The Atacama Cosmology Telescope (ACT)

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The Atacama Cosmology Telescope(ACT)
UC Berkeley October 3, 2006 Michael Niemack
Princeton University
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ACT
Science
Observations
CMB to l10,000
Growth of structure
Eqn. of state
Cluster (SZ, KSZ X-ray, optical)
Neutrino mass
Diffuse SZ
Ionization history
OV
Power spectrum
Lensing
X-ray
Optical
Theory
Collaboration
NIST
Haverford
CUNY
INAOE
Princeton
Columbia
Cardiff
NASA/GSFC
U. Toronto
Rutgers
UBC
UPenn
U. KwaZulu-Natal
U. Catolica
UMass
U. Pittsburgh
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CMB Temperature Power Spectrum
WMAP
ACT
PLANCK

(Tegmark and Oliveira-Costa)

• Measure the linear regime and the transition
  to the non-linear
• Overlap with WMAP for calibration

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Thermal SZ effect

• Inverse Compton Scattering
• Spectral Signature
• ACT Bands bridge SZ null
• Redshift independent
• unbiased cluster selection

150GHz SZ Simulation
PLANCK
MBAC on ACT
lt 1 of survey area 2 of high quality area
1.4
(Seljak and Burwell 2000)
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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)

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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)
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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
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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)

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ALMA Support
APEX
Mark Devlin
ACT 5200 meters
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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 gt 0.96

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ACT at AMEC Dynamic Structures in PoCo, B.C.
9/06
? M. L.
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Cold OpticsMillimeter Bolometer Array Camera
(MBAC)

• 145, 220, 280 GHz
• Mirrors vs. Lenses
• Absorption of lenses
• Off-axis impossibility
• of F1 with mirrors
• Lyot stop accessibility
• B shielding
• Beam-splitters
• Mirror issues
• Flatness size issues
• Solution
• AR-coated Silicon Lenses
• gt 70 overlap between bands

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Optical Design Analysis
Spillover (S. Dicker)
Strehl Ratios
Median Strehls 0.98,0.98,0.99
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Filled Detector Arrays
Light

• Three 32 x 32 pop-up detector arrays
• (SHARC, HAWC)
• ½ F ? detector spacing (at 2mm)
• 1mm2 bolometers

8x32 Prototype ACT array (Judy Lau) ACT first
light instrument
8x32 Mechanical Model
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Detectors and Readout
(Following trend started at UCB)

• Transition Edge Sensor (TES) bolometers
• 0.3 K operation
• Voltage biased at superconducting transition
• Negative electrothermal feedback
• Low-T current readout gt SQUIDs

MoAu TES
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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 muxing at 500kHz/row 15kHz array
sampling
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Prototype Measurements

• Column Camera (CCam) Prototype Testing
• Bolometer coupling, G, ??
• Muxd readout Shielding
• AR coated silicon lenses
• Capacitive mesh filters
• Pulse tubes He7 cryo
• Super-Rapid Dip Probe (SRDP) Testing
• Bolometer saturation powers and Gs
• NEP (noise and impedance)
• Column confirmation

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Prototype Measurements - CCam
After NSF Funding
Prior to NSF Funding
Gingerbread prototype by Judy Lau
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CCam 0.3K Detectors Chips
Unfolded 1mm detectors ? Optical Test Assembly ?
2
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Load Measurements
Cold load Coupling and Bolometer Gs

• I-V curves
• Convert to R-P plane
• Gs for MBAC
• bolometers
• Coupling 0.2 pW/K
• Nearly uniform
• Optical Coupling

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Time Constants

• Constraints
• Upper limit scan strategy
• Lower limit multiplexing rate (? gt 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
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2-mm Radiation Detection

• FTS filter measurements of optical elements

Combined Transmission
Frequency (GHz)
145 GHz ? 2.07mm
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Prototype NEP Characterization

• Great data from SRDP
• non-multiplexed
• analog electronics
• Exploring complex
• bolometer models

• (T. Marriage R. Dunner)

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First Moon Light
Pointing calibration Sidelobe analysis
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Saturn Measurements 11-2005
(E. Switzer)
Real-time scan using Multiple MULTIPLEXED TES
detectors.
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Next Steps

• Finish testing and assembly of prototype 8x32
  first light array
• 1 month
• ship ACT to Chile
• begin testing of 145GHz bolos
• 3 months ACT installed in Chile
• 5 months Observe with 256 bolometer array!
• Summer 07 kilopixel array in MBAC on ACT
• Summer 08 3-band MBAC

• ACT Telescope in Vancouver

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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!

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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

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Multiplexing Digression

• Time-domain (NIST) vs. Freq.-domain (Berkeley)

4K
(Lanting et al.)
0.3K chips

• Both use 1 NIST Series Array for each
  column
• TDM has 2 more SQUID stages

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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

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Critical Bolometer Parameters
Loading Prediction

• Saturation Power, Psat
• Psat gt 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