The Atacama B-mode Search:The Atacama B-mode Search:A TES-Based CMB Polarization InstrumentA TES-Based CMB Polarization Instrument

CMBpol Workshop, ChicagoCMBpol Workshop, Chicago

July 2, 2009Joe Fowler

Princeton University

Science Goal: Primordial Polarization B-modesScience Goal: Primordial Polarization B-modes

Target inflation Target inflation B-mode range: B-mode range: 30 < 30 < ℓ < 300ℓ < 300

Development Development for an ACT-POLfor an ACT-POL

InstitutionsInstitutions:: PrincetonPrinceton UBC UBC NISTNIST

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ABS ℓ range

Overview of ABS InstrumentOverview of ABS Instrument Focal plane array of NIST polarization-sensitive TES bolometersFocal plane array of NIST polarization-sensitive TES bolometers 240 machined aluminum feeds240 machined aluminum feeds Cryogenic crossed Dragone mirrorsCryogenic crossed Dragone mirrors Feeds and on-chip filters define a band around 150 GHzFeeds and on-chip filters define a band around 150 GHz Rotating half-wave plate outside cryostatRotating half-wave plate outside cryostat 0.60.6º (FWHM) beams, 20º overall field of viewº (FWHM) beams, 20º overall field of view Compact telescope, easy to deployCompact telescope, easy to deploy

ABS: Experiment SummaryABS: Experiment Summary

FrequenciesFrequencies 145 only145 only GHzGHz

Angular resolutionsAngular resolutions 35’35’ arcmin at each freqarcmin at each freq

Field centers and sizesField centers and sizes 44hh and 20 and 20hh, 55, 55°°S (S (not not fixed)fixed)~300 sq deg each~300 sq deg each

Ra/Dec/Sq-DegRa/Dec/Sq-Deg

Telescope typeTelescope type GregorianGregorian Refractor, Gregorian, Compact-range etcRefractor, Gregorian, Compact-range etc

Polarization ModulationsPolarization Modulations HWP, Sky rotation, HWP, Sky rotation, ScanScan

Waveplate, boresight rot., sky rot., scan etc. Waveplate, boresight rot., sky rot., scan etc. – list all that apply– list all that apply

Detector typeDetector type BolometersBolometers Bolometer, HEMT etc.Bolometer, HEMT etc.

LocationLocation Atacama (Cerro Toco)Atacama (Cerro Toco)

Instrument NEQ/UInstrument NEQ/U 20 Q, 20 U20 Q, 20 U K sK s1/21/2 for both Q for both Q andand U U

Observation start dateObservation start date 20102010

Planned observing timePlanned observing time 600 d elapsed, 600 d elapsed, 150 d science data150 d science data

Elapsed/effective daysElapsed/effective days

ABS reflecting opticsABS reflecting optics 60 cm mirrors60 cm mirrors Crossed-Dragone designCrossed-Dragone design Cold stop inside window Cold stop inside window

(25 to 30 cm diameter)(25 to 30 cm diameter) Rotating HWP outside Rotating HWP outside

window.window. 240 feeds in focal plane240 feeds in focal plane

Sapphire HWP

Focal plane

ReceiverReceiver Pulse tube cryocooler plus Pulse tube cryocooler plus

44He+He+33He sorptionHe sorption 50-60 cm cold mirrors50-60 cm cold mirrors Cryostat delivery: June 2009Cryostat delivery: June 2009

Window

Up ↑

Direct-machined aluminum feedDirect-machined aluminum feed 48 corrugations48 corrugations 1” long, ½” packing1” long, ½” packing 1616° FWHM beam° FWHM beam Glen Atkinson (PU shop)Glen Atkinson (PU shop) Fabricate ~15/weekFabricate ~15/week

Feed beam patternsFeed beam patterns Beam measured warm Beam measured warm

to –30 dB at 147 GHzto –30 dB at 147 GHz Cold measurements with Cold measurements with

NIST TES soon.NIST TES soon.

200 Hz chopped source (Gunn)

Test feed on rotary stage

Focal planeFocal plane 24 “pods” of 10 feeds24 “pods” of 10 feeds Polarization TDB (mix of X,+)Polarization TDB (mix of X,+) Full set: 25-30 cm acrossFull set: 25-30 cm across

MUX package on rigid + flex

150 GHz CMB Polarimeter (NIST)150 GHz CMB Polarimeter (NIST)

One TES

Bandpass filter in microstrip

Bond pads

“Dark TES”

OMT

More: Mike Niemack (ACTpol)

Atacama site: 5200 metersAtacama site: 5200 meters

ACT infrastructureACT infrastructure 2323° south latitude° south latitude

Telescope and platformTelescope and platform Portable ABS ContainerPortable ABS Container Shippable container with a hole in the roofShippable container with a hole in the roof Can raise load without motorsCan raise load without motors Electronics and computers next to liftElectronics and computers next to lift Legacy telescope (2000): az/alt mountLegacy telescope (2000): az/alt mount Adding a linear actuator for scanningAdding a linear actuator for scanning

Scan approachScan approach

Requirements for B-mode sensitivity:Requirements for B-mode sensitivity: Smallest (deepest) possible areaSmallest (deepest) possible area Uniform coverageUniform coverage Many crossing anglesMany crossing angles

~2.3 Fλ detector spacing

Short scan for deep observationsShort scan for deep observations

Sky regionsSky regions Co-ordinate with QUIET and POLARBEARCo-ordinate with QUIET and POLARBEAR 2 main regions at 502 main regions at 50° South° South

SystematicsSystematics

Similar concerns to other low-Similar concerns to other low-ℓ experiments:ℓ experiments: ΔΔT T E+B (differential beam shape) E+B (differential beam shape) ΔΔT T E+B (differential pointing) E+B (differential pointing) AtmosphereAtmosphere HWP rate limits scan rateHWP rate limits scan rate

Some ABS-specific:Some ABS-specific: Ground shieldGround shield Stop and HWP don’t coincideStop and HWP don’t coincide Can we spin HWP? Fast enough?Can we spin HWP? Fast enough? Control of mirror temperatureControl of mirror temperature ForegroundsForegrounds

Sapphire HWP

Focal plane

Half-wave plates at oblique incidenceHalf-wave plates at oblique incidence

Ideal HWP modulation, spin frequency Ideal HWP modulation, spin frequency ωω::

PPH/VH/V = I ± Q [cos 4 = I ± Q [cos 4ωωt] ± U [sin 4t] ± U [sin 4ωωt]t]

Fields at Fields at ψψ=12° off axis pass through HWP at angle =12° off axis pass through HWP at angle ψψ..

1.1. Apparent Apparent ωω is not constant is not constant

(puts 0.1% of power into 2(puts 0.1% of power into 2ωω and 6 and 6ωω))

2.2. Rays Rays notnot orthogonal to orthogonal to ee-axis see n’ ≠ n-axis see n’ ≠ nee..

n’ = [ (cos n’ = [ (cos ψψ/n/nee))22 + (sin + (sin ψψ/n/noo))22 ] ]-½-½

For ABS, a 1° shift in phase lag.For ABS, a 1° shift in phase lag.

This, plus band center shift and finite width:This, plus band center shift and finite width:

(a 1% suppression of Q, U averaged over band)(a 1% suppression of Q, U averaged over band)

PPH/VH/V = I ± Q [cos 4 = I ± Q [cos 4ωωt (1-t (1-εε) + ) + εε] ± U [sin 4] ± U [sin 4ωωt (1- t (1- εε)] ± V [-sin 2)] ± V [-sin 2ωωt ] (2t ] (2εε½½))