micro-bolometer arrays and the south pole telescope · micro-bolometer arrays and the south pole...

Micro-bolometer arrays and the South Pole Telescope

Clarence L. ChangSLAC AIS Seminar

March 18, 2009

The CMB: A Cornerstone to our understanding of

Cosmology• Universe is flat

• Measurement of the relic abundance of CDM

• Seeds of structure formation

• Inflation

• Dark Energy

WMAP

CMB: the next generation

• Continues to provide the best window into the early universe. Polarization signal will be the unique measurement of the energy scale of inflation

• Well understood distant source serves as a backlight of intervening structure through secondary anisotropies

tSZ, 150GHz, σ8~0.8

kSZ/OV

20uK-arcmin from point sources

10uK-arcmin from point sources

Projections for a 100-square deg survey, 150GHz (red), 220GHz (blue)

Figure by Tom Crawford

The South Pole Telescope

• 10-m off-axis Gregorian telescope at the South Pole

• SPT-SZ

• SPTpol

OutlineMicro-bolometers and TESs

SPT-SZ

GoalsTelescopeDetectorsSeason OneSeason TwoSeason Three

SPTpol

Bolometer preliminaries

• Measure thermal power, not single photons

• Two fundamental noise sources

- “loading” - fluctuations of photon arrival

- “thermal carrier” - non-zero heat sinking

• Non-zero loading sets a lower limit on bolometer noise - “background limited”

C

G-1

Tbath

T

Poptical

Bolometers have reached the background limit

Second results from QUaD 21

0 500 1000 1500 200010

2

103

104

multipole

l(l+

1)C

l / 2! (µ

K2)

TT

WMAP5

ACBAR

QUaD

0 500 1000 1500 2000!200

!150

!100

!50

0

50

100

150

200

multipole

l(l+

1)C

l / 2! (µ

K2)

TE

WMAP5

B03

CBI

QUaD

0 500 1000 1500 2000

100

101

102

multipole

l(l+

1)C

l / 2! (µ

K2)

EE ! only >2" detections plotted

WMAP5

B03

CBI

CAPMAP

DASI

QUaD

0 500 1000 1500 2000

100

101

multipole

l(l+

1)C

l / 2! (µ

K2)

BB 95% confidence upper limits

WMAP5

B03

CBI

CAPMAP

DASI

QUaD

FIG. 22.— QUaD power spectra compared to results from WMAP (Nolta et al. 2008), ACBAR (Reichardt et al. 2008), B03 (Piacentini et al. 2006;Montroy et al. 2006), CBI (Sievers et al. 2007), CAPMAP (Bischoff et al. 2008) and DASI (Leitch et al. 2005). The BB upper limits are stated values whereprovided, and otherwise the 95% point of the positive part of the bandpower pdf.

• Sensitivity: Noise Equivalent Temperature (NET) defined as rms of fluctuations in one sec of integration (Kelvin √s)

• ACBAR and QUAD have ~16 detectors with NET ~350 μK √s (Background limited for ground based observations)

Mapping speed

• Mapping speed: rms noise in a map pixel for a given exposure

• scales as Nbolo / NET2

• Apply a voltage bias across a thin superconducting film

• Superconducting transition has steep R(T)

TES basics

R

T

Constant voltage, measure current

• Low impedance, low noise current measurement using Superconducting Quantum Interference Devices (SQUIDs)

• Readout can be multiplexed

0 1 2 Φ / Φ 0

V

A case for TESs?• Pros

- Improved linearity

- Increased bandwidth

- Fixed detector noise

- no microphonics

- reduced wiring from MUX

- Low power dissipation from SQUIDs

• Cons

- None (of course)


SPT-SZ


SPTpol

• Survey for clusters using the Sunyaev-Zel’dovich effect

• Expect a nearly red-shift independent mass threshold

• Measure the evolution of the cluster mass function when combined with

SPT-SZ

Gil Holder

The Sunyaev-Zeldovich effectA

dapt

ed fr

om L

. Van

Spe

ybro

eck

• Distortion of CMB spectrum

- Null @ 220 GHz, decrement below, increment above

- ~100 μKCMB for 2×1014 Msun

- Need lots of sensitivity!

• Clusters are a few arcmins

- Need resolution!


SPT-SZ


SPTpol

Want the right tool for the job

Why the South Pole?

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itab

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ater

Vap

or

(mm

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er)

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3

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4/95-9/95 10/95-3/96 4/95-9/95 10/95-3/96 Jan-June July-Dec

South Pole Atacama Mauna Kea

25%

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From radiosonde Computed from measured 225 GHz opacity

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High throughput, high resolution

• ~260 panels aligned to 25 μm rms over 10-m surface gives 95% efficiency at 220 GHz

• 8-10 meter dish gives 1’ resolution at 150 GHz

Optics: minimizing the load

• Only two optical elements, 10-m primary and 1-m secondary

• Secondary is inside a cryostat at 10K. Acts as the system Lyot stop

SPT: arcmin resolution

• 1.5’ FWHM @ 90 GHz

• 1.0’ FWHM @ 150 GHz

• 0.8’ FWHM @ 220 GHzFigures: Ryan Keisler

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Figures: Ryan Keisler


SPT-SZ


SPTpol

The TES Spiderweb bolometer

4 m

m

• Spiderweb geometry minimizes cosmic ray cross section• Sheet impedance of web tuned to maximize in band absorption

•Suspended on 1 μ-thick low stress SiN membrane for thermal isolation• G defined by 100 Å-thick gold strip• Bandwidth Limiting INterface made of Gold (BLING)

• TES is a Al/Ti bilayer, Tc ~ 550 mK

Lots of bolometers!

• Bolometers packaged as 160 element arrays (wedge)

• Radiation pattern defined by monolithic feedhorn block

• Optical band defined by waveguide diameter and mesh filters

Multiplexed readout: the fMUX

• AC bias TES (100kHz-1MHz)

• LC filters in series to determine unique bias frequency for each TES

• Sum signals at SQUID input coil

• Demodulate SQUID Feedback to recover individual bolometer timestreams

• 7 TESs per SQUID

250 mK


SPT-SZ


SPTpol

A lot of hard work reduced to one slide...

29

SPT Season 1

December 2006mount assembled

12 February 2007:Cryostats come together

April 2007:First SZ cluster detection

3 Jan 2007Dish lifted into place,Receiver goes to Pole

November 2006

16 February 2007:First light

June 2007:SZ survey

18 February 2007:Pole Closes

December 2006BUS assembled

December 2006primary assembled

31 January 2007Telescope in place,

Photogrametry used to set primary

Seeing clusters w/ SZE

• 90 GHz: 120 bolos @ 1500 μKCMB √s

• 150 GHz:140 bolos @ 1500 μKCMB √s

• 220 GHz: unstable operation

•2007 SPT SZ measurement cluster AS1063•95 and 150 GHz, 1 hour•5 sigma detection

SZ Survey• Surveyed 40 sq deg to ~40 μKCMB in two bands

(90 GHz and 150 GHz)

• Overlap with BCS 5hr field

Photo Credit: Keith Vanderlinde

Lessons: stability

• As with all feedback systems, there are oscillations

• Increased bandwidth from ETF is sensitive to internal thermal circuit

• Simple thermal model for first season bolo reveals the problem... needed better coupling to bling

The fix

• Spiderweb structure for bling improves isothermal behavior

• Move TES “inside” of bling to improve thermal connection

120 μm

100 μm

Words of caution: Tc

• ETF fixes operating temperature at Tc

• G(Tc) is fixed

• Tc control is critical

• Proximity effect with nearby materials is non-negligible!


SPT-SZ


SPTpol

Same cluster, same exposure, better noise

• 90 GHz: saturated

• 150 GHz: 320 bolos @ 360 μKCMB√s


•2008 observation of cluster AS1063•150 GHz 40 minutes

•16 sigma detection

SZ Survey

• Surveyed 200 sq deg to better than 17 μKCMB in two bands (150 GHz and 220 GHz)

• overlap with BCS 5hr and 23hr fields

• together with Season I gives a 40 sq deg field with three band imaging


Clear SZ signature

Submitted to ApJ 10/10/08; Staniszewski et al, astro-ph/0810.1578


SPT-SZ


SPTpol

More power!!!




More power!!!




As good as it gets!

Plans

• Observe 800 sq deg over the next two years

• Plan to have 1000 sq deg to better than 20 μKCMB

• High l CMB Power spectrum

• Point sources (high-z dusty galaxies?)



SPT-SZ


SPTpol

90 GHz Detectors

• Similar detector architecture to PSBs (QUaD, BICEP, B2K, Planck)

• Coupling strictly in waveguide, choke suppresses leakage out of gap

• Absorbers consist of crossed dipoles (1 ea pol)

input waveguide

2 Gold Absorbers (on

separate planes)

Prototype properties

• Mo/Au bilayers on suspended SiN bridges

• G defined by SiN legs

• Au absorber bar

• G close to target

Prototype optical properties

• Cross-polar coupling <1.6% (simulations predict <1%)

• Good in band performance (structure from measurement)

• Coupling seems low (20% compared to > 90% from simulations)

150 GHz detector

• TES Mo/Cu bilayer suspended on SiN island

• G defined by SiN legs

• Couple to waveguide via OMT to Nb/NbO microstrip

• Microstrip filters to define bandpass

Prototype properties

Prototype optical properties

• Bandpass filters work (again, structure from the measurement)

• broad out of band coupling (already reduced to <1%)

• cross-pol <1% as predicted by simulations

• coupling ~60%

Improving spectral measurement

• Top: unmodulated spectra showing low level broad signal outside of the band

• Bottom: modulated signal. Standing waves in spectrometer remain as before, but true spectral response appears in sidebands of the

Expensive photos

Zak Staniszewski2007

KeithVanderlinde2008

Dana Hrubes 2008

Steve Padin2007

Erik Shirokoff2009

Ross Williamson2009

http://www.new.facebook.com/photo.php?pid=2388644&id=815010507






























• SPT-SZ is the most powerful SZ cluster survey instrument in existence

• Success demonstrates that TES micro-bolometer technology is mature enough for the next generation of CMB experiments

•New detector efforts for SPTpol look promising

micro-bolometer arrays and the south pole telescope · micro-bolometer arrays and the south pole...

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