MONALISA

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MONALISA
WP 3
Monitoring Alignment and Stabilisation with high
Accuracy (Previously known as StaFF)

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

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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
measurement distance

• 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

launch fibre
receiving fibres
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Reference Interferometer
Parallel
s

• 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

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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
Measurement Interferometer

• Start with raw photodiode voltages
• Extract reference phase
• Fit sinusoids to measurement interferometer
  voltages

Reference Interferometer
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Future Development

• Move ahead with distance meter development
• Hardware design
• Analysis methods
• Change to evacuated interferometers

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Thank you for listening
time for lunch?