Thermal Environment & Mechanical Support

Undulator System ReviewMarch 3-4, 2004

J. Welch, SLAC

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

Thermal Environment & Mechanical Support

•Phase and Trajectory Tolerances–Foundation Considerations–Thermal Distortions

•Support Design


J. Welch, SLAC


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 ~ +-0.2 C

• Vertical undulator alignment 50 m causes 10 degrees of additional slippage

2 m deviation from straight over 10 m is about the average curvature of the Earth’s surface


J. Welch, SLAC


Path Length Increases due to Bumps

• LCLS: A < 3.2 m• LEUTL: A < 100 m• VISA: A < 50 m

rr L

A

L

A

λπ

λπϕ

22 422=⎟⎟

⎠

⎞⎜⎜⎝

⎛=Δ

from H-D Nuhn


J. Welch, SLAC


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


J. Welch, SLAC


• 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

Beam Based AlignmentIf errors are too big they must be fixed rather than “corrected for”

offsets don’t depend on energy

1/month is ignorable, 1/day is intolerable


J. Welch, SLAC


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 m 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


J. Welch, SLAC


Support and Monitoring Schematic


J. Welch, SLAC


Foundation Instability


J. Welch, SLAC


Settlement Implications for LCLS

• Expect settlement of order – ~ 300 - 1000 m / year = 1 - 3 m / 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


J. Welch, SLAC


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


J. Welch, SLAC


Vibration

• Normally vibration amplitudes are much less than 1 micron, typically 10 - 100 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€

′ y rms ≈ yrms2π × 300[m /s]/ f [Hz]


J. Welch, SLAC


Thermo-Mechanical Instabilities

• Dilatation (ordinary thermal expansion)• Warp caused by thermal gradients (heat flux)


J. Welch, SLAC


DilatationSupport column height from (fixed?) bedrock 3+ meters.

Temperature coefficient for Anocast 12 ppm/C

Temperature change for 1 micron vertical motion is 0.03 C

--> BBA re-measure at 0.06 C change

-->stability during BBA procedure 0.03 C/ 8 hr, (~1 degree/week)


J. Welch, SLAC


Warping from Heat Flux

• 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


J. Welch, SLAC


Heat Flux Example

• Heat flow a the bar for 1 degree temperature difference

T14

€

T24

T 4

T 4

σ(T14 −T 4 )=σ (T14 −[T14

2+

T24

2])=σ(

T14

2−

T24

2)

σ(3014

2−

3004

2) =3 W/m2


J. Welch, SLAC


Heat Flux Distortions

• Bar Warp

δ =αL2q8σ

δq

=0.70 microns/Wm2

α = expansion coefficient

q= heat flux

€

σ = thermal conductivity

L = 3 m, titanium

2 microns is the walk-off tolerance,-> Max wall temperature difference is ~1 degree C

3 W/m2 -> 2 micron warp for an undulator segment


J. Welch, SLAC


Thermal Environment

• Air temperature in both time and space• Surface temperatures• Heat sources and sinks


J. Welch, SLAC


Air Temperature IllustrationAir Temperature

Match MMF temperature


J. Welch, SLAC


more temp specs


J. Welch, SLAC


Girder Concept

• Stability of bedrock is not good (1-3 m/day)

• Long girder to provide good relative alignment stability

• Length > gain length ( ~ 5 m)• Reduce the number of supports req’d

If the girder is truly stable, linearly correlated motion along the girder can be identified and corrector for. The longer the girder the better


J. Welch, SLAC


Girder Concept


J. Welch, SLAC


Why Granite?

• 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

PRO CON


J. Welch, SLAC


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!


J. Welch, SLAC


Support Assembly Concept


J. Welch, SLAC


Earthquake bracing


J. Welch, SLAC


Support in Tunnel


J. Welch, SLAC


Adjustable support platform


J. Welch, SLAC


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


J. Welch, SLAC


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


J. Welch, SLAC


Extra Slides


J. Welch, SLAC


Temperature specs


J. Welch, SLAC


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 m) beam/radiation overlap error.


J. Welch, SLAC


Assembly Concept exploded

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Thermal Environment & Mechanical Support