1. Thermal Environment & Mechanical Support
Phase and Trajectory Tolerances
Foundation Considerations
Thermal Distortions
Support Design
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

2. Phase error tolerance implications
2 micron rms trajectory tolerance (perfect undulator)
Segment to segment strength variation of 1.5 x 10-4
Temperature coefficient of NdFeB is 0.1%/C
Undulator compensation via Ti/Al assembly) magnet temperature tolerance ~ C
Vertical undulator alignment 50 mm causes 10 degrees of additional slippage
2 mm deviation from straight over 10 m is about the average curvature of the Earth’s surface
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

3. Path Length Increases due to Bumps
LCLS: A < 3.2 mm
LEUTL: A < 100 mm
VISA: A < 50 mm
from H-D Nuhn
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

4. Alignment and Stability Strategy
Three layers of defense against trajectory errors
Beam based
fast orbit feedback for launch errors
full BBA with multiple beam energies to measure BPM and Quad offsets.
Wire Positioning System and Hydrostatic Leveling System
HLS systems have shown good long term stability
WPS system have shown good short term stability
Make foundation and supports as stable as possible
thermal stability, geotechnical, and support mechanical design
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

5. Beam Based Alignment
If errors are too big they must be fixed rather than “corrected for”
BBA is the fundamental LCLS tool to obtain and maintain ultra-straight trajectories over long term.
Corrects for
BPM mechanical and electrical offsets
Field errors, (built-in) and stray fields
Field errors due to alignment error
Input trajectory error
Does not correct undulator alignment errors
Establishes a best fit straight line electron trajectory
Procedure
Take orbits with three or more very different beam energies, calculate corrections
Move quadrupoles and/or adjust steering coils to correct orbit
Disruptive to operation
offsets don’t depend on energy
1/month is ignorable, 1/day is intolerable
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

6. BPM and Quad Stability Requirements
After BBA, changes of BPM offsets will be seen erroneously as orbit errors
Stability of BPM mechanical and electrical offsets determine trajectory stability
need BPM stability of ~ 2 mm rms
BPM’s have to be mechanically more stable than all other components
Known BPM motions are taken out in software
Quad stability requirements are more like 5 microns
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

7. Support and Monitoring Schematic
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

8. Foundation Instability
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

9. Settlement Implications for LCLS
Expect settlement of order
~ mm / year = mm / day,
not well correlated with location
Good alignment lasts only a day or so
Mover range cannot accommodate much of the drift; need another mechanism with plenty of range and periodic realignment
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

10. Foundation Design Guidance
Uniformity of construction along length
avoid fill areas which settle much faster
try to avoid kinks, gentle bends are more tolerable
Strong thick floor
~ 3 ft, essentially monolithic
Buried/tunneled
research yard has poor stability
good thermal insulation
Water table considerations
desire either wet or dry all year
keep sandstone wet between exposure and concrete
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

11. Vibration
Normally vibration amplitudes are much less than 1 micron, typically nm.
~10 nm measured on top of berm.
Possible areas of concern
air handling units
passage of vehicles over undulator hall tunnel.
Pointing sensitivity ~ 10-7 radians (1/10 angular divergence)
e.g. 10 Hz -> yrms ~ 1 micron
Q factors for equipment can be 100’s, supports need to be checked
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

12. Thermo-Mechanical Instabilities
Dilatation (ordinary thermal expansion)
Warp caused by thermal gradients (heat flux)
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

13. Dilatation Support column height from (fixed?) bedrock 3+ meters.
Temperature coefficient for Anocast 12 ppm/C
Temperature change for 1 micron vertical motion is C
--> BBA re-measure at 0.06 C change
-->stability during BBA procedure 0.03 C/ 8 hr, (~1 degree/week)
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

14. Warping from Heat Flux T1 T2
Long beams bend easily if there is a heat flux across them.
Heat fluxes can arise from
Temperature differences between walls and radiant heat transfer
Air temperature differences
Contact with supports or other materials
It is easy to show the bar goes to “average” temperature T1 T2
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

15. Heat Flux Example
Heat flow a the bar for 1 degree temperature difference
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

16. Heat Flux Distortions Bar Warp d
L = 3 m, titanium
3 W/m2 -> 2 micron warp for an undulator segment
2 microns is the walk-off tolerance,
-> Max wall temperature difference is ~1 degree C
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

17. Thermal Environment Air temperature in both time and space
Surface temperatures
Heat sources and sinks
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

18. Air Temperature Illustration
Match MMF temperature
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

19. more temp specs
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

20. Girder Concept Stability of bedrock is not good (1-3 mm/day)
If the girder is truly stable, linearly correlated motion along the girder can be identified and corrector for. The longer the girder the better
Stability of bedrock is not good (1-3 mm/day)
Long girder to provide good relative alignment stability
Length > gain length ( ~ 5 m)
Reduce the number of supports req’d
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

21. Girder Concept
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

22. Why Granite? PRO CON Good overall long term stability
common choice for metrology and magnet measurement benches
Large thermal mass
averages temperature fluctuations, good passive stability
Low thermal expansion coefficient
~ 1/2 cte of steel, similar to ceramics
Reasonable cost in large sizes
~ $40,000 for 12 x 0.8 x 0.8 m, finished and delivered (enough for 3 undulator segments)
Low thermal conductivity
sensitive to heat fluxes
Variable mechanical properties
Doesn’t take a tap
hard to add features
Not ductile
handle with care
Heavy
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

23. Other Girder Options Aluminum tubes with temperature stabilization
Steel or cast iron girders
Engineered stone (Anocast)
Carbon reinforced plastic tube trusses
Specialized concrete
NLC technology
SiC girders!
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

24. Support Assembly Concept
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

25. Earthquake bracing J. Welch, SLAC Undulator System Review
March 3-4, 2004
J. Welch, SLAC

26. Support in Tunnel J. Welch, SLAC Undulator System Review
March 3-4, 2004
J. Welch, SLAC

27. Adjustable support platform
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

28. Support R&D
Testing a 6 m piece from Barre Vt for long term stability - start this summer
does it slowly sag?
how much does it warp with temperature and humidity changes in the surrounding tunnel?
What does sealing do?
does insulation help? how much?
thermal stabilization time?
Prototype mounting schemes for adjustable support platform and kinematic supports
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

29. Schedule & Cost
Granite manufacture and shipping time 10 weeks for first item
don’t know at what rate they can be produced, need at least 11.
Quarry closed Jan - Mar
Stabilization time ~ 2 months, before ready to measure
Integration into installation schedule under development
Granite beams ~ $500,000
Other support costs ~ $500,000
Thermometry, kinematic supports, insulation, tubes, plates, eq bracing, etc
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

30. Extra Slides
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

31. Temperature specs J. Welch, SLAC Undulator System Review
March 3-4, 2004
J. Welch, SLAC

32. Basic Tolerance Requirements from Simulations
Saturation length (86 m) increases by one gain length (4.7 m), for the 1.5 Angstrom case if there is:
18 degree rms beam/radiation phase error
1 rms beam size ( ~ 30 mm) beam/radiation overlap error.
Undulator System Review
March 3-4, 2004
J. Welch, SLAC

33. Assembly Concept exploded
Undulator System Review
March 3-4, 2004
J. Welch, SLAC