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LCLS Undulator Magnetic Measurements

This document outlines the general approach and techniques for magnetic measurements of undulators at LCLS, including alignment, gap adjustments, trajectory straightening, phase error minimization, and phase matching.

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LCLS Undulator Magnetic Measurements

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  1. LCLS UndulatorMagnetic Measurements Zack Wolf, Scott Anderson, Ralph Colon, Brendan Dix, Scott Jansson, Dave Jensen, Luis Juarez, Seva Kaplounenko, Yurii Levashov, Wei Wang, Achim Weidemann

  2. Undulator Tuning, General Approach • Use ANL and DESY experience • Techniques have been developed at ANL and DESY which work very well. • We will use the best of the ANL and DESY measurement techniques as our starting point (both have been very generous in sharing with us). • We need to adapt for production measurements.

  3. SLAC Magnetic Measurement Facility • Floor plan divided into three functional areas • Magnetic Measurements (± 0.1º C) • Fiducialization and Assembly (± 1º C) • Storage (± 2.5º C) • Test stand lay-out is driven by requirement to match the Earth Magnetic Field conditions in lab to Undulator Hall, i.e. azimuth and gap orientation need to be identical LCLS-TN-04-1

  4. MMF Under Construction Photos courtesy of Javier Sevilla Beneficial occupancy in March

  5. Important Dates (Approximate) MMF Major Construction Finished Feb. 17, 2006 MMF Beneficial Occupancy March 6, 2006 Kugler Bench Complete April 15, 2006 Kugler Bench At SLAC May 15, 2006 Kugler Bench Handover To SLAC June 15, 2006 1st Article Arrives At SLAC July 2, 2006 MMF Ready For Measurements July 28, 2006 Production Measurements Start August 29, 2006

  6. Undulator Measurement Benches Goal: Move probes along a very straight line through the undulator. ANL Bench DESY Bench LCLS-TN-03-7

  7. Kugler Bench On order, expected at SLAC May 15, 2006. Ready for use June 15, 2006.

  8. SLAC Software Development Bench (While we wait on the Kugler bench) Bench software by Seva Kaplounenko

  9. Undulator Measurement Steps • Place undulator • Mechanically align undulator to bench • Magnetically align Hall probe to undulator • Perform any required large gap adjustments and re-align • Straighten the X and Y trajectories • Minimize phase errors • Perform phase matching • Determine K vs X, move probe to the X value which gives the specified K • Add fiducialization magnets to undulator ends, locate center of fiducialization magnets • Move undulator to CMM, finish fiducialization LCLS-TN-03-7

  10. 1) Place Undulator Ben Poling placing the ANL prototype on the SLAC prototype bench 12/9/05.

  11. 1) Place Undulator

  12. Place Undulator Bearing SLAC CAM Movers Cam Potentiometer Bearing Harmonic Drive Motor Brake Built by Gordon Bowden, Yurii Levashov, Scott Jansson

  13. 2) Mechanically Align to Bench Use Capacitive Sensors Yurii Levashov We tested capacitive sensors in TTF undulators at DESY

  14. 2) Mechanically Align To Bench Undulator aligned to fixed height of reference pole.

  15. 2) Mechanically Align to Bench Previous experience from PEP II and SPEAR III • Use 6 capacitive sensors on an arm • Gives x, yaw, y, pitch, and roll • Have reference poles at each end • Calibrate sensors with micrometers

  16. By By By y x 3) Magnetically Align Hall Probe y x • Technique • Every N’th pole, move probe vertically, find minimum • Every N’th pole, move probe horizontally, find midpoint between edges • Plot (x, y) vs z, fit for magnetic alignment

  17. 3) Magnetically Align Hall Probe SLAC Measurements

  18. 4) Perform Any Large Gap Adjustments Tapered Shim ANL TB-48

  19. 5) Straighten X And Y Trajectories Simultaneously measure Bx and By (Hall) and Bx from a coil LCLS-TN-05-5

  20. 5) Straighten X And Y Trajectories Isaac Vasserman’s Ideas ANL/APS/TB-48 ANL/APS/TB-48 • Apply shims to top and bottom poles • Shims weaken By, don’t cause Bx • Can’t strengthen pole, instead place shims on next pole to reduce deflection in other direction • Developing software to try to automate shim placement LCLS-TN-04-7

  21. 5) Straighten X And Y Trajectories Measured X Trajectory Calculate Shims Modeled X Traj With Calc Shims Measured X Traj After Calc Shims Applied Automate Shimming, Under Development

  22. 5) Check Hall Probe Field Integrals LCLS-TN-05-22 Long Coil 150 Turns I1 I2

  23. 5) Earth’s Field LCLS-TN-05-4 • We will either • Measure the field integrals and shim in the tunnel • Put a mu-metal shield around the undulators (Isaac Vasserman)

  24. 6) Minimize Phase Errors • A magnet which is too strong can cause phase errors. • The trajectory is shifted, but there is no residual slope. • Correct with phase shims. Poles 51 and 52 are 1% too strong. LCLS-TN-04-7 Measured Phase Errors Calculated Shims Under development

  25. 6) Minimize Phase Errors LCLS-TN-04-7 ANL/APS/TB-48 • Measure By with a Hall probe • Calculate phase error • Calculate shims to correct error • Apply shims, repeat • Developing software to automate shim placement • We don’t have shims to strengthen a magnet, only weaken • Must locally reduce the gap to increase phase shift

  26. 7) Phase Matching pi pi/2 pi/2 (mod 2pi) Program provides shim information Phase Matching Shim Data Entrance: Number of end poles = 5 Measured Phase At The Entrance Poles: (Phase = 0 at the entrance cell boundary.) Pole Number = 1 2 3 4 5 6 Phase (deg) = 393.80 436.28 624.41 811.05 986.83 1157.97 Expected phase at pole number 6 = 1170.00 deg Entrance phase error (from pole 6) = -12.03 deg Entrance phase match shim dimension = 0.0000e+000 m (under development)

  27. K0 K X 8) Determine K vs X Sinusoidal Field Canted Poles LCLS-TN-04-7 Analysis Program Gives K For Each X Run K vs X Calculated Undulator Parameters: Keff = 3.627747 Beff = 1.295076 T Lambda_rad = 1.595811e-010 m K Shim Data Measured K value = 3.627747 Desired K value = 3.500000 Required field change dB / B = -3.6499e-002 Required gap change dgap = 2.1330e-004 m Beam x motion required dx = 4.7401e-002 m (under development) (prototype) X0 Set the probe position to give the nominal K value.

  28. 9) Add Fiducialization Magnets Need to relate magnetic field to tooling balls. Yurii Levashov Attach to undulator ends, measure offsets LCLS-TN-05-10

  29. 10) Move to CMM, Finish Fiducialization Want D D1 : Magnetic Measurement D2 : Calibration D3 : CMM D = D1 + D2 + D3

  30. Conclusion • Our group’s next big magnetic measurement project is the LCLS. • A new magnetic measurements lab is being built. • We will use Hall probes and coils to tune the undulators. • Long coils will check the first and second field integrals. • High gradient magnets with well defined centers will be used to fiducialize the undulators. • Algorithms are being developed to automate shimming.

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