lezione11 2016 cos.ppt [modalità compatibilità]oberon.roma1.infn.it/lezioni/cosmologia...stack cold, stepping HWP polarizer arrays of multimode feedhorns and bolometers UHMWPE lens

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CMB observables• Spectrum (specific brightness <I()>) :

• Measured by COBE‐FIRAS• Blackbody, T=2.725K• Deviations < 0.01% of peak brightness

• Anisotropy (map of the brightness I(,)):

• Measured full sky, by many experiments, latest is Planck• Gaussian, rms around 90 K• Power spectrum cl consistent with the adiabatic inflationary model for structure formation

• Linear Polarization (maps of Q(,) and U(,) ):

• rms around 3 K, consistent with anisotropy results• Power spectrum of E‐modes (irrotational component) measured by several experiments

• Power spectrum of B‐modes (curl component) due to dark matterstructures lensing detected

• Power spectrum of B‐modes from Inflation not detected yet2

http://arxiv.org/abs/1502.01589

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CMB polarization map from Planck (Feb.5, 2015)r < 0.1

D. Molinari et al.

Polarized foregrounds

Planck coll. 2015

Foregrounds are complex and polarized

http://arxiv.org/abs/1409.5738

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Polarized emission of the ISM

• Often the result of superposition of several clouds along the line of sight

• Different temperature distribution for dust, different magnetic field orientation in different clouds, different electron populations, …

• For example, the orientation of linear polarization resulting from the superposition of dust grains differently aligned and with different temperatures changes with frequency.

• For this reason, scalar extrapolation, based on the brightness spectrum alone, is only a zero‐order approximation. Has worked to some extent to point‐out the presence of ISD emission in BICEP2 data (using 350GHz data from Planck extrapolated to 150GHz, see arXiv:1409.5738). But this is just a rough approximation. For the final mission we need to carry out precise corrections.

• Similar arguments apply to synchrotron emission at low frequencies.

• Extrapolation of dust to long wavelengths and of synchrotron to high frequencies is non‐trivial, unless you have a number of high and low frequency channels.

T1

T2

CMB

B1

B2

Need for space‐based measurements

• Extrapolation of dust to long wavelengths and of synchrotron to high frequencies is non‐trivial, unless you have a number of highly sensitive channels at high and at low frequencies, basically filling the range 30 to 700 GHz.

• Because of the earth atmosphere, this frequency coverage cannot be obtained entirely from the ground.

• In addition, operation in space (L2)

– Permits the use of cold telescopes, reducing the radiative background on the detectors and improving their sensitivity

– Enhances the stability of the instrument

– Avoids atmospheric noise

– Reduces ground‐spillover signals.

COrE+26/11/2014 9

0.5 mm PWV2 mm PWV

40 km

240K=2%

240K=0.1%

Atmospheric fluctuations : quantum

space • Just taking into account photon background from the atmophere and its noise, you need many more detectors in a ground‐based experiment than in a space‐based experiment, to obtain the same instantaneous sensitivity.

• Integration time can be longer for a ground‐based experiment, but not for a large factor.

• High‐frequency measurements are necessary, and require space‐based observations.

J. Delabrouille

Atmospheric fluctuations : Turbulence

measuring CMB fluctuations from the ground at f > 220 GHz is extremely difficult, even in the best sites

We need more bands than componentsCount components (or parameters)

CMBThermal SZ2‐component thermal dust2‐component synchrotronFree‐freeSpinning dustCIBZodiacal lightRadio source backgroundSurprises

TOTAL

I

1264‐61‐2a fewmany1‐3a few?

15‐20 +

P

1064‐60 ??0 ?0 ?

a few?

11‐13 +

In cleaner regions of the sky, less parameters are needed, but this depends on the sensitivity of the survey.

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CMB research strategy

CMB Stage 4Ground based

500000+ polarizationsensitive pixels (several

large telescopes)1‐2’FWHM @CMB f40, 95, 150 GHz

CMB ESA‐M5Space mission

5000 polarization sensitive pixels (20 bands, 1.5m telescope in space)

1‐2’FWHM @high f (220 +)4‐6’ @CMB f

CMB Stage 3A large number of current experiments, to demonstrate

technologies and methods (in Europe: OLIMPO, QUBIC, LSPE …)

1‐2’FWHM high fidelity maps of polarization

anisotropy of the CMB and the foregrounds

CMB SpectrumsatelliteAbsolute

measurement, 1‐2°, many bands, clear large scales

(PIXIE)

1‐2’FWHM high fidelity, absolute mapsof the CMB and the

foregrounds

Examples of S3 experiment

• BICEP‐2: a ground‐based experiment

• LSPE: a balloon‐borne experiment

http://www.kicc.cam.ac.uk/sites/default/files/talks/BICEP2_IoA_2014.pdf

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http://www.kicc.cam.ac.uk/sites/default/files/talks/BICEP2_IoA_2014.pdf

LSPEthe Large‐Scale

Polarization Explorerhttp://planck.roma1.infn.it/lspe

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Scientific Target : B‐modes• Red line : contribution from each

multipole to the total mean square fluctuation of the tensor component of CMB polarization (B-modes, r = 1).

• Thin blue line : the cumulative of the B-modes, i.e. the variance measured by an experiment sensitive from multipole 2 to a given multipole l.

• The top blue thick line : the beam function B2

l for an experiment with a 1.5o FWHM Gaussian beam.

• Despite of the coarse angular resolution such an experiment collects most of the polarization signal from B-modes.

2

main target : reionization peak

2

A difficult but important target, to complement measurements of the l=80 peak !

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the reionization peak is difficult• Large angular scales: wide sky

coverage required.

• Foreground contamination ishigh. From Planck intermediate results XXX: The angular power spectrum of polarized dust emission at intermediate and high Galactic latitude

Dust B-modes in the best 30% of sky at 350 GHz:

Extrapolating to 150 GHz (factor 0.04^2)

2

south

north

402.8

402.8

402.8

• Large sky coverage and wide frequency coverage call for a space mission. See e.g. COrE+.

• On a shorter time‐scale, experimentation is required to qualify specific instrumentation (optical systems, polarization modulators, detectors …) and methods (sky scan, mapping procedures, polarized foregrounds separation …) and possibly to get detections !

• A balloon‐borne instrument can

– avoid atmosperic noise and loading

– exploit a wide frequency coverage

– access a large fraction of the sky during night‐time

– offer a stable environment during night‐time

– reject ground spillover using very large ground‐shields

Experiment Strategy

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29/Dec/1998

Balloon at 30 Km of altitude:Note the spherical shape

• The disadvantage of these balloons is that they can vent He when the temperature increases. So the volume decreases at each diurnal cycle. As a consequence, the float altitude decreases.

• Long Duration Balloon flights of a few weeks can be obtained in polar regions, where the diurnal illumination change is minimum. Example: The BOOMERanG flight in 1998, 10.6 days long:

0 1 2 3 4 5 6 7 8 9 1 0 1 12 0 0 0 0

2 5 0 0 0

3 0 0 0 0

3 5 0 0 0

4 0 0 0 0

B 9 8

alti

tud

e (

m)

t (d a ys )

• The Large‐Scale Polarization Explorer is :– an instrument to measure the polarization of the Cosmic Microwave Background at

large angular scales

– using a spinning stratospheric balloon payload to avoid atmospheric noise

– flying long‐duration, in the polar night

– using a polarization modulator to achieve high stability

• Frequency coverage: 40 – 250 GHz (5 channels, 2 instruments: STRIP & SWIPE)

• Angular resolution: 1.3o FWHM

• Sky coverage: 20‐25% of the sky per flight

• Combined sensitivity: 10 K arcmin per flight

• Current collaboration: Sapienza, UNIMI, UNIMIB, IASFBO‐INAF, IFAC‐CNR, Uni.Cardiff, Uni.Manchester. INFN‐GE, INFN‐PI, INFN‐RM1, INFN‐RM2

• See astro‐ph/1208.0298, 1208.0281, 1208.0164 and forthcoming updates

LSPE in a nutshell

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SWIPE

STRIP

STAR SENSORS

PIVOT

RACK

BATTERIES

BALLAST

FRAME

LSPE gondola : frame + pivot + STRIP + SWIPE to balloon

Actuators: Azimuth pivot with torque motors

Linear elevation actuators

Processor: PC104 with ADC in / PWM out

H-bridges for motors

Attitude sensors: Star sensors (Nati et al. RSI 2003)

Laser GyroscopesElevation Encoders

TMTC

ACSblock diagram

Preliminary sketch of the LSPE experiment, without thermal protections. The total mass is around 2.5 tons, the overall dimensions are 5.8m(w) x 3.2m(d) x 4.6m (h).A 800000 m3 balloon is used to lift the instrument at 37 km of altitude.

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South

B-modes from dust @140 GHz, as estimated from Planck 343 GHz dust polarization - Planck PIP XXX 1409.5738

1010.10.01

North

Sky coverage of LSPE (Launch from Longyearbyen, Svalbard)

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The STRIP Instrument• STRIP is the STRatospheric Italian Polarimeter, aimed at accurate measurements of the low‐frequency (44 and 90 GHz) polarized emission, dominated by Galactic synchrotron. • Its sensitivity at 44 GHz in a single flight is twice better than the final sensitivity of the Planck LFI survey. • The correlation radiometers are contained in a large cryostat and cooled at 20K by evaporating 4He.

2100

mm

7

The STRIP Instrument The beam is defined by a 600 mm aperture side‐fed crossed‐Dragone telescope, selected for best polarization purity

Challenging for spillover, stray‐light and obscuration

Modular Primary and secondary mirrors to reduce fabrication costs

Lightened structure to reduce weight

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The STRIP Instrument• In the focal plane, an array of 44 GHz platelet feedhorns (already manufactured) feeds high performance OMTs and LNAs derived from the QUIET exp.• The measured response of the corrugated feedhorns confirms the expected performance down to ‐55 dB

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• SWIPE is the Short Wavelength Instrument for the Polarization Explorer

• It is a Stokes Polarimeter, based on a simple 50 cm aperture refractive telescope, a cold HWP polarization modulator, a beamsplitting polarizer, and two large focal planes, filled with multimode bolometers at 140, 220, 240 GHz.

• Everything is cooled by a large L4He cryostat and a 3He refrigerator, for operation of the bolometers at 0.3K

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The SWIPE Instrument

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Low inputwindow

thermal fliters stack

cold, stepping HWP

polarizerarrays of multimode feedhorns and bolometers

UHMWPE

lens

4He tank (290L) 3He fridge

1370

A cryogenic Stokes polarimeter

SWIPE

SWIPE – polarization modulator• Is a cold (2K), large (50 cm

useful dia.), wide band metamaterials HWP, placed immediately behind the window and thermal filters stack.

• HWP characteristics for the ordinary and extraordinary rays are well matched:(To-Te)/To < 0.001, Xpol<0.01, over the 100-300 GHz band.

• Its orientation is stepped by 11.25° or 22.5° every few scans.

500 mm

The cryogenic HWP rotator made for the PILOT experiment. The LSPE one will be based on the same design, and scaled up in dimensions (see Salatino et al. A&A 528 A138 2011)

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SWIPE – optical system• Single lens UHMWPE @4K,

AR coating, D=480, f=800• Two curved focal planes

populated with multimode bolometric detectors, resulting in 1.2°FWHM beams

reflected focal plane transmitted focal plane

Scan direction

1.2°

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Band (GHz)

Width (%) Total # detectors

# 2

modes

140 GHz 30 110 10

220 GHz 5 110 21

240 GHz 5 110 23

M. De Petris

SWIPE – multimode feedhorns• 20 mm aperture• High efficiency coupling

structure, easy to machine• Nice top-hat beams• 10, 21, 23 2 modes @ 140,

220, 240 GHz

150 GHz

cold aperture stop

dB

Feedhorn + detector assemblyFinal design23g each

Feedhorn + detector assemblyTested Prototype

L. Lamagna

G. CoppiT. Marchetti

SWIPE ‐ multimode absorbers & TES• The absorbers are large Si3N4

spider-webs (8 mm diameter, multimode)

• Sensors are Ti-Au TES• Photon noise limited• = 2 ms

SWIPE ‐ cryostat• mass = 460 kg

• He volume = 0.9 x 290 lt

• Hold time = 19 .. 23 days

S. Masi, A. Schillaci

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• Scanning strategy: payload spin in azimuth, at 3 rpm (18°/s)

• Coverage of the same sky area by the two instruments

• Elevation changes once a day, at the same time for both instruments

• Specific calibration observations of

– Jupiter (to map the main beam, see figure below, samples = white dots)

– the Crab nebula and the Moon Limb (to calibrate the main axis of the polarimeters)

– the Moon can be used to map sidelobes

Observations and Calibration PlanElevation Coverage Unmasked

SWIPE [30‐40] 31% 23%

SWIPE [40‐50] 27% 20%

SWIPE 35 24% 19%

SWIPE 45 22% 18%

SWIPE [30‐50] 35% 26%

STRIP 45 27% 20%

STRIP 30 33% 24%

LSPE coverage for different sets of elevation changes. The first column reports the boresight elevation range in degrees for the two instruments. Second column, the full coverage. Third column, the coverage after masking the galaxy with the WMAP polarization mask.

Source Culmination (deg)

S/N per sampleat 44 GHz


S/N persampleat 145 GHz


Moon 30 37500 200000 700000 2000000

Crab 34 20 18 23 28

Mars 0 0.30 1.6 5.6 18

Jupiter 27 15 80 275 850

Saturn -6 1.4 7 24 70

Uranus 16 0.05 0.24 0.8 2.5

Sources culmination angle, and expected S/N per sample. Sampling rate is set at 60 Hz. We assume full Moon, as it is when it is observable by LSPE. The Crab flux is based on the free‐free spectrum reported in Macías‐Pérez, et al. Ap. J., 711, 417 (2010)

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STRIP SWIPE

Performance Forecast• The presence of

the HWP allows to fully exploit the sensitivity of LSPE-SWIPE.

• Realistic simulations to assess systematic effects (mainly beam asymmetries) which become irrelevant if the HWP is used.

• The final sensitivity target for r is around 0.02

LSPE noise level

LSPE noise level Spurious signal

Spurious signal

Expected / measured signals

Expected / measured signal

14L. Pagano, F. Piacentini

SWIPE Performance Forecast (1st flight)

L. Pagano, F. Piacentini

SWIPE Performance Forecast (1st flight)

L. Pagano, F. Piacentini

• The experiment is flown as a stratospheric balloon payload during the polar night, in a long duration flight launched from Longyearbyen (Svalbard). In this way it can access most of the northern sky in a single flight,

– without contamination from the sun in the sidelobes

– within a very stable (cold!) environment

– Accumulating more than 14 days of integration at float (38 km altitude).

• Flight scheduled by ASI for end of 2016

Mission

See Peterzen, S., Masi, S., et al., “Long Duration Balloon flights development ”, Mem. S. A. It., 79, 792-798 (2008) for further information on balloon flights from the Svalbard.

Bottom: Ground path of a small pathfinder test flight performed in January 2011, in the middle of the polar night. The eastward trajectory is evident.. Top: Launch of a heavy-lift balloon from the Longyearbyen airport (Svalbard Islands, latitude 78oN).

4

54

Launched - June 14th, 2006

Svalbard

Impact – July 1st, 2006

17 DAY FLIGHT

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55

34km

Ballast Drop

sample flight profile

Ballast release

termination

launch

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1° LDB launched on Jan. 9°, 2011From CNR Dirigibile Italia base With support from ISTAR, AWIPEV Ny Alesund, Svalbard Islands

5 days at 32 Km, Eastward pathPayload prepared by La Sapienza

Night Time Long Duration Stratospheric Balloon Flights

57 58

References

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• The LSPE collaboration: “The Large-Scale Polarization Explorer (LSPE)” Proc. SPIE 8446, Ground-based and Airborne Instrumentation for Astronomy IV, 84467A (2012); doi: 10.1117/12.926095; astro-ph/1208.0281

• P. de Bernardis, et al. “SWIPE: a bolometric polarimeter for the Large-Scale Polarization Explorer” Proc. SPIE 8452, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VI, 84523F (October 5, 2012); doi: 10.1117/12.926569; astro-ph/1208.0282 (2012).

• M. Bersanelli, et al. “A coherent polarimeter array for the Large Scale Polarization Explorer balloon experiment” Proc. SPIE 8452, Proc. SPIE 8446, Ground-based and Airborne Instrumentation for Astronomy IV, 84467C (24 September 2012); doi: 10.1117/12.925688 ; astro-ph/1208.0164 (2012).

• P. de Bernardis, S. Masi, for the OLIMPO and LSPE teams, “Precision CMB measurements with long-duration stratospheric balloons: activities in the Arctic”, In Astrophysics from Antarctica - IAU Symposium 288, Proceedings of the Internatonal Astronomical Union, 8, 208-213 (2013) M. G. Burton, X. Cui & N. F. H. Tothill, eds., Cambridge. doi: 10.1017/S1743921312016894

• Peterzen, S., Masi, S., et al., “Long Duration Balloon flights development ”,Mem. S. A. It., 79, 792-798 (2008)

• F. Nati, A. Benoit, P. de Bernardis, A. Iacoangeli, S. Masi, D. Yvon, A fast and reliable star sensor for spinning balloon payloads, Review of Scientific Instruments, 74, 4169-4175, (2003)

• http://planck.roma1.infn.it/lspe

Cosmic Origins Explorer ++

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Overview

1.Scientific goals of the ESA-M5 CMB polarization mission

2.Why in space3.Fundamental limits and mission/instrument

design4.Mission implementation5.Conclusions

Paolo de Bernardis – CORE++ – New challenges in Cosmic Microwave Backgroud studies – ASI 30 March 2016

COrE++ science


COrE++ is optimized to measure inflationary B-modes

Goals of the CMB polarization mission for M5


• Final measurement of B-mode polarization, able to extract the cosmological signal from overwhelming polarized foregrounds.

• Starobinsky model, R2 (Higgs) inflation have a tensor to scalar ratio r > 2x10-3.

• The mission should target at r<4x10-4 .

• Such a sensitivity tests Planck-scale physics of the field values in the large-field inflation models:

o Lyth bound: o A null-result would disfavor the entire class of large-

field (>Mp) models, and very few would survive.

• r<4x10-4 should be possibly established without l<10 .

223

60102.2

P

slowslow

M

Nr

(Boubeker and Lyth 2005)



ns would also be measured much better, so that Trehcan be estimated.

Grey: WMAPBlue: PlanckOrange: COrE+



COrE++ has enough angular resolution to vastly improve the measurement of gravitational lensing from LSS

Gravitational lensing from dark matter structures


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With the same angular resolution and sensitivity required for the inflationary B-modes, COrE+ produces a high fidelity map of the gravitational potential integral, due to dark matter structures from here to recombination:Direct detection of dark matter structures.

COrE+ (simulation)



With the same angular resolution and sensitivity required for the inflationary B-modes, COrE+ produces a high fidelity map of the gravitational potential integral, due to dark matter structures from here to recombination:Direct detection of dark matter structures.



COrE++ has enough angular resolution and frequency coverage to extract 100000 SZ clusters from the maps.

Extract and catalogue 100000 SZ clusters !


Simulation SZ only (input) Mixed to other components and noiseReconstructed after component separation (output)

Catalogue

COrE+ simulations(Remazeilles, Karakci,..)


Constraining the neutrino sector

3.046

60meV m(eV)

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Why in space: 1) background fluctuations


Photon background

Ratio of the number of detectors needed, for a given sensitivity, due to statistical photon background fluctuations.

200

>200GHzforbiddenfrom the ground, butneeded for foregroundsremoval

Why in space: 2) atmospheric instability


10K

0.1% fluctuations of atmospheric parameters

upper limit for B-modes signal

10‐5

Why in space: 3) systematic effects


• Atmospheric fluctuations larger at large scales, where the inflation signal is. • The effects of ground pickup (from the sidelobes) are larger at large scales.• The environment temperature is not stable at long timescales• Duty cycle of ground-based measurements << 100%

• All these effects can be vastly reduced with a space mission in L2 (as WMAP, Planck).

• In L2, the solid angle occupied by the Earth is reduced by a factor 10000.• Looking at anti-solar directions, the Earth, the Moon and the Sun are very

far from the boresight, so that pickup is minimized.• As long as the solar elongation is kept constant, the environment is

extremely stable, and so is the instrument performance.

• The effect of cosmic rays is heavier in space than on the ground, and must be properly mitigated with special detector design, and monitored in the data analysis.

Instrument/mission design driven by fundamental limitations

• Current precision (Planck) r~0.05; our goal r~0.0004 • Fundamental limitations to Accuracy:

• Overwhelming B-mode signals are produced:o Along the path of CMB photons, by gravitational lensing (to be monitored

with high angular resolution)o In our Galaxy, by polarized foregrounds (to be monitored with many

bands and wide frequency coverage)o In the instrument, if not properly designed (minimize polarizing

components in the optical path, use proper optical design)• Fundamental limitations to Sensitivity:

• Photon noise: the CMB and the emission of the instrument are fluctuating according to photon statistics.

• Mitigation: work in a stable, low-background environment, for a long time (cold telescope, in space, with active coolers) with many detectors (kilopixel arrays)


Frequency coverage to monitor foregrounds


Frequency coverage to monitor foregrounds


• Results from WMAP show that at low frequency the polarized synchrotron background is strong and has spectral index fluctuations.

• Preliminary results from Planck-HFI show that polarized dust emission must be monitored with great spectral and spatial accuracy to avoid biases in r, even at l=100 (fluctuations of the spectral index).

• Monitoring polarized dust at 340 GHz and extrapolating at 140 GHz to remove it (as in BicepKeckPlanck) is only a first approximation, and is not enough for our goal accuracy. Same for monitoring synchrotron at 30 GHz.

• The final mission must have excellent sensitivity and accuracy in a wide interval of frequencies above 200 GHz (which cannot be monitored from the ground) to extrapolate reliably the polarized emission from interstellar dust at 90-140 GHz.

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Multipoles coverage to monitor lensing B-modes


Required sensitivity and resolution

• The survey sensitivity (K arcmin) depends on total integration time, number

of detectors, noise of the detectors.

• Limit on r : depends on survey sensitivity, multipoles coverage, and lensing

confusion (below 4.5K arcmin the survey becomes lensing‐limited).

• De‐lensing efficiency depends on the angular resolution of the telescope :

• Requirements: ~ 2 K arcmin and ~ 6’ resolution in the CMB channels

• High resolution implies additional science results (SZ, neutrino masses etc.)


Kendrick Smith et al, JCAP, 06, id. 014 (2012)

Beam ellipticity

• The ellipticity of the beam converts unpolarized CMB anisotropy into spurious

polarization. The effect at large scales is mitigated for small beams:

• For small apertures, a Half‐Wave Plate is a must (e.g. LITEBIRD, D = 40 cm)


Inflationary B-modes (r=0.05)

spurious B-modes (e=0.05)FWHM=20’D=0.4m140GHz

FWHM=6’D=1.5m140GHzFWHM=3.8’D=1.5m220GHz

Additional considerations

• We want to detect CMB polarization with more than one channel (preferably 3 channels for cross-spectra, jackknives, comparisons), with enough sensitivity in each CMB channel individually. Long integration time and excellent stability needed.

• We will observe small signals embedded in many polarized local foregrounds and instrumental effects.

• Need to increase the number of spectral channels above the number of components parameters

• Need to increase the angular resolution to mask polarized compact sources (radio & IR)

• Very large scales will be hard to measure, since foregrounds increase at large scales. But detection of both the reionization and recombination bumps will be convincing.

• Systematic effects at very low level must be forecasted and monitored.



Systematics: focal plane rotation


spurious B-modes produced by an uncorrected rotation (1o) of the main axis of the polarimeter


Systematics: pointing errors


spurious B-modes produced by a direction mismatch in the directions of the two orthogonal intensity measurements =1"

=6"

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Mission/instrument implementation

Given all this, we need to implement an imaging polarimeter: • With a cold (< 60K) telescope• Aperture > 1.2m (4.8’FWHM@220GHz) • Covering a wide frequency range: 60 to 600 GHz • With a large number of single-mode photon-noise-limited detectors optimally

distributed among different frequencies, but with several hundred detectors in the CMB bands (90-140-220 GHz). If wide band (/ ~ 0.5), a total of 2000 detectors will be needed for a survey sensitivity of 2 K arcmin.

• The sky survey will be long (3yrs) and thermal stability is a must (detectors: continuous dilution cooler at 100 mK, no ADR; telescope: passive cooling)

• The satellite should operate in L2 (as WMAP and Planck) with a sky scan strategy covering a large sky fraction in a short time (days) and observing the same sky pixel with very different orientations of the polarimeter.

• A rotating HWP should be avoided, to reduce complexity and cost, if at all possible.


~

Mission/instrument implementation


Mission/instrument implementation: scan strategy


The telescope and the polarimeter must be heavily shielded from solar radiation, and solar illumination angle depends on scan strategy.

Spin

Mission/instrument implementation: scan strategy


• Spin (1 rpm) +Precession (0.25 rpd)

• Advantage: with far from 90o every pixel is observed with a wide range of orientations of the polarimeter: necessary condition for avoiding the HWP.

• For full sky coverage +> 90°.

• Baseline: ==45o.cfr: Planck =80o, =0o.

• To be optimized during phase-A.

• Feasible with large flywheels (5-6).

Anti‐solarDirection =PrecessionAxis

=beam off-axis wrt spin axis

=precession angle

Mission/instrument implementation: shielding


The best way to cool the telescope and the instrument is to use passive cooling V-grooves.Wrt Planck (open V-grooves), is smaller, and the solar illumination angle has a wider range, so V-grooves must have a «bucket» configuration:

With a bucket configuration, the telescope beam can be orthogonal to solar illumination

Mission/instrument implementation: telescope


• Aperture: 1.2 – 1.5 m• Optimized for wide focal

plane and polarizationpurity.

• Consideredconfigurations:

• Cross-Dragone• Open-Dragone• Gregorian

• The Gregorianconfiguration offers the best combination of usedvolume in the bucket, wide polarization-pure focal plane, and control of straylight.

Focal Plane Unit

Primary

Secondary

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• Aperture: 1.2 – 1.5 m• Optimized for wide focal

plane and polarizationpurity.

• Consideredconfigurations:

• Cross-Dragone• Open-Dragone• Gregorian

• The Gregorianconfiguration offers the best combination of usedvolume in the bucket, wide polarization-pure focal plane, and control of straylight.

Focal Plane Unit

Primary

Secondary

Cold baffle, black inside



Images from ESA CDF study: «CMB B-modes polarization mission». To be published (April 2016).

The telescope fits in the V-grooves and the assembly fits in the fairing



Images from ESA CDF study: «CMB B-modes polarization mission». To be published (April 2016).

The bucket V-grooves radiatively cool the telescope assembly down to < 50K


HWP / no HWP tradeoff

Two purposes for the HWP:

1. Move the signal bandwidth above the 1/f noise knee of detectors

2. Modulate polarization so that beam ellipticity and othersystematic are mitigated.

M4 approach: No HWP, no mechanisms, wider bandwidths and frequency coverage, no HWP-related systematic effects.

Solve 1. and 2. in the post-processing:

1. Can be solved with good detectors (1/f knee < 0.1Hz) and proper decorrelation/destriping.

2. Can be solved if the aperture of the telescope is large, i.e. the beams are much smaller than the large-scale where B-modesare to be detected.

Mission/instrument implementation: focal plane


• M4 proposal baseline: horns-coupled focal plane.• Main advantages: high TRL, consolidated technology;

clean definition of bolometer FOV and edge-taper on reflectors; reduction of straylight; polarization clean

• Main disadvantages: high cost, high mass@100mK• Recent developments (in Europe):

– 3D-printed horns in plastic material, metal coated(for low freq. bands)

– Planar lenses arrays (EAS-ITT study ITT AO/1-7393/12/NL/MH)

• Alternative: Filled-array focal plane. • Main advantages: Fabrication simplicity; reduced cost;

low mass@100mK.• Main disadvantages: Nyquist sampling of Airy disk

requires 4x sensors and lower detector NEP; requires coldstop in optical system and cold (< 1K) BB box surrounding the focal plane to reduce stray-light and loading.



CMB channels

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horn-horn spacing = 3FF/#=2

2408

Dual polarization, single f pixels



horn-horn spacing = 3FF/#=2

4816 Dual polarization dichroic pixels

focal plane: European detectors for CMB


• TES• Developed in Europe in Paris, Cambridge, Genova …• European MUX tecnology demonstrated in the lab (128:1, QUBIC) • Single-mode TES successfully operated at telescopes (SPT, ACT, BICEP, ….) and flown on

balloons (EBEX, SPIDER) by US teams • European multimode TES to be flown on a balloon with LSPE (ASI)

• KID• Developed in Europe in Grenoble, Groningen, Cambridge, Rome, ….• Operation down to 60-80 GHz demostrated (A&A 580, A15 (2015), astro-ph/1601.01466)• Large European matrix already operated at a telescope (NIKA & NIKA2) • For a filled array, 10 aW/sqrt(Hz) sensitivity demostrated in a laboratory setup simulating the

radiative background in L2 and 30% bands @100 and 150 GHz - Astro-ph/1511.02652; The sensitivity target for use in COrE+ is around 3 aW/sqrt(Hz) for a 35% band.

• Study of cosmic ray effects on-going (space-KIDs, see e.g. Astro-ph/1511.02652). Glitches are very short; cross section slightly larger than for TESs.

• To be flown on balloons (Adv.Blastpol in the USA, OLIMPO and Plan-B in Europe)• MID

• MEMS metal insulator detectors developed at CEA-Leti for Herschel-PACS have been improved to reach aW/sqrt(Hz) sensitivity operating at <100 mK, and in-pixel polarization measurements. European program CESAR developed suitable readout electronics.

• Still to be operated at telescopes• CEB

• Developed in Chalmers• Instrinsically insensitive to Cosmic Rays• Still to be operated at telescopes.


focal plane: European detectors for CMB: TES

TES multimode detectors for LSPE

TES detectors for QUBIC(Paris)

(Genova / Rome)

focal plane: European detectors for CMB: TES

Frequency coverage: Down to 40 GHz : CLASS, see astro-ph/1408.4789


focal plane: European detectors for CMB: KIDs

LEKID for 150 GHz(Rome)

NIKA2 array 200-300 GHz(Grenoble) -> IRAM30m

AMKID array - submm(Groningen) -> APEX ALMA

THz camera for safety scanner(Cardiff)

Horn-coupled KIDs for CMB(Cardiff + ASU)

10/05/2016

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Low-f operation of KIDs demonstrated:• Catalano et al. A&A 580, A15 (2015)• Paiella et al. Astro-ph/1601.01466

Al-Tif > 65 GHz



Catalano et al. Astro-ph/1511.02652



Catalano et al. Astro-ph/1511.02652

Flagged data : 1%

Flagged data : 10-15 %



Requirement for COrE+(horns-based)

Requirement for COrE+(filled array) Catalano et al. Astro-ph/1511.02652


cryo chain

Progress with this design and synergies with ATHENA - Gerard Vermeulen (inst. Néel, Grenoble)


cryo chain

Image from ESA CDF study: «CMB B-modes polarization mission». To be published (April 2016).

Martin Linder (ESA)

10/05/2016

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Preliminary budgets


• Wet Mass: 2185 kg• Volume: diameter 4m,

h=4.5m• Momentum: 420 Nms• v: 131 m/s for large

amplitude Lissajous orbit around L2

• Power: 1970 W (requires hinged solar panels)

• Communications: 200 Gb/day (K-band, 20 cm derotated antenna)

Image from ESA CDF study: «CMB B-modes polarization mission». To be published (April 2016).

COrE++ : Conclusion


1. A space mission for CMB polarization like CORE++ is the only way to obtain a reliable detection of B-modes. This cannot be done from the ground only.

2. This mission promises outstanding results for cosmology and fundamental physics, and an extremely rich legacy of data for Astrophysics.

3. The mission is technically feasible with current European technology and scientific competence, and within the timeframe 2025-2030.

4. This mission is expensive, and proper support from ESA member states and other partners is mandatory to fit within the budget of M5.

5. The Italian community can have a leading role, but support is required to keep it alive and well.

Documents

lezione11 2016 cos.ppt [modalità compatibilità]oberon.roma1.infn.it/lezioni/cosmologia...stack cold, stepping HWP polarizer arrays of multimode feedhorns and bolometers UHMWPE lens