stephen gibson, atlas offline alignment, 2 nd july 2002 1 incorporating fsi with the offline...
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Stephen Gibson, ATLAS Offline Alignment, 2nd July 20021
Incorporating FSIIncorporating FSIwith the Offline Alignmentwith the Offline Alignment
Overview
ATLAS Group, University of OxfordStephen Gibson
• Brief overview of FSI
• Demonstration System
• Length Measurements to Module Co-ordinates
• Grid simulations
• Future Work
Stephen Gibson, ATLAS Offline Alignment, 2nd July 20022
Frequency Scanning InterferometryFrequency Scanning Interferometry
• Alignment grid of length measurements help constrain the SCT shape to ~ 10 m.
• Each line of the grid must be measured to ~ 1 m.
• ~800 simultaneous length measurements.
• Components: rad-hard, low mass, operate >10 years.
Stephen Gibson, ATLAS Offline Alignment, 2nd July 20023
FSI Length MeasurementFSI Length Measurement
TUNABLELASER
sweep
To interferometer withOPD to be measured
DETECTOR
M1
M2
Reference Interferometerwith fixed OPD
IMEASURED
IREF
Ratio of phase change = Ratio of OPDs
/c]D /c]L
Stephen Gibson, ATLAS Offline Alignment, 2nd July 20024
Interferometers inside ATLASInterferometers inside ATLAS
• Each line of the alignment grid inside ATLAS will consist of a quill (two optical fibres & beam splitter) and a retro-reflector.
quill
jewels
beam splitter
variable path
fixed path
deliveryfibre
returnfibre
support structure
Stephen Gibson, ATLAS Offline Alignment, 2nd July 20025
Demonstration system: Square GridDemonstration system: Square Grid
• 6 simultaneous length measurements made between four corners of the square.
• +7th interferometer to measure stage position.
• Displacements of one corner of the square can then be reconstructed.
Stephen Gibson, ATLAS Offline Alignment, 2nd July 20026
Square Grid Jewel Reconstruction ResultsSquare Grid Jewel Reconstruction Results
Std Dev = 400 nm
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
0 50 100 150 200 250 300
X stage / micron
Rec
on
stru
cted
X s
tag
e,re
sid
ual
s /
mic
ron
Stephen Gibson, ATLAS Offline Alignment, 2nd July 20027
Current Work: Tetrahedral GridCurrent Work: Tetrahedral Grid
• Stage raised up by 100mm to form tetrahedral grid.
• Currently investigating the reconstruction of three dimensional jewel co-ordinates.
Stephen Gibson, ATLAS Offline Alignment, 2nd July 20028
From FSI Measurements to Module Co-ordinatesFrom FSI Measurements to Module Co-ordinates
• Problem – how to incorporate the FSI information into the offline alignment?
• First an overview of how FSI can be used.• Then some current work on the reconstruction
process.
• Essential steps to reach module co-ordinates: FSI scan Grid lengths Reconstruct node coordinates Interpolate nodes to give module co-ordinates Use tracks to refine the module co-ordinates
• The reality is more complicated…
Stephen Gibson, ATLAS Offline Alignment, 2nd July 20029
Phase unwrappingFringe fitting
Dual-laser drift correctionSubscan linking
Refractive index correction
FSI Grid Lengths
Reconstruction Software
FSI Scan
ModuleCo-ordinates
Node Co-ordinates
Opto-geometrical model of systemDegrees of freedom definition
Database of nominal jewel coordinates
Node topologyJewel internal dimensions
Reconstructed Jewel Co-ordinates
InterpolationSoftware
Shape parameterisationData from initial X-ray survey
FEA: barrel and disc eigenmodes(Check with ESPI studies)
CalibrationOffline
Alignment
Level-3 trigger?
Quasi real time
Stephen Gibson, ATLAS Offline Alignment, 2nd July 200210
FSI & Offline Alignment IntegrationFSI & Offline Alignment Integration
• FSI will produce quasi real time module co-ordinates with associated errors.
• Ultimate precision on module co-ordinates will come from tracks.
• How can FSI help? Offline alignment could use the FSI measurements of module co-ordinates: as the starting co-ordinates for iterative analysis. to correct for short-timescale motions in the analysis of long-
timescale track data. as a cross-check of the final calculated co-ordinates. to help with those distortions that tracks are less sensitive to:
• Sagitta• Z motion (affects rapidity)• Multipole radial distortions (elliptical/pear shaped)• Relative rotations of distant sections of InDet (invariant masses) ref1
Stephen Gibson, ATLAS Offline Alignment, 2nd July 200211
Barrel Grid SimulationsBarrel Grid Simulations
FEA model of carbon fibre FEA model of carbon fibre support structuresupport structure
7035m0m
Stephen Gibson, ATLAS Offline Alignment, 2nd July 200212
Simulgeoref2 model of Alignment Grid nodes
(jewels)
Z X
Y
ASSUME: end flanges are rigid rings ¢ral jewels constrained in rotation
Stephen Gibson, ATLAS Offline Alignment, 2nd July 200213
Lines of sight for one quadrant of Alignment Grid
Stephen Gibson, ATLAS Offline Alignment, 2nd July 200214
Single Barrel Grid Simulation ResultsSingle Barrel Grid Simulation Results
Measured object
Degree of Freedom
Calculated Error
End Flange
Translation in X Translation in Y Translation in Z
Rotation about X Rotation about Y Rotation about Z
0.29 m 0.29 m 0.34 m 1.31 rad 1.31 rad 0.61 rad
Each Central Jewel
Translation in PHI Translation in R Translation in Z
Rotation about PHI Rotation about R Rotation about Z
2.19 m 13.54 m 0.90 m
97.07 rad 9.91 rad
99.47 rad
• NB: rigid end flanges assumed – currently repeating with increased number of degrees of freedom.
• 1 micron precision assumed throughout.
• Fixed inner barrel.
Central jewels constrained in
rotation
Result without radial lines to
modules
Stephen Gibson, ATLAS Offline Alignment, 2nd July 200215
Cross-check of Grid SimulationsCross-check of Grid Simulations
• Full barrel grid simulations should predict errors on all nodes of grid, for given measurement precisions.
• Idea: Take FEA model of perfect barrel
• Extract grid line lengths
• (add random errors to lengths)
• Pass to reconstruction software for calibration of model
Distort FEA model eg, twist and/or multipole distortions
• Extract new lengths
• (add random errors to lengths)
• Pass to reconstruction software
• Calculate reconstructed node co-ordinates and compare with those in FEA model
• Repeat later including interpolation software.
Stephen Gibson, ATLAS Offline Alignment, 2nd July 200216
Future WorkFuture Work
• Continuing 2D and 3D grid testing & modelling.
• More detailed, full barrel simulations in progress.
• Check reconstruction software model with known distortions.
• Tony Weidberg + new post doc: Interpolation software Continuing FEA/ ESPI studies
• References• D.F. Howell et al.,’ATLAS-SCT-Alignment Overview’, University of Oxford, ATL-IS-ES-0026.
• P. Coe Doctoral Thesis, University of Oxford 2001.
• S.M. Gibson, ATLAS-SCT-Alignment Forward Grid Simulations, ATL-IS-AP-0054.
• ref1 S. Haywood, ‘Alignment, Stability and FSI’, RAL, SCT End-cap Engineering, 6 December 2001.ref2 used with kind permission of the author:
• L. Brunel, ‘SIMULGEO: Simulation and reconstruction software for opto-geometrical systems’, CERN CMS Note 1998/079.