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STAR HFT Pixel Detector

Howard WiemanLawrence Berkeley National Lab

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TOPICS

Detector location Purpose of the detector Why it has to be very low mass Mechanical design Prototyping plans Part names

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STAR detector at RHIC – Brookhaven Lab – Long Island

STAR

BRAHMS

PHENIX

PHOBOS

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STAR detector

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Jon Wirth inside the TPC

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STAR Detector

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Pixel geometry

2.5 cm radius

8 cm radius

Inner layer

Outer layer

End view

One of two half cylinders

20 cm

coverage +-1

total 40 ladders

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Pixel detector function – find displaced tracks

~50 mdisplacementbefore decay intotwo particles

HFT pixel layers

other STARdetector layers

purpose is to identify these tracksthat don’t come from the main vertex

D mesons travel a few tens of microns from the main vertex and then decay into 2 particles

So, tracks with a starting point away from the main vertex are candidates for Ds

The pixel detector provides high precision points for locating the starting points of the tracks.

main vertexfrom gold on gold collision

Gold on Gold collision

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material at the inner layer limits pointing precision

particle path disrupted by material in the detector layer

real vertex

apparent vertex

HFT pixel detector very thin

5 times thinner than ATLAS or PHENIX

pixel detector layers

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Some pixel features and specifications

Layers Layer 1 at 2.5 cm radiusLayer 2 at 8 cm radius

Pixel size 18.4 m X 18.4 m

Hit resolution 10 m rms

Position stability 20 m envelope

Radiation thickness per layer

X/X0 = 0.28%

Number of pixels 436 M

criticalanddifficult

~ 2 cm

~ 2 cm

pixel chips

50 m thick640 x 640pixels

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Rapid installation and replacement

pixel support hinges

cam followers and linear camslide rails

sliding carriage

kinematic dock

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Cam guided insertion operation

Open Closed

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Kinematic support in operating position

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Spatial mapping

Spatial map of the half cylinder will be done in a vision coordinate machine while supported by kinematic mounts Both inner and outer

silicon layers are visible for mapping

Structure must remain stable between measuring environment and the operating environment, i.e. should not change by more than 20 microns with changes in: gravity direction 10-15 deg C

temperature change humidity changes

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Stability requirement drives design choices

The detector ladders are thinned silicon, on a flex kapton/aluminum cable

The large CTE difference between silicon and kapton is a potential source of thermal induced deformation even with modest 10-15 deg C temperature swings

Two methods of control ALICE style carbon

composite sector support beam with large moment of inertia

Soft decoupling adhesive bonding ladder layers

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Ladder design with soft adhesive (6 psi shear modulus)

cable bundle

drivers

pixel chips

adhesive

wire bonds

capacitors

adhesive

composite backer

kapton flex cable

adhesive:3M 200MP2 mil, film adhesive

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Air cooling of silicon detectors - CFD analysis

air flow path – flows along both inside and outside surface of the sector

Silicon power: 100 mW/cm2 (~ power of sunlight)

240 W total Si + drivers

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Prototyping and testing

build prototype sectors and supports wind tunnel test to measure vibration of detector structure with

air cooling wind tunnel tests to measure cooling measurements of deformation induced by temperature change

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air velocity probetwo positions shown

capacitance vibration probetwo positions shown

carbon fiber sector beam

wind tunnel setup to test vibration and displacement

adjustablewall for airturn around

air in

air out

C:\Documents and Settings\Howard Wieman\My Documents\aps project\mechanical\PXL phase 1 sept 2008\sector ph1 wind tunnel.SLDASM

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air input and output

air input fits vacuum cleaner connection

air exhaust

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latest design – starting to make prototype parts

C:\Documents and Settings\Howard Wieman\My Documents\aps project\mechanical\PXL phase 1 oct 24 2008 A\half cyl sector cluster.SLDASM

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HFT pixel mechanical WBS definitions

Sept 2008

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pixel mechanical components

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Names

sector sector base ladder sector beam

sector support D tube kinematic mounts pantograph support release

cart system cart rails card cage service bulkhead

cooling system (not shown)

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Sector

sector beam

ladderssector base

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Sectorcable bundle

drivers

pixel chips

adhesive

wire bonds

capacitors

adhesive

composite backer

kapton flex cable

Ladder

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Sector Support

kinematic mounts

all the restare D tubes

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Sector Support

pantograph

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Sector Support

Items not shown support release

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cart system

service bulkhead card cage cart

rails