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 &central 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.