1. LCLS Undulator Fiducialization
by Yurii Levashov, SLAC

2. Outlook LCLS Parameters Fiducialization Procedure Pointed Magnets
PM Test Results
Fiducialization Error Budget
Summary

3. LCLS Parameters and Tolerances
Total length of the undulator
112 m
Segment length
3.4 m
Period (u)
3 cm
Pole Gap
6.8 mm
Pole Cant Angle
4.5 mrad
Nominal Magnetic Field B0
1.276 T
Nominal K Value
3.5
Electron phase deviation per segment
100
ΔK/K = ΔB/B0
Vertical Positioning Error, rms
70µm
Horizontal Positioning Error, rms
180µm
Longitudinal Positioning Error, rms
1mm
1.5*10-4

4. Fiducialization Procedure
Goal to find position of undulator axis with respect to mechanical references.
Based on results of magnetic measurements.
Magnetic measurements and tuning should be done before fiducialization.
Magnetic axis with respect to Hall probe sensitive area, i.e. magnetic reference.
Coordinate transfer from magnetic to mechanical references.
Pointed magnets as an intermediate reference.

5. Fiducialization Procedure (cont.)
X,Y,Z

6. Fiducialization Procedure (cont.)
Alignment to the bench. Capacitor sensor measurements..
Position of the axis
Hall probe scan in Y at different Z positions. Pitch correction.
Hall probe scan in Z at different Y. Effective K-value.
Hall probe centering w.r.t. PM center. Offset between undulator axis and PM.
Measurements at CMM. Offset between tooling balls.

7. Pointed Magnet Fixture
Pointed magnet misalignment?
* I. Vasserman Quadrupole magnetic center definition using the hall probe measurement technique.
APS-Pub. LS-285, Argonne, 2004

8. Two-Point Measurement Algorithm
By= 0

9. Hall probe centering accuracy
Starting from random positions (±0.2mm) from center, scan in X and Y.
Differences in centering results w.r.t first scan shown.
Std (in X)= 3µm

10. Pointed Magnet Calibration
A1,2 = D/2 ± Δy
Sentron 2-D XZM12 Hall probe
Newport X-Y, model 406, stages with CMA-12CCCL actuators and ESP-300 controller

11. Calibration Test Results
Do centering in one position
Rotate fixture at 180˚
Do centering in second position
Calculate offset
Calibration accuracy = 1µm in Y,
3µm in X

12. Fiducialization Error Budget
Total Fiducialization error includes the following components:
Finding undulator magnetic axis ~ 5µm
Hall probe centering ~ 1µm
Pointed magnet calibration ~ 3µm
Tooling ball eccentricity = 5µm
CMM measurement ~ 15µm
Other possible errors ~ ? (10µm)
Total: µm
Alignment budget: sqrt(702 – 202) = 67µm

13. Summary Fiducialization procedure has been finalized.
Pointed magnet fixture has been developed, fabricated, and tested.
Adequate measurement algorithm has been proposed.
Fiducialization accuracy is expected to be ~ 20 µm.

14. Acknowledgement
Author would like to thank Z. Wolf (SLAC) and I. Vasserman (ANL) for ideas and fruitful discussions.
Special thanks to D. Jensen (SLAC) and K. Hacker (DESY) who started the work on pointed magnets.

15. End of presentation
Thank you!