Sct endcap module initial alignments using survey data
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SCT Endcap Module Initial Alignments Using Survey Data. Paul S Miyagawa University of Manchester. Outline. Objectives Available survey data Calculation of alignment constants Comparison with CSC constants Summary and future work. Objectives.

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Sct endcap module initial alignments using survey data

SCT Endcap Module Initial Alignments Using Survey Data

Paul S Miyagawa

University of Manchester


Outline
Outline

  • Objectives

  • Available survey data

  • Calculation of alignment constants

  • Comparison with CSC constants

  • Summary and future work

ATLAS Software & Computing Workshop


Objectives
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

ATLAS Software & Computing Workshop


Module survey data 1
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

ATLAS Software & Computing Workshop


Module survey data 2
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)

ATLAS Software & Computing Workshop


Disc survey data 1
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

ATLAS Software & Computing Workshop


Disc survey data 2
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

ATLAS Software & Computing Workshop


Athena conventions

Y

x

y

z

X

Z

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

ATLAS Software & Computing Workshop


Stereo centre of module
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

ATLAS Software & Computing Workshop


Angle between wafers
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

ATLAS Software & Computing Workshop


Alignment parameters
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

ATLAS Software & Computing Workshop


Comparison with csc numbers
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

ATLAS Software & Computing Workshop


Summary and future work
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

ATLAS Software & Computing Workshop


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