The Laser Reference Line Method and its Comparison to a Total Station in an ATLAS like Configuration. JINR: V. Batusov, J. Budagov, M. Lyablin CERN: J-Ch. Gayde, B. Di Girolamo, D. Mergelkuhl, M. Nessi Presented by V. Batusov, M.Lyablin

Formulation of the ATLAS needs Beam-pipe at cavern end Beam-pipe Central part ATLAS Experimental Hall Base of the ATLAS Beam-pipe at cavern end Т BP 1 BP 2 Tasks that can be solved using the LRL :  - Metrological measurements in inaccessible conditions for existing methods  - On-line position control of ATLAS detector and subsistence in date taking period  - Connection of the on-line coordinate systems of the LHC and detectors in date taking period

Laser Reference Line: Operation and Design General design Laser beam The center of angular positionerО 1 The end pointО 2 of the laser reference line - the center of the quadrant photoreceiver QPr 2 Laser in the angular positioner β A Measured object - В Position of the measuring quadrant photoreceiverQPr 1 О1О1 О2О2 Φ Θ О3О3 Laser reference line includes as a “key points”: Starting point O1 Endpoint O2 Measuring point O3

Pipe adjustment – use parts of pipes for combining of the laser and total station measurements BP1,BP2-parts of pipes to install the laser and quadrant photodetector T-measurement pipe XYZ-global coordinate system Laser with angular positioner T Laser beam Collimator Final QPr 2 with adapter А 2 adapter А 1 with QPr 1 AdapterАwith total station target BP 1 BP 2 Measuring stations in global coordinate system Y Z X

LFL adjustment of the pipe For measurements of the coordinates of the centers of ends of the measured pipe T one use a local coordinate system X’Y’Z’ Part of the beam-pipe mock-up for the adjusting QPr 1 with adapter А 1 BP 2 Laser beam Final QPr 2 with adapter А 2 Laser with angular positioner Z´ X´ Y´ T BP 1

Joint LFL and Total Station measurement procedure Basic scheme The measurement stations– global coordinate system B A Laser beam Y Z X Laser The quadrant photoreceiver QPr 1 with adapterA 2 The Total Station target with adapter A 1 D C В2В2 В1В1 Т 2D – linear positioner Т1Т1 Т2Т2 O X’ Z’ Y’ we used universal adapters A 1 and A 2 for the points A, B, B 1 and B 2 measurements in the LFL we aligned the endpoint B of the LFL with 2D – linear positioner

Local coordinate system in the joint measurements of the laser and Total Station measurement systems measurements were made at 16m distance from the laser length of the laser reference line was ~50m T QPr with adapter Y’Y’ A B1B1 B2B2 B Z’Z’ X’X’ T1T1 16m 49.6m T2T2

LRL measurement procedure offsets of total station target and of quadrant photodetector in the adapters has coincided D QPr with adapter А 1 D Measuring tube T Base tube BP 1 or BP 2 D Laser ray D Total station target with adapter A

Dimensionless values S up, S down, S left, S right, used in the construction of calibration curves Quadrant detector was installed in the same position relative to the gravity vector The laser ray multimeters QPr displacement of QPrin steps of 50 ± 3µm precision positioner in four directions U1U1 U2U2 U3U3 U4U4 QPr1 Gravity vector QPr3 QPr2 QPr4 U 1, U 2, U 3, U 4 - signal from photodiodes U= U 1 + U 2 + U 3 + U 4 Laser measurements calibration

calibration curves were determined in 4 directions- Up, Down, Left, Right then they were paired into the Horizontal and Vertical directions Laser measurements calibration

An averaged calibration curve was used for the measurements of the positions of the centers of the ends of measured tube T Laser measurements calibration

The following sources influence on the LRL measurement accuracy: Inaccurate mechanical setting of the laser beam reference points with respect to the ends of the reference pipes. Fluctuation of refractive index of the air in which the laser beam propagates. Distortion of the laser beam shape by the collimation system. Accuracy of the calibration measurement system. Perpendicularity of the QPr with respect to the laser beam during the measurement. LFL measurement precision

By using of the calibration curve the values d z, d x were determined This values are the coordinates of the center B of the end of the pipe measured in the local coordinate system X ’, Z ’ Determination of the coordinates of the pipe ends using the averaged calibration curve В X´ Z’Z’ d X´ d Z´ QPr Laser beam spot 2D coordinate system:X´,Z´

Total Station– LRL difference Δ Set 1Set 3Set 2 Pipe end centers B1B1 B2B2 B1B1 B2B2 B1B1 B2B2 Horizontal (mm) −0.07− Vertical (mm)−0.13−0.11−0.07−0.15−0.41−0.35 Comparison of the Laser and Total Station measurements Two series of measurements (Set 1, Set 3) have been available in which the position of the pipe T relative to the LRL has been chosen to be misaligned by d ≤ 0.5 mm corresponding to the linear portion of the calibration curve and one series of measurements (Set 2) with d ≥ 0.5 mm In the Set 1 and Set 3 data the average difference is = −0.07 mm with a spread of individual differences in the interval from −0.15 to 0.06 mm (σ=0.08mm) In the Set 2 data the values are = 0.24 mm with a spread of individual differences in the interval from −0.41 to 0.37 mm (σ=0.38mm)

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 middle of a 50m line. The test shows that the proposed LRL system is a promising method for the on-line positioningand monitoring of 2D coordinates of fiducial marks. It could be used for highly precise alignment of equipments linearly distributed. The tested system could be improved using the innovative laser-based metrological techniques that employ the phenomena of increased stability of the laser beam position in the air when it propagates in a pipe as it works as a three-dimensional acoustic resonator with standing sound waves could be integrated in the setup. This property is the physical basis for the development of a measurement technique with a significant gain in attainable accuracy. Conclusion