1-3 July, 20091-3 July, 2009 The Path to CMBPolThe Path to CMBPol

Bolometric Adding Interferometry:MBI & QUBIC

Peter Timbie University of Wisconsin - Madison

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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

j

n1 n2

uij €

VijU = dn1∫ dn2Gix (n1 )G jy (n2 ) Eix (n1 )E jy (n2 )

i

€

= dn∫ Gix (n)G jy (n)U(n)ei 2πuij ⋅n€

U(n1 )e2πiu ij ⋅n1δ(n1 − n2 )

Beam mismatch, distortion, etc. do not couple T into Stokes U visibility. [E.F. Bunn PRD 75, 083517 (2007)]

y

x

X

Interferometers measure visibilities:

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”

Adding Interferometer

for Many Horns OMTs

€

E⊥1 + E ||1 2||2 EE +⊥

N

EEEE

N

EEEE NNNN∗

⊥⊥⊥⊥ +++×

+++ )...()...( ||1||1||1||1

€

=(E⊥12 + ...E⊥N

2 ) + (E⊥1E||1 + ...E⊥NE||N ) + (E⊥1E||2 + ...E⊥1E||N ) + (E⊥1E⊥2 + ...E||E||N )

N

total power single-horn auto-correlation

Stokes U visibilities

N horns

2N phase modulators

beam combiner

detectors

€

E⊥N + E||N

Stokes I visibilities

// // //

….

….

Bolometer Array

Parabolic mirror

Phase Shifters

Feed horn antennasCryostat

45° CW twist rectangular wave guide

45º CCW twist rectangular wave guide

Quasioptical Beam Combiner

Interference pattern

1 horn 1 baseline 1 baseline 1 baseline total signal

•The interference pattern is imaged on the bolometer array

•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]

Both systems have:

• 256 horns

• 1 angular resolution

• background-limited bolos

• 25 % bandwidth

Interferometer:

• co-adds ‘redundant’ visibilities

• has 1000 detectors

Sensitivity - comparison to imager

[Hamilton et al., arxiv:0807.0438, A&A 491-3 (2008) 923-927] updated with bandwidth and accurate NET calculations]

data pts fromsimulation

The Millimeter-Wave Bolometric Interferometer (MBI-4)

• Fizeau (optical) beam combiner

• 4 feedhorns (6 baselines)

• 90 GHz (3 mm)

• ~1o angular resolution

• 7o FOV

Antennas

Liquid nitrogen tank

Liquid helium tank

Secondary mirror

3He refrigerator

Primary mirror

Bolometer unit

Phase modulators

MBI Assembly

19 spider-web bolos (JPL)(PSB’s not required)

15 cm

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, Jean-Christophe Hamilton, Michel Piat

MBI-4 at

Pine Bluff ObservatoryMadison, WI

• First light March 2008• Beam maps March 2009• See poster by Amanda Gault

MBI-4 interference fringes

• Baseline formed by horns 2 and 3• Observed Gunn oscillator on tower

Observed Signal (Bolometer #9)

Simulated Signal

MBI Interference Fringes

The QUBIC collaborationUniversity of

Wisconsin USAUniversity

of Richmond

USA

IUCAA, Pune IndiaLa

Sapienza, Roma, Italia

Universita di Milano-Bicocca Italia

CESR Toulouse France

Maynooth University Ireland

Manchester University

UK

CSNSM Orsay France

IAS Orsay France

APC Paris France

Brown University

USA

QU Bolometric Interferometer for CosmologyGoogle Maps

A merging of MBI (USA) with BRAIN (Europe)

The QUBIC instrument concept• Off-axis quasi-optical beam combiner

Bolometer arrayBolometer array

phase phase shiftersshifters

hornshorns

backbackhornshorns

4K

300 mK

4K

4K

4K

4K

Cryostat

Sky

~70 cm

~60 cm

~10 cm

~25 cm

~40 cm

6 modules of 144 entry horns– 14 deg. primary beams

– square compact configuration

– multipole range : 25-150

– ~900 TES bolometers / module– ~10000 baselines / module

– phase switch redundant baselines simultaneously- phase steps of 15 degrees- sequence length ~500 steps

3 channels: 90,150,220 GHz25% Bandwidth

Modular Cryogenics

– One 4K pulse tube for 6 modules

– 100 mK focal plane

r ~ 0.01 in one year of data

QUBIC Design Primary (entry) horns

~ 25cm

QUBIC (144x6, (

Signifi

cance

Secondary (reemitting) horns

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QUBIC program

2006

2007

2008

2009

2010

BRAINPathfinder

QUBICfirst module

QUBIC

2011

MBI-4

2012

• MBI-4 Prototype– 4 horns bolometric interferometer

– works in Wisconsin (2008 and 2009)

– Fringes observed !

• BRAIN Pathfinder– Site testing, logistics

– Atmosphere characterization at Dome C– (effective temperature, polarization ...)

• 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

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