Philip Lubin UCSB

1

• Philip Lubin - UCSB

2

• Presentation structure
• COFE primary goals.
• COFE basic characteristics balloon flights,
  frequency coverage, telescopes, detectors, horns,
  cryogenic.
• COFE sky coverage.
• COFE year schedule.

3
COFE primary goals

• Measurement of the polarization characteristics
  of galactic foregrounds at microwave frequencies
  below 40 GHz.
• Exploration of low-l systematic limits to
  sub-orbital CMB polarization experiments for
  large scale balloon borne missions and future
  CMBPOL foreground characterization.

4
Balloon borne
Flights of 12-24 hours, at an altitude of 35 km,
in the Northern and Southern Hemispheres. Could
go LDB in future.
Frequency coverage
Baseline bands at 10, 15 and 20 GHz and
resolution of 80, 60 and 40 arcmin.
5
For the target altitude of 35Km, COFE expects
under 1 mK total emission from the atmosphere.
6
Gaussian integrator with FWHM 30
7
Telescope
Copies of the BEAST optics1,2, a 2.2 m
aperture, lightweight, off-axis telescope
optimized for low cross-polar contamination and a
wide focal plane. Each band occupies an
independent telescope,while sharing data
acquisition, computing, housekeeping electronics,
and liquid Helium (LHe) mass storage.
1 Childers, J. et al. 2005, ApJS, 158, 124 2
Figueiredo, N. et al. 2005, ApJS, 158, 118
8
(No Transcript)
9
Optical layout for the telescope modules
The rectangle on the left is the cryostat with
the horn array. The beams from the horns are
traced first through the secondary mirror then
off the polarization modulator. The beams then
reflect to the primary mirror and exit upper
left.
10
A layout of the telescopes in the gondola
The suspension structure rises from the back,
leaving the front open for the beam exit and
baffling. The large cylinder represents the LHe
storage dewar.
11
Detector technology
InP MMIC amplifiers from NGST integrated into
simple total power receivers (no phase matching,
no waveguide outputs, and no OMT).
Radiometer schematic. All RF gain, filtering and
diodes are within the cryostat.
12
Expected Receiver Sensitivity
13
Feed horns
COFE has a conservative number of feeds required,
and no ortho mode transducers or Hybrid tees, so
the passive components are minimal.
The BEAST Q and Ka array for reference. COFE
horns and cryostat will be constructed with
similar techniques.
14
10GHz Horn
15
10GHz Step Transition
16
Polarization modulation
COFE uses a reflection wave plate design, that
allows simultaneous measurement of Q and U, and
intrinsically removes some of the most common
sources of systematic error in polarization
experiments.
17
(No Transcript)
18
Test configuration
A small telescope to test the polarization
modulator on the sky. By calibrating with an
external wiregrid, we were able to confirm our
sensitivity to Q or U.
19
Data from test configuration
Signal from a polarized thermal source.
Commutating using this signal gives Q, for
instance, while demodulating with a reference
phase shifted by ?/4 gives U.
Data from a warm test radiometer viewing the sky.
The undemodulated PSD displays the 1/f knee of
the HEMT radiometer of 10 Hz and a white noise of
7.6 mK/vHz. The demodulated data have no visible
1/f and a white noise level consistent with
expectation
20
Cryogenics
Baseline is lightweight LHe storage tank with a
very low parasitic continuous transfer line
coupled to heat exchangers at the receivers. This
highly efficient system was developed for BEAST
and is robust, reliable, and simple to use.
Working on options for LDB and beyond.
21
Full Scale COFE Prototype Built and Being Tested
Now

• Ground based telescope using the same optical and
  modulation design as COFE
• Systematics investigations at 40 GHz, using
  existing equipment (optics, receivers, etc)
• Test of Atmospheric loading sensitivity, Q,U,I
  cross talk etc

22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
Polarizing Grid w/ Backshort
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
10g Stress Analysis
41
Prototype Testing UCSB
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
(No Transcript)
48
(No Transcript)
49
Example Comparison of Q and U demodulations
while Bmachine views a small thermal source in
the farfield through 2 full rotations of the
source,
50
Thermal Source, wires Vertical, left panel Q
demodulation, right panel U demodulation
(different color stretch).
51
Channel 6, small src at 45 deg, U azrange5
deg, elrange
Channel 6, Q, small thermal src at 45 degrees
52
(No Transcript)
53
(No Transcript)
54
COFE

• -Multiple, independent telescopes.
• Off-axis optics optimized for low cross-polar
  contamination and a wide focal plane.
• 2.2 meter primary
• Cryogenically cooled HEMT receivers

55
Sample Amplitude Spectral Densities while scanning
UCSB, Dec 7
56
Demodulated 1/f
57
Azimuth binned data
58
Moon crossing
59
Moon Crossing (magnified)
60
T measurement
While foreground polarization is the primary
goal, we will investigate ways of modifying COFE
to allow total power or differential T
measurements (internal Dicke switching, focal
plane chopping etc)
61
COFE sky coverage
Signal to noise per 1 degree pixel anticipated if
the galactic foreground is 30 polarized. This
map is for the 10 GHz band, 24 hours of data
from the northern hemisphere and 24 hours from
the southern hemisphere. Note the doubly sampled
data on the celestial equator where the maps
overlap.
Integrated histogram of anticipated signal to
noise ratio for several assumed fractional
polarizations at 10 GHz. We plot the fraction of
the entire sky measured with better than a given
signal to noise for a full range of polarization
fractions. Note that 100 is a rough guide to our
T sensitivity.
62
Tentative schedule
2006 Funding begins - Finalize optical frame,
gondola, and polarization modulator
prototype. 2007 Design and build first two
CFRP mirror sets. Assemble first telescope
system, and perform ground tests. 2008 Build
second two CFPR mirror sets. Assemble full
payload 2009 -Two Northern Hemisphere
flights. 2010 - Analysis of flight data and
preparation for Southern Hemisphere flights.