Design Features
• Outer radius ~ 6 cm• Barrel length ~ 14 cm• Ladder widths 1-2 cm• Disks to cover
forward region
(GLD)
(LDC)
(SID)
A bit larger than this
Optimizing Vertex Performance
• Close to IP – Reduce extrapolation error– Inner radius ~1.5cm
• Position resolution (<5 microns)– Impact parameter resolution
≤ 5µm 10µm/(p sin3/2 )• Minimise multiple scattering
– Material ~ 0.1X0/layer
• 5 m resolution or better is possible with current sensor technology– Need good alignment to exploit this
• Minimal mass is crucial– Constraints on mechanics– Constraints on power
• Cooling• Power delivery
– Alignment
Parametric simulation assuming:• 0.1% RL per layer• 5 micron resolution• 1.4 cm inner radiusVarying each parameter
IP Resolution, 1 GeV tracks
0
5
10
15
20
25
0 5 10 15 20 25
Hit resolution (micron) or RL x 10^-3 or IR (mm)
Mic
ron
s
varying resolution
varying radiation length
Varying inner radius
ILC target
Material budget
• Service handling at ends of barrel are the problem
• The boring stuff is important!
• Breakdown for pixels
cos=0.95 cos=0.95ATLAS Tracker
Sensors (300m) 1.1%
Ro+bump bonds 1.4%
Hybrid 1.0%
Local support+cooling 5.4%
Cables 0.3%
Global support 1.5%
Total for 3 layers 10.7%
Beam pipeCF supportepoxySilicon
Mechanical Support• 0.1% X0/layer 100m of Si
• Need to start with thin Si, typically 20m• Thin supports
– Carbon fiber-based supports, similar to D0 layer 0/CDF Layer00
– Foam-based (SiC, RVC) supports (LCFI)
– Silicon picture frame (MPI)
• System Issues– Planarity of the sensors
– Bonding to thin silicon
– Thermal bowing
– Connection to external cables
MPI Design
(University of Washington)
(LCFI)
(SID inside support cylinder)
SiC Foam Ladder
• 20 um thick silicon• 1.5 mm thick SiC foam
– 8% relative density• Silicone adhesive pads
– 1mm diameter 200 microns high on ~5mm pitch
• ~0.14% X0SiC ladder
ladder block
glue
annulus block
mm
um
mm
um
LCFI
RVC Foam/Silicon Sandwich Ladder
• 20 micron thick silicon• 1.5 mm thick RVC foam
– 3% relative density• Silicone adhesive pads
– on ~5mm pitch• Tension ~1.5 N• ~0.08% X0
RVC sandwiched ladder
silicon spacer
ladder block
glue
annulus block
Tension
umum
mm
mm
LCFI
Air Cooling
• Air cooling is crucial to keep mass to a minimum– Require laminar flow through available apertures– This sets total mass flow – other quantities follow– Implies a limit on power dissipation
• For SiD design – Use the outer support CF cylinder as manifold (15mm r)– Maintain laminar flow (Remax = 1800). – Total disk (30W) + barrel (20W) power = 50W average
• For SiD ~ 131 µW/mm2.• Max T ~ 8 deg
(Cooper, SID)
Cooling StudiesTest model of 1/4 Barrel• Cold nitrogen cooling• Heaters at ladder ends• Parallel CFD simulations
• Flow 5-20 SLM
– 0.52 g/s whole detector
– Laminar flow
Power Extracted (W)
Temperature Difference (K)
LCFI
Alignment is critical
• ILC physics programme depends on identification of secondary vertices
• Ability to do this depends on tracking resolution
• Tracking resolution dependent on alignment precision
• Individual hit resolution may be O(5) m– Alignment must be better, so that contribution in quadrature
does not degrade hit resolution
Alignment – LHCb VELO
Rigiditylow CTEoverlaps10m alignment
Hardware Design SoftwareMetrology
Measurement machineIndividual modules during assemblyComplete system10m alignment
Alignment at few m levelIterative / non -iterative methods
BEFORE / AFTER
For ILC vertex detectorPosition of detectors on ladders to ~10mThin detectors Warping (SLD)Thin ladders not rigidLow mass beam pipe Vertex detector will move wrt experiment
Design• Design into system features for alignment
– Rigidity, thermal and humidity expansion• This is difficult at low mass
– Overlaps – not just for coverage, e.g. – VELO left, right half overlap– SLD CCDs
Metrology - importance• Starting point for alignment parameters• Constrains degrees of freedom not accessible from
alignment system• e.g. large systematic on particle lifetimes is radius of barrel e.g. +/- 40
um on 4cm = 1%• e.g. aspect ratio of vertex detector gives systematic – important for FB
asymmetries
• Define/understand elements:
– Ladders• Ideally rigid, 6 dof/ladder (372 for LCFI barrel)• Ladders are not a rigid object eg detector bow, CTE
– Develop models? Difficult to measure during construction need to understand effect of thermal changes eg CTE, tension due to mechanics and services? (CTE studies by LCFI)
– Greater no. of degrees of freedom than ladders x 6 (ATLAS has 34,992 dof)
– Requires good initial survey and understanding of changes» Difficult to do under in-situ conditions
Power delivery
• High currents to drive CCD clock pulses• Minimise voltage drop on power cables
– Low resistance more conductor mass (Cu)– 0.5V drop at 6cm ~ 0.5%X0
• Use serial powering– Power at higher voltage, locally regulate at detector– Reduces conductor mass– 0.5V drop at 6cm ~ 0.04Xo
• Issues– Failure in string– Coherent noise– Increase complexity of interconnects
• UK-ATLAS activity for sLHC upgrade
UK Experience
• ATLAS barrel and endcap silicon tracker, LHCb VELO– Sensors (strips)– Readout electronics– Module construction– Engineering– Cooling – liquid based– Alignment
• LCFI• SLD CCD based vertex detector• ALEPH, DELPHI, OPAL strip-based vertex detectors• CDF Layer-00 strip-based vertex detector
Summary/conclusions• Low mass critical to achieve required IP
– Challenging eg ATLAS is ~ 10.7%X0 for 3 pixel layers– Dominated by support and cooling
• Target layer thickness 0.1%X0 (100m Si)– Thin sensors– New support materials– Air cooling limits power to ~O(10W)– Also implications for services serial powering
• Need to consider alignment in hardware– Design: overlaps in system (increase material)– Metrology during assembly– Warping of thin detectors and ladders– Report of LHC alignment workshop: CERN yellow report 2007-004
• Thanks to: Mark Thomson, Tim Greenshaw, Joel Goldstein, Chris Parkes, Val O’Shea, Richard Bates
Barrel Layout
Beam pipe Ladder (detector element)
Foam cryostat
Beryllium support shell
Spring
Ladder block
Annulus block
Fixed end Sliding end
Readout and drive chips
Substrate
Silicon sensor
Beryllium support shell
Annulus and ladder blocks
Barrel Layout
Layer no
No of Ladders
Radius(mm)
Active length(mm)
Active width(mm)
Tilt angle
Overlap(mm)
1 8 15(19) 100 13 0 0
2 8 26(28.5) 250 22 0 0.42
3 12 37 250 22 15 1.3
4 15 48 250 22 15 0.86
5 19 60 250 22 15 1.2
• Looking at:– the radius of the layers– width of elements– tilt angle
Metrology - Equipment• Smartscope
• Small scale items – not full system– High precision O(2) m XY O(10) m Z– Optical head– Automatic pattern recognition– Excellent for measuring sensor curvature– Individual sensors not double sided modules – no
alignment to reverse side
Residuals are function of the detector resolution and the misalignments
From this…
The geometry we are looking for is the one which minimizes the tracks residuals
… to that
Alignment principle :
Software Alignment
Each individual ‘unit’ has six degrees of freedomNeed to apply global transformation constraints
•All software alignment procedures follow one of these two forms:
conclusion : both methods can be made to work well.
Misaligned detector
Geometry not corrected
Plot and fit the residuals
distributions
Best mean and values ?
Detector aligned
YES
NO
Fit the tracks
Modify the
geometry
ITERATIVE
Misaligned detector
Geometry not corrected
Detector aligned
YES
NOFit the tracks & the residuals
Outliers rejected ? Non-linearities
corrected ?
NON-ITERATIVE
Iterative / Not Iterative
Iterative: fit biased tracks then fit alignment constants, iterate to reduce biasNon-Iterative: fit tracks and alignment constants simultaneously
① Establish linear expression of residuals as a function of mis-alignments.
Fit the tracks simultaneously with the alignment constants
Get all track parameters and all misalignment constants simultaneously
1 single system to solve. But this system is huge ! (Ntracks∙Nlocal+Nglobal
equations)
BUT…
xclus = xtrack + x
Parameters i of the tracks(different for each track)
xclus = ∑i∙i + x
LOCAL PART
xclus = ∑i∙i + ∑aj∙j
Residuals expressed as function of misalignments
i
GLOBAL PART
Global Alignment Method – H1, LHCb, ATLAS
rclus = (xclus - x)∂ 2
∂ ∆i
∂ 2
∂ i
= = 0
Alignment minimise 2res = ∑ ∑wclus∙r2
clus
The matrix to invert has a very special structure:
Inversion in section (implemented in the code MILLEPEDE V.Blobel - NIM. A 566), The problem becomes only Nglobal x Nglobal
If Nglobal 100 , the problem can be solved in seconds
kCkglobal Hk
HkT
k
=0
0
Cklocal 00
0
0 …
…
……
……
kwkxk
kwkk
… ………
Nglobal Nlocal x Ntraces
Matrix Inversion