
E
θθ
θθ
cossin
sincos
'
'
UEEEE yxyx ==− 22'
2'
Example: for /4
x
y
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Ground Screens
The Spinning CorrelationPolarimeter
Ex Ey
yExE yx ˆˆ+
Gx Gy
OMT
Multiplier
UGGEE
EEOutput
yxyx
yx
00±∝
×∝( ) ( )αα 2sin2cos ⋅+⋅= UQSignal
E
Nx
y
CMB
α
0°, 180° Phase Shifter
TP-x TP-y
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Correlation Polarimeter
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Ryle’s Phase-switching Interferometer (1952)
Correlation of signal from 2 antennas
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3-Element Interferometer Angular Response Functions
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Examples of window functions for a 2-element interferometer.Window Functions
2-element interferometer baselines
64 diameter filled dish
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Polarized Foregrounds
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EPIC Overview•Goal 1: measure gravitational waves from inflation
•Goal 2: measure gravitational lensing of CMB
•4-year mission, observe full sky 2X per year
•> 6 frequency bands for foreground removal
•Multiple interferometric arrays (>2) at each wavelength for l-space ranges covering l = 2 to >400
•Measures Stokes I, Q, U interferometrically for l > 40, directly for l < 40
•Bolometric (TES) detectors (> 2700) cooled to ~ 50 mK
•Multiplexed SQUID readout
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The Millimeter-Wave Bolometric Interferometer (MBI)
• 8 feedhorns (23 baselines)
• 90 GHz (3 mm)
• ~1o angular resolution – search for B-mode pol’n
• 7o FOV
• under construction, first light expected winter 2005
• White Mountain, CA (13,500 ft)
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Single-Baseline Test
horn antennas
beam combiner
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EPIC Mission Concept Study Tasks
•Sensitivity analysis
•Optimize l-space coverage of arrays
•Optimize frequency coverage for foregrounds (WMAP, Planck, etc. results are key)
•Beam combiner
•Phase shifters
•Data analysis/simulations of aperture synthesis
•Cryogenics