Physics Issues for Conventional Facilities

1. Physics Issues for Conventional Facilities Review and Update 4/7/05 J. Welch

2. Sensitive CF Areas X most critical

3. Topics • MMF status • Undulator Hall Floor Stability • Undulator Hall Thermal Environment

4. MMF Status • Reviewed by Javier Sevilla • 100% Title II • Vibration mitigation included • Isolated 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

5. 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.

6. Undulator Hall Floor Stability Requirement • “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: 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

7. 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

9. Jacobs Floor Calculations • Put 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.

10. 18 inch slab subfloor Prescribed bulge (greatly exagerated)

11. Floor Design Preliminary Review • Chris Laughton, Roland Sharpe, Fred Asiri • Panel 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.

12. Undulator Hall Thermal Environment • Design Requirements Clarification • Title I Design Issues • Plans for HVAC design development

13. 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.

14. Title I HVAC Design Issues • Title I design has some questions marks • Air 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)

15. Jacobs Initial Response to Issue

16. 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.

17. Extra Slides

18. 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.

19. Undulator Hall Profile Fill Area

20. 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. (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.

21. 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

22. 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

23. Magnet Support Studies • Motion of the floor affect quadrupole motion differently depending the support scheme

24. 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.

25. Single Column Support ±10 m uniform distribution of quad ctrs

26. 3 Quads per Girder ±10 m uniform distribution of quad ctrs

27. Phase Error Correlations (Assuming 3 Quad per girder)

28. 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.

29. 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 • PEP Ring Road crosses FEE near UH • "Static" deformation due to truck yet to be estimated. • We need vibrations to be below 1 m

30. 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 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)

31. 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)

32. Movie on Transient

33. 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

34. 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 Slip planes

35. Title I Undulator Hall HVAC Alcoves with AHU’s Make up air Cross flow to ducts AHU in alcoves 9X 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

36. 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.

37. 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.

38. 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.

39. Xray Beam Pointing Sensitivity ’FEL ~ 1 rad Near Hall FEL ~ 400 m Far Hall Undulator 250 m ~ 320 m ~ 400 m

40. 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 • electron trajectory angular change of ~ 1/10 rad

41. FEL Mechanism Micro-bunching Narrow Radiation Cone ~1 mr, (1/g ~ 35 mrad) • 2p radiation phase advance per undulator period Relationship of Xray phase to wiggle phase is critical

42. Phase Sensitivity to Orbit Errors Path Length Error Phase Error from H-D Nuhn LCLS: A < 3.2 mm LEUTL: A < 100 mm VISA: A < 50 mm

43. 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

44. 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

45. 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

46. Motion Due to Temperature Change • Dilitation CTE ppm/deg C 1.4 m T ~ 2 m / 1.4 m x 10 x 10-6 = 0.1 deg C (for a nominal 10 ppm/deg C)

47. Motion Due to Heat Flux or temperature gradients d L = 3 m, titanium strongback 3 W/m2 -> 2 micron warp for an undulator segment ∆T ≈ 0.05 deg C across strongback Note that 3 W/m2 can be generated by ~1 degree C temperature difference between the ceiling and floor via radiative heat transfer

48. Motion of the Foundation 1 mm/year = 3 m/day

49. 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.