The LiCAS project has developed a prototype robotic survey system for rapid and highly accurate surveying of long linear accelerator tunnel networks. It is aimed at the International Linear Collider (ILC). This Rapid Tunnel Reference Surveyor (RTRS) is an RandD instrument for evaluating the performance of the RTRS concept and its survey technology. The prototype has been commissioned in a test tunnel at DESY with initial calibrations and measurements ongoing. We will report recent results where they improve over previously reported work

Brockill, P

Cohen, S

Dale, J

Dawson, M

Estrada, CU

Grzelak, G

Handford, T

Jones, M

Moss, G

Prenting, J

Rainbow, LA

Reichold, A

Schlösser, M

Tacon, M

Urner, D

Wastie, R

Yang, S

Dawson, Mike

Yang, Stephanie

Oxford University Research Archive

First data from the linear collider alignment and survey project (LiCAS)

The LiCAS project has developed a prototype robotic survey system for rapid and highly accurate surveying of long linear accelerator tunnel networks. It is aimed at the International Linear Collider (ILC). This Rapid Tunnel Reference Surveyor (RTRS) is an R&D; instrument for evaluating the performance of the RTRS concept and its survey technology. The prototype has been commissioned in a test tunnel at DESY with initial calibrations and measurements ongoing. We will report recent results where they improve over previously reported work

Reichold, Armin

Brockill, Patrick

Cohen, Sigal

Dale, John

Handford, Tony

Jones, Mark

Moss, Gregory

Rainbow, Lee

Tacon, Michael

Uribe Estrada, Cecilia

Urner, David

Wastie, Roy

FIRST DATA FROM THE LINEAR COLLIDER ALIGNMENT ANDSURVEY PROJECT (LiCAS) ∗Armin Reichold, Patrick Brockill, Sigal Cohen, John Dale, Mike Dawson, Tony HandfordMark Jones, Gregory Moss, Lee Anthony Rainbow, Michael Tacon, Cecilia Uribe EstradaDavid Urner, Roy Wastie, Stephanie Yang:John Adams Institute for Accelerator Physics, University of Oxford, UKJohannes Prenting, Markus Schlösser: DESY, Hamburg, GermanyGrzegorz Grzelak: University of Warsaw, Warsaw, PolandAbstractThe LiCAS project has developed a prototype roboticsurvey system for rapid and highly accurate surveying oflong linear accelerator tunnel networks. It is aimed atthe International Linear Collider (ILC). This Rapid Tun-nel Reference Surveyor (RTRS) is an R&D instrument forevaluating the performance of the RTRS concept and itssurvey technology. The prototype has been commissionedin a test tunnel at DESY with initial calibrations and mea-surements ongoing. We will report recent results wherethey improve over previously reported work.INTRODUCTIONThe International Linear Collider (ILC) is an e+e−-collider aiming to achieve a luminosity of 2 ×1034cm−2s−1. The necessary ultra low emittance of 30nmrad can only be maintained throughout its 100km ofbeam line if all elements are accurately aligned. In themain linacs the required reference network survey accuracystands at 200 (500) µm in the vertical (horizontal) directionover distances of 600m. The dependence of the emittanceon the details of the alignment process is very complex andstill subject of current research [1].The high sensitivity to misalignments demands frequentrealignment. This mandates a rapid and preferentiallyrobotic survey system [3] to keep the costs of machinedown-time and manpower at an acceptable level [2]. TheLiCAS project addresses the most challenging problem ofthe long distance reference survey. The functional princi-ples, measurement technology and co-ordinate system con-vention of the LiCAS RTRS have been described earlier in[6]. Figure 1 shows a photograph of the prototype RTRS inthe test tunnel at DESY.MEASUREMENT PERFORMANCELaser Straightness Monitors (LSM)A detailed description of the LSM system can be foundin [4]. The LSM beams are detected by analogue CCDcameras with pixel size of 8.6 (hor.) × 8.3 (vert.) µm2 and∗Work supported by STFC in the LC-ABD collaboration and by theCommission of the European Communities under the 6th Framework Pro-gramme Structuring the European Research Area, contract number RIDS-011899.Figure 1: The prototype RTRS after commissioning in theDESY test tunnel (Jan. 2008). The electronics crates inthe service cars have temporarily been supported by metalbricks during an analysis of vibration sources.760(hor.) × 572 (vert.) pixels, running asynchronously at25 frames per second (fps). The frames are digitised by afour channel pci-x frame grabber card.For image analysis we apply a low-pass Butterworth fil-ter to the Fourier-transformed image to remove effects fromdust. This takes 1 second per image. We have evalu-ated two beam fitting procedures. The simple fit fits a 1-DGaussian to the vertical and horizontal image projectionsand takes 0.2 seconds. Because the CCD cameras weaklyreflect, some cameras detect reflections from their oppo-site camera (ghosts). Therefore we fit multiple 2-D Gaus-sians to these image, identifying the primary via its smallerwidth. This takes approximately three minutes.Analysis of 9000 images taken at 25 fps revealed broadand slowly moving vertical bands of 0.1% of normal beamintensities. These are caused by interference betweenframe grabber channels. The interference patterns slowlymove due to the asynchronicity of the cameras. This leadsTUPC118 Proceedings of EPAC08, Genoa, Italy06 Instrumentation, Controls, Feedback & Operational Aspects1344T17 Alignment and SurveyFigure 2: Horizontal beam position versus time before av-eraging (simple fits).Figure 3: RMS of horizontal beam position vs. averagingwindow size. Averages of 40 (20) simple fits shown in dot-ted red (solid black).to oscillatory shifts of the fitted horizontal beam positionsof up to 10 µm as shown in figure 2.Two techniques for removing these were evaluated.Firstly the averaging of multiple fits and secondly fitting anaveraged image. Figure 3 shows how the former technique,using simple fits, reduces the RMS noise for averages of20 (40) fits as a function of the period over which imageswere taken. Averaging 20 simple fits taken over 20 secondsreduced the RMS below 200 nm.Figure 4 shows how the vertical (horizontal) RMS variesfor different analyses. Here we average 40 images over aperiod of 117 s. The data spans 13 hours.Frequency Scanning Interferometry (FSI)A detailed description of the FSI system can be foundin [5]. FSI measures the length ratio of an unknown inter-ferometer to a reference interferometer. Therefore accuratecalibration of the reference interferometers length Lref isessential. To do this, a computer controlled linear stagemoves a pair of back-to-back retro reflectors over a dis-tance of two meters. An FSI interferometer measures thedistance from one end of the stage to the nearest reflectors.A laser tracker anti-co-linearly measures the distance fromthe other end to the other reflector. Figure 5 shows a linearfit to the length change measured by the laser tracker versusthe FSI length ratio. The slope of this fit determines Lrefto an accuracy of 0.6 µm (0.19 ppm). The perpendicularresiduals have an RMS of 0.4 µm.AllImagesSimpleEntries  16000Mean      169RMS    0.6689m)μCorrected Y Mean Difference (164 166 168 170 172 1740102030405060708090AveragedImageFullEntries  400Mean   169.96RMS    0.12451AveragedImageSimpleEntries  400Mean   168.98RMS    0.20092SimpleFitsAveragedEntries  400Mean   168.95RMS    0.20093Fitting Precision Comparison for Y Mean Fittinga)b)c)d)AllImagesSimpleEntries  16000Mean    237.7RMS      1.26m)μCorrected X Mean Difference (232 234 236 238 240 24201020304050 AveragedImageFullEntries  400Mean    240.36RMS    0.28768AveragedImageSimpleEntries  400Mean    237.55RMS    0.40885SimpleFitsAveragedEntries  400Mean    237.68RMS    0.40939Fitting Precision Comparison for X Mean Fittinga)c)b)d)Figure 4: Histograms of vertical (bottom) and horizontal(top) image position for: (a) simple fits, (b) averaged sim-ple fits, (c) simple fitted averaged images and (d) 2D fittedaveraged imagesFigure 6 shows histograms of the the changes of lengthsmeasured by the evacuated internal FSI system over a pe-riod of 14 hours. Resolutions of 45nm have been achieved.CALIBRATIONTo calibrate an RTRS car approximately 150 internal pa-rameters, such as positions and orientations of CCDs or in-terferometer components must be determined. To this endwe have developed a Gauss Markov model of the calibra-tion process in which a laser tracker witnesses a set of 50moves (small translations and rotations) of the car undercalibration while the RTRS measures all its sensors. Weuse an iterative least squares procedure to find those inter-nal parameters that best reproduce the laser tracker obser-vations [7] [8]. Neighbouring cars and the LSM beam areassumed to be stationary during calibration.The design matrix A for this model has 2320 rows and447 columns. Each row represents a measured value, eachcolumn an unknown internal parameter. The latter not onlyinclude the original 150 internal parameters, but also thetranslations and rotations for the 50 moves, as well as someconstraint equations.This problem is well-determined and the solution con-Proceedings of EPAC08, Genoa, Italy TUPC11806 Instrumentation, Controls, Feedback & Operational Aspects T17 Alignment and Survey1345Figure 5: Linear fit to laser tracker lengths vs. FSI length-ratio (top) and histogram of the perpendicular residualsFigure 6: Histograms of the length changes of the 4.5mlong internal FSI lines over a 14h periodverges. A simulated calibration is shown in figure 7. Thetrue component positions are depicted in orange, and as-sumed initial positions in gray. After several iterations, thecomponents converge to their true values, as shown in thelower half of figure 7. Two sets of experimental calibrationdata are currently being processed. We expect to be able topublish these results shortly.REFERENCES[1] Simulation Studies of Correlated Misalignment in the ILCMain Linac and the Influence of Ground Motion, FreddyPoirier, Dirk Kruecker, Isabell Melzer-Pellmann, NicholasJohn Walker, DESY, Hamburg, Germany. Proceedings ofthe 11th biennial European Particle Accelerator Conference,Genoa, Italy, 23-27 June 2008Figure 7: True (grey), initial (orange top) final (orange bot-tom) positions of components during calibration[2] The LiCAS-RTRS – A Rapid and Cost Efficient SurveySystem for the ILCA. Reichold for the LiCAS collaboration, Slide 27–29 ofpresentation, see # belowhttp://www.slac.stanford.edu/econf/C06092511/presents/WE008 PPT.PDF[3] The LiCAS Rapid Tunnel Reference Surveyor - The Statusafter CommissioningA. Reichold for the LiCAS collaboration, see # below[4] First measurements from the Laser Straightness Monitor ofthe LiCAS Rapid Tunnel Reference SurveyorGregory Moss for the LiCAS collaboration, see # below[5] Initial Calibration and Stability Results from the LiCASRTRS FSI SystemJohn Dale for the LiCAS collaboration,# Proceedings of the 10th International Workshop on Ac-celerator Alignment, February 11-15, 2008 KEK, Tsukuba,Japan[6] THE LICAS-RTRS - A SURVEY SYSTEM FOR THE ILCA. Reichold for the LiCAS collaboration,Proceedings of the 10th biennial European Particle Acceler-ator Conference, Edinburgh, UK 26-30 June 2006http://cern.ch/AccelConf/e06/PAPERS/MOPCH195.PDF[7] The Method of Least Squares, D.E. Wells and Ed-ward J. Krakiwsky, University of New Brunswick, 1971,http://gge.unb.ca/Pubs/LectureNotes.html[8] Geodätische Netze in Landes- und Ingenieurvermessung II:p76–120, Prof. Dr.-Ing. Hans Pelzer, published by KonradWittwer, Stuttgart Germany, 1985, ISBN 3-87919-140-9TUPC118 Proceedings of EPAC08, Genoa, Italy06 Instrumentation, Controls, Feedback & Operational Aspects1346T17 Alignment and Survey

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First data from the linear collider alignment and survey project (LiCAS)

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