GUILLAUME STERN

Summary and conclusions of the mini workshop

on laser based alignment systems

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OUTLINE

Overview of the workshop

Presentations given during the workshop

Conclusion

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Introduction

G. Stern

CLIC project has very tight tolerances for the alignment of beam-related 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

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Workshop goals

G. Stern

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

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Workshop organisation

G. Stern

Participants (around 25 persons) CERN DESY (Germany) KEK (Japan) SPring 8 (Japan) JINR (Russia) ETHZ (Switzerland) Agilent (Switzerland)

Program Thursday 30th: Introduction + presentations Friday 31st: Visit on CERN site + brainstorming +

conclusion

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Presentation: Chao Zhang, Developing an Iris Diaphragm Laser Alignment System for Spring 8 Storage Ring Magnets

G. Stern

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

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Presentation: Mikhail Lyablin, A Laser Based Fiducial Line For High-Precision Multipoint Alignment System

G. Stern

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

QPre

Ae

Ab

Laser spot

Laser

Collimator

Tube with atmospheric air

Transparent windows

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Presentation: Tsuyoshi Suwada, Propagation and Stability Characteristics of a 500m Long Laser Based Fiducial Line For High-Precision Alignment of Long Distance Linear Accelerators

G. Stern

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

130mmϕ

QPD sensorQPD sub-holder

stopper

QPD holdersignal pick-up

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Presentation: Johannes Prenting, Status Report on the laser based Straight Line Reference System at DESY

G. Stern

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

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Presentation: Mikhail Lyablin, The Search For And Registration of the Superweak Angular Ground Motions

G. Stern

Principle: observing laser spot with quadrant photoreceiver (QPR) after reflection on water surface Resolution: 5 nrad

θ

ψ

LaserQPR

Original direction of the reflected beam

BaseCuvette with a liquid The surface of the liquidin case of horizontal basis The surface of the liquid

with tilt base

Directionthe reflected beamafter tilt base

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Presentation: Guillaume Stern, Laser Alignment Multipoint Based – Design Approach (LAMBDA project)

G. Stern

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

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Presentation: Sébastien Guillaume, Validation of Laser Alignment Systems by Systems Referred to Gravity

G. Stern

Many alignment systems refer to gravity (e.g. Hydrostatic Levelling Systems) PhD 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

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Conclusion

G. Stern

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