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Bolometric Adding Interferometry: MBI & QUBIC. Peter Timbie University of Wisconsin - Madison. CMB Interferometers. Why CMB Interferometry? Systematics!. simple optics - beams can be formed with corrugated horn arrays

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Bolometric adding interferometry mbi qubic l.jpg
Bolometric Adding Interferometry:MBI & QUBIC

Peter Timbie University of Wisconsin - Madison

The Path to CMBPol



Why cmb interferometry systematics l.jpg
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 l.jpg
    Interferometer Beam Systematics

    Interferometers measure visibilities:

    n1

    n2

    y

    i

    uij

    j

    x

    X

    Beam mismatch, distortion, etc. do not couple T into

    Stokes U visibility. [E.F. Bunn PRD 75, 083517 (2007)]


    Slide5 l.jpg

    Beam Combination for Large N

    • 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?

    • 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)



    Adding interferometer for many horns l.jpg

    //

    //

    //

    ….

    ….

    Adding Interferometerfor Many Horns

    N horns

    OMTs

    2Nphase modulators

    beam combiner

    detectors

    single-horn

    auto-correlation

    Stokes U visibilities

    Stokes I visibilities

    total power


    Slide8 l.jpg

    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 l.jpg

    1 baseline

    1 baseline

    1 baseline

    total signal

    1 horn

    Interference pattern

    • 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]


    Sensitivity comparison to imager l.jpg
    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 l.jpg

    Antennas

    Phase modulators

    The Millimeter-Wave Bolometric Interferometer (MBI-4)

    Liquid nitrogen tank

    Liquid helium tank

    Secondary mirror

    3He refrigerator

    Primary mirror

    Bolometer unit


    Mbi assembly l.jpg
    MBI Assembly

    15 cm

    19 spider-web bolos (JPL)

    (PSB’s not required)



    Mbi 4 at pine bluff observatory madison wi l.jpg

    MBI-4 at Pine Bluff ObservatoryMadison, WI

    • First light March 2008

    • Beam maps March 2009

    • See poster by Amanda Gault


    Mbi 4 interference fringes l.jpg
    MBI-4 interference fringes

    Observed Signal (Bolometer #9)

    Simulated Signal

    • Baseline formed by horns 2 and 3

    • Observed Gunn oscillator on tower



    Slide17 l.jpg

    The QUBIC collaboration

    University of Wisconsin USA

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

    IAS Orsay France

    CSNSM Orsay

    France

    University of Richmond USA

    Maynooth University Ireland

    APC Paris France

    Brown University USA

    Universita di Milano-Bicocca Italia

    IUCAA, Pune India

    La Sapienza, Roma, Italia

    Manchester University UK

    CESR Toulouse France

    QU Bolometric Interferometer for Cosmology

    Google Maps


    The qubic instrument concept l.jpg

    phase shifters

    horns

    Bolometer array

    The QUBIC instrument concept

    Sky

    ~25 cm

    • Off-axis quasi-optical beam combiner

    4K

    4K

    4K

    back

    horns

    4K

    ~60 cm

    ~40 cm

    4K

    ~10 cm

    Cryostat

    300 mK

    ~70 cm


    Qubic design l.jpg

    Primary (entry) horns

    QUBIC (144x6,

    (

    Secondary (reemitting) horns

    Significance

    QUBIC Design

    ~ 25cm

    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 GHz

      25% Bandwidth

      Modular Cryogenics

    • One 4K pulse tube for 6 modules

    • 100 mK focal plane

      r ~ 0.01 in one year of data


    Qubic program l.jpg
    QUBIC program

    2006

    MBI-4

    BRAIN

    Pathfinder

    2007

    • 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

    2008

    2009

    2010

    QUBIC

    first module

    2011

    QUBIC

    2012


    Next steps for bolometric interferometry l.jpg
    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


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