1

CMB Polarimetry with BICEP:Probing Inflationary Gravitational Waves

IAS - Polarization 2005 Denis Barkats

2

Background Imager of Cosmic Extragalactic Polarization

Caltech / JPL

Andrew LangeDenis BarkatsJohn BattleJames BockCynthia ChiangDarren DowellGreg GriffinViktor Hristov

Eric HivonJohn KovacChao-Lin KuoPete MasonHien NguyenIan SullivanKi Won Yoon

UC Berkeley

Bill HolzapfelYuki Takahashi

UC San Diego

Brian KeatingEvan BiermannTom Renbarger

CEA Grenoble

Lionel Duband

Cardiff

Peter Ade

3

State of the CMB polarization field in August 2005

EE and TE polarization

BB polarization Upper limits ~ 2 K2

(from DASI, CBI, B03) T/S < 0.36 from CMB+LSS

WMAPBOOMERANG 03CBIDASICAPMAP

What do we need?• Significant advance system sensitivity• Control systematic errors at < 0.1 K levels• Distinguish CMB from Galactic Foregrounds• Distinguish Gravity-wave Signal from Lensing

BICEP

4

Overview of the BICEP instrument 10 cm thick Zotefoam window

IR-blocking filters

Cold polyethylene lenses

Feed horn array

Helium sorptionrefrigerator

Cryostat

PSBs

Faraday rotators

Minimize polarization systematics

• Simple refractor, no mirrors• Azimuthal symmetry• Alt-az telescope, with continuous boresight rotation• Wide-band polarization modulation with FRMs

Optimize to 10 < < 400

• Beam sizes ~ 1 deg, 0.6 deg • Field of view ~ 17 deg• Observed sky fraction ~ 5%

Separate CMB / foregrounds

• Two frequency bands at100 and 150 GHz

Signal-to-noise considerations

• 49 light PSB pairs at 250 mK (98 bolos)• Multiple levels of modulation• South Pole location: long integrationover contiguous patch of sky, reducedatmospheric loading

5

Photon

Parallel metal lines,Polarization in x-axis Polarization

in y-axis

New Technology: Polarization Sensitive Bolometers

Courtesy of Jamie Bock, NASA JPL

6

Cryostat and mount

Az-El mount + boresite rotation

Upward-lookingcryostat with toroidalLN2 / LHe tanks

Long hold time (4-5 days)

Helium sorption fridge tocool focal plane to 250 mK

Rotation essential formap cross-linking

4He, 1.5 K

3He, 350 mK

3He, 250 mK

Hold time ~ 2 days, cycle ~ 5 hours

7

Zotefoam windowTeflon IR-blocking filters

25 cm

180

cm

Polyethylene lenses

Front-end optics

• Telecentric design for flat focal plane• AR-coated filters and lenses• Cross-polarization < 0.01%,instrumental polarization < 1%from physical optics simulations

8

The BICEP insert

All RF-sensitive componentsenclosed in large faraday cage

Drop-in focal plane

Trussed structureto isolate 250 mKplate from 4 KCold JFETs for signal buffering,

refrigerator, thermal connectionsto focal plane

Lens tube mounted on top of insert

9

100 GHz150 GHz

Image: J. Kovac

Full focal plane map

• 49 spatial pixels = 98 polarization-sensitive bolometers

• Divided into 6 similar hextants

• Each hextant has 4 pixels at each band

• Adjacent hextants measure Q and U.

10

A closer look at the focal plane

A photon's view of the focal plane

Primary beam-definingfeed horn (4 K)

Re-expanding horn (4 K)

Band-defining metalmesh filters, baffles

Refocusing horn (250 mK)

Polarization-sensitive

bolometers

Faraday rotator module

Imag

e: K

. Y

oon

11

Home, sweet (frozen) home: South Pole station, Antarctica

“100 GHz band”

Bandwidth: 24 GHz

Optical efficiency:27.5%

“150 GHz band”

Bandwidth: 41 GHz

Optical efficiency:25%

12

What can BICEP do for you?

- Measure EE polarization at intermediate , complementary to current detections

BB polarization: if anyone's gonna do it (in the next N years), we will!

- Return information on polarized foreground emission

1 year of Planck ~ 6 x sensitivity of 8 years of WMAP

BICEP has similar instantaneous sensitivity to polarization as Planck, and ismore sensitive to peak BB signal due to concentration on a small patch of sky

Detect BB polarization if T/S > 0.05 (assuming “reasonable” integration time),otherwise set a bomber upper limit

N ~ number of years before SPIDER, EBEX, CMBpol, Planck etc.

- Winter 2005 / 2006: deployment to south pole

http://www.astro.caltech.edu/~lgg/bicep_front.htm

13

Expected BICEP performance

System NET ~ 35 uK√s(350 uK√s per PSB, 98 detectors)

Total integration time: somewherebetween 100 days and 200 days

Observed sky fraction ~ 5%

Beam width ~ 1 degree

EE

BB

T/S = 0.05 and = 0.17

14

A day in the life of a BICEPer

15

BICEP ELECTRONICS

ROTARY JOINT

ELECTRONICS BOX“DIRTY” DIGITAL COMPARTMENT

“CLEAN” ANALOG COMPARTMENT

RF FILTER

POWER REGULATORS

ELECTRONICS BACKPACK

16

Band "100 GHz" "150 GHz"

Band Center 95.4 GHz 151.5 GHz

Effective Bandwidth23.8 GHz (24.9%)

41.2 GHz (27.2%)

Band-averaged optical efficiency

27.5% 25.0%

0 F( ) dF( ) d

Beff F( ) d 2F 2( ) d

17

TYPICAL BOLOMETER CHARACTERISTICS

R0 100 41.8 K

G0 60 pW/K

1.5

opt 15 ms

Upper limit on scanning speed set by the time constant: ~ 0.25 (FWHM) / opt = 10.5 deg/s… is not a limiting factor.

18

Band "100 GHz" "150 GHz"

Band Center 95.4 GHz 151.5 GHz

Effective Bandwidth23.8 GHz (24.9%)

41.2 GHz (27.2%)

Band-averaged optical efficiency

27.5% 25.0%

“100 ”GHz band

:24Bandwidth GHz

:27.5%Optical efficiency

“150 ”GHz band

:41Bandwidth GHz

:25%Optical efficiency

19

QUAD Electronics in Operation

PID Controller

Digital B.O.B.

Thermometry

readout

Power supplies

Interface boxes

RF-filtering

Electronics boxes 4 x lockin

1 x bias

1 x F.P. T.C.

1 x GRT amp

VME DAS 128 ch ADC

DIO Cards

Real time computer

20

QUAD Electronics Overview• 96 channels of readout

– 62 light bolometers– 4 darks– 3 thermistors– Ample spares

• Cold JFET amplifiers• AC biased / lockin

demodulation• Focal plane temp. control• Fully computer controlled

• 96 channels of readout– 62 light bolometers– 4 darks– 3 thermistors– Ample spares

• Cold JFET amplifiers• AC biased / lockin

demodulation• Focal plane temp. control• Fully computer controlled

QUAD Amplifier Box (1 of 4)

21

QUAD Readout Electronics summary

Gain: 100,000 (nominal)

97,000 (at DC)

91,500 (at 90 Hz)

Proven Design

•Bolocam

•SuZIE

•BOOMERANG

Bias Generator

•AC / DC

•Freq: 40 – 200 Hz

•Amp: 0.36 mV steps

•Fully computer controlledLockin Cards

•DC-offset removal

•Phase adjustment 45° range at 90 Hz, 7-bit resolution

•Fully computer controlled

cryostat

22

/ AC DCBiasGe

.n

RL

RL

RB C

OLD

JFETS

LPF ADC

MSP

CPLD

R

FFIL

TER

- RF TIGHT FARADAY CAGE

&PREAMPSSIGNAL

CONDITIONERS

RF FILTER

R

FFIL

TER

, ,SYNCH HSCKCMD , SYNCH HSCK SPI

CONTROLLERS

/ACDC

SPI

ETHERNET CARDS ETHERNET HUB

DIGITALLOCKINS

( )DLIAS

BICEP BOLOMETER READOUT ELECTRONICS

OPTICAL FIBER

DAQ

PC

23

BICEP NOISE MEASUREMENTS

24

25

OPTICAL CHAIN AND FILTERING

10 cm-thick Zotefoam window

270 K

77 K

4 K

Teflonblockers

Polyethylene lenses

FRM

250 mK

Band 100 GHz 150 GHz

Edge filter B829(3.65 cm-1)

B647(5.9 cm-1)

2nd blocker B822(4.0 cm-1)

B807(5.77 cm-1)

3rd blocker B657(6.6 cm-1)

B712(8.5 cm-1)

Waveguide cut-on

83 GHz(2.77 cm-1)

130 GHz(4.33 cm-1)

20 K