1 STAR HFT Pixel Detector Howard Wieman Lawrence Berkeley National Lab

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

3 STAR detector at RHIC – Brookhaven Lab – Long Island STAR BRAHMS PHENIX PHOBOS

4 STAR detector

5 Jon Wirth inside the TPC

6 STAR Detector

7 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

8 Pixel detector function – find displaced tracks ~50  m displacement before decay into two particles HFT pixel layers other STAR detector layers purpose is to identify these tracks that 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 vertex from gold on gold collision Gold on Gold collision

9 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

10 Some pixel features and specifications LayersLayer 1 at 2.5 cm radius Layer 2 at 8 cm radius Pixel size18.4  m X 18.4  m Hit resolution10  m rms Position stability20  m envelope Radiation thickness per layer X/X 0 = 0.28% Number of pixels436 M critical and difficult ~ 2 cm pixel chips 50  m thick 640 x 640 pixels

11 Rapid installation and replacement pixel support hinges cam followers and linear cam slide rails sliding carriage kinematic dock

12 Cam guided insertion operation Open Closed

13 Kinematic support in operating position

14 Spatial mapping  Spatial map of the half cylinder will be done in a vision coordinate machine while supported by kinematic mounts uBoth 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: ugravity direction u10-15 deg C temperature change uhumidity changes

15 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 deg C temperature swings  Two methods of control uALICE style carbon composite sector support beam with large moment of inertia uSoft decoupling adhesive bonding ladder layers

16 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 200MP 2 mil, film adhesive

17 Air cooling of silicon detectors - CFD analysis air flow path – flows along both inside and outside surface of the sector  Silicon power: 100 mW/cm 2 (~ power of sunlight)  240 W total Si + drivers

18 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

19 air velocity probe two positions shown capacitance vibration probe two positions shown carbon fiber sector beam wind tunnel setup to test vibration and displacement adjustable wall for air turn 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

20 air input and output air input fits vacuum cleaner connection air exhaust

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22 latest design – starting to make prototype parts C:\Documents and Settings\Howard Wieman\My Documents\aps project\mechanical\PXL phase 1 oct A\half cyl sector cluster.SLDASM

23 HFT pixel mechanical WBS definitions Sept 2008

24 pixel mechanical components

25 Names  sector usector base uladder usector beam  sector support uD tube ukinematic mounts upantograph usupport release  cart system ucart urails ucard cage uservice bulkhead  cooling system (not shown)

26 Sector sector beam ladders sector base

27 Sector cable bundle drivers pixel chips adhesive wire bonds capacitors adhesive composite backer kapton flex cable Ladder

28 Sector Support kinematic mounts all the rest are D tubes

29 Sector Support pantograph

30 Sector Support  Items not shown usupport release

31 cart system service bulkhead card cage cart rails