Transcript Physics Requirements

Physics Issues for Conventional
Facilities
Review and Update
10/12/04
J. Welch
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Topics
Physics Sensitivities Review
Ground Motion and Magnet Support
Studies
Vibration Studies
Undulator Hall Thermal Calculations
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Sensitive CF Areas
Vibration
Thermal
Undulator
Hall
X
X
MMF
X
X
Sector 20
X
X
Near Hall
X
Settlement
X
X most critical
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Xray-Beam Phase Tolerance
Trajectory Straightness
2 m rms tolerance for the electron beam 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 Strength 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.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Alignment Stability
Ultra-straight trajectory will be lost if
BPM’s move a few microns and feedback incorrectly
corrects the beam
Quads move a few microns
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)
unless the actual motion is known, there is no effective way
to re-establish the undulator position except through
conventional alignment.
BBA once a month is OK, once a day intolerable
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Implications for Undulator Hall
Make foundation as stable as possible
Thermally stabilize the Undulator Hall
Heat fluxes must be reduced to a minimum to avoid
thermal distortions
The tunnel air temperature must be regulated to within a ±
0.2 deg C band everywhere in the Undulator Hall.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Ground Motion Studies
Linac and PEP data Analyzed
Correlation with distance measured
Histograms of actual motion of adjacent points
Startup effect
Estimated UH floor motion revised
Short term motion is under analysis
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
17 Year Linac Elevation Change
Measured
motion of
points along
the linac every
12 m over a 17
year period.
Scale Is 1000X
bigger than our
sensitivity
Linac has 2 ft
thick, heavily
reinforced floor
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Linac 17 year Motion
17 year average rate of
change of differences
between adjacent
points (12.3 m
separation) is plotted
Tails are non-gaussian,
but relatively small.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Startup Effect
PEP data
Much greater
velocities occur in
the first few years
after construction
Motion continues
at a signficant level
indefinitely
Model of Seryi and
Raubenheimer give
about a factor of two
between 17 year
average rate and
first three average
rate.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Correlation with Distance
Relative motion
correlates with
distance between
measurement
points.
LCLS will have
support points
around 10 m apart,
and quad
separation of 4 m.
Stiffness of
foundation may
improve this
correlation.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Predicted UH Slow Floor Motion
Estimate for typical
motion during first
three years. It is twice
the 17 year average
differential rate for the
linac.
Doesn't include
motions of supporting
structures
Doesn't include daily or
seasonal effects
Motion is cumulative.
That is rms grows
linearly with time.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Undulator Hall Profile
Fill Area
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Short term motions in Linac
Short term motions were
measured on linac
24 hour average rms ~
7 microns
1 hour average rm ~
1.2 microns
Motions mostly due to
atmospheric pressure and
tides.
Measurements were over
a 1000 m baseline
Need to extrapolate to
10 m, ATL?
Seasonal effects not
included
10/12/04
Facility Advisory Committee Meeting
pressure
From A. Seryi
J. Welch
[email protected]
Magnet Support Studies
Motion of the floor affect
quadrupole motion differently
depending the support scheme
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Single Column Support
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
3 Quads per Girder
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Phase Error Correlations
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Support Study Conclusions
Griders couple the motion of adjacent quadrupoles, thereby
largely canceling the steering effects caused by the motion
of the tunnel floor.
Analysis shows a five fold reduction in phase error is
possible with girders compared with single column support.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Vibration
UH borehole vibration
measurements at 20 ft depth
Ambient ~ 4 nm rms
Ave dumptruck ~ 18 nm rms
Ave dumptruck on gravel ~
40 nm rms
Max dumptruck on gravel ~
150 nm rms
Higher vibration levels near
surface
"Static" deformation due to
truck yet to be estimated.
We need vibrations to be
below 1 m
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Heat Transfer Problem
Basic problem is that it is hard to heat the hillside
without introducing temperature gradients in the tunnel
air
Temperature drops at boundary between tunnel wall
and bulk tunnel air due to boundary layer. Amount of
drop depends of heat transfer coefficient.
dq  hc dA(T0  T )
Estimates of hc based on
McAshen (laminar forced convection): 0.59 W/m2C
Kreith (free conv. enclosed box): 0.5 - 2.0 W/m2C
Mark's H'book (horz. Cylinder): 0.6 - 2.3 W/m2C
higher hc result
Lower estimate are for small ∆T (0.1˚C),
for larger ∆T, (5-10 ˚C)
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
ANSYS Calculation
Wall Temperature
After
6 months = 17.1 C
(Tunnel air at
20.0C)
h = 0.6 W/m2˚C
(note the movie of the
transient
temmperature
response on the next
slide will not work on
some computers)
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Movie on Transient
QuickTime™ and a
Microsoft Video 1 decompressor
are needed to see this picture.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Summary of Physic Issues
Ground Motion Studies
0.5 m rms/day cumulative differential motion, plus
some short period motion, expected for floor stability
Girder support, in principle, can reduce sensitivity to
floor motion
Vibration Studies
Don't appear to be a significant problem in Undulator
Hall
Undulator Hall Thermal Stability
Potential problem with cold tunnel walls. Analysis
continues
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Extra Slides
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Title I Undulator Hall Foundation
•Completely underground
•Impervious 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
10/12/04
Facility Advisory Committee Meeting
Slip planes
J. Welch
[email protected]
Title I Undulator Hall HVAC
Alcoves with AHU’s
Cross flow to ducts
AHU in alcoves 9X
Variable flow
local recirculating
loop in AHU
10/12/04
Facility Advisory Committee Meeting
Make up air
Return Air
Tempered water, slightly
warmer and cooler than
the tunnel air, is supplied
to each of the AHU’s
J. Welch
[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
m motion causes 1 x10-4
error.
Measurements show
vibrations below 100 nm.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[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.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Near Hall
Hutches, to house a variety of experiments, need
Thermal, humidity, and dust control
Class 10,000 equivalent
Adjacent to Near Hall are Xray beam deflectors
which have significant vibration sensitivities.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Xray Beam Pointing Sensitivity
’FEL ~ 1 rad
Near Hall
FEL ~ 400 m
Undulator
250 m
~ 320 m
~ 400 m
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Far Hall
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 m) beam/radiation overlap
error.
Xray beam will move 1/10 sigma if
electron trajectory angular change of ~ 1/10 rad
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
FEL Mechanism
Micro-bunching
• 2p radiation phase advance
per undulator period
Narrow Radiation
Cone ~1 r,
(1/g ~ 35 rad)
Relationship of Xray phase to wiggle
phase is critical
10/12/04
Facility Advisory Committee Meeting
J. Welch
[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 m
LEUTL: A < 100 m
VISA: A < 50 m
10/12/04
Facility Advisory Committee Meeting
from H-D Nuhn

J. Welch
[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
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Pointing Stability Tolerance
0.1  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 crystals
Corrector magnets in BTH must be stable to better
than 1/10 sigma deflection net.
Electron beam stability is expected to be not
quite as good as 1/10 sigma
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]
Vibration and Pointing Stability
Angular tolerance can be converted to a vibration
amplitude for a specific frequency, for CF spec.
y=A cos(kx-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/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
10/12/04
Facility Advisory Committee Meeting
J. Welch
[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 m / 1.4 m x 10 x 10-6 = 0.1 deg C
(for a nominal 10 ppm/deg C)
10/12/04
Facility Advisory Committee Meeting
J. Welch
[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
10/12/04
Facility Advisory Committee Meeting
Note that 3 W/m2 can be
generated by ~1 degree C
temperature difference
between the ceiling and floor
via radiative heat transfer
J. Welch
[email protected]
Motion of the Foundation
1 mm/year = 3 m/day
10/12/04
Facility Advisory Committee Meeting
J. Welch
[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.
10/12/04
Facility Advisory Committee Meeting
J. Welch
[email protected]