Transcript The Atacama Cosmology Telescope (ACT) UC Berkeley

The Atacama Cosmology
Telescope
(ACT)
UC Berkeley
October 3, 2006
Michael Niemack
Princeton University
Science:
Growth of structure
Eqn. of state
Neutrino mass
Ionization history
Power spectrum
ACT
Observations:
CMB to l~10,000
Cluster (SZ, KSZ
X-ray, & optical)
Diffuse SZ
OV
Lensing
X-ray
Cardiff
Rutgers
Optical
Theory
NIST
Columbia CUNY Haverford INAOE NASA/GSFC
Princeton
UBC U. Catolica U. KwaZulu-Natal UMass UPenn U. Pittsburgh U. Toronto
Collaboration:
CMB Temperature Power Spectrum
WMAP
PLANCK
ACT
(Tegmark and Oliveira-Costa)
 Measure the linear regime and the transition to the non-linear
 Overlap with WMAP for calibration
Thermal SZ effect
• Inverse Compton Scattering
• Spectral Signature
ACT Bands bridge SZ null
• Redshift independent
unbiased cluster selection
150GHz SZ Simulation
MBAC on ACT
PLANCK
< 1% of
survey area
1.4°
~2% of high
quality area
(Seljak and Burwell 2000)
SZ Studies
Cluster physics, evolution of structure
Follow-up redshifts + mass estimates
(optical – SALT)
(x-ray, lensing, or velocity dispersions)
 Ncluster (m,z)
Sensitive to both w and neutrino mass
w  0, earlier dark energy domination
 fewer low-z clusters relative to high-z
m   suppression of growth of structure
KSZ – Baryon evolution (Shirley Ho, last week)
Gravitational Lensing of CMB
• Remapping of source by intervening mass
• Conserves surface brightness
• CMB as the source has a well known redshift
Pre-lensing
Post-lensing
(Ryan Scranton – website)
(Bartelmann and Schneider 1999)
Lensing Studies
• Power Spectrum of mass fluctuations
• Detection requires a map with K noise
with ~1’ resolution
– Map the mass distribution!
– Trace dark matter to high redshift!
Future experiments:
polarization will help
How are we doing it?
• Atacama Plateau
• Careful Optical Design
• Crosslinked, simultaneous
3 band observations
• Close-packed kilopixel
TES arrays (GSFC)
• Time-domain SQUID
Multiplexing (NIST)
APEX
ALMA Support
Mark Devlin
ACT –
5200 meters
ACT Optical Design
Some Constraints
–
–
–
–
–
Diffraction limited Gaussian beams
Clear aperture
6-meter primary
Fast/Compact system
High A
Semi-analytic Approach
• Dragone Condition
– Minimizes astigmatism and coma
– Cassegrain vs. Gregorian
• Aplanatic Condition
– Minimizes spherical aberrations
• Numerical Optimization
– Aplanatic-like solution
 Gregorian focus 0.75deg2
Strehl > 0.96
ACT at AMEC Dynamic Structures
in PoCo, B.C.
9/06
 M. L.
Cold Optics
Millimeter Bolometer Array Camera (MBAC)
• 145, 220, & 280 GHz
• Mirrors vs. Lenses
– Absorption of lenses
– Off-axis impossibility
of F~1 with mirrors
– Lyot stop accessibility
– B shielding
window
• Beam-splitters
40K
3K
1K
– Mirror issues
– Flatness & size issues
• Solution
270 mK
15 cm
– AR-coated Silicon Lenses
– > 70% overlap between bands
Optical Design Analysis
Strehl Ratios
Median Strehls
0.98,0.98,0.99
Spillover (S. Dicker)
Light
Filled Detector Arrays
Three 32 x 32 “pop-up” detector arrays
(SHARC, HAWC)
½ F  detector spacing (at 2mm)
~1mm2 bolometers
8x32 Prototype ACT array
ACT first light instrument
8x32 Mechanical Model
(Judy Lau)
Detectors and Readout
(Following trend started at UCB)
Transition Edge Sensor (TES) bolometers
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–
–
–
0.3 K operation
Voltage biased at superconducting transition
Negative electrothermal feedback
Low-T current readout => SQUIDs
MoAu TES
SQUID Multiplexing
• NIST time-domain
multiplexing (TDM)
• Reduce array connections
4096  384 wires
• 3 SQUID Stages
• Critical low L connection
0.3K S2  4K SQUID amplifier
 = L/R limit
• UBC/SCUBA-2 readout
Prototype mux’ing at 500kHz/row ~ 15kHz array sampling
Prototype Measurements
Column Camera (CCam) Prototype Testing
• Bolometer coupling, G, & 
•
•
•
•
Mux’d readout & Shielding
AR coated silicon lenses
Capacitive mesh filters
Pulse tubes + He7 cryo
Super-Rapid Dip Probe (SRDP) Testing
• Bolometer saturation powers and G’s
• NEP (noise and impedance)
• Column confirmation
Prototype Measurements - CCam
After NSF Funding
Prior to
NSF Funding
Gingerbread prototype
by Judy Lau
CCam 0.3K Detectors & Chips
Unfolded
2
1mm detectors 
Optical Test
Assembly 
Load Measurements
Cold load Coupling
and Bolometer G’s
• I-V curves
• Convert to R-P plane
• G’s for MBAC
bolometers
• Coupling ~ 0.2 pW/K
• Nearly uniform
Optical Coupling
Time Constants
• Constraints
– Upper limit – scan strategy
– Lower limit – multiplexing rate ( > 20us)
• Optical Chopper on CCam
– Vary chopper frequency
– Fit Fourier transform peak response
• Bias step measurements
(Following notation
of Irwin and Hilton)
(Need to finish analysis)
Preliminary results compare well!
Prototype - ~ few ms
2-mm Radiation Detection
Combined Transmission
FTS
filter measurements
of optical elements
Chopped
145 GHz Source
145 GHz
 = 2.07mm
Frequency (GHz)
Prototype NEP Characterization
Great data from SRDP
• non-multiplexed
• analog electronics
Exploring complex
bolometer models
TES
Si
Absorber
(T. Marriage & R. Dunner)
First Moon Light
Pointing
calibration
Sidelobe
analysis
Saturn Measurements 11-2005
(E. Switzer)
Plate Scale analysis
“Real-time” scan using
Multiple MULTIPLEXED
TES detectors.
Next Steps
• Finish testing and assembly of
prototype 8x32 “first light array” ACT Telescope in Vancouver
• 1 month:
– ship ACT to Chile
– begin testing of 145GHz bolos
• 3Design
months: ACT
installed in Chile
Inspiration
• 5 months: Observe with 256
bolometer array!
• Summer 07: kilopixel array in
MBAC on ACT
• Summer 08: 3-band MBAC
Conclusions
• ACT is on track to begin probing
exciting physics in the coming year
• Successful CCam Prototyping
• Detector characterization is well
underway
• Detected astronomical sources!
Acknowledgements
• CCam & SRDP crew – Asad Aboobaker, Judy Lau, Eric Switzer,
Adam Hincks, Toby Marriage, Ryan Fisher, Rolando Dunner, Yue
Zhao, Norm Jarosik, Joe Fowler, Suzanne Staggs,
and
Lyman Page
• TES Bolometers – GSFC Detector Development Lab
• SQUID Multiplexer – NIST/Boulder; Readout – UBC
• MBAC dewar and He fridge designs – UPenn
• Filters – Cardiff (FTS measurements UBC & Case W.)
• Housekeeping Readout – U. Toronto & Upenn
• 1.5m Telescope – WMAP team
• Discussions – ACT collaboration and friends
Multiplexing Digression
Time-domain (NIST) vs. Freq.-domain (Berkeley)
4K
0.3K
chips
• Both use 1 NIST Series Array for
each “column”
• TDM has 2 more SQUID stages
(Lanting et al.)
Location, Location, Location!
The Atacama in Chile:
The ideal site for our science.
• 5200 meter elevation
• One of driest places on planet
• Gently sloping topography  low turbulence
• The future site for ALMA
• Logistical support available
• Only 26 hours travel from East Coast to site
Critical Bolometer Parameters
• Saturation Power, Psat
Loading Prediction
– Psat > predicted load
– I-V curve measurements
• Time Constants, 
– Upper limit – scan strategy
– Lower limit – multiplexing rate
– Chopped source and bias step
measurements
• NEP
– Calibration Bolometer
– Noise and Impedance
– Responsivity calculation
Atm.
(T. Marriage)
Crosslinked Scans