physics requirements for conventional facilities
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Physics Requirements for Conventional Facilities. Thermal, Settlement, and Vibration Issues J. Welch. General Background. What are Physics Requirements for CF? Needed to accommodate technical systems Distinguished from programming and site requirements - PowerPoint PPT PresentationTRANSCRIPT
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Physics Requirements for Conventional Facilities
Thermal, Settlement, and Vibration Issues
J. Welch
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
General Background
What are Physics Requirements for CF?Needed to accommodate technical systemsDistinguished from programming and site requirementsUsed by system managers as input for further design
Where do they come from?GRD, System physicists, system managers
Types of RequirementsEnvironmental, Layout, Space, Utility and Radiation
Critical Issues are Thermal, Settlement, and Vibration
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Sensitive CF AreasVibration Thermal Settlement
Undulator
Hall
X X X
MMF X X
Sector 20 X X
Near Hall X
… Start with Undulator Hall (UH)
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Physics Sensitivities for UH
FEL 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 error1 rms beam size ( ~ 30 m) beam/radiation overlap error.
Xray beam will move 1/10 sigma if~ 1/10 rad change in angular alignment of various Xray deflecting crystalselectron trajectory angular change of ~ 1/10 rad
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
FEL Mechanism
Exponential Gain
Micro-bunching
Narrow Radiation Cone ~1 r,(1/ ~ 35 rad)• 2 radiation phase advance
per undulator period
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Phase Sensitivity to Orbit Errors
2r
2A2
L
4A2
Lr
from H-D Nuhn
LCLS: A < 3.2 m
LEUTL: A < 100 m
VISA: A < 50 m
Path Length Error Phase Error
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
LCLS Phase ToleranceTrajectory Straightness
2 m rms tolerance for the electron trajectory deviation from an absolutely straight line, averaged over 4.7 m
Maintaining an ultra-straight trajectory puts demanding differential settlement and thermal requirements on the Undulator Hall
Undulator magnet uniformity∆K/K <= 1.5 x 10-4 for 10 degrees error per undulator segment
Undulator alignment error limited to 50/300 micron vertical/horz.
Temperature coefficient of remanence of NdFeB is 0.1%/C, which, because of partial compensation via Ti/Al assembly, leads to a magnet temperature tolerance of ± 0.2 C.
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Obtaining an Ultra-Straight BeamBBA is the fundamental tool to obtain and recover an ultra-straight trajectory over the long term.Corrects for
BPM mechanical and electrical offsetsField errors, (built-in) and stray fieldsField errors due to alignment errorInput trajectory errorDoes not correct undulator placement errors
ProcedureTake orbits with three or more different beam energies, calculate corrections, move quadrupoles to get dispersion free orbitDisruptive to operation
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Maintaining AlignmentUltra-straight trajectory will be lost if
BPM’s move and feedback incorrectly corrects the beam
Quads move
Stray fields change
Launch trajectory drifts
Phase accuracy will also be lost if undulator segments move ~ 10 m, (50 m assuming zero fiducialization and initial alignment error)
note that unless the actual motion is known, there is no effective way to re-establish the undulator position except through magnetic measurements.
BBA once a month OK, once a day intolerable
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Motion Due to Temperature Change
Dilitation
1.4 m
l lT
Granite 6-8
Anocast 12
Steel 11
Aluminum 23
CTE ppm/deg C
T ~ 2 m / 1.4 m x 10 x 10-6 = 0.1 deg C
(for a nominal 10 ppm/deg C)
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Motion Due to Heat Flux or temperature gradients
L2q
8
q
0.70 microns/Wm 2
expansion coefficient
q heat flux
thermal conductivity
L = 3 m, titanium strongback
Note that 3 W/m2 can be generated by ~1 degree C temperature difference between the ceiling and floor via radiative heat transfer
3 W/m2 -> 2 micron warp for an undulator segment
∆T ≈ 0.05 deg C across strongback
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Motion of the Foundation
1 mm/year = 3 m/day
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Implications for Undulator Hall
Expect differential settlement of 1 - 3 m / day, in some locations.
Make foundation as stable as possiblegeotechnical, foundation design, uniformity of tunnel
construction and surrounding geologic formation, avoid fill areas
Thermally stabilize the Undulator Hallreduce heat fluxes to a minimum
HVAC designed to precisely regulate temperature to within a ± 0.2 deg C band everywhere in the Undulator Hall
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Title I Undulator Hall Foundation
High Moment of Inertia, T shaped foundation
Pea Gravel support Slip planes
•Completely underground•Imprevious membrane blocks groundwater•Located above water table (at this time anyway)•Low shrink concrete, isolated foundation•“Monolithic”
Pine, Bldg 48, Room 232
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Title I Undulator Hall HVAC
Cross flow to ductsAHU in alcoves 9X
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Magnetic Measurement FacilityAir Temperature
± 0.1 deg C band everywhere in the measurement area. 23.50 deg C year round temperature
VibrationHall probe motion is translated into field error in an undulator field such 0.5 m motion causes 1 x10-4 error.Measurements show vibrations below 100 nm.
Pine, Bldg 48, Room 232
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Sector 20
RF electronicsTiming signals sensitive to temperatureSpecial enclosure for RF hut
Laser opticsSensitive to temperature, humidity and dust, vibrationClass 100,000 equivalent, humidity control, vibration isolated foundation (separated from klystron gallery), fix bumps in road nearby.
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Near Hall
Hutches with a variety of experiments to houseThermal, humidity, and dust control
Class 10,000 equivalent
Adjacent to Near Hall are Xray beam deflector which have significant vibration sensitivities.
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Xray Beam Pointing Sensitivity
250 m
~ 320 m
Near Hall Far Hall
Undulator
~ 400 m
FEL ~ 400 m’FEL ~ 1 rad
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Pointing Stability Tolerance0.1 spot stability in Far Hall (conservative) implies 0.1 rad pointing stability for deflecting crystals and electron beam
Feedback on beam orbit or splitter crystal can stabilize spot on slow time scale. Typical SLAC beam is stable to better than 1/10 with feedback.Still have to face significant vibration tolerances on deflecting crystalsCorrector magnets in BTH must be stable to better than 1/10 sigma deflection net.
Electron beam stability is not expected to be not quite as good as 1/10 sigma
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Vibration and Pointing Stability
Angular tolerance can be converted to a vibration amplitude for a specific frequency, for CF spec.
y=A coskx-t where y is the height of the ground, dy/dx is the slope.
We want average rms(dy/dx) ≤ 0.1 rad
A ≤ 0.1 rad/2. is the wavelength of the ground wave
Typical worst case is around 10 Hz and speed of ground wave is around 1000 m/s.
A ≤ 10-5/ 2 ~ 10-6 m, which is quite reasonable since typical A~100 nm or less
High Q support structures could cause a problem
Pine, Bldg 48, Room 232
J. Welch [email protected]
4/29/04
Conclusion
Reliable production of ultrahigh brightness, FEL x-rays requires
Exceptional control of the thermal environment in the Undulator Hall and MMF
Excellent long term mechanical stability of the Undulator Hall foundation
Care in preventing undesirable vibration near sensitive equipment at several locations
Requirements are understood, what remains is to obtain and implement cost effective solutions.