MONALISA

David Urner, Armin Reichold , Paul Coe, Matthew Warden, Geoff Rayner

Monitoring Alignment and Stabilisation with high Accuracy

(Previously known as StaFF)

WP 3

12 April 2007 MONALISA - M. Warden 2

Contents

• Motivation

• Overview of system

• The distance meter– Design– Construction– Data analysis

• Future developments

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Motivation

• A critical requirement for achieving and maintaining luminosity in ILC is:

• Stability of Beam Delivery System– This is true for BDS as a whole– And particularly so for the final focussing

quadrupoles

• Achieving stability requires accurate monitoring of magnet positions

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Motivation

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The Challenge:

• Develop an optical system to accurately determine relative position and orientation in 6D

• Direct line of sight may not be available

• In general, such a system needs:– Distance meters– Straightness monitors

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The Distance Meter

• Components:– Reference interferometer– Measurement interferometers

• Two modes:– Absolute distance measurement, using

frequency scanning interferometry– Small displacement measurement, using

fixed frequency interferometry

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The importance of absolute distance measurement

• Take two fixed points:

• Measure distances to a third point:

• Triangulate this point:

• Calculate axes for displacement measurements:

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Compact Measurement Interferometer

• Simple, compact design

• Gold-coated beam-splitter cube acts as one interferometer arm

• Will replace far mirror with corner cube– Allows for easy alignment– Can simultaneously measure

distances to many points

measurement distance

launchfibre

receivingfibres

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Reference Interferometer

• Both interferometers share the same phase step from piezo mounted mirror

• Taking two measurements gives a measure of accuracy

• Can keep one interferometer as a benchmark, and test alternatives with the other

Parallel s

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From design to reality

• Have constructed both reference and measurement interferometers

• Testing them now

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Preliminary Data Analysis

• Start with raw photodiode voltages

• Extract reference phase

• Fit sinusoids to measurement interferometer voltages

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Future Development

• Move ahead with distance meter development– Hardware design– Analysis methods

• Change to evacuated interferometers

Thank you for listening

…time for lunch?