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Options for interferometric monitoring of CLIC test magnet
M. S. Warden, P. A. Coe, D. Urner, A. Reichold
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Outline
• Interferometers– Distance Meters– Compact Straightness Monitors
• Complementary to accelerometer readings
• Options for the CLIC test magnet– Sequence of instrumentation
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Interferometer: Distance meter
Absolute distanceDisplacement
• Operates in two modes– Absolute Distance (< m resolution)– Displacement measurement (nm resolution)
• Two modes combined– Displacements referred to absolute distance– Tolerant to interruption of measurements
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Instruments: CSM• Compact Straightness Monitor• Example from ATF2
– Measures plane to plane• Internal displacements and rotations measured• CSM always blind to 6 external DoF
100 mm
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Interferometers: Make relative measurements
• Distance Meters measure point to point– Range and displacements ( changes)
• Compact Straightness monitor– Combines distance meters to measure object
to object• 3 translational degrees of freedom• 3 rotational degrees of freedom
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Compare and contrast with accelerometer
• CSM measures internal DoF– network distances between lines of sight– blind to external rotations / translations
• Accelerometer measures local deviations from free fall– multiple axes of test mass(es)– blind to free fall
• (local 1g can be cancelled off)
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Flexible range of options
• Interaction on CLIC is still in its infancy– No process yet for
• drawing up interferometer required specifications• understanding conflicting uses of space
• Initial discussions lead to “bizarre” first ideas• We envisage flexible programme
– First: making simple studies– Later: Installing more sophisticated systems
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Instrumentation could be staged
• Build up number of interferometers
– First study with simple distance meters• May increase number of distance meters
– Upgrade later to simple CSM arrangement
– Final stage complete suite of CSMs
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First measure most important DoF
• Start with simplest interferometers– Distance meters (DMs)
• measuring the vertical coordinate wrt floor
– Learn which issues are most important
• Suitable reference datum• Structural Vibrations• Vacuum / Protected air
– Would compare with accelerometers• one accelerometer at each end of line
Reflector
Launch Head
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Monitor several points independently
Floor
Magnet• Test several points along the magnet– at first independent DMs
• Compare readings with accelerometers– on the magnet– and on the floor
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These might be cross linked DMs
• Subject to constraints– we don’t know these
• Only possible– if planned in advance
• We would like to understand– what is possible– what is impossible– with respect to using spaces under/around the magnet
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Ultimately: Install cross linked CSMs
• With some form of enclosure– Although it need not take this form
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Summary
• We propose a staged build up of interferometer installation
• Many DoF can be measured with CSMs
• Can learn a lot with simple instruments (DMs)– These can be installed as soon as magnet is ready– Would like to compare with accelerometers
• We need to better understand the constraints