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CMB Polarimetry with BICEP:Probing Inflationary Gravitational Waves
IAS - Polarization 2005 Denis Barkats
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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
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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
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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
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Photon
Parallel metal lines,Polarization in x-axis Polarization
in y-axis
New Technology: Polarization Sensitive Bolometers
Courtesy of Jamie Bock, NASA JPL
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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
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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
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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
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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.
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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
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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%
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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
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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
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BICEP ELECTRONICS
ROTARY JOINT
ELECTRONICS BOX“DIRTY” DIGITAL COMPARTMENT
“CLEAN” ANALOG COMPARTMENT
RF FILTER
POWER REGULATORS
ELECTRONICS BACKPACK
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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
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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.
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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
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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
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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)
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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
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/ 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
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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