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Summaries of the discussion

Summaries of the discussion. 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 pa ttern Up to 40 m with an iris of 3mm

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Summaries of the discussion

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  1. Summaries of the discussion D. Missiaen

  2. The iris diaphragm laser alignment system for Spring 8 storage ring magnets • Alignmultipoeson a commongirder 4-5 m • Laser beam as a reference, lccd,4 ccd cameras • Iris (circularloe) 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 othersopened • 10 microns at 2sigma • Reproducibilityof the diaphragmopening : 2-3 microns • Measurement for the 4 points in 30s, no long termstabilitypb

  3. a 500 m long laser based fiducial line at KEK • Laser is in a beam pipe below the girdersunder vacuum • Quadrant silicon photo diode (QPD) mounted in a subholder 10mm de diameter • Linked to the pipe by joinflanging, manuallymovablefromthebeam • 48 girders on 500m • Based on fresnellens • Laser installationrathersophisticatedat atmosphericenvironmentisolatedfrom the floor • Diameter of 30mm at the beginning of laser beam,21 mm at500 m • Stability0,1 mm during 8 hours at 500m • Errors0,1mm isgaranted by thismeasurements • Multipoints • Not radiation-hard

  4. 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. The SLRS poisson based alignment system at DESY • Accurary for initial alignmentis 0.3mm on 150 length • Relative alignmentafterbba • Principle : • Laser, achromaticlens, poisson points, achromaticlens , ccd • In vacuum • Permanent Relation betweenoutside and insideisdonethrough a flange, calibration donewith 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. 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. The lambda system at CERN • Laser beam, beamexpander • Camera and a shutter • Range between +-3mm • At short distance • Different types of shutter : papersheet,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. The laser alignment validation by system refered to gravity • How to determine the equipotential • Astrogravimetry : deflection of vertical withzenital camera and gravimmetry • At CERN, on 800m thereis a variation of 4mm due to the Jura • Locally on 200m, 10 to 20 microns accuracy, 10-7 • Geodeticdeflectometer at CERN • Interferometeris the straight line measuring angles • with respect to a clinometer • The differenceisgiving the variation of the deflection of vertical

  9. 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. Open questions • 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. Open questions • 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

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