1. The LiCAS FSI Subsystem Current Status and Initial Measurements John Dale for the LiCAS Collaboration IOP HEP April 2008

2. Introduction ILC Alignment Requirements Linear Collider Alignment and Survey (LiCAS) Rapid Tunnel Reference Surveyor (RTRS) –concept –prototype current status External and Internal FSI Subsystems –Frequency Scanning Interferometry (FSI) –Concept/design –Precision measurements

3. ILC Alignment Requirements Alignment of the ILC effects collider luminosity Main Linac has ~30km tunnel to survey Needs to be surveyed quickly and effectively –Reduce down time –Reduce labour cost Required Accuracy 200 μm over 600m vertically (a betatron wavelength) 500 μm over 600m horizontally Difficult using conventional surveying techniques

4. LiCAS RTRS Concept collider component Tunnel Wall Reconstructed tunnel shapes (relative co- ordinates) wall markersinternal FSI external FSISM beam

5. LiCAS RTRS Prototype Current Status 3 car prototype under construction at DESY Hamburg Design COMPLETED Manufacture COMPLETED Assembly COMPLETED Commissioning COMPLETED Currently Entering Calibration Phase

6. Frequency Scanning Interferometry Tunable Laser Reference Interferometer: L Measurement Interferometer: D Change of phase: Δ Φ meas Change of phase: ΔΦ ref time I Ref time I meas Idea is adapted from the Michelson interferometer Instead of moving the mirror we change the frequency of the laser

7. Retro Reflector External FSI Sub-System System responsible for measuring wall markers Unit has 6 FSI Lines Note: These are bare fibres with no collimators or beam splitters All 6 fibres monitor the same retro reflector LiCAS RTRS Unit FSI Line Wall Retro Reflector FSI Lines

8. Initial Stability of External FSI Sub- System RMS 1.71E-6 RMS 1.06E-6 RMS 1.54E-6RMS 0.78E-6 RMS 1.70E-6 RMS 1.25E-6

9. External Marker Reconstruction Using External FSI Lines RMS 1.26E-6 RMS 0.57E-6 RMS 3.12E-6

10. Internal FSI Sub-System Used to determine the distance from one unit to the next First Unit has 6 collimated fibres Second Unit has 6 retro Reflectors Each Fibre Monitors a different retro reflector LiCAS RTRS Unit Collimated fibre Retro Reflector

11. Initial Stability of Internal FSI Sub- System

12. 1 23 4 65 0.8 E-6 0.6 E-6 0.25 E-6 0.3 E-6 Units Have Rotated By : 16 μradian RMS : 61nm RMS : 45nm RMS : 70nm RMS : 102nm

13. Summary Prototype RTRS is constructed and entering calibration phase External FSI System is giving precision of 1-1.5 µm We have the ability to reconstruct wall marker positions to a precision of order 1.5µm Internal FSI System giving precision of 45 -100 nm