LCLS Undulator Fiducialization

Yurii LevashovLCLS Undulator Fiducialization [email protected] September 28, 2005

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*Work supported in part by DOE Contract DE-AC02-76SF00515

LCLS Undulator Fiducialization

by Yurii Levashov, SLAC


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


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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


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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.


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Fiducialization Procedure (cont.)

X,Y,Z


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Fiducialization Procedure (cont.)

Alignment to the bench. Capacitor sensor measurements..

Y

Z

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.

Position of the axis


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Pointed Magnet Fixture

Tooling Balls

Frame

Permanent Magnet

Needles

Pointed magnet misalignment?

* I. Vasserman Quadrupole magnetic center definition using the hall probe measurement technique. APS-Pub. LS-285, Argonne, 2004


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Two-Point Measurement Algorithm

N

N

0

Zero field line

Error

-0.2 -0.1 0 0.1 0.2 0.30.109

0.1091

0.1092

0.1093

0.1094

0.1095

0.1096

0.1097

0.1098

0.1099

0.11

Position in mm

B(T

)

B vs. Xat 0.2mm from the needle tip

-300 -200 -100 0 100 200 300 400-500

-400

-300

-200

-100

0

100

200

300

400

500

Magnetic Field v.s Distance from Mechanical center

Position in µm

B (

G)

dB/dY = 1G/µm

Y

X

By= 0


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Hall probe centering accuracy

-30 -20 -10 0 10 20 30-5

-4

-3

-2

-1

0

1

2

3

4

5

X position in µm

Y p

osi

tion

in µ

m

Hall Probe centering (20 scans)

± 5 µm

Std (in X)= 3µm

Starting from random positions (±0.2mm) from center, scan in X and Y. Differences in centering results w.r.t first scan shown.


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Pointed Magnet Calibration

Δy

D

D/2

2Δy

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


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Calibration Test Results

Do centering in one position Rotate fixture at 180˚

Do centering in second position Calculate offset

0 5 10 15 2040

41

42

43

44

45

46

47

48

49

50

Calibration number

Offs

et i

n µ

m

Offset between magnetic and mechanical centers

(Calibration results in Y-direction)

1µm

Calibration accuracy = 1µm in Y, 3µm in X


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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: 20 µm

Alignment budget: sqrt(702 – 202) = 67µm


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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.


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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.


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End of presentation

Thank you!

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LCLS Undulator Fiducialization