Transcript Physics Requirements

Physics Requirements for
Conventional Facilities
Thermal, Settlement, and Vibration Issues
J. Welch
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
General Background
What are Physics Requirements for CF?
Needed to accommodate technical systems
Distinguished from programming and site requirements
Used by system managers as input for further design
Where do they come from?
GRD, System physicists, system managers
Types of Requirements
Environmental, Layout, Space, Utility and Radiation
Critical Issues are Thermal, Settlement, and
Vibration
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Sensitive CF Areas
Vibration
Thermal
Undulator
Hall
X
X
MMF
X
X
Sector 20
X
X
Near Hall
X
Settlement
X
… Start with Undulator Hall (UH)
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
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 error
1 rms beam size ( ~ 30 mm) beam/radiation overlap
error.
Xray beam will move 1/10 sigma if
~ 1/10 mrad change in angular alignment of various Xray
deflecting crystals
electron trajectory angular change of ~ 1/10 mrad
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
FEL Mechanism
Micro-bunching
• 2p radiation phase advance
per undulator period
Narrow Radiation
Cone ~1 mr,
(1/g ~ 35 mrad)
Exponential Gain
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Phase Sensitivity to Orbit Errors
Path Length Error
Phase Error
2p 2A 2  4 pA 2
 


r  L  Lr
LCLS: A < 3.2 mm
LEUTL: A < 100 mm
VISA: A < 50 mm
4/29/04
J. Welch
from H-D Nuhn

Pine, Bldg 48, Room 232
[email protected]
LCLS Phase Tolerance
Trajectory Straightness
2 mm 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.
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Obtaining an Ultra-Straight Beam
BBA is the fundamental tool to obtain and recover an
ultra-straight trajectory over the 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 placement errors
Procedure
Take orbits with three or more different beam energies,
calculate corrections, move quadrupoles to get
dispersion free orbit
Disruptive to operation
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Maintaining Alignment
Ultra-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 mm, (50 mm 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
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Motion Due to Temperature Change
l  lT
Dilitation
CTE ppm/deg C
Granite
6-8
Anocast

Steel
12
Aluminum
23
1.4 m
11
T ~ 2 mm / 1.4 m x 10 x 10-6 = 0.1 deg C
(for a nominal 10 ppm/deg C)
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Motion Due to Heat Flux
or temperature gradients

 L2 q

8

q
  expansion coefficient
q  heat flux
  thermal conductivity
 0.70 microns/Wm
2
L = 3 m, titanium
strongback
3 W/m2 -> 2 micron warp for an
undulator segment
∆T ≈ 0.05 deg C across
strongback
4/29/04
J. Welch
Note that 3 W/m2 can be
generated by ~1 degree C
temperature difference
between the ceiling and floor
via radiative heat transfer
Pine, Bldg 48, Room 232
[email protected]
Motion of the Foundation
1 mm/year = 3 mm/day
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Implications for Undulator Hall
Expect differential settlement of 1 - 3 mm / day,
in some locations.
Make foundation as stable as possible
geotechnical, foundation design, uniformity of tunnel
construction and surrounding geologic formation, avoid fill
areas
Thermally stabilize the Undulator Hall
reduce heat fluxes to a minimum
HVAC designed to precisely regulate temperature to within
a ± 0.2 deg C band everywhere in the Undulator Hall
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Title I Undulator Hall Foundation
•Completely underground
•Imprevious membrane blocks
groundwater
•Located above water table (at
this time anyway)
•Low shrink concrete, isolated
foundation
•“Monolithic”
High Moment of Inertia,
T shaped foundation
Pea Gravel support
4/29/04
J. Welch
Slip planes
Pine, Bldg 48, Room 232
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Title I Undulator Hall HVAC
Cross flow to ducts
AHU in alcoves 9X
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Magnetic Measurement Facility
Air Temperature
± 0.1 deg C band everywhere in the
measurement area.
23.50 deg C year round
temperature
Vibration
Hall probe motion is
translated into field error in
an undulator field such 0.5
mm motion causes 1 x10-4
error.
Measurements show
vibrations below 100 nm.
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Sector 20
RF electronics
Timing signals sensitive to temperature
Special enclosure for RF hut
Laser optics
Sensitive to temperature, humidity and dust, vibration
Class 100,000 equivalent, humidity control, vibration
isolated foundation (separated from klystron gallery), fix
bumps in road nearby.
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Near Hall
Hutches with a variety of experiments to house
Thermal, humidity, and dust control
Class 10,000 equivalent
Adjacent to Near Hall are Xray beam deflector
which have significant vibration sensitivities.
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Xray Beam Pointing Sensitivity
’FEL ~ 1 mrad
Near Hall
FEL ~ 400 mm
Undulator
250 m
~ 320 m
~ 400 m
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
Far Hall
Pointing Stability Tolerance
0.1  spot stability in Far Hall (conservative)
implies 0.1 mrad 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 crystals
Corrector 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
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
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 mrad
 A ≤  0.1 mrad/2p.  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/ 2p ~ 10-6 m, which is quite reasonable since typical
A~100 nm or less
High Q support structures could cause a problem
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]
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.
4/29/04
J. Welch
Pine, Bldg 48, Room 232
[email protected]