sct endcap module initial alignments using survey data

SCT Endcap Module Initial Alignments Using Survey Data

Paul S MiyagawaUniversity of Manchester

11 December 2006 ATLAS Software & Computing Workshop 2/13

Outline

• Objectives• Available survey data• Calculation of alignment constants• Comparison with CSC constants• Summary and future work


Objectives

• Extensive survey data available for SCT endcap modules and discs

• Combine the survey data to produce “as-built” module-on-disc (level-3) alignments

• Compare with the distributions used for CSC production

• Use alignments as initial step in alignment algorithms


Module Survey Data (1)• Modules consist of two (or

four) wafers mounted at an angle of 40 mrad– (For outer and middle

modules, each wafer is split into two parts)

• Hole and slot used to mount the module on disc

Nominal values

Parameter Tolerance Outer Middle Short Middle Inner

mhx (mm) 0.020 -78.136 71.708 41.764 45.060

mhy (mm) 0.020 0.000 0.000 0.000 0.000

msx (mm) 0.100 62.244 -66.672 -96.616 -34.320

msy (mm) 0.020 0.000 0.000 0.000 0.000

midxf (mm) 0.010 0.000 0.000 0.000 0.000

midyf (mm) 0.005 -0.040 -0.053 -0.652 0.000

stereo (mrad) 0.130 -20.000 -20.000 -20.000 -20.000


Module Survey Data (2)• Modules surveyed

during assembly at Manchester, NIKHEF and Geneva

• Survey information on positions of wafers, hole + slot, angle between wafers

• Uncertainties in module construction < O(10 μm)


Disc Survey Data (1)• Modules mounted on disc

in three rings– 40 modules each in inner

and middle rings, 52 in outer ring

– Outer and inner rings mounted on front face of disc, middle ring on rear face

• At each position on disc, main/secondary pins insert into hole/slot on module

• 2 reference holes define survey coordinates– Holes also used to align

discs within the endcap


Disc Survey Data (2)• Discs surveyed during

assembly at Liverpool and NIKHEF

• Positions of pins and reference holes surveyed on disc

• Uncertainties in pin positions O(60 μm)– Should be dominant

over module uncertainties


Athena Conventions• Level-3 AlignableTrans-

forms define translations and rotations of modules in local frame

• Centre of rotations taken to be stereo centre on rφ face of module– Strips of rφ face point

along radial direction– Strips of stereo face

rotated 40 mrad• Transforms are for entire

module; not available separately for each face of a module– Cannot reflect shift of

stereo centre or non-nominal angle between wafers

rφ

y

stereo

x

X

Y

Z

y

x

z


Stereo Centre of Module• Stereo centre defined to be

intersection of central strips of each wafer

• Shift in wafer positions relative to each other causes shift in stereo centre– Positions of overlaps

relative to stereo centre are unaffected

– Endpoints of strips relative to stereo centre are changed

• Leads to inefficiency at one end of strips

• Cannot be reflected by AlignableTransforms


Angle Between Wafers• Central axis of module

chosen such that angle between wafers is symmetric about nominal angle

• Non-nominal angle affects positions of overlaps– Cannot be reflected by

AlignableTransforms

nominal

actual


Alignment Parameters• Calculated in-plane

translations and rotations for modules– Translations < O(100 μm)– Rotations O(400 mrad)– Distributions are (vaguely)

Gaussian– Largely determined by

positions of pins on disc• Still need to complete

verification of data– Using Michal Dwuznik’s

viewer– Running alignment

algorithm on this set of misalignments


Comparison with CSC Numbers• CSC misalignment set

used flat distributions• estimates for CSC

misalignments were slightly pessimistic

• CSC misalignments are random; survey misalignments are correlated– Relative alignment

between modules could be used as a constraint

type of misalignment

half-width

dx 100 μm

dy 100 μm

dγ 1 mrad


Summary and Future Work• Extensive survey data available for SCT endcap modules and discs

– Uncertainties in module construction < O(10 μm)– Uncertainties in disc construction

• Combined survey data to produce “as-built” in-plane level-3 alignments– Translations < O(100 μm)– Rotations O(400 mrad)– Roughly Gaussian distributions– Numbers used for CSC misalignments were slightly pessimistic

• AlignableTransforms not available separately for each face of a module– Cannot reflect shift of stereo centre or non-nominal angle between

wafers

• Work to come– Complete verification of data– Compare reconstruction performance on real data with survey

misalignments versus nominal geometry

sct endcap module initial alignments using survey data

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