thermal environment & mechanical support
DESCRIPTION
Thermal Environment & Mechanical Support. Phase and Trajectory Tolerances Foundation Considerations Thermal Distortions Support Design. Phase error tolerance implications. 2 micron rms trajectory tolerance (perfect undulator) Segment to segment strength variation of 1.5 x 10 -4 - PowerPoint PPT PresentationTRANSCRIPT
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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 ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
• 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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Support and Monitoring Schematic
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Foundation Instability
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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 ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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]
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Thermo-Mechanical Instabilities
• Dilatation (ordinary thermal expansion)• Warp caused by thermal gradients (heat flux)
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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)
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Thermal Environment
• Air temperature in both time and space• Surface temperatures• Heat sources and sinks
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Air Temperature IllustrationAir Temperature
Match MMF temperature
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
more temp specs
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Girder Concept
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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 ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Support Assembly Concept
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Earthquake bracing
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Support in Tunnel
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Adjustable support platform
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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 ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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 ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Extra Slides
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Temperature specs
Undulator System ReviewMarch 3-4, 2004
J. Welch, SLAC
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
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.