1 star hft pixel detector howard wieman lawrence berkeley national lab
TRANSCRIPT
1
STAR HFT Pixel Detector
Howard WiemanLawrence 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 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
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
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
11
Rapid installation and replacement
pixel support hinges
cam followers and linear camslide 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 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
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 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
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 200MP2 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/cm2 (~ 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 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
20
air input and output
air input fits vacuum cleaner connection
air exhaust
21
22
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
23
HFT pixel mechanical WBS definitions
Sept 2008
24
pixel mechanical components
25
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)
26
Sector
sector beam
ladderssector base
27
Sectorcable bundle
drivers
pixel chips
adhesive
wire bonds
capacitors
adhesive
composite backer
kapton flex cable
Ladder
28
Sector Support
kinematic mounts
all the restare D tubes
29
Sector Support
pantograph
30
Sector Support
Items not shown support release
31
cart system
service bulkhead card cage cart
rails