1. Final Doublet Stability and in-detector Interferometry MONALISA David Urner Oxford University

2. MONALISA MONitoring ALIgnment and Stabilisation with high Accuracy Is an interferometric metrology system for continuous monitoring of position critical accelerator components Consists of a fixed network of evacuated interferometric distance meters with nanometre type resolutions over O(10m)

3. MONALISA at ILC Survey and initial alignment required. Working alignment needs to be maintained / restored. –between trains 200 ms is long enough for several 100 nm movement –Take into account long term drifts –after push-pull events: IR hall floor will move after rolling two heavy detectors –Restore luminosity quickly after shutdown periods A position monitoring system of critical elements is your friend.

4. Main Component: CSM ( Compact Straightness Monitor) 6D position transferred from left to right –Integral use of sturdy endplates required. –Relative measurements O(1nm) –To understand geometry absolute measurement O(1  m) 10cm

5. FSI Phase = 2π (Optical Path Distance) / Wavelength Φ = 2π D / λ = 2π D (ν / c) D = (c/ 2π) (ΔΦ/Δnu) R = (c/ 2π) (Δθ/Δnu) D = R (ΔΦ/Δθ) Frequency Scanning Interferometry frequeny scanning Reference interferometer

6. Interferometer operation Phase = 2π (Optical Path Distance) / Wavelength Φ = 2π D / λ = 2π D (ν / c) D = (c/ 2π) (ΔΦ/Δnu) R = (c/ 2π) (Δθ/Δnu) D = R (ΔΦ/Δθ) ΔD = (c/2π ν) ΔΦ Fixed Frequency Interferometry Frequency Scanning Interferometry frequeny scanning

7. Interferometer operation Intensity

8. Distance meter Measurement Frequencies: –FFI:up to 10kHz –FSI:up to 1Hz Long term stability determines low frequency behaviour –For FSI given by quality of reference interferometer –For FFI we are building a system to lock the laser frequency to spectral feature of rubidium. Advantage of interferometric measurement system is fairly low cost per line. –Use of telecom frequency allows use of cheap commercial hardware. –Cheap amplification of light.

9. QD0 Pit ground QD0 Several lines needed to wall and ground used to reposition detector Distance meter in air (protected) Distance meter in vacuum (5 cm) CSM (18 cm) External Plates QD0 ~30 o QD0 enclosure External Plate

10. Access to QD0 (ILD) Platform attached To Detector 5cm vacuum tubes

11. Access to QD0 (ILD) Break vacuum by removing short tube pieces. Vacuum inserts to access QD0. Direct view of Reflector mounted on either Cryostat or Coldmass

12. Access to QD0 (ILD)

13. Ideal Case: Direct View of QD0 Yoke QD0 Enclosure Needs retraction mechanism 2d laser grid QD0 Only small connection force required to kick-start vacuum.

14. Separation of Tasks: No direct view Yoke QD0 Enclosure 2d laser grid In air: unclear how accurate this can be. In vacuum Produces fairly difficult to understand region. 4cm

15. How to go from here Need real engineering –Who is doing what? –Conceptual design would be good basis to decide on direct/indirect view SID will be different – should we try to keep commonalities? Not heard from 4 th concept yet.