Download Document

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 B-polarization is a LSS experiment
• Deep polarization measurements (4 mK rms) on 1.5% of the
sky can significantly improve Planck+SNAP constraints on
{w0, wa, Wk, ∑mn},
Hu , Huterer and Smith, 2006
pL=wrL
w=w0+wa(1-a)
• There is a strong theoretical preference:
w0= -1, wa=0, Wk <10-4 → lensing B provides a constraint on ∑mn
The Status of B-Polarization
Measurements (07/2009)
Lensing B-mode
Gravity wave
r=0.1
Chiang et al.
• 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.
The simple strategy
to 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
Crossed Dragone
Gregorian
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
Strehl Ratio
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.
H. Tran et al., CMBPOL Technology Workshop, 2008
The simple strategy
to 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:
An array of 5-10 crossed-Dragone multifrequency
telescopes, each with ~2-meter primary aperture and
~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
(major technology
dev. required)
1 Telescope +
8,000 bolometers
5-10 Telcps., each
w/8,000 detectors
(minor technology
dev. required)
LDRD funds
1 Telescope
1 Telescope +
512* bolometers
1 Telescope +
2,000 bolometers
5 Telescopes, each
w/ 2,000 bolometers
Deployment for field observations
*#
of detectors projected for 150 GHz
data/design
feedback
EPIC-IM mission
The “major” technology development
• By reducing the size of the feeds
we can pack more detectors (~4x) onto the
focal plane (~1.5 fl)
warm baffle
cold stop
• The price to pay is increased spillover
– which must be intercepted at 4K
• 8,000 detectors to read per dewar
Zotefoam
Vacuum
window
IR filter
receiver
cryostat
Teflon (50 k)
HR-10
OFHC (4K)
cold stop
Also a great gravity wave B-mode experiment (for r<0.1)
Compared to degree beam experiments (BICEP/Keck,
ABS), a 2 m class telescope offers:
•
•
•
•
Smaller maps → lower noise
Smaller maps → potentially less foreground
Small beams → de-lensing possible
Small beams → less Beam systematics
(Polarized Dust, 5%)
3.6 deg
7.2 deg
14.4 deg
28.8 deg
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?