Options for interferometric monitoring of CLIC test magnet

1. Options for interferometric monitoring of CLIC test magnet M. S. Warden, P. A. Coe, D. Urner, A. Reichold CLIC stabilisation day 5 - LAPP OXFORD MONALISA

2. Outline • Interferometers • Distance Meters • Compact Straightness Monitors • Complementary to accelerometer readings • Options for the CLIC test magnet • Sequence of instrumentation CLIC stabilisation day 5 - LAPP OXFORD MONALISA

3. Interferometer: Distance meter • Operates in two modes • Absolute Distance (< mm resolution) • Displacement measurement (nm resolution) Absolute distance Displacement • Two modes combined • Displacements referred to absolute distance • Tolerant to interruption of measurements CLIC stabilisation day 5 - LAPP OXFORD MONALISA

4. Instruments: CSM • Compact Straightness Monitor • Example from ATF2 • Measures plane to plane • Internal displacements and rotations measured • CSM always blind to 6 external DoF CLIC stabilisation day 5 - LAPP OXFORD MONALISA

5. Interferometers: Make relative measurements • Distance Meters measure point to point • Range and displacements (e changes) • Compact Straightness monitor • Combines distance meters to measure object to object • 3 translational degrees of freedom • 3 rotational degrees of freedom CLIC stabilisation day 5 - LAPP OXFORD MONALISA

6. 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) CLIC stabilisation day 5 - LAPP OXFORD MONALISA

7. 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 CLIC stabilisation day 5 - LAPP OXFORD MONALISA

8. 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 CLIC stabilisation day 5 - LAPP OXFORD MONALISA

9. 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 CLIC stabilisation day 5 - LAPP OXFORD MONALISA

10. Monitor several points independently • Test several points along the magnet • at first independent DMs • Compare readings with accelerometers • on the magnet • and on the floor Magnet Floor CLIC stabilisation day 5 - LAPP OXFORD MONALISA

11. 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 CLIC stabilisation day 5 - LAPP OXFORD MONALISA

12. Ultimately: Install cross linked CSMs • With some form of enclosure • Although it need not take this form CLIC stabilisation day 5 - LAPP OXFORD MONALISA

13. 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 CLIC stabilisation day 5 - LAPP OXFORD MONALISA