Visions of Antarcitc Astronomy Sydney 19.07.2003

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Precision CMB Polarization from Dome-C Paolo de
Bernardis for the B-modes collaboration
Looking for the signature of stochastic
gravitational waves background in the primordial
universe
Visions of Antarcitc Astronomy - Sydney 19.07.2003
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The Observable
Sub-atomic dimensions

• The inflation process in the early universe
  boosts quantum fluctuations into fluctuations at
  cosmological scales.
• Generic preditions of this scenario are
• A flat geometry of the Universe
• Generation of scalar (density) fluctuations
• Adiabatic
• With a nearly scale invariant spectrum
• Generation of tensor fluctuations (gravitational
  waves)

inflation
Cosmological dimensions
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The Observable

• The inflation process in the early universe
  boosts quantum fluctuations into fluctuations at
  cosmological scales.
• Generic preditions of this scenario are
• A flat geometry of the Universe
• Generation of scalar (density) fluctuations
• Adiabatic
• With a nearly scale invariant spectrum
• Generation of tensor fluctuations (gravitational
  waves)

OBSERVABLE CONSEQUENCES
Temperature fluctuations in the CMB, with a very
precise power spectrum
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The Observable

• The inflation process in the early universe
  boosts quantum fluctuations into fluctuations at
  cosmological scales.
• Generic preditions of this scenario are
• A flat geometry of the Universe
• Generation of scalar (density) fluctuations
• Adiabatic
• With a nearly scale invariant spectrum
• Generation of tensor fluctuations (gravitational
  waves)

OBSERVABLE CONSEQUENCES
Temperature fluctuations in the CMB, with a very
precise power spectrum
OBSERVED BY BOOMERanG, DASI, WMAP ..
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The Observable

• The inflation process in the early universe
  boosts quantum fluctuations into fluctuations at
  cosmological scales.
• Generic preditions of this scenario are
• A flat geometry of the Universe
• Generation of scalar (density) fluctuations
• Adiabatic
• With a nearly scale invariant spectrum
• Generation of tensor fluctuations (gravitational
  waves)

OBSERVABLE CONSEQUENCES
Temperature fluctuations in the CMB, with a very
precise power spectrum
Stochastic Background of gravitational waves
6
The Observable

• The inflation process in the early universe
  boosts quantum fluctuations into fluctuations at
  cosmological scales.
• Generic preditions of this scenario are
• A flat geometry of the Universe
• Generation of scalar (density) fluctuations
• Adiabatic
• With a nearly scale invariant spectrum
• Generation of tensor fluctuations (gravitational
  waves)

OBSERVABLE CONSEQUENCES
Temperature fluctuations in the CMB, with a very
precise power spectrum
Curl-like polarization of the CMB (B-modes)
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E ?
T/S0.28
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rms B-modes polarization signal 2 orders of
magnitude smaller than rms T anisotropy !
E ?
T/S0.28
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The signal is extremely weak

• Nobody really knows how to detect this.
• Pathfinder experiments are needed
• Whatever smart, ambitious experiment we design to
  detect the B-modes
• It needs to be extremely sensitive
• It needs an extremely careful control of
  systematic effects
• It needs careful control of foregrounds
• It will need independent experiments with
  orthogonal systematics.

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• Bolometric experiments feature higher
  instantaneous sensitivity.
• Ex. BICEP at south pole is a bolometer camera
  with 100 bolometers at 100 and 150 GHz, with
  resolution of the order of 1o, and with a
  rotating analyzer for polarization detection.
• We want to use bolometric detectors to have high
  instantaneous sensitivity, but interferometric
  techniques to have orthogonal systematics.

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• The collaboration
• UK (Cardiff University)
• (L. Piccirillo, W. Gear, P. Ade, P. Mauskopf, M.
  Griffin, G. Pisano, B. Maffei, A. Orlando, C.
  Calderon, S. Melhuish, ...)
• UK (Cambridge University)
• (A. Lasenby, G. Yassin, M. Jones, S. Withington,
  ...)
• France (IAS / College de France / Obs. de
  Paris)
• (J.L. Puget, J.M. Lamarre, Y. Giraud-Heraud, J.
  Delabrouille, F. Pajot, ...)
• Italy (University of Milan Bicocca)
• (G. Sironi, M. Gervasi, ...)
• Italy (University of Rome La Sapienza)
• (Silvia Masi, P. de Bernardis, G. Polenta ...)

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• Main aims
• Build a 256 horns bolometric interferometer
• High sensitivity map of large angular scales CMB
  anisotropy polarization from Dome-C
• Subtract the gravitational lensing contribution
• Obtain the power spectrum of the B-modes

Space
This is part of a long term plan.
Balloon
Antarctica (Dome-C)
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Adding interferometer using passive correlators
and direct detectors
phase shift
Complex visibility

horns
direct detector
beam combiner
phase shift
Complex visibility
complex correlator
horns
amplifiers
heterodyne bolometric amplifier/mixer (low
noise elem.) nothing digital/analog
correlator beam combiner (passive) diodes di
rect detectors (low noise elem.) Low freq. (GHz) high freq. ( 90 GHz)
Michelson and Fizeau, followed by COAST in
Cambridge, pioneered these ideas
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What signal we expect to see at the detector?
recovered with spatial or temporal chopping
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Recovered visibilities
Fourier Transform
Average
Image of the sky
Power spectrum
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Pupil plane interferometry (fringes are
temporally displayed)
Method of combining the two beams using
polarizers (or half-silvered mirrors) and then
focusing on a single pixel detector. Also called
Michelson interferometer.
Beam splitter has the property that the phase
difference between transmitted and reflected beam
is exactly 90 degrees. Thats why the /-
D1
Dz(t) variable delay
D2
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• In general we have N horns spaced with
  baselines Bij
• we can form n(n-1)/2 baselines each requiring a
  correlator to recover the corresponding visibility

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• Each telescope/optical element has its own phase
  switcher (for example Dz(t) in the Michelson)
• Each phase switcher is modulated at a different
  audio-frequency Fi bigger than 1/? of the direct
  detector
• Each detector receives radiation from all the
  phase switchers
• All the n(n-1)/2 beating frequencies Bij Fi-Fj
  are within the electrical bandwidth of the
  detectors
• n(n-1)/2 phase sensitive detection provides phase
  and quadrature signals corresponding to the
  output of a n(n-1)/2 matrix of complex
  correlators

phase switching frequencies
beating frequencies
det. bandpass
f
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Receiver Architecture (real instrument is 256
horns)
corrugated feed-horns
Ortho-Mode Transducers (OMT)
Rectangular wave-guide phase switchers
Wave-guide to strip-line transitions
Stokes-parameters extraction
one direct detector per line (contains all the
beating frequencies)
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Facts about bolometric interferometry

• A bolometric interferometer has same sensitivity
  as an array of total power bolometers
• clean modulation of input polarization
• can measure 4 Stokes parameters simultaneously
• Has different systematics and no aberrations
• chop phase instead of rotation of polarization
  vector
• Ground-based atmospheric fluctuations reduced by
  a big factor (tens or hundreds M. Jones)
• Little sensitivity to microphonics. The use of
  pulse tube coolers coupled with ADR or 3He
  fridges allows extended observations in remote
  areas (like Dome-C)

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Sensitivity of Planck HFI
0.1K 1.6K 4K 60K detectors filters horns mir
ror
from A. Lange Detectors for future CMB
observations
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The ultimate sensitivity
from A. Lange Detectors for future CMB
observations
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• Ground based fsky0.2 NET150µK.s1/2 20,000
  baselines, 200 horns, 1 year

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• Planck HFI- like fsky1 NET60µK.s1/2

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• Ultimate fsky1 NET16µK.s1/2

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shield
tent
electronics
Cryo detector
container
Alt-AZ mount
Roof of tower
Dome-C Tower
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Rotary valve assembly
Demonstrator Dome-C 2004
270K
Cryomec PT-405

• Atmospheric noise
• Planet
• No polarization

30K
2.5K
628 mm
ADR
Beam A
Beam B
0.1K
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cryogenic system

• Pulse tube refrigerator Cryomec PT-405 (0.5W _at_4K,
  air cooled, 5kW)
• Keeps the as there is power). Service every 20000 hours.
• Sub-K cooler 3He fridge (our design) or ADR
  (Timbies design) depending on bolo needs.
• Heat switches (Rome design)
• Control electronics (readout and regulation)
  including cryo harness.

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Measurements on the water-cooled version of
PT405 installed in Rome La Sapienza
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Measurements on the water-cooled version of
PT405 installed in Rome La Sapienza
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Full Array Dome-C 2005