1. D. Missiaen Summaries of the discussion

2. 2 H. Mainaud Durand The iris diaphragm laser alignment system for Spring 8 storage ring magnets Align multipoes on a common girder 4-5 m Laser beam as a reference, lccd,4 ccd cameras Iris (circular loe) Gives an iris pattern Up to 40 m with an iris of 3mm Laser beam 4.5-6 mm diameter Multipoints system with 4 measurements points with an iris one closed and the others opened 10 microns at 2sigma Reproducibility of the diaphragm opening : 2-3 microns Measurement for the 4 points in 30s, no long term stability pb

3. 3 H. Mainaud Durand a 500 m long laser based fiducial line at KEK Laser is in a beam pipe below the girders under vacuum Quadrant silicon photo diode (QPD) mounted in a sub holder 10mm de diameter Linked to the pipe by join flanging, manually movable from thebeam 48 girders on 500m Based on fresnel lens Laser installation rather sophisticated at atmospheric environment isolated from the floor Diameter of 30mm at the beginning of laser beam, 21 mm at500 m Stability0,1 mm during 8 hours at 500m Errors 0,1mm is garanted by this measurements Multipoints Not radiation-hard

4. 4 H. Mainaud Durand The Laser Beam Fiducial Line Application by JINR Dubna Laser in an air filled pipe with acoustic waves Station laser, collimator End point Measurement point Equipped with 2 parallel plates not to destroy the reference laser line. It is an idea At 150m, it can go up to 2km because of the size of the laser Multipoints. Yes Geodetic refraction bends the beam because you are not in vacuum,1/10 of the geodetic curvature Possibility to adjust the QPD in the center of the laser beam with adjustment screws

5. 5 H. Mainaud Durand The SLRS poisson based alignment system at DESY Accurary for initial alignment is 0.3mm on 150 length Relative alignment after bba Principle : Laser, achromatic lens, poisson points, achromatic lens, ccd In vacuum Permanent Relation between outside and inside is done through a flange, calibration done with laser tracker Detections of translation 25 microns in y and 50 microns y (vertical) Test avec 4 targets : 2 fixed and 2 variables Estimated achivable accuracies 0.1-0.2mm 16 spheres Vacuum 10-2mbar

6. 6 H. Mainaud Durand The superweak angular groud motion : search and registration Liquid surface, laser, QPD Demultiplication of the angles with semi-transparaent lenses And reflexions on the water Resolution in the range of 5.10-9 rad Earth surface oscillation Slope And a hole for the minutes echantillons Microseismicpeak observation : vibration 2 microrad 0.1 microrad industrial noise Long base experimental proposal to align/stabilize linear collider System installed at CERN

7. 7 H. Mainaud Durand The lambda system at CERN Laser beam, beam expander Camera and a shutter Range between +-3mm At short distance Different types of shutter : paper sheet,aluminium no very good results, ceramic plate, 20 microns At long distance at 4*50m in CERN calibration base To check the size of the beam Stability ???

8. 8 H. Mainaud Durand The laser alignment validation by system refered to gravity How to determine the equipotential Astrogravimetry : deflection of vertical with zenital camera and gravimmetry At CERN, on 800m there is a variation of 4mm due to the Jura Locally on 200m, 10 to 20 microns accuracy, 10-7 Geodetic deflectometer at CERN Interferometer is the straight line measuring angles with respect to a clinometer The difference is giving the variation of the deflection of vertical

9. 9 H. Mainaud Durand Laser reference line mehod and comparison to a total station Following of the presentation of ML (JINR) At the request of Atlas people, a comparison was organised Difference up to 80 microns Much worse in V than H Is it due to the laser or to the Total station ??

10. 10 Open questions H. Mainaud Durand The laser beam as a reference line diameter of the beam w.r.t length, optimal laser wavelength HeNE, Beam expanders, CERN achromatic lenses, DESY 20-30 mm size over 500m seems achievable KEK stability of the beam, stability of the laser source At short distance, quick measurement, not really a pb SPRING8 At long distance, not so clear Lambda CERN Stability0,1 mm during 8 hours at 500m Possibility to measure angles up to 5.10-9 (JINR) is vacuum needed? Over which distances? Which vacuum? Other solutions: helium? In a beam pipe JINR In vacuum DESY (10-2) and KEK, CERN in the future Yes to avoid environmental effects and geodetic refraction Impact of temperature, humidity and other parameters Not really mentionned How to be sure of the straightness of the beam? not addressed Additional instruments used such as beam expander, lens, diaphragm? Proposal to add two parallel plates to be tested JINR not to destroy the beam laser straightness

11. 11 Open questions H. Mainaud Durand Which type of sensor? Iris diaphragm (spring8), optical shutter (CERN) : no need to remove it from the beam QPD (JINR.,KEK), Balls, spheres (DESY) Impact of the diameter of the beam / longitudinal distance / shape of the laser spot Beam diameter bigger than QCD How to attach a sensor to a component, and measure w.r.t. a laser beam under vacuum? How to transfer the position of the laser beam outside the vacuum pipe without any constraints? Through a flange : DESY, Removable from the beam system manually : KEK Direct link for Spring8 Rad hard sensors Not really adressed N sensors along the beam line, with N > 200 16 max for DESY, some limitations for Spring8, lambda (???), kek (48 at least) Algorithm for image processing? Software used? Number of measurements to determine beam position? Not really adressed Sensor size / weight / resistance to vacuum, radiations / price Not really adressed