The Linear Collider Alignment and Survey (LiCAS) Project Richard Bingham*, Edward Botcherby*, Paul Coe*, Grzegorz Grzelak*, Ankush Mitra*, Johannes Prenting , Armin Reichold* *LiCAS Group, Particle Physics sub-department, University of Oxford, UK  Applied Geodesy Group, DESY, Germany

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project2 Contents Introduction LiCAS Project Overview Description of Measurement System Summary

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project3 Introduction Next generation of Linear Colliders will require precision alignment (eg:- TESLA: 33km Tunnel, Alignment: 200  m over 600m) The problem –Current open air survey techniques are not sufficient –Ground motion will bring accelerator out of alignment Solution: Proposed DESY survey train with LiCAS : A novel optical system

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project4 Accelerator Alignment Accelerator Component Tunnel Wall Reference Markers Place reference markers along tunnel wall Measure accelerator component with respect to reference markers How are the reference marker positions measured ? Tunnel Rail Use a survey train

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project5 LiCAS Project Internal Measurement System (FSI+SM) inside a vacuum pipe Tunnel Wall Tunnel Rail External Measurement System (FSI) Measurement system for the alignment and survey of a Linear Collider An optical metrology system for the survey train − Vacuum enclosure between cars – Frequency Scanning Interferometry (FSI) to measure absolute distance – Laser Straightness Monitors (SM) to measure transverse displacements 4.5 m 22.5 m 0.5m z x

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project6 Survey Train in Action Tunnel Wall Tunnel Rail Internal FSI Lines and SM Reference Wall MarkersExternal FSI Lines Reconstructed Tunnel Shape

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project7 Laser Straightness Monitor (SM) Measures inter-car transverse displacements (and rotations) Provides single reference straight line for entire train Require measurement precision of 1  m over length of train (2x22.5m) CCD Camera Translation: Both spots move to the right Rotation: The spots move in opposite directions Beam-Splitter Retroreflector z y

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project8 SM: Two Beams Use two parallel beams to measure rotation about z-axis z y x y CCD Image SM beams coming out of the screen Image of beam spots observed on CCD Camera

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project9 Frequency Scanning Interferometry Tunable Laser Interferometric length measurement system Aim for measurement precision of 1  m over 5m Reference Interferometer: L Measurement Interferometer: D Change of phase:  GLI Change of phase:  Ref time I Ref time I GLI (Grid Line Interferometer (GLI))

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project10 FSI in LiCAS Delivery Fibre Return Fibre LiCAS Collimated Quill Fibre Splitter fibre end Collimation Optics Retroreflector

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project11 Extensions of FSI for LiCAS Move to Telecoms wavelength (1510 nm-1640 nm) Exploit cheap high quality tunable lasers Reduce drift errors – Greater continuous tuning range (130 nm) – Faster tuning rate (40 nm/sec) Easier separation of laser signals – Use amplitude modulation Use Erbium Doped Fibre Amplifiers (EDFA) Modular power distribution

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project12 LiCAS Survey Train FSI Laser Straightness Monitor Rails attach to tunnel wall Measures 3D position of accelerator wall reference markers Vacuum tube z x y Internal FSI+SM measures train’s internal positions

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project13 LiCAS Survey Train: 2D z x Tunnel Wall z y reference markers for accelerator (Ball-mounted retroreflectors) View from above Side on view

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project14 Survey Train Simulation Simulations of train performance using “SIMULGEO” Simulation includes whole system: Internal & External FSI + SM Studies have highlighted areas for improvements in the design Eg: Train sensitivity to rotation about z axis Consider addition of tilt sensors to cars and/or 2 rows of wall markers

14 November 2002The Linear Collider Alignment and Survey (LiCAS) Project15 Summary The LiCAS group has proposed an automated optical measurement system for the survey and alignment of any future Linear Collider The current design for TESLA alignment is under development at Oxford