04/18/23 Robert King, Oxford University - Graduate Seminar Series

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Electronic speckle pattern

interferometry at the SLHC

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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Overview

• What is the SLHC?– How is Oxford involved?

• Electronic Speckle Pattern Interferometry (ESPI)– What is it?– How does it work?– How are we using it?

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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SuperLHC• ATLAS upgrade required

– Radiation damage ~10 years– Higher luminosity of SLHC

• ATLAS built for <700 fb-1

• SLHC must cope with >3000fb-1

→ New central tracker

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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The ‘stave’

• Detectors mounted on carbon fiber staves

– Low mass– Integrated cooling and services– Intrinsic mechanical stability

Bus cable

Hybrids Coolant tube structure

Carbon honeycomb or foam

Carbon fiberfacing

Readout IC’s

Silicon sensors

Staves inter-leaved

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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Where does ESPI come in?

• Accurate track resolution– Need thermo-mechanical stability to -25°C

• ESPI can verify this– Sub-micron precision– Large area– Frequent sampling– Non-invasive

• Oxford has experience

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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How ESPI Works (1)

• An expanded laser beam on rough surface gives laser speckle

• Interference caused by λ scale variations on surface

How ESPI Works (2)

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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04/18/23 Robert King, Oxford University - Graduate Seminar Series

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How ESPI Works (3)

Initial pixel value

Final pixel value

|Subtraction|

Bright Bright Dark

Dark Dark Dark

Dark Bright Bright

Bright Dark Bright

→ Intensity contours = displacement contours

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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How ESPI works (4)

• Silicone diaphragm under pressure

• Each ‘fringe’ ~ λ/2 displacement

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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The Oxford Setup

• Sensitive to in-plane and out of plane motion

•In-plane •Out-of-plane

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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Laser Fiber coupling

Camera Fibers

Test Object

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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In-plane deformation example

Video made by Sam Whitehead

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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Summary

• Integrated stave forms part of the SLHC upgrade• Validate thermo-mechanical stability• ESPI gives submicron accuracy over large areas• Testing on prototype staves should begin soon

Images sourced from Daniel Buria-Clark’s Thesis

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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Backup slides

• Out of plane measurement detail

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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In plane measurement detail

04/18/23 Robert King, Oxford University - Graduate Seminar Series

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Speckle pattern formation