Physics Requirements for Conventional Facilities

Pine, Bldg 48, Room 232

J. Welch [email protected]

4/29/04

Physics Requirements for Conventional Facilities

Thermal, Settlement, and Vibration Issues

J. Welch



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



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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)



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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



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FEL Mechanism

Exponential Gain

Micro-bunching

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

per undulator period



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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



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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.



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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



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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



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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)



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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



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Motion of the Foundation

1 mm/year = 3 m/day



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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



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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”



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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.



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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.



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Xray Beam Pointing Sensitivity

250 m

~ 320 m

Near Hall Far Hall

Undulator

~ 400 m

FEL ~ 400 m’FEL ~ 1 rad



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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



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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



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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.

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Physics Requirements for Conventional Facilities