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VISA Fiducialization and Alignment

VISA Fiducialization and Alignment. R. Ruland, B. Fuss, Z. Wolf, D. Arnett, G. Bowden, R. Carr, B. Dix and C. Le Cocq, SLAC G. Rakowsky, J. Aspenleiter, J. Skaritka BNL. Presented by Brian Fuss. Tasks. Fiducialization Relate fiducials to magnetic centerline Alignment

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VISA Fiducialization and Alignment

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  1. VISAFiducialization and Alignment R. Ruland, B. Fuss, Z. Wolf, D. Arnett, G. Bowden, R. Carr, B. Dix and C. LeCocq, SLAC G. Rakowsky, J. Aspenleiter, J. Skaritka BNL Presented by Brian Fuss

  2. Tasks • Fiducialization Relate fiducials to magnetic centerline • Alignment Position undulator magnets with respect to each other • Reference Laser Beam Setup RLB with respect to undulator position

  3. First Task Fiducialization Relate fiducials to magnetic centerline

  4. Fiducialization Procedural Steps • Position wire to represent magnetic centerline • Detect wire with Wire Finders and reference wire position to mechanical fiducials (metric measurement) • Measure WF and undulator fiducials with respect to straight line using SI (relative measurements) • Calculate undulator fiducial offsets using a similarity transformation • Repeat above steps with undulators rolled in 90° increments • Check closure

  5. Fiducialization: Step 2Wire Finder Design A PSD detects light from a laser diode which is aperture limited by a slit. Slit width is a fraction of wire diameter. Detector assembly scans across wire. PSD response clearly indicates wire edges.

  6. Fiducialization: Step 2 Wire Finder Measurements • Measuring wire position • Detector assembly is driven across wire profile. Micrometer readings are recorded at two defined detector voltage output levels on either side of the wire. The mean of the micrometer readings yields the wire center position.

  7. Fiducialization: Step 2Wire Finder Implementation

  8. Fiducialization: Step 2Wire Finder Calibration Objective: Calibration relates wire position measurements to reference fiducial Principle: Distance between fiducials known. Wire position is determined two times but with WF yawed 180° after 1st measurement

  9. Fiducialization: Step 2Wire Finder Calibration • From these two wire measurements we obtain AI and AII; these are all the parameters needed to calculate calibration offset

  10. Fiducialization: Step 2Wire Finder Calibration Calibration Example

  11. Fiducialization: Step 2Wire Finder Repeatability Both Wire Finders were calibrated four times each in the morning before a fiducialization run and after the run in late afternoon.

  12. Fiducialization: Step 3 Measure fiducials w/r to straight line • Requested straightness tolerance excludes standard surveying methods • Straightness interferometry method of choice Straightness Interferometer cannot measure directly w/r to fiducials Interface between fiducials and Wollaston prism provided by constant length rod

  13. Fiducialization: Step 3 Arcing • Rod needs to be placed perpendicular to SI reference line • Not a new problem, typical to optical tooling measurements • Solution: arcing (best-fit circle)

  14. Fiducialization: Step 3 Arcing

  15. Fiducialization: Step 4 Calculate fiducial offsets • All information now available to calculate the undulator fiducial offsets

  16. Fiducialization: Step 4 Repeatability, Data • Steps one through four were repeated four times; to guarantee independent measurements, the undulators and the SI reference line were moved after each iteration

  17. Fiducialization: Step 4 Repeatability, Results All but two of the 16 individual measurements agree to within 2 µm compared to the respective mean. Standard deviation of all measurements is 2.3 µm.

  18. Fiducialization: Step 5 Repeat in other roll orientation • To avoid first order errors, all measurements are recorded in the principal planes, i.e. TB on the side is used for horizontal measurements, TB on the top for vertical measurements only • Hence, all fiducialization measurements are one-dimensional plus distance along beam • To determine “second” dimension, undulator is rolled by 90°, and above measurements are repeated

  19. Fiducialization: Step 6 Closure Check • To check for systematic errors, the undulators are also measured in their 180° and 270° positions • Adding the fiducial offsets of opposing TBs should equal the spatial distance between the two TBs as previously measured on high accuracy CMM

  20. Fiducialization: Step 6 Closure Data • Undulator one and two as a pair were used to commission the fiducialization set-up. Several closure measurements are available

  21. Fiducialization: Step 6 Closure Data • Another check is provided by comparing fiducial offsets from different iterations

  22. Second Task Alignment Position undulator magnets with respect to each other inside the vacuum chamber

  23. AlignmentPhilosophy • Alignment step uses analogous approach to fiducialization measurements: straightness interferometry. To permit simultaneous measurement of both dimensions, two straightness interferometers are used

  24. AlignmentProcedural Steps • Conventional alignment techniques are used to support installation and to achieve global alignment in the beam line coordinate system • Dual interferometer system is used to map the undulators’ positions • Fit a straight line & apply similarity transformation to data such that necessary position corrections are minimized and magnetic centers are at nominal positions (i.e., follow a RLB) • Apply position corrections under control of interferometers • Iterate if necessary • Quality Control, re-map undulators; include Laser Finder in both upstream and downstream positions

  25. Alignment: Step 1Conventional Alignment • Routine work, should yield 100 to 150 mm type position accuracy relative to beam line coordinate system

  26. Alignment: Step 2Dual Interferometer System • Test measurements showed that it would be desirable to adjust the position of the undulators under simultaneous horizontal and vertical control: hence dual system • Special jig was designed to facilitate the set-up of both straightness interferometers • Jig should be bucked-in w/r to beam line to about 0.5 mm (conventional alignment)

  27. Alignment: Step 2Dual Interferometer System

  28. Alignment: Step 2Dual Interferometer System

  29. Alignment: Step 2Dual Interferometer System

  30. Alignment: Steps 2 - 5Mapping Undulator Fiducials • Fiducials are mapped analogously to the technique described before for the fiducialization measurements. A full map of horizontal and vertical measurements takes about one hour • On-line data flow and custom programming allows automatic measuring and data analysis • Straight line fit optimized to minimize position corrections • Yields position corrections for undulators which are expressed in fractions of rotations of the adjustment screws • Re-map, check, iterate if necessary

  31. Alignment: Step 6Quality Control • Produce final map including the fiducial positions of the Laser Finder in its upstream and downstream position See Poster: “Very High Precision Alignment of Undulator Magnets in a Vacuum Chamber” for details on these alignment steps

  32. Third Task Reference Laser Beam Setup RLB with respect to undulator position

  33. Reference Laser BeamPurpose • An optical diagnostics system is integrated into the system design which will aid in steering the electron beam to coincide with the photon beam • A laser beam is used to reference the diagnostic system to the undulator axis • Therefore the laser beam needs to be pointed such that it coincides with the axis of the undulator assembly • Initially a green laser is used which will be replaced with an infra-red (invisible) laser for final operations • A Laser Finder has been designed to relate the optical beam to mechanical fiducials

  34. Reference Laser BeamLaser Finder Principle • The LF consists of a frame which carries tooling balls in the same geometry and dimensions as they are mounted to the undulator • A quadrant detector is mounted on a two-dimensional cross-slide centered to the frame • The quadrant detector is used as nulling device. The laser intensity readings are detected on each of two halves of the QD and compared; this arrangement is then electronically rotated by 90° to measure the other dimension

  35. Reference Laser BeamLaser Finder Implementation

  36. Reference Laser BeamLaser Finder Calibration • The detector’s coordinate system needs to be related to the reference tooling ball by a calibration measurement • Calibration is performed analogously to the Wire Finder

  37. Reference Laser BeamLaser Finder Calibration

  38. Reference Laser BeamLaser Finder Buck-in Procedure • The position of the LF in both its upstream and downstream kinematic mount is known from quality control mapping • Based on these parameters, the nominal LF readings for both positions can be calculated • First, the beam is pointed such that the LF, preset to the nominal micrometer readings in the downstream position, detects the beam at the center of the QD • Second, the laser is translated, horizontally and vertically, in the upstream position such that the LF, preset to the nominal micrometer readings, detects the beam at the center of the QD • Third, the last two steps are iterated until the corrections become insignificant

  39. The End

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