Thoughts on Ground-based lensing measurements

Chao-Lin Kuo

Stanford/SLAC

KIPAC

The primordial, Gaussian E-polarization

Large Scale Structure

B-polarization

J Tolan

Lensing Lensing BB-polarization is a LSS experiment-polarization is a LSS experiment• Deep polarization measurements (4 K rms) on 1.5% of the

sky can significantly improve Planck+SNAP constraints on

{w0, wa, k, ∑m},

p=w

w=w0+wa(1-a)

• There is a strong theoretical preference:

w0= -1, wa=0, k <10-4 → lensing B provides a constraint on ∑m

Hu , Huterer and Smith, 2006

The Status of B-Polarization Measurements (07/2009)

• QUaD/BICEP (50~100 detectors) still miss the (lensing) B-polarization by ~ 2 orders of magnitude.

• The current round of experiments (~1000 detectors) can only hope for a statistical detection.

• To perform high S/N imaging of lensing B-polarization, one must increase the survey speed by 102.

• The ground based platforms (DASI “drum”, SPT) will be maxed out already in the current round of exp.

Chiang et al.

Lensing B-mode

Gravity waver=0.1

The simple strategyto get ~10,000 detectors on the sky…

• Use an optical design that has the largest possible focal plane area

• Choose an aperture size that optimizes throughput/dollar

Optics Comparison

H. Tran et al., CMBPOL Technology Workshop, 2008

Crossed Dragone Gregorian

Str

ehl R

atio

The advantage of a crossed-Dragone system

(1). > 4X more FOV area than a Gregorian

(2). Flat/telecentric focal plane, no re-imaging

Optics

-Good polarization properties verified in numerous

studies

The required primary aperture for lensing

B-mode is ~2 meters – for 10m class telescopes

the measurements will be sensitivity (throughput)

limited, not resolution limited.

The simple strategyto get ~10,000 detectors on the sky…

• Use an optical design that has the largest possible focal plane area

• Choose an aperture size that optimizes throughput/dollar

• The Proposed Experiment: The Proposed Experiment:

An An array array of 5-10 crossed-Dragone of 5-10 crossed-Dragone multifrequencymultifrequency

telescopes, each with ~2-meter primary aperture and telescopes, each with ~2-meter primary aperture and

~2,000+ detectors~2,000+ detectors

A Pilot Project: one 1.5-2m telescope• Serving as the prototype for two experiments

– Pol-Len: Polarimeter array for Lensing

– EPIC-IM (in collaboration w/ JPL)

• The telescope will be integrated with

– Room temperature sources/detectors

– A BICEP-2 style 512-detector bolometric

receiver

– A larger format camera – see the next page

• Many issues can be characterized in full

details with this pilot projet:

– Near and far sidelobe responses, baffling

– Infrared filtering

– Magnetic field shielding

– Detector loading

– Mitigation of polarization systematics

The expansion prospects

1 Telescope +512* bolometers

1 Telescope +2,000 bolometers

5 Telescopes, each w/ 2,000 bolometers

LDRD funds1 Telescope

Deployment for field observations

(minor technologydev. required)

1 Telescope +8,000 bolometers

5-10 Telcps., each w/8,000 detectors

(major technologydev. required)

EPIC-IM mission*# of detectors projected for 150 GHz

data/designfeedback

warm baffle

receivercryostat

Vacuum window

The “major” technology development• By reducing the size of the feeds

we can pack more detectors (~4x) onto the

focal plane (~1.5 f)

• The price to pay is increased spillover

– which must be intercepted at 4K

• 8,000 detectors to read per dewar

Zotefoam

Teflon (50 k)

HR-10

OFHC (4K)

IR filter

cold stop

cold stop

Also a great gravity wave B-mode experiment (for r<0.1)

• Smaller maps → lower noiseSmaller maps → lower noise

• Smaller maps → potentially less foregroundSmaller maps → potentially less foreground

• Small beams → de-lensing possibleSmall beams → de-lensing possible

• Small beams → less Beam systematicsSmall beams → less Beam systematics

Compared to degree beam experiments (BICEP/Keck, ABS), a 2 m class telescope offers:

3.6 deg7.2 deg14.4 deg28.8 deg

(Polarized Dust, 5%)

The Trade-offs• No Half-Wave-Plate modulators.

• No full - rotation.

• Modulation relies on scanning – QUaD/BICEP style.

• For the same , 2 possible angles can serve as a systematic check.

),(

Funding/fielding prospects

• SLAC “LDRD” under review (1 telescope, warm tests)

• An NSF proposal will go in this August (“Pol-Len1”, one telescope

+mount+ receiver development)

• BICEP/Keck collaboration supportive of the deployment of the

telescope to the South Pole DSL site in 2011. Pending approval

from NSF-OPP (office of polar programs).

• We have not thought about how to fund the full array…Let me

know if you have $ or are interested.

The End.Question?