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 Presentation
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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
• 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