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K. Gilmore - SDW2005

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The Large Synoptic

Survey Telescope(LSST)

Status SummaryKirk GilmoreSLAC/KIPAC

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LSST Technical Concept

8.4 Meter Primary Aperture– 3.4 M Secondary– 5.0 M Tertiary

3.5 degree Field Of View3 Gigapixel Camera

– 4k x 4k CCD Baseline– 65 cm Diameter 200 detectors200 detectors

30 Second Cadence– Highly Dynamic Structure– Two 15 second Exposures

Data Storage and Pipelines Included in Project

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LSST is designed to go wide – deep – fast

~10 deg2 per field

~6.5m effective collecting aperture

m~24 AB mag per 15 sec. exposure (2 per pointing)

wide coverage > 20,000 square degrees

multiple filters (e.g. grizy - maybe u)

accumulated depth of 27 AB magnitude in each filter

LSST System Summary

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The Science ofThe Science of KIPACKIPAC

P a rtic le A s tro p h y s ic sB la c k H o le s , N e u tro n S ta rs , W h ite D w a rfs …G R B s , m a g n e ta rs , s u p e rn o v a e …A c c re tio n d is k s a n d je ts …R e la tiv is tic s h o c k s , p a rtic le a c c e le ra tio n , U H E C R …

C o s m o lo g y D a rk e n e rg y , d a rk m a tte rG ra v ita tio n a l le n s e sC lu s te rs o f g a la x ie s a n d in te rg a la c tic m e d iu mM ic ro w a v e b a c k g ro u n d

o b s e rv a tio n sF irs t s ta rs , g a la x y

fo rm a tio n

QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.

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Why is the LSST unique?Primary mirror

diameterField of view

(full moon is 0.5 degrees)

KeckTelescope

0.2 degrees10 m

3.5 degrees

LSST

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Optical Design

0.6”

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Science Goals Observational Requirements

Telescope/Camera/Site Requirements

Nature of Dark Energy 1 w to 2%

2 dw/dt to 5%

3 w( over 2

4 correlate with CMB

All sky weak lensing (WL). Rapid revisit SN (2nd param studies)

5 WL shear > 0.001 vs z

6 15,000 sq deg to V=26.5 AB mag (WL)

7 color-z to 0.1(1+z)

~200 exposures per sky patch per fi lter

9 Photometric calibration: 0.02 mag goal

10 900 sec/filter/field/night, repeat every 5 nights on small # of fields (SN)

11 Image qual ity: < 0.7Ó FWHM in V, R, or I bands, PSF quad moment stable < 1% per 10 sec. Shear systematics < 0.0002 in 200 image stack

12 5 bands, for photometric redshifts (WL) & 2nd parameter studies (SN): 350 nm to 1 m

13 Southern site to match Antarctic SZ surveys?

A 250, noise/read < 5e

15 Dark sky equal to bes t sites

Optical Tra nsients 16 Extreme physics

17 Rare new objects

18 Orphan GRB statistics

19 SNe in arcs + lensing

20 Broad coverage in cadence, 20 sec to year t ime scale

21 Evolution of spectral energy distribution

22 Requires deep initial multiband template

23 Frequent revisits, max sky coverage

24 Requires multi-colors

25 Targe t latency of <1 min for alerts , high throu ghput pipeli ne

26 A 200 in a single camera to see events as rare as 1/night over 1/5 of the sky: fast pace. Noise/read < 5e.

Solar System 27 PHAs down to 100m

28 Small KBOs + colors

29 MBA statistics, colors

30 Max coverage in ecliptic. Magic elongation

6 visits, 15 min sep, per sky patch per lun ation

32 Area coverage > 1100 0 square degrees

33 Sufficient A to get 90% completeness for PHAs in

34 Maximum exposure of 15 sec to avoid trailing losses

35 Image qual ity < 1Ó FWHM

36 A 200 per camera, noise/read < 5 e.

37 Multiple 500-800nm filters

Science Objectives DriveSystem Requirements

• Image Quality Is the Key

• f/1.25 beam

• Large focal Plane

• Construction Techniques

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From LSST Science Reqts to Sensor Reqts

High QE to 1000nm thick silicon (> 75 µm)

PSF << 0.7” (0.2”) high internal field in the sensor high resistivity substrate (> 5 kohm∙cm)

high applied voltages (30 - 50 V) small pixel size (0.2” = 10 µm)

Fast f/1.2 focal ratio sensor flatness < 5µm package with piston, tip, tilt adj. to ~1µm

Wide FOV ~ 3200 cm2 focal plane > 200-CCD mosaic (~16 cm2 each) industrialized production process required

High throughput > 90% fill factor 4-side buttable package, sub-mm gaps

Fast readout (1 - 2 s) segmented sensors (~6400 TOTAL output ports) 150 I/O connections per sensor

Low read noise < ~ 5 rms electrons

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Camera ChallengesCamera Challenges

Detector requirements:Detector requirements:– 10 10 m pixel sizem pixel size– Pixel full-well > 90,000 ePixel full-well > 90,000 e––

– Low noise (< 5 eLow noise (< 5 e–– rms), fast (< 2 sec) readout ( rms), fast (< 2 sec) readout ( < –30 C) < –30 C)– High QE 400 – 1000 nmHigh QE 400 – 1000 nm– All of above exist, but not simultaneously in one detectorAll of above exist, but not simultaneously in one detector

Focal plane (75cmFocal plane (75cm22)) position precision of order 3 position precision of order 3 mmm, flat to 5 u rmsm, flat to 5 u rmsPackage large number of detectors, with integrated readout electronics, with high fill factor and Package large number of detectors, with integrated readout electronics, with high fill factor and

serviceable designserviceable designLarge diameter filter coatingsLarge diameter filter coatingsConstrained volume (camera in beam)Constrained volume (camera in beam)

– Makes shutter, filter exchange mechanisms challengingMakes shutter, filter exchange mechanisms challengingConstrained power dissipation to ambientConstrained power dissipation to ambient

– To limit thermal gradients in optical beamTo limit thermal gradients in optical beam– Requires conductive cooling with low vibrationRequires conductive cooling with low vibration

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Strawman CCD layout under Study

4k x 4k, 10 µm pixels, 32 output ports;Pixel full-well >90,000 e; Noise < 5 rms e

Segmented readout to achieve the required readout time (2 seconds required, 1 second target) with moderate clock frequency (to minimize read noise and crosstalk), (e.g., 0.5 Mpixels/output read out at 250-500kHz).

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LSST Sensor Design

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A hybrid Si-PIN-CMOS detector, analogous to near-infrared (NIR) array detectors.

Separation of photon detection from readout facilitates separate optimization of- CMOS readout electronics

(multiplexer)- Si PIN detector array

Thickness, QE, PSF, operating voltage considerations are the same as for CCDs.

Bump bonding technology on 10 µ scale required.

Si PIN array bump-bonded to CMOS readout

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Raft Assembly

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Integrating structure

Raft structure

AlNUP

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3.5° FOV 64 cm

4096x4096 pixels;10 µm pixels1678 mm2 active41.7 mm x 41.7 mm Si42 mm pitch (0.3 mm gaps)95% fill factor

25 x 3x3 = 225 chipsIf allow dummies outside 64cm, then:21 rafts with 9 live;+4 corners with 3 live ea

= 201 live chips total

wea 8/6/04

8/5/04 workshop CCDs: 3x3

4° FOV 74 cm

X X XX X

X

XX X

X X X

XX XX X X

X X XX XX

WFS

Tiling of the Focal Plane

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Effect of displacement of the focal plane:

(a) position of best focus for short-wavelength light;

(b) focal plane displaced 10µm in direction of incoming rays (best for long wavelength-light).

Refraction causes position of focal point to move about 5 times farther than sensor displacement.

Si100 µm

Air

incident rays

sensor displaced 10m

Best focus moves 50µm inside Si

Geometric radius at surface increases from 1.5µm to 5.8 µm with defocus.

best focus at surface of Si

(a)

(b)

Si100 µm

Air

incident rays

sensor displaced 10m

Best focus moves 50µm inside Si

Geometric radius at surface increases from 1.5µm to 5.8 µm with defocus.

best focus at surface of Si

(a)

(b)

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0m

-10m

+10m

100m

FP displacement:

0m

0m

-10m

-10m

+10m

+10m

100m

FP displacement:

PSF SimulationsPSF Simulations

Monte-Carlo simulation of long-wavelength light

absorption in silicon sensor.

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FPA Flatness Allocations Established

Sensor Module

5m p-v flatness over entire sensor surface

Raft Assembly

6.5m p-v flatness over entire surfaces of sensors

Focal Plane Assembly

10m p-v flatness over entire surfaces of sensors

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Camera layout

1.6m

L1 L2 L3

Filter Focal plane array

Shutter

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Spin Casting of large optics at the U of Arizona

LSST is in the queue

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LSST Filter Development at SLACLSST Filter Development at SLAC

lambda 1 Filter Lambda 2

410 g 552

550 r 694

694i

847

847 z

960 Y 1028

930

CHALLENGECHALLENGEFabricate large curved filters Fabricate large curved filters (76cm) with uniform coating to(76cm) with uniform coating to do accurate photometrydo accurate photometry

STATUSSTATUSDiscussions with multiple vendors Discussions with multiple vendors ongoingongoing

– Preliminary feedback from Preliminary feedback from vendors – no show-stoppersvendors – no show-stoppers

Study RFQ’s going out to vendors Study RFQ’s going out to vendors in FY06in FY06

– Will include solicitation for Will include solicitation for design and development design and development funding needed to qualify funding needed to qualify vendors for fixed price contractvendors for fixed price contract

• Current LSST baseline uses filter Current LSST baseline uses filter set comprised of g, r, i, z, and Y set comprised of g, r, i, z, and Y bands. Approximate FWHM bands. Approximate FWHM transmission points are shown transmission points are shown below.below.

• Final specifications beingFinal specifications beingdriven by simulations modeling.driven by simulations modeling.

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Science Simulator Overview

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LSST Data RatesLSST Data Rates

3.2 billion pixels read out in 2 sec (15 second integration)3.2 billion pixels read out in 2 sec (15 second integration)

1 pixel = 2 Bytes (raw)1 pixel = 2 Bytes (raw)

Over 3 GBytes/sec peak raw data from cameraOver 3 GBytes/sec peak raw data from camera

Real-time processing and transient detection: < 10 secReal-time processing and transient detection: < 10 sec

Dynamic range: 4 Bytes / pixelDynamic range: 4 Bytes / pixel

> 0.6 GB/sec average in pipeline> 0.6 GB/sec average in pipeline

5000 floating point operations per pixel5000 floating point operations per pixel

2 TFlop/s average, 9 TFlop/s peak

~ 20-30 Tbytes/night

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