JINR: V. Batusov , J. Budagov , M. Lyablin , G. Shirkov

1. Precision laser metrology for the modern Accelerators JINR: V. Batusov, J. Budagov, M. Lyablin, G. Shirkov CERN:J-Ch. Gayde, B. Di Girolamo, H. Mainaud Durand,D.Mergelkuhl, M. Nessi, G. Stern Presented by M. Lyablin

2. Precision Laser Fiducial line in air Introduction • The next generation of linear colliders is very demanding concerning the alignment tolerances of their components. For the CLIC project, the reference axis of the components will have to be pre-aligned within 10 µm at 1 sigma with respect to a straight line in a sliding window of 200 m • A new proposal is using a laser beam over 150 m as a straight alignment reference. • The method is based on the laser beam space stabilization effect when a beam propagates in atmospheric air inside a pipe with standing acoustic wave.

3. Observation of the effect of the stabilization of the laser ray space location inside the tube with the standing acoustic waves Demonstration to the CERN delegation (R.Cashmore at all) of the laser ray stabilization effect inside the tube. This photo was made during the period of high precision laser controlled assembly in Dubna of the MODULES of ATLAS TAIL Hadron Calorimeter. Our experimental R&D’s have shown that independent of direct sun rays and of an air heat fluxes we found as a very significance by an order of magnitude- decrease of the laser beam space noise oscillation.

4. σT(μ) R=σA(μ)/ σT(μ) We found that the laser beam space uncertainty is strongly decreased upon ray exit of a tube with the STANDING ACOUSTIC WAVES in an atmospheric air inside.The left Figure is theσT uncertainty for the “case with the tube“.The right Figure is the R= σA/ σT ratio with σA for “no tube ” case.The factor R≈120xgain is an impressive result we observed for 70 m tube. We propose to use as an EXTENDED COORDINATE AXIS the low σTlaser beam obtained on the base of above described new effect.

5. QPre δ Ab Ae Laser Am QPrm Colimator Laser spot Laser Fiducial line: operation and design The Laser Fiducial Line (LFL) measuring system uses a laser beam as the reference of alignment, with its beginning and end points Ab and Ae determined in the global reference frame of the tunnel.

6. Angular positioner Laserbeam Opticalfiber Support Collimator Laser Concretebasis Final QPR Two-axis linear positioner Ae Laser beam Support Concrete basis • Beginningand end points of the Laser Fiducial Line The fiber-optic input of the laser radiation into the LFL 2-axis positioners are needed for precise alignment center of the quadrant photodetector with the laser beam axis

7. Measuring QPR • Spacestabilizedlaserbeam (fiducial line) Two-axislinearpositioners Plane-parallelplate(PP) Measuredpoint-O • Measuringstationwith measurdpoint-O Intermediate points of measurements Not destroying control system position measured point O

8. Thermostabilizedairflux Laserbeam Tube Laserbeam Systemofshort-termstabilization Transparentglass Outertubewithaheatinsulationcoating Thermal stability of the laser ray position We use effect of laser beam stabilization when it propagates inside an atmospheric air filled pipe with standing acoustic waves The short term laser ray stabilization scheme Two tubes set was used. Between tubes the termostabilised air flux is propagating Long term stability system With allowed few microns for the laser ray displacement from primary direction the long-term temperature stabilization is to be in the level of 0.5 0C

9. Zmax Zmax Laserbeamdiameter(mm) √2 D0=Dmax D0 Lk(m) Theprofileofcollimatedlaserbeam Thetelescopiccollimator Optimal collimation laser beam √2 D0 The laser beam profile with optimal collimation (A) (B) The collimation length Lkof single mode laser beam in function of beam starting diameter: (A) for D by 10mm ;(B) for D by 50 mm

10. Including of the Laser Fiducial Line to the global coordinate system; the LFL precision control by Total Station in an open air media The Total Station target with adapter A1 2D – linear positioner Z’ Т Т1 X’ B Т2 A Y’ В1 Laser beam В2 Laser Z The quadrant photoreceiver QPr1 with adapterA2 O Y X C D The measurement stations– global coordinate system For the 50m laser line an Total Station measurements the difference was nearly100μmfor 16 meters length

11. Original direction of the reflected beam QPR Direction of the reflected beam after tilt of base Laser θ ψ Base The surface of the liquid in case of horizontal basis Cuvette with a liquid The surface of the liquid with tilt base Angular seismic stabilization by the precision INCLINOMETER Main principle : use reflected laser beam from horizontal surface liquid The principle of construction of the registration device to measure the seismic slope of the Earth’s surface.

12. 50 cm QPr SM CF L О1 50 cm О Sensor S C О2 The experimental set-up • L-laser • QPr-quadrant photodiode • O,O1,O2- bases • SM-semitransparent mirror • C-calibration screw • CF- collimator with • changeable focus • frequency internal of 10-4Hz÷1Hz • The achieved inclinometer angular precision is 5 10-9 rad

13. The inclinometer tests • The Earth quake in Siberia on February 26, 2011 • Average amplitude of quake in Siberia was 6.5 units • The distance to Geneva- L=6160km • Calculated time of Earth quake begin • Tcalc=6h 21 min in Siberia (world time) • practically coincides with the published Tpub=6h 17min • Amplitude of angular oscillations was 2 10-6 rad The angular component of the Earth quake • The observation of an earth surface • “single inclination” effect • Amplitude was a few μrad Earth surface single oscillation

14. Earth angular surface oscillations of an industrial noise origin Industrial origin noise: -high activity of auto– traffic, -works in the neighboring (with our set-up) Lab room, -people movement close to detecting set-up etc. σ values : -in work period(CD) 0.3 μrad -In dinner time(AB) 0.04 μrad The day measurement angular movement of the concrete floor • Concrete floor inclination due • to man presence in 3 meters distance • from the experimental set-up • Amplitude was 0.3μrad The measured inclination of the concrete floor

15. The microseismic peak observation by ground angular motion • The seismogram of an earth surface angular oscillation • at the “microseismic peak” frequency Amplitude of Earth surface oscillation at the “microseismic peak” frequency was 0.03μrad with frequency fd=0.13Hz. Inclinometer sensitivity estimate gives ≈5·10-9 rad. Fourier analyses of oscillation at the “microseismic peak

16. Experimental Hall Linear accelerator-collider Line of horizon θmp θmp The Earth surface fixed time picture: surface deformation induced by the standing waves originated by the interference of “microseicmic peak” The long experimental setups space location stability and an earth surface angular oscillations The accelerator-collider positioning on the earth surface deformed by the microseismic peak wave Different accelerator parts are inclined relative to the ”basic” horizontal line and consequently particle beams going through the focusing elements leave them with some angular spread θmp relative to the nominal. As a result it leads to random motion of position of focuses accelerators If we can stabilize the angular movements of the accelerator with an accuracy of 10-9rad we will be able to stabilize position of its focuses to within 50 nm

17. As a summary, different technical issues of a 150 m and accuracy 10μm LFL in atmospheric air were discussed, showing that the combination of: • Single mode laser associated with a fiber beam coupler • for the light emitting point • An optimal laser ray focusing collimation • An intermediate sensor having no impact on the straightness of the beam • The calibration of each sensor • The suppression of air media refraction index and long term • variation of temperature • The isolation of the laser source from angular seismic industrial noise • can lead to an alignment system providing the location of points within 10µm. • Such an alignment system opens new perspectives • to reach a new precision level of alignment for projects like CLIC, ILC. Conclusion • An original method for precision measurements when alignment of beam pipe ends on a reference axis has been proposed and tested. The test measurements have been performed using jointly the LRL in a 2D local coordinate system and a Total Station survey instrument in a global 3D coordinate system. The fiducial marks at the pipe ends have been measured with both instrumentations. A transformation to a common coordinate system has been applied to allow the comparison of the results. • The results of the measurements coincide to an accuracy of approximately ±100 µm in the directions perpendicular to a common reference line close to the laser beam and for a pipe placed at the middle of a50mline.

18. Conclusion • The ground motion was studied by the detection of an earth surface angular oscillation. Instrumentally method is based on the conceptually new design laser inclinometer using the reflecting surface liquid, as a space stable (horizontal) reference level. The achieved inclinometer measurement precision was experimentally proved to be ≈5·10-9 rad. • The achieved laser inclinometer sensitivity was proved by observation (in Geneva) of: • Ground 2µrad oscillation caused by the Siberian earth quake (6160 km); • Single 1÷2 µradoscillation of origin to be studied; • Industrial origin noise of about 310-7 rad amplitude; • Microseismic peak for the first time recognized as a ground ≈3 10-8rad angular oscillation at 0.13Hz frequency. • The last observed effect if properly “compensated” by adequate instrumental method could give significant colliders luminosity increase by reduction of beams intersection area to about 50nm level (an estimate) due to some suppression of the lateral focus effect. • The instrument of this sort may happen to be useful for modern high precision research equipment stabilization, for example, of large telescope to reach an extreme resolution.