Summary and conclusions of the mini workshop on

Summary and conclusions of the mini workshop on laser based alignment systems GUILLAUME STERN

OUTLINE ü Overview of the workshop ü Presentations given during the workshop ü Conclusion 2

Introduction § CLIC project has very tight tolerances for the alignment of beamrelated components § Requirement: 10 μm (at 1 σ) over a sliding window of 200 m § Solution based on stretched wires has some drawbacks (difficult implementation, cost) § Idea: replace stretched wire by laser beam 3 G. Stern

Workshop goals § Many institutes throughout the world work on laser based alignment systems § Workshop goals § Reviewing existing systems § Sharing experience, problems § Talking about on-going developments, perspectives § Improving collaboration between institutes 4 G. Stern

Workshop organisation § Participants (around 25 persons) § CERN § DESY (Germany) § KEK (Japan) § SPring 8 (Japan) § JINR (Russia) § ETHZ (Switzerland) § Agilent (Switzerland) § Program § Thursday 30 th: Introduction + presentations § Friday 31 st: Visit on CERN site + brainstorming + conclusion 5 G. Stern

Presentation: Chao Zhang, Developing an Iris Diaphragm Laser Alignment System for Spring 8 Storage Ring Magnets § Principle: observing diffraction pattern of an iris § Goal: accuracy of 10 μm (at 2σ) over 10 m § Already achieved: pointing stability of 8 μm (at 2σ) over 10 m 6 G. Stern

Presentation: Mikhail Lyablin, A Laser Based Fiducial Line For High. Precision Multipoint Alignment System § Principle: observing laser spot when laser beam propagates in a tube with atmospheric air § Goal: accuracy of 10 μm (at 1 σ) over a sliding window of 200 m § Already achieved: pointing stability of 1. 5 μm (at 1σ) over 70 m Tube with atmospheric air Ab QPre Ae Laser Collimator Transparent windows 7 Laser spot G. Stern

Presentation: Tsuyoshi Suwada, Propagation and Stability Characteristics of a 500 m Long Laser Based Fiducial Line For High-Precision Alignment of Long Distance Linear Accelerators § Principle: observing laser spot with quadrant photodectectors (QPD) that are mechanically switched across the laser beam propagating in vacuum pipe § Goal: accuracy of 100 μm (at 1σ) over 500 m § Already achieved: pointing stability of 40 μm, estimated accuracy of 100 μm (at 1σ) over 500 m stopper QPD sub-holder QPD sensor 130 mmϕ signal pick-up 8 QPD holder G. Stern

Presentation: Johannes Prenting, Status Report on the laser based Straight Line Reference System at DESY § Principle: observing diffraction pattern of spheres § Goal: accuracy of 300 μm (at 1σ) over 150 m § Estimated achievable accuracy: 100/200μm (at 1σ) over 150 m 9 G. Stern

Presentation: Mikhail Lyablin, The Search For And Registration of the Superweak Angular Ground Motions § Principle: observing laser spot with quadrant photoreceiver (QPR) after reflection on water surface § Resolution: 5 nrad Laser Direction the reflected beam after tilt base Original direction of the reflected beam QPR θ ψ Cuvette with a liquid 10 Base The surface of the liquid in case of horizontal basis The surface of the liquid with tilt base G. Stern

Presentation: Guillaume Stern, Laser Alignment Multipoint Based – Design Approach (LAMBDA project) § Principle: observing laser spot with camera/shutter assemblies that are mechanically switched across the laser beam § Goal: accuracy of 10μm (at 1σ) over 200 m § Already achieved: pointing stability of 10μm (at 1σ) over 3 m 11 G. Stern

Presentation: Sébastien Guillaume, Validation of Laser Alignment Systems by Systems Referred to Gravity § Many alignment systems refer to gravity (e. g. Hydrostatic Levelling Systems) § Ph. D thesis: determining the equipotential of gravity with respect to a straight line (part of the work: development of the deflectometer) § Possibility of performing inter-comparison between different alignment systems 12 G. Stern

Conclusion § Two very intense days § Many institutes working on laser based alignment systems, though each of them with a different approach § So far, no institute has been able to meet CLIC requirements in terms of accuracy or resistance to radiation § Brainstorming highlighted following aspects § Necessity to work under vacuum § Quality of laser beam profile very important to guarantee a straight reference § Validation of the beam straightness through dedicated benches and through inter-comparison with other alignment systems § Collaborations for future work 13 G. Stern