J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Physics Issues for Conventional Facilities

Review and Update

4/7/05

J. Welch

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Sensitive CF AreasVibration Thermal Settlement

Undulator

Hall

X X X

MMF X X

Sector 20 X X

Near Hall X

X most critical

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Topics

MMF status

Undulator Hall Floor Stability

Undulator Hall Thermal Environment

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

MMF StatusReviewed by Javier Sevilla

100% Title II

Vibration mitigation includedIsolated slabs

Large slab under magnet measurement bench

Mechanical equipment moved as far away as feasible

Isolators under the HVAC equipment

Need to keep Hall probe from vibrating more than 5 microns - not too hard

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

MMF Status (cont.)Thermal control

+- 0.1 C in critical areas: (~1600 sf)

Air washes down on equipment and is returned near the bottom of the walls.

Excess heat sources are water cooled

Racks and computers are put near the end of the airstream.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Undulator Hall Floor Stability Requirement

Differential settlement and shrinkage of the foundation, even at very small levels will cause misalignment of the undulator components. The foundation and supporting soil must be designed to minimize these effects. These parameters have been faced at the ESRF European Synchrotron Radiation Facility), APS (Argonne Photon Source), and the ALS (Advanced Light Source). The Undulator Hall floor long term stability should be designed to be at or beyond state of the art

“State of the art”, re-defined as nearby SLAC Linac, is about of 0.2 mm RMS / year over 10 m separations.Desired rate is about 1/5 of Linac, i.e. ~ 0.04 mm RMS / year over 10 m separations, or less, for a ~ once per month realignment interval

A&E Design Guidelines for CF A&E Design contract:

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Undulator Hall Floor Design

Jacobs Engineer has presented new calculations of the performance of the Title I floor design

SLAC called in a panel of experts for a preliminary review of Title I floor concept

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Jacobs Floor CalculationsPut 1/2 inch bulge up at the center of a floor and calculate the resulting radius of curvature

#1, “Ordinary 18 inch thick reinforced concrete slab#2, A “Tri-Tee” slab on grade#3, A “Tri-Tee” slab on confined pea gravel

Results: Minimum radius of curvature#1, 3659 ft#2 10714 ft#3, infinite (by assumption)

Pea gravel flows perfectly to accommodate the bulge, floor slightly rises uniformly without bending.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Prescribed bulge (greatly exagerated)

subfloor

18 inchslab

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Floor Design Preliminary Review

Chris Laughton, Roland Sharpe, Fred AsiriPanel recommended tunnel and floor both be designed together to minimize the differential settlement and distortion of tunnel shape due to local swelling.Panel felt the “Tri-Tee” design raised many questions, however Jacobs was not present to answer them.Plan to re-convene together with Jacobs engineers later this month.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Undulator Hall Thermal Environment

Design Requirements Clarification

Title I Design Issues

Plans for HVAC design development

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Requirements Clarification

+-0.2 C (+-0.36 F) everywhere in the main air stream+-50 W/m of tunnel limit on heating/cooling load from equipment and lights.

5 W/m is maximum fluctuating heat/cool load from equipment and lights during normal operation.

This is to provide a nearly constant T along an air stream

Wall temperature stability 0.5 deg C RMS.Walls can be cooler than 19.8 C as long as the temperature doesn’t change in time much and as long as they don’t affect the main air stream temperature much.

This is to provide a constant radiant heat flux.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Title I HVAC Design Issues

Title I design has some questions marksAir velocity is quite low ~10 fpm average

Air flow could be dominated by natural convection which could cause cold drafts and temperature gradients

Cold wall and floor temperatures and thick boundary layers result

Lack of mixing means heating and cooling sources don’t efficiently cancel

Design cfm is based on providing sufficient air flow to control the imbalance between the heating sources, (assumed to be 50 W/m x 2 and constant) and the cooling sources which is only the tunnel walls. Both loads are quite uncertain.

Heat transfer coefficient to walls and floor is very low, resulting in cold walls and floor. (~18 C even after six months)

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Jacobs Initial Response to Issue

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Undulator Hall HVAC Design Development

SLAC HVAC engineer to met with Jacobs

Second meeting planned for later this month

Expect to see air flow modeling

May need to change/refine the air flow pattern

HVAC equipment is to be housed on the surface buildings, always accessible

Ducting in 7 or 8 vertical shafts will bring air to and from the Undulator Hall

The final mixing of the supply air is done in the tunnel.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Extra Slides

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Startup EffectPEP 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.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Undulator Hall Profile

Fill Area

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Predicted UH Slow Floor MotionEstimate for typical motion during first three years. It is twice the 17 year average differential rate for the linac. (0.5 m/day rms)

Doesn't include motions of supporting structures

Doesn't include daily or seasonal effects

Motion is cumulative. That is rms grows linearly with time.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

17 Year Linac Elevation ChangeMeasured 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

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Short term motions in LinacShort 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

pressure

From A. Seryi

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Magnet Support StudiesMotion of the floor affect quadrupole motion differently depending the support scheme

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Correlation with DistanceRelative 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.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Single Column Support

±10 m uniform distribution of quad ctrs

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

3 Quads per Girder

±10 m uniform distribution of quad ctrs

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Phase Error Correlations

(Assuming 3 Quad per girder)

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

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.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

VibrationUH 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

PEP Ring Road crosses FEE near UH

"Static" deformation due to truck yet to be estimated.

We need vibrations to be below 1 m

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Heat Transfer ProblemBasic 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.

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

Lower estimate are for small ∆T (0.1˚C), higher hc result for larger ∆T, (5-10 ˚C)

€

dq = hcdA(T0 − T∞)

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

ANSYS CalculationWall Temperature

After6 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)

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Movie on Transient

QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Summary of Physic IssuesGround 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

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Title I Undulator Hall Foundation

High Moment of Inertia, T shaped foundation

Pea Gravel support Slip planes

•Completely underground•Impervious membrane blocks groundwater•Located above water table (at this time anyway)•Low shrink concrete, isolated foundation•“Monolithic”

J. Welch

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4/7/05Facility Advisory Committee Meeting

Title I Undulator Hall HVAC

Cross flow to ductsAHU in alcoves 9X

Alcoves with AHU’s

Make up air

Return Air

Tempered water, slightly warmer and cooler than the tunnel air, is supplied to each of the AHU’s

Variable flow local recirculating loop in AHU

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

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.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

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.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Near Hall

Hutches, to house a variety of experiments, needThermal, humidity, and dust control

Class 10,000 equivalent

Adjacent to Near Hall are Xray beam deflectors which have significant vibration sensitivities.

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Xray Beam Pointing Sensitivity

250 m

~ 320 m

Near Hall Far Hall

Undulator

~ 400 m

FEL ~ 400 m’FEL ~ 1 rad

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

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 ifelectron trajectory angular change of ~ 1/10 rad

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

FEL Mechanism

Relationship of Xray phase to wiggle phase is critical

Micro-bunching

Narrow Radiation Cone ~1 r,(1/ ~ 35 rad)• 2 radiation phase advance

per undulator period

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Phase Sensitivity to Orbit Errors

€

Δϕ =2π

λ r

2A2

L

⎛

⎝ ⎜

⎞

⎠ ⎟=

4πA2

Lλ r

from H-D Nuhn

LCLS: A < 3.2 m

LEUTL: A < 100 m

VISA: A < 50 m

Path Length Error Phase Error

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

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

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

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 expected to be not quite as good as 1/10 sigma

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

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/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

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Motion Due to Temperature Change

Dilitation

1.4 m

€

Δl = αlΔT

Granite 6-8

Anocast 12

Steel 11

Aluminum 23

CTE ppm/deg C

ΔT ~ 2 m / 1.4 m x 10 x 10-6 = 0.1 deg C

(for a nominal 10 ppm/deg C)

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Motion Due to Heat Flux or temperature gradients

δ=αL2q8σ

δq

=0.70 microns/Wm2

α = 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

J. Welch

welch@slac.stanford.edu

4/7/05Facility Advisory Committee Meeting

Motion of the Foundation

1 mm/year = 3 m/day

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4/7/05Facility Advisory Committee Meeting

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.