1. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Physics Issues for Conventional Facilities Review and Update 10/12/04 J. Welch

2. welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Topics Physics Sensitivities Review Ground Motion and Magnet Support Studies Vibration Studies Undulator Hall Thermal Calculations

3. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Sensitive CF Areas VibrationThermalSettlement Undulator Hall XXX MMFXX Sector 20XX Near HallX X most critical

4. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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.

5. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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

6. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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.

7. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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

8. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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

9. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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.

11. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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.

12. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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.

13. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Undulator Hall Profile Fill Area

14. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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 pressure From A. Seryi

15. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Magnet Support Studies Motion of the floor affect quadrupole motion differently depending the support scheme

16. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Single Column Support

17. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 3 Quads per Girder

18. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Phase Error Correlations

19. J. Welch welch@slac.stanford.edu 10/12/04 Facility 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.

20. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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

21. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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. Estimates of h c based on McAshen (laminar forced convection): 0.59 W/m 2 C Kreith (free conv. enclosed box): 0.5 - 2.0 W/m 2 C Mark's H'book (horz. Cylinder): 0.6 - 2.3 W/m 2 C Lower estimate are for small ∆T (0.1˚C), higher h c result for larger ∆T, (5-10 ˚C)

22. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting ANSYS Calculation Wall Temperature After 6 months = 17.1 C (Tunnel air at 20.0C) h = 0.6 W/m 2 ˚C (note the movie of the transient temmperature response on the next slide will not work on some computers)

23. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Movie on Transient

24. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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

25. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Extra Slides

26. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Title I Undulator Hall Foundation High Moment of Inertia, T shaped foundation Pea Gravel supportSlip planes Completely underground Impervious membrane blocks groundwater Located above water table (at this time anyway) Low shrink concrete, isolated foundation “Monolithic”

27. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Title I Undulator Hall HVAC Cross flow to ducts AHU 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

28. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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.

29. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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.

30. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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.

31. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Xray Beam Pointing Sensitivity 250 m ~ 320 m Near Hall Far Hall Undulator ~ 400 m  FEL ~ 400  m  ’ FEL ~ 1  rad

32. J. Welch welch@slac.stanford.edu 10/12/04 Facility 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 if electron trajectory angular change of ~ 1/10  rad

33. J. Welch welch@slac.stanford.edu 10/12/04 Facility 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

34. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Phase Sensitivity to Orbit Errors from H-D Nuhn LCLS: A < 3.2  m LEUTL: A < 100  m VISA: A < 50  m Path Length Error Phase Error

35. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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

36. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting 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

37. J. Welch welch@slac.stanford.edu 10/12/04 Facility 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

38. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Motion Due to Temperature Change Dilitation 1.4 m Granite6-8 Anocast12 Steel11 Aluminum23 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)

39. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Motion Due to Heat Flux or temperature gradients 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/m 2 -> 2 micron warp for an undulator segment ∆T ≈ 0.05 deg C across strongback 

40. J. Welch welch@slac.stanford.edu 10/12/04 Facility Advisory Committee Meeting Motion of the Foundation 1 mm/year = 3  m/day

41. J. Welch welch@slac.stanford.edu 10/12/04 Facility 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.