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LCLS Undulator Tuning And Fiducialization

This progress report discusses the tuning and fiducialization of 15 undulators at LCLS, including the success of the MMF temperature control and stable Hall probe calibrations. Challenges include setting K to a specified value and addressing issues such as bad bolts and machining accuracy. Proposed solutions involve gap shimming, capacitive sensor feedback, and better coordination of technician time. Other projects mentioned include a girder alignment plan and building quadrupole coils for gun solenoids.

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LCLS Undulator Tuning And Fiducialization

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  1. LCLS Undulator TuningAnd Fiducialization Zack Wolf, Yurii Levashov, Achim Weidemann, Seva Kaplounenko, Scott Jansson, Ralph Colon, Dave Jensen, Scott Anderson

  2. Progress Since Last FAC Progress We have 15 undulators tuned and fiducialized. The MMF temperature control is working well. The reference undulator measurements repeat within spec. The Hall probe calibrations are stable. The Hall probe reference magnet measurements are stable. A study of the stainless steel beam pipe and steel support was made. A study of undulator mounting effects is under way. The undulator quadrupole fiducialization system was commissioned. Challenges Now we need to set K to a specified value. Can’t re-assign slot number. Bad bolts. Machining accuracy of tapered shims. The rough tuning is taking longer than expected. New air compressor still not installed.

  3. Hall Probe Calibrations In Fixed Mount The Hall probe is calibrated in the same mount it is used in. Measurements are made in a reference magnet before the final data set is taken.

  4. Reference Undulator, Reference Magnet within spec change probe mount (4 undulators tuned, will re-measure) temperature? need more studies taken during reference undulator measurements Y. Levashov

  5. Schedule Present Status: 15 undulators tuned and fiducialized 2 in fine tuning 1 in rough tuning 2 deferred for major re-work (bad end magnets, large sag might hit beam pipe) (minor problems like bad bolts or requiring gap shim replacement are fixed as we go) Present Schedule: 17 tuned and fiducialized 1 tuned We are 2 to 4 weeks behind schedule (which is 6 months ahead of installation).

  6. Actions To Help The Schedule Problems Rough tuning is taking a long time Difficult to set K to a specified value (can no longer just re-assign slots) Need to replace bad bolts Need to replace many gap shims (±50 micron strongback tolerance, ±20 micron shim range) Problems with large tapered shim dimension deviations (need to measure shim removed and measure shim replaced) Need to set gap to 4 microns (!) for beam axis to be within ±1 mm of magnetic center (±2 mm good field region) Solutions New gap shimming stand Measure size of removed shim and size of replacement shim Use capacitive sensors for rapid feedback Kugler bench assists with rough tuning when required Coordinate technicians time better (start shimming at 7am) Set K and do phase shimming in one step

  7. Phase Relative To A Reference WaveIs Used To Set Gap And Do Phase Shimming after an iteration measurement requires alignment of undulator and probe problem problem need phase matching shim, not a problem problem

  8. Gap Shim, Capacitive Sensor Feedback check gap shimming with capacitive sensors shims were replaced at the error locations error the removed shims were undersize, the replaced shims were oversize fast, doesn’t require much alignment error error can catch these problems much quicker now

  9. Installed New Gap Adjustment Stand tuning can continue while the technicians adjust the gap the Kugler bench was used for rough tuning when required can use CMM for feedback on gap adjustment

  10. Beampipe Magnetic Effect Study

  11. Undulator Mounting Tests MMF Tunnel flat on flat: over-constrained, however, there is compliance in aluminum feet and in the stages, and undulator (?) kinematic mount: well defined, repeatable

  12. Undulator FootUsed For Mounting And Positioning

  13. Issue Under Test 1 mrad roll tolerance, twist is smaller Ideal Error in slot for foot Correction Move axis to correct height by adjusting foot Twists undulator?, distorts foot? Axis at wrong height twist is not the issue Entrance end Exit end Tooling ball gives axis y position

  14. Tests Of Mounting Method Differences The undulator appears to sit the same way on flat feet as on the kinematic mount. 0.03 mrad, negligible negligible difference in twist of two undulators tested so far will check on all undulators

  15. To-Do List • When we are done with production • fix undulators with severe problems • (we need to buy more tapered shims) • study temperature dependence of K • re-measure first five undulators • study further undulator handling requirements • Other Projects • girder alignment plan • build quadrupole coils for gun solenoids

  16. Undulator Quadrupole Fiducialization Plan

  17. Undulator Quadrupole FiducializationSystem Commissioning Repeatable flip magnet, center position doesn’t change no bias from Earth’s field

  18. Undulator Quadrupole Measurements Scott Anderson will do the fiducialization Andrew Fisher will do the strength and harmonics measurements

  19. Leftovers From Last FACHall Probe Position Problem Problem: The vertical trajectories on the Dover bench and Kugler bench did not agree. The horizontal field integrals from the Hall probe had a large y dependence. Coil measurements showed no such dependence. We stumbled onto a paper Isaac wrote in 1997! The Sentron probes are sensitive to planar Hall effects after all!

  20. Solution To The Hall Probe Problem Isaac’s hypothesis: planar Hall effect (30 microns Dover bench, 10 microns Kugler bench) Solution: Measure the positions of the Hall elements. Tune the horizontal trajectory with the By probe on the midplane. Tune the vertical trajectory with the Bx probe on the midplane. Use only the long coil for final field integral measurements.

  21. Undulator Sag Changes Hall Probe Y Position Relative To The Midplane

  22. Effect Of Hall Probe Error On Trajectories μm μm X Trajectory Y Trajectory 2 12 y=+200 μm -2 -2 6 y=+100 μm -1 2 y=0 μm -2 1 y=-100 μm -6 2 y=-200 μm -14

  23. Constant Bx0 Corrects Bx To Long Coil Field Integral μm Y Trajectory μm Corrected Y Trajectory 12 2 y=+200 μm Bx0=+0.52 G -2 -2 6 y=+100 μm Bx0=+0.29 G -1 2 y=0 μm Bx0=0.00 G -2 1 y=-100 μm Bx0=-0.29 G -6 2 y=-200 μm Bx0=-0.63 G -14

  24. Effect Of Undulator Sag And Hall Probe Error On K Conclusion: The trajectory curvature caused by the Hall probe error when the undulator sags by 100 microns will change K by less than 0.016% if no correction is applied. We do apply a correction, making the effect much smaller.

  25. Conclusion Production undulator tuning is underway. The lab and equipment are performing well. (But we still need the new air compressor installed.) 15 undulators are tuned and fiducialized. Hall probe calibrations are now stable. Reference undulator measurements are within spec. Reference magnet measurements are stable. The magnetic effect of a stainless steel beam pipe was studied. We are checking that the way the undulator is mounted will not change the fiducialization, and twist can be compensated by a pitch adjustment. We have a quadrupole fiducialization plan. The quadrupole fiducialization system was commissioned. After production, we will fix undulators and continue studies.

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