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Bolometric Adding
Interferometry:
MBI & QUBIC
Peter Timbie
University of Wisconsin - Madison
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1-3 July, 2009
The Path to CMBPol
CMB Interferometers
(GHz)
FOV
# ant’s
receivers
DASI
30
5o
13
HEMT
CBI
30
44’
13
HEMT
MINT
150
30’
4
SIS
VSA
30
7o
14
HEMT
BIMA
30
6’
6
HEMT
OVRO
30
4’
9
HEMT
T-W
45
5o
2
SIS
BAM
90-270
42’
2
Bolo
VLA
5, 8, 16
7’
27
HEMT
SZA
30, 90
10’, 3’
8
HEMT
Why CMB Interferometry? Systematics!
• simple optics
- beams can be formed with corrugated horn arrays
- symmetric beam patterns, low sidelobes, no mirrors
- no off-axis aberrations
• correlates Ex and Ey on a single detector to measure Stokes U
(no differencing of detectors)
• differences sky signals (measures visibilities) without scanning
• simple observing strategy - measure U and Q on each field by
rotating about optical axis
• measures Temp and Polarization power spectra directly
• angular resolution ~ 2X better than imager of equivalent diameter
• coherent (HEMTs) or incoherent (bolometers) systems possible
Interferometer Beam Systematics
Interferometers measure visibilities:
n1
VijU 
n2
 dn1 dn2Gix (n1 )G jy (n2 ) Eix (n1 )E jy (n2 )
y
i
x
uij
j
U(n1 )e


X

2iu ij n 1
dnG
ix (n)G jy (n)U(n)e
(n1  n2 )
i 2u ij n
Beam mismatch, distortion, etc. do not couple T into
Stokes U visibility. [E.F. Bunn PRD 75, 083517 (2007)]

Beam Combination for Large N
1. Pairwise (Michelson): signals are split and combined pairwise
•
N(N-1)/2 pairs (78 for N = 13, 4950 for N =100)
•
multiplying correlator (coherent receivers only)
a. analog (DASI/CBI)
b. digital (most radio interferometers)
- power?
- bandwidth?
2. Fizeau (Butler): signals from all antennas appear at all detectors
•
Guided-wave adding interferometer (Butler combiner, Rotman lens)
•
Quasioptical adding interferometer using a telescope (MBI, EPIC-I, QUBIC)
Ryle’s Adding Interferometer (1952)
“visibility”
E 1  E| |1 E  2  E||2

N horns

OMTs
2N phase
modulators
EN  E||N
//

//

//

Adding
Interferometer
for Many Horns
….
beam combiner
detectors
….
( E 1  E||1  ...E N  E||N ) ( E 1  E||1  ...E N  E||N ) 

N
N
2
2
(E1
 ...EN
)  (E1 E||1  ...EN E||N )  (E1 E||2  ...E1 E||N )  (E1 E 2  ...E|| E||N )

N
total power
single-horn
auto-correlation
Stokes U
visibilities
Stokes I
visibilities
Quasioptical Beam Combiner
Cryostat
Feed horn antennas
Phase Shifters
45° CW twist
rectangular
wave guide
45º CCW twist
rectangular
wave guide
Bolometer Array
Parabolic mirror
Interference pattern
•The interference pattern is imaged on the bolometer
array
1 horn
1 baseline
1 baseline
1 baseline
total signal
•Each pixel measures a linear combination of all visibilities
with different phase shifts
•Sequences of phase shift modulations allow
reconstruction of all visibilities in optimal way
•In a close-packed array, many baselines are redundant these need to be ‘co-added’
[Charlassier
et al., arxiv:0806.0380, A&A 497 (2009) 963]
[Hyland et al., arXiv :0808.2403v1, MNRAS 393 (2009) 531]
Sensitivity - comparison to imager
Both systems have:
•
•
•
•
256 horns
1 angular resolution
background-limited bolos
25 % bandwidth
Interferometer:
•
•
co-adds ‘redundant’
visibilities
has 1000 detectors
data pts from
simulation
[Hamilton et al., arxiv:0807.0438,
A&A 491-3 (2008) 923-927]
updated with bandwidth and
accurate NET calculations]
The Millimeter-Wave Bolometric
Interferometer (MBI-4)
Antennas
• Fizeau (optical) beam combiner
Phase modulators
• 4 feedhorns (6 baselines)
• 90 GHz (3 mm)
• ~1o angular resolution
• 7o FOV
Liquid nitrogen tank
Liquid helium tank
Secondary mirror
3He
refrigerator
Primary mirror
Bolometer unit
MBI Assembly
15 cm
19 spider-web bolos (JPL)
(PSB’s not required)
MBI Team
Brown University
Greg Tucker, Andrei Korotkov
Jaiseung Kim
University of Richmond
Ted Bunn
University of Manchester
Lucio Piccirillo
Cardiff University
Peter Ade, Carolina Calderon
National University of Ireland - Maynooth
Creidhe O’Sullivan, Gareth Curran
University of Wisconsin - Madison
Peter Timbie, Amanda Gault
Peter Hyland, Siddharth Malu
University of Illinois
Ben Wandelt
UC San Diego
Evan Bierman, Brian Keating
University of Paris - APC
Romain Charlassier, JeanChristophe Hamilton, Michel Piat
MBI-4
at
Pine Bluff Observatory
Madison, WI
• First light March 2008
• Beam maps March 2009
• See poster by Amanda Gault
MBI-4 interference
fringes
Observed Signal (Bolometer #9)
Simulated Signal
• Baseline formed by horns 2 and 3
• Observed Gunn oscillator on tower
MBI Interference Fringes
The QUBIC collaboration
University of
Wisconsin
USA
University of
Richmond
USA
Brown
University
USA
A merging of MBI (USA) with BRAIN
(Europe)
IAS Orsay
CSNSM Orsay France
France
Maynooth
University
APC Paris
Ireland
France
Manchester
University UK
Universita di
IUCAA, Pune
MilanoIndia
Bicocca Italia
La Sapienza,
Roma, Italia
CESR
Toulouse
France
QU Bolometric Interferometer for Cosmology
Google Maps
The QUBIC instrument concept
• Off-axis quasi-optical beam combiner
Sky
~25 cm
horns
4K
4K
phase
4K
shifters
back
horns
4K
~60 cm
~40 cm
4K
~10 cm
Bolometer array
300 mK
~70 cm
Cryostat
QUBIC Design
Primary
(entry)
horns
6 modules of 144 entry horns
–
–
–
–
–
–
14 deg. primary beams
square compact configuration
multipole range : 25-150
~900 TES bolometers / module
~ 25cm
Secondary
(reemitting)
horns
~10000 baselines / module
phase switch redundant
baselines simultaneously
- phase steps of 15 degrees
- sequence length ~500 steps
QUBIC
(144x6,
3 channels: 90,150,220 GHz
Modular Cryogenics
–
–
One 4K pulse tube for 6 modules
100 mK focal plane
r ~ 0.01 in one year of data
Significan
ce
25% Bandwidth
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(
•
–
–
–
MBI-4 Prototype
QUBIC program
4 horns bolometric interferometer
works in Wisconsin (2008 and 2009)
Fringes observed !
2007
•
BRAIN Pathfinder
–
Site testing, logistics
Atmosphere characterization at Dome C
(effective temperature, polarization ...)
–
–
•
–
–
–
–
–
–
2006
•
•
MBI-4
BRAIN
Pathfinde
r
2009
2 campaigns, January 2006 and 2007
Third campaign starting next Antarctic
summer
QUBIC
Search for primordial B-modes (50 < l < 150)
6 Bolometric interferometer modules
144 horns/module (90, 150, 220 GHz)
25% Bandwidth
Full instrument in 2012-2013
Target : r ~ 0.01 in 1 year of data
2008
2010
QUBIC
first module
2011
2012
QUBIC
Next steps for Bolometric Interferometry
• phase modulators are critical
- multiple phase states (~ 5 bits)
- 1 ms switching speed
- several technologies under study: Faraday,
MEMs, s/c nanobridge switches, varactor diode
• simulations of systematic effects, scan strategies
• foreground removal in visibility space
• QUBIC
• see poster by T.K. Sridharan for alternate BI approach